Review Article A Minireview of the Natures of Radiation...

Hindawi Publishing CorporationPhysics Research InternationalVolume 2013 Article ID 379041 14 pageshttpdxdoiorg1011552013379041

Review ArticleA Minireview of the Natures of Radiation-InducedPoint Defects in Pure and Doped Silica Glasses and TheirVisibleNear-IR Absorption Bands with Emphasis onSelf-Trapped Holes and How They Can Be Controlled

David L Griscom

Impact Glass Research International San Carlos SON Mexico

Correspondence should be addressed to David L Griscom david griscomyahoocom

Received 9 May 2012 Accepted 19 October 2012

Academic Editor Robert McLeod

Copyright copy 2013 David L Griscom This is an open access article distributed under the Creative Commons Attribution Licensewhich permits unrestricted use distribution and reproduction in any medium provided the original work is properly cited

The natures of most radiation-induced point defects in amorphous silicon dioxide (a-SiO2) are well known on the basis of 56

years of electron spin resonance (ESR) and optical studies of pure and doped silica glass in bulk thin-film and fiber-optic formsMany of the radiation-induced defects intrinsic to pure and B- Al- Ge- and P-doped silicas are at least briefly described hereand references are provided to allow the reader to learn still more about these as well as some of those defects not mentionedThe metastable self-trapped holes (STHs) intrinsic to both doped and undoped silicas are argued here to be responsible for mosttransient rednear-IR optical absorption bands induced in low-OH silica-based optical fibers by ionizing radiations at ambienttemperatures However accelerated testing of a-SiO

2-based optical devices slated for space applications must take into account

the highly supralinear dependence on ionizing-dose-rate of the initial STH creation rate which if not recognized would lead tofalse negatives Fortunately however it is possible to permanently reduce the numbers of environmentally or operationally createdSTHs by long-term preirradiation at relatively low dose rates Finally emphasis is placed on the importance and utility of rigorouslyderived fractal-kinetic formalisms that facilitate reliable extrapolation of radiation-induced optical attenuations in silica-basedphotonics recorded as functions of dose rate backward into time domains unreachable in practical laboratory times and forwardinto dose-rate regimes for which there are no present-day laboratory sources

1 Introduction

Optical fibers and metal-oxide-semiconductor (MOS) de-vices based on amorphous forms of SiO

2(119886-SiO

2) are

components of many photonic devices and systems thatrequire hardness against nuclear andor space radiationsDevelopment of radiation-hardened optical fibers based onglassy silica as well as MOS devices with amorphous SiO

2

gate insulators is dependent on a fundamental understand-ing of radiation-induced defect formation in the 119886-SiO

2

component The multitude of relevant radiation damageprocesses are schematically illustrated in Figure 1 whichis taken from [1] where these processes are discussed inconsiderable detail The present paper will limit its focusto the natures of the radiation-induced point defectsmdashalsotermed ldquocolor centersrdquomdashthat are known to absorb light in

the wavelength range sim500 to sim2000 nm in silica-basedoptical fibers and other photonic devices A concise reviewof radiolytic trapped-oxide charges in 119886-SiO

2-based MOS

structures and their relation to interface-state formation canbe found in [2]

The molecular-scale structures of those point defectsthat are paramagnetic (ie possessing an unpaired electron)have been determined primarily by the technique of electronspin resonance (ESR) spectrometry The most commonlymeasured ESR parameters are the 119892 values and hyperfinecoupling constants whichwill bementioned in passing belowbut will not be defined here Rather the reader is referredto [3] for the meanings of these terms as well as a highlycondensed review of the theory and application of ESR toboth insolating crystals and glasses andor to [4] for a morecomprehensive review of both the theory and practice of ESR

2 Physics Research International

I II III IV VIrradiation Prompt occurrences Excited state relaxation

recombinationCarrier trappingdefect formation

UV light Photolytic defects

X raysLight emission(Compton electrons) Recombination Radiolytic fragments

(principally H )Transient defectsElectron-hole pairsFast electrons Free carriers Trapping at

radiolytic defects(Secondary electrons)NeutronsTrapping at

preexisting defectsFast ions

Atomic displacementsTrapping atimpuritiesRecombination

Dimerization

Stabilization bydiffusion of charge-compensating ions

Aggregatescolloids bubbles and so forth

Trapping atknock-on damage

Self-trapping

Free vacanciesand interstitials

Furtherdiffusion-limitedreactions

Diffusion-limited reactions

120574-rays

Figure 1 Modes of defect formation in insulators subjected to various types of ionizing radiations andor particles of sufficiently high energyto create ldquoknock-onrdquo damage See [1] for discussions of the indicated processes

100 200 300 400 500 600 700 800 900 100001

1

10

100

Ge(2)

Ge(1)

STH

44 eV58 eV

52 eV shifted

24 eV

Isochronal anneal temperature (K)

Sym

bols

opt

ical

inte

nsity

(eV

cm

)Cu

rves

ESR

spin

den

sitie

s (au

)

Ge 119864prime

Figure 2 ESR-determined number densities (bold curves relative units) and independently determined optical-band intensities (symbolseVcm) for X-ray-induced defect centers in separate samples of a Ge-doped-silica fiber-optic perform following irradiations to the same doseat 100 and 77K respectively and subsequent 5-minute isochronal anneals to the higher temperatures (The ESR data were also recorded atdiscrete temperatures but are displayed here as continuous curves as an aid to the eye) It is seen here that the self-trapped holes (STHs) andthe Ge(1) trapped-electron centers correlate well with optical absorption bands centered near 24 and 44 eV respectively (and have identicaloscillator strengths [5 6]) The upshifted Ge(2) number-density curve (dashed blue curve relating to Ge(2)rsquos higher oscillator strength)strongly matches the 58 eV optical data below 300K and is cryptically correlated with those data above 300KThe diamonds representing a52-eV band not associated with any ESR-detectable defect are shown here displaced upward by a factor of 24 from their originally recordedoptical intensities in order to discover their perfect match with the red curve in the range 200ndash370K which comprises the sum of the changesof the Ge(1) and Ge(2) number densities in the range 200ndash370K multiplied by negative 05 This figuremdashadapted from [5]mdashwas recentlypublished in [6] where full explanations of the meanings and implications of these data can be found

as applied to paramagnetic ions and radiation-induced pointdefects in (mostly silica-based) oxide glasses

The associations of ESR-determined defect-center struc-tures with specific optical absorption bands are generally

established by ESR-optical correlations obtained for exam-ple by means of postirradiation isochronal thermal anneal-ing experiments Figure 2 provides an example of such aparallel set of ESR and optical isochronal anneal sequences

Physics Research International 3

recorded for a germanium-doped silica glass initially x-irradiated at sim100K and annealed for 5 minutes at eachsequence of higher temperatures [5 6]

During the past half century many trapped-hole-typepoint defects in pure silicas have been identified by ESR (seefor example [4]) in most cases unambiguously (It shouldbe noted however that silicas containing minor amounts oftechnological impurities such as OH CO Cl or O

2are often

termed ldquopurerdquo whereas these impurities frequently take partin the formation of defect centers extrinsic to the pure glass)By contrast many of the counterpart trapped-electron-typedefects in pure silicas have historically appeared to be ESRsilent Very recently I reviewed in considerable detail whatis presently known about radiation-induced trapped-electroncenters in both pure and B- Al- Ge- and P-doped silicaglasses [7] Among many other conclusions in [7] I wasforced to reject and to replace certain models that I myselfhad posited earlier [4 8] for radiation-induced defects inotherwise high-purity silicas containing high concentrationsof chloride ions

2 What We Know for Certain about PointDefects in Glassy Silica

21 Pure Silica Among the best understood intrinsic defectsin glassy silica is a family of oxygen-vacancy defects termed1198641015840 centers [9] which have been found to occur in a

number of distinctly different variations termed 1198641015840120572120573120574 and 120575

(eg [8 10ndash13]) Until very recently all of these wereregarded as trapped-hole centers However there is sub-stantial evidence [7 12] that the low-temperature versionof 1198641015840120572 1198641015840120572119871119879

(nomenclature proposed in [7]) may be atrapped-electron center whereas the high-temperature ver-sion of 1198641015840

120572 1198641015840120572119867119879

has been unambiguously shown to bea trapped hole center [13] The historical confusion owesto both 1198641015840

120572versions sharing approximately the same 119892

valuesmdashwhich is a necessary but far from sufficient con-dition for their being sterically and electronically identi-cal

Still the majority of all 1198641015840 centers result from trappingof holes (ℎ+) at a neutral oxygen vacancies in pure-silica-glass networks otherwise comprising SiOslash

4tetrahedra linked

at the corners (the notation ldquoOslashrdquo indicates that in a hypothet-ically defect-free silica glass each oxygen O forms a bridgebetween and is thus shared by the central Si and one of itsfour nearest-neighbor silicons) The most famous exceptionis 1198641015840120575 which was originally proposed to involve an unpaired

electron delocalized over four silicons [8] has since beenwidely argued by theorists to involve just two silicons buthas finally been experimentally proven to involve at least fourvirtually equivalent silicon neighbors and possibly five [14]Some other recently proposed exceptions involve 1198641015840

120574centers

induced in silicas with high Cl contents (now regarded in[7] to have been misinterpreted in [8]) and 1198641015840-type centersassociated with oxygen ldquopseudo vacanciesrdquo to be explainedin Section 22

In the simplest case of preexisting neutral oxygenmono-vacancies in the pure-silica glass structure the

radiolytic process of 1198641015840 center creation can be representedas

[equivSiSiequiv]0 + ℎ+ 997888rarr [equivSi∙ +Siequiv]+ (1)

where ldquoequivrdquo represents bonds to 3 bridging oxygens ldquoOslashrdquo inthe glass network ldquordquo represents a pair of electrons sharedbetween the two silicons on opposite sides of the vacancyand ldquo∙rdquo is an unpaired electron localized in a dangling 1199041199013orbital of a single silicon as determined by ESR studiesof irradiated samples Most commonly the defect structureldquoequiv Si∙rdquo on the right-hand side of (1) is an 1198641015840

120574center although

in certain cases it may be an 1198641015840120572or 1198641015840120573center signaled

by small but easily discernable differences between theirrespective spin Hamiltonian parameters [3 4 13] and oftendepending on their respective modes of creation andorthermal stabilities [8 10ndash13] In general these variants arebelieved to correspond to different distortions or relaxationsof the structure equiv Si∙ andor the structure of the surroundingglass in which this unit is embedded (see especially [11])

In addition there are nonbridging-oxygen hole centers(NBOHCs ldquoequiv SindashO∙rdquo see eg [4])) peroxy radicals (PORsldquoequiv SindashOndashO∙rdquo see eg [4]) and two types of self-trappedholes (STH

1and STH

2[15 16] the structures of which will

be elucidated in Section 3) The literature is enormous butreferences [1 4 12] are recommended entry points

22 Doped Silicas The best understood defects in dopedglassy silica are those for which Si is substituted by BAl Ge or P This is because the radiation-induced thealuminum-oxygen hole center (Al-OHC) the so-calledGe(1)and Ge(2) centers and the P

2trapped-electron center in

the respectively-doped glasses have each been shown to bevirtually identical with a doppelganger in similarly-dopedcrystalline 120572 quartz as discussed in detail in [7] These 120572-quartz doppelgangers are unambiguously understood thanksto tedious highly specialized and meticulously performedsingle-crystal ESR angular dependence studies carried outby John Weil and his students and colleagues (see [17] for alisting of reviews) It should be noted that the boron-oxygenhole center (B-OHC) has no doppelganger in 120572 quartzhowever it is isomorphous with the Al-OHC

221 Ge-Doped Silica As seen in Figure 2 the correspon-dences of the ESR data (curves) and optical measurements(data points) show that the Ge(1) and Ge(2) centers in Ge-doped silica glass have optical absorption bands at 44 eV and58 eV respectively

Of particular importance to understanding the naturesof these Ge(1) and Ge(2) defects are the remarkable inter-relationships (described in greater detail in [6 7]) betweenthe Ge(1) and Ge(2) centers in Ge-doped silica glass and theGe(II) and Ge(I) centers respectively in 120572 quartz

(A) Given that the Ge(1) center in Ge-doped silica glass[5ndash7 18] is characterized by virtually the same 119892values and mean hyperfine coupling constant asthose of the Ge(II) center in quartz [19 20] it mustbe concluded that (i) ldquo120572-quartz-crystal-likerdquo GeOslash

4


tetrahedra preexist in the glass and (ii) Ge(1) sharesthe Ge(II) property of being an electron trapped in aGe sp orbital parallel to the twofold axis of symmetryof this tetrahedron

(B) Given that the Ge(I) center in 120572 quartz [19 20]is characterized by 119892 values only slightly differentfrom andmean hyperfine coupling constant virtuallyidentical to those of the Ge(2) center in silica glass[5ndash7 18]mdashand it is known [19 20] that Ge(I) isan electron trapped in symmetry-breaking orbitalsperpendicular to the twofold axis a GeOslash

4tetrahedron

in the 120572-quartz lattice (thusmaking it an energeticallydifferent state of the same defect responsible forGe(II) [19])mdashit must be concluded that (i) Ge(I) isa ldquoglass likerdquo defect even though it occurs in perfectcrystal and (ii) the ldquodefaultrdquo interpretations of Ge(1)and Ge(2) are that they are two energetically differentstates of the same defect in Ge-doped silica glass

Notwithstanding insights (A) and (B) above observedvariations in the Ge(1)-to-Ge(2) concentration ratios atroom temperature continue to convince some researchersthat Ge(1) and Ge(2) cannot be two energetically differentstates of the same precursor (eg [21]) For example inFigure 2 the Ge(1) Ge(2) ratio is seen to be sim2 1 after x-irradiation at 100K and a 5-min warming at 300K [6]whereas this ratio has been found in [21] to be 08 1 forGeO

2-

doped silica optical fibers and preforms 120574-irradiated at roomtemperature and stored at ambient temperatures for a fullmonth before recording the data However this is hardly aserious contradiction given that in Figure 2 it is seen that afurther 5-min anneal at 370K also results in a Ge(1) Ge(2)ratio of sim08 1

Here below I will summarize and analyze a very dif-ferent examplemdashone that cannot be dismissed without fur-ther consideration Nagasawa and coworkers [22] providedstriking evidence of selective destruction of 120574-ray-inducedGe(2) centersmdashbut not Ge(1) centersmdashin Ge-doped-silica-core optical fibers by postirradiation ambient-temperaturein-diffusion of molecular hydrogen They also reported alinear relationship between (i) the numbers of Ge(2) centersrecorded by ESR in five different samples immediately follow-ing 120574-irradiation and (ii) the numbers of [=Ge∙-H]0 defectssubsequently created in these same samples by identical H

2

treatmentsThe [=Ge∙-H]0 defect commonly termed the H(II) cen-

ter results when a charge-neutral twofold-coordinated ger-manium [=Ge]0mdashcommonly termed the Germanium LonePair Center (GLPC0)mdashreacts with a neutral hydrogen atomH0 a process that has been extensively studied by Bobyshevand Radtsig on the surfaces of Ge-doped silica glasses [23](Confirmation of the structure of the analogous [=Si∙-H]0defect in pure bulk silica denoted H(I) is given in [24])

In order for H(II) centers to have formed in Nagasawa etalrsquos [22] bulk glasses both of the following processes musthave taken place [23] (i) two Ge-Oslash bonds must have beenbroken at each of an equal number of tetrahedrally coordi-nated germanium sites and (ii) the introduced molecular H

2

must have been ldquocrackedrdquo into a pair of free hydrogen atomsOne possible cracking site could have been nonbridging-oxygen hole centers (NBOHCs) [25] if any were presentConceivably however H

2might have been cracked in the

process of destroying Ge(2) centers

[GeOslash4∙]2

minus

+H2997888rarr [GeOslash

4H]2

minus

+ ∙H0 (2)

where ldquo[GeOslash4]rdquo denotes a substitutional germanium ldquo∙rdquo a

trapped electron the superscript ldquominusrdquo a negative electrostaticcharge and the subscript ldquo2rdquo a Ge(2)-type trapped-electronon the left-hand side of the reaction and the ldquoHrdquo on theright-hand side is an H0 bonded to this Ge(2)-type orbital

Cracking reactions of H2dissolved in silica glass can be

determined by its diffusion coefficient alone if the reactioncoefficient pertaining to the entity upon which it cracks ismore rapid than the diffusion time (an explicit example ofthis is given in [25]) Conversely the reaction could be greatlyslowed if the reaction coefficient should happen to be muchslower than the diffusion coefficientThus if Ge(1) andGe(2)are ldquotwo energetically different manifestations of the samedefectrdquomdashas it certainly appears that they aremdashit is not at allunreasonable to suggest from the results of [22] that Ge(1)has a much slower reaction coefficient for a cracking H

2than

does Ge(2)Apropos by tracing the ESR intensities of Ge(1) and

Ge(2) together with the 52-eV optical intensity of GLPC0in the range sim200 to 370K in Figure 2 it was determined[6] that GLPC0s had trapped a number of holes equal to thecombined number of electrons trapped at Ge(1) and Ge(2)sites However the number density of hole-trapping GLPC0sdeduced in [6] was only 50 of this number [6]mdashthusproving that GLPC0s stably trap holes only in pairs (therebybecoming GLPC2+s) Because they possess no unpairedelectrons both GLPC0 andGLPC2+ are ESR silentMoreoverit is empirically apparent that neither one has a strong opticalband in the range 1 to 6 eV [5 6]

222 Boron- and Aluminum-Doped Silicas Boron does notsubstitute in 120572 quartz However in a 120574-irradiated binaryB2O3-3SiO

2glass borons substituted for silicons were found

to trap holes to form boron-oxygen hole centers (B-OHCs)[26] This result is in perfect analogy to the Al-OHCsreported to occur in both Al-containing quartz [27] and Al-doped silica glass [28] By contrast trapped-electron-type B-1198641015840 centers [26] and Al-1198641015840 centers (reported by Brower in

[29] and reviewed in [7]) are created upon irradiation of abinary B

2O3-3SiO

2glass and an Al-doped silica respectively

whereas no counterparts to either of these trapped-electrondefects exist in 120572 quartz

In [26] it was proposed that the radiation-induced B-1198641015840centers [equivB∙]minus in the binary B

2O3-3SiO

2glass result from

electron trapping at the sites of preexisting oxygen ldquopseudovacanciesrdquo diagrammed as [equivB +Siequiv]+ This model wasextended in [7] to apply also to the Al-1198641015840 centers [equivAl∙]minus inAl-doped silica Thus

[equivAl +Siequiv]+ + 119890minus 997888rarr [equivAl∙minus +Siequiv]0 (3)


Note the similarity of the right-hand sides of (1) and (3)However the paramagnetic defect on the right of (1) is apositively charged trapped-hole center whereas the param-agnetic defect on the right of (3) is a charge-neutral trapped-electron center as discussed in greater detail in [7] Note thatin this model the unirradiated glasses must maintain chargeneutrality by assuring that the numbers of negatively chargedsubstitutional [BOslash

4]minus and [AlOslash

4]minus tetrahedra exactly equal

the numbers of [equivB +Siequiv]+ and [equivAl +Siequiv]+ ldquopseudovacanciesrdquo respectively

It has recently been shown [30] that subband-gap-excitedluminescence bands at 28 and 44 eV recorded for a silicasample to which was added 0015 wt elemental silicon(introducing true oxygen vacancies) are virtually identicalto those recorded for silica doped to the same degreewith Al

2O3 This particular luminescence is unambiguously

attributed to charge-neutral twofold-coordinated silicons([=Si]0 an ESR-silent oxygen-vacancy defect see [7] andreferences therein) and its strength in the 0015 wt-Si-doped sample is sim50 to 100 times greater than that ofundoped silica [30] Therefore the results of the experimentof [30] imply that a commensurate degree of Al

2O3doping

somehow creates the same high number and type of oxygenvacancies (specifically involving twofold coordinated silicons)as does doping with elemental Si The only conceivableway that this could happen must somehow relate to thepresence of Al ldquopseudo vacanciesrdquo [7 26] in the as-quenchedalumina-rich glass that is in the form of [equivAl +Siequiv]+ unitsAlthough the explanation for the appearances of twofold-coordinated silicons under these conditions is necessarilymore complicated (as is also the case of silica doped only withelemental Si) a possible model explaining the results of bothof these cases is proffered in [7]

3 Space Applications Narrow the SubjectMostly to Self-Trapped Holes

The facts are that (i) the most radiation-hard nonlaser silica-based optical fibers employ little or no cationic dopants (ii)the commonly used fluorine dopants appear not to take partin color-center formation [31] (though chloride impurities areproblematic [31]) and (iii) for dose ratessim6Gys the transientoptical absorption near 660 nm induced at short times inlow-OH pure-silica fibers (due to STHs see below) is sim3orders of magnitude greater than that of the concomitantlyinduced 620 nm band of (nondecaying) NBOHCs followinga total dose of 107 Gy [31] It therefore follows that the trueldquoelephant in the roomrdquo with respect to nuclear and spaceapplications of glassy silica would seem to be the STHs [1516] Metastable STHs are always created in low-OH glassysilica by ionizing radiation so long as there are no stronglycompeting hole-trapping dopants or impurities present Aswill be explained in greater detail in Section 35 STHs in high-OH silicas are instantly quenched by reaction with atomichydrogen released by radiolysis of OH groups [2 32 33]

The discovery and ESR characterization of the STHs areextensively discussed in [15 16] so most of the details willnot be reprised here However it can be stated that two

SiO

Si

119910

119909

119911

(a)

Si

O

O

O

O119910

119909

119911

(b)

Figure 3 Models for self-trapped holes in silica-based glasses (a)STH1and (b) STH

2 These structures were deduced experimentally

on the basis of a highly detailed ESR study [15] involving bothg-value distributions and 29Si hyperfine splittings (and theoriesthereof) and have since been successfully calculated by ab intiomethods for example [35 36] Here the shaded ldquoballoonsrdquo repre-sent the orbitals of the unpaired electron spins (denoted by verticalarrows)

distinct variants of STHs termed STH1and STH

2 have been

identified in irradiated silica glasses as the local structuresportrayed in Figure 3 In principle the potential hole trappingsites leading to STH

1formation can be virtually anywhere in

the glass network By contrast the sites that become STH2s

upon hole trapping are likely to be relatively rare since theseprecursor sites have been shown [15 16] to have 120572-quartz-likelocal structure whereas a comparison of X-ray-diffractionradial-distribution functions of glassy silica with those the 120572quartz cristobalite and tridymite crystalline polymorphs ofSiO2has shown quartz to be the least similar to structure to

silica glass (correlation coefficient of only 026 versus 069and 082 for cristobalite and tridymite respectively [34])

The ideal ldquodefect-freerdquo [37] structures of inorganic glassesare best determined by means of carefully controlled X-rayand neutron diffraction methods followed by data analysesgoverned by a branch of materials science termed ldquoamor-phographyrdquo [38] It is stated in [37] that

ldquo since the ideal structure (of an inorganicglass) is disordered departures from normality


can occur in the direction of both decreased andincreased order the former leading to what arecommonly known as defectsrdquo

However in light of the quartz-like Ge(1) and Ge(2)trapped electron centers in Ge-doped silicas discussed inSection 22 and the quartz-like precursor structures deducedfor STH

2in pure silica glasses [15 16] it appears that

departures from normality in the direction of increased ordercan also serve as electron- or hole-trapping sites which aretermed defects in such silica-based glasses when they trapelectrons or holes loosed by ionizing radiations

31 Optical Spectra of Self-Trapped Holes Self-trapped holesin silica were first identified in bulk silica glasses by ESR stud-ies the initial results of which I reported in 1989 [39]The firstSTH-related optical bandwas reported practically simultane-ously by Chernov et al [40] and pertained to low-OH pure-silica-core fibers irradiated at 77K This band termed by itsdiscoverers ldquolow-temperature infrared absorption (LTIRA)rdquo[40] consisted of a broad absorption beginning in the visibleand increasing with increasing wavelength until peaking near1800 nm Its isochronal annealing characteristics were foundto be very similar to a component of trapped positive chargein an a-SiO

2thin film as reported by Harari et al [41]

However to my knowledge no follow-up studies of 1800 nmband have since been published

Similarly soon after completing my main paper on theESR-determined properties of STHs [15] for publication inthe proceedings of the International Seminar Point Defectsin Glasses (Riga Latvia July -August 1991) my activities attheNaval Research Laboratory (NRL)were redirected towardradiation hardening of fiber optics for ITER diagnosticsunder a contract from theUS Department of Energy (DOE)Due to this redirection I found no opportunity to look foroptical manifestations of STHs in bulk silicas Indeed I hadnearly forgotten about STHs when five years later I began tothink that the intense absorption bands at 660 and 760 nm(originally reported by Nagasawa and coworkers [42 43])that leaped up inmy aluminum-jacketed low-OHpure-silica-core and F-doped-silica-core test fibers immediately uponinserting the sample coils into the NRL ldquoswimming poolrdquo 120574-ray source might be due to STHs [44 45]

It was another five years later and a year after my January2001 retirement from NRL when I finally devised a means toobtain isochronal anneal data for the 660 and 760 nm fiber-optic bands following 120574-irradiation at 77-K And I managedto carry out the experiment during the final two weeks of my10 month invited professorship of research at Tokyo Instituteof Technology Then two more years passed before I becamesufficiently inspired to analyze those very convoluted data setsand publish the results in [46] These results indeed agreedquite well with my previously published isochronal annealcurves for STH

1and STH

2in bulk silica [15 16 39] as well

as with Harari et alrsquos trapped positive charge curve [41]In the meantime Sasajima and Tanimura [47] had

reported both ESR and dichroic optical spectra of a wellselected suite of bulk silica samples subjected to 1-Mev 20-ns-duration electron pulses at 77 K They reported that their

1 15 2 25 3 35 4 45 5

0

002

004

006

008

Opt

ical

den

sity

Photon energy (eV)

STH2

STH1

Figure 4 Optical bands of STH2and STH

1induced in a low-OH

low-Cl bulk fused silica by pulsed electron irradiation at 77KThesebands were separated from a series of bands peaking at successivelyhigher energies (not shown) by means dichroic red-light bleachingand it was these dichroic bands (shown here) that correlated withthe ESR spectra recorded for the very same samples This figure isreplotted from [47] using the original data and fitted curves kindlyprovided in digital form by Tanimura

lowest-OH lowest-Cl bulk samples yielded the strongestSTH ESR signals Notably my lowest-OH lowest-Cl opticalfibers yielded the strongest 760 and 660 nm bands (163 and188 eV resp) during ambient-temperature 15 Mev 60Co 120574-irradiation However I have never recorded ESR spectrafor my irradiated fibers whereas Sasajima and Tanimuraunambiguously associated their induced optical bands at 216and 260 eV (Figure 4) with the classical [15] ESR signalsof STH

2and STH

1 respectively recorded for the very same

samples as used for their optical studies So if I have correctlyinterpreted the 163 and 188 eV bands induced in my pure-silica core fibers [16 31 44ndash46] as being due to STHs thenatures of these optical-fiber STHs must differ considerablyfrom those in bulk silica

In my recent review article on STHs [16] I cited data inthe literature for STH spin densities per unit dose increasingwith increasing fictive temperature and remarked that fictivetemperatures of silica-core optical fibers are much higherthan those of bulk glasses thus invoking fictive temperatureas a possible reason for the difference between 216 and260 eV STH optical bands in bulk silica [47] and the 163and 188 eV bands in silica fibers [31 44ndash46] However inretrospect it might also be considered that the structures ofsilica glasses drawn into fibers surely have residual uniaxialstrains superposed on the SiO

2random network And these

strains would affect the SindashOndashSi bond angles anisotropicallythereby changing the properties of STHs created thereinrelative to those in isotropic bulk glasses studied undersimilar experimental conditions

32 Yet Another Difference between the Optical Spectra ofSelf-Trapped Holes in Bulk and Optical-Fiber-Form SilicasSasajima and Tanimura [47] determined that the STH

1

absorption band peaking at 260 eV in bulk silica glass though


Gaussian in shape is homogeneously broadenedmdashmeaningthat bleaching just a small part of the band destroys theentire band rather than burning a hole in it Thus at least inthe case of the STH

1band the bulk-silica bands cannot be

decomposed into sums of component subbands By contrastas illustrated in Figure 5 the putative STH bands includingprominent peaks at 163 eV (760 nm) and 188 eV (660 nm)recorded for irradiated low-OH F-doped and pure-silica corefibers [44] are clearly much narrower and more numerousthan those in bulk silicas [47] The reasons for this remainunknown but are surely related to one or more of the issuesraised in Section 31

33 Growth and Decay Kinetics of Self-Trapped Holes inPure-Silica-Core Optical Fibers Figure 6 [44] illustrates theintensities at 760 nm of the spectra (including those ofFigure 5(a)) recorded during in-the-dark 60Co 120574-irradiationat 1 Gys using the CCD-camera-based prism spectrometerdescribed in [31] (light on for sim2 to 5 s per screen grab) attime intervals varying by factors of sim3 and ranging from32 sec to 24 days This process was briefly interrupted torecord ambient-temperature ex situ thermal bleaching andsubsequent recoverywhen this Al-clad fiber coil was returnedto its original position in the source [48] The in situ opticalbleach and recovery spike in this figure was taken from anearlier experiment using the same fiber type and radiationdose rate

The crosses in Figure 6 represent a classical second-orderkinetic fit to the data recorded at times above 104 s Acceptingthis fit as the correct representation of reality a 119905minus1 decrease ininduced absorption is to be expected at still longer irradiationtimes t I later determined that this decline in induced lossduring continued irradiation is permanent Specifically in[45] I found that upon reirradiation at 1 Gys of a pure-silica-core fiber that 3 months previously had been subjected to thesame dose rate for 107 s the incremental optical absorption-versus-time curve was two orders of magnitude weaker at119905 sim 200 s than observed during the initial irradiation sim20times weaker than the original curve recorded near 104 s andabout one order of magnitude weaker at 106 s Describingthe same data from a different perspective this fiber hadbeen radiation hardened to such a degree by the originalirradiation that the results of re-irradiation 3 months later atthe same dose rate resulted in newly induced absorption thatwas generally less than the final value at the end of the firstirradiationMoreover I discovered in [44] that this RadiationStimulated Reconfiguration (RSR) process (a terminologythat I introduced in [48]) is purely a function of timemdashnot ofdosemdashfor dose rates ranging between 015Gys and 55Gys

One additional experiment reported in [45] involvedpulling the irradiated sample coils out of the ldquoswimmingpoolrdquo 120574-ray source rapidly recording a spectrum at roomtemperature and immediately afterward thrusting the coilinto liquid nitrogen and then recording a second spectrumTaking the difference between these two spectra revealedthe 77-K spectrum to be characterized by (i) an addedgray absorption (ii) a shift of the principle peak positiondownward from 660 nm to sim630 nm and (iii) a component

18000

16000

14000

12000

10000

8000

6000

4000

2000

0400 500 600 700 800 900 1000

Dose [Gy(Si)]In

duce

d lo

ss (d

Bkm

)

Wavelength (nm)

(1) 34(2) 244

(1)

(2)

(3)

(4)

(3) 17 times 105(4) 25 times 106

(1)

(2)

(3)

(4)

(a)

1 15 2 25 3Photon energy (eV)

3000

2000

1000

0

1 2

Indu

ced

loss

(dB

km)

(b)

Figure 5 (a) Visiblenear-IR spectra of a low-OH F-doped-silica-core optical fiber at selected times during continuous 120574-irradiationat 1 Gys in the dark (b) A decomposition of similar spectra ofa low-OH high-purity-silica-core fiber concomitantly irradiatedand recorded under identical conditions This decomposition wasachieved by first separating the rednear-IR peaks (1) from theinduced absorptions at higher energies (2) by means of cut-and-trysubtractions of several members of the full set of recorded spectraof which the four displayed in (a) are corresponding examples(adapted from [44]) Superposed circles and squares in (b) representin arbitrary units optically stimulated release of trapped positivecharge from an X-irradiated a-SiO

2thin film (data from [41])


Radiationbleaching

1

23

4

Indu

ced

loss

(dB

km)

102 103 104 105 106

104

103

Growth Recoveries

In situoptical bleach

Steady state

Ex situthermal bleach

Time (s)

Figure 6 Kinetics of the 120574-ray-induced optical absorption mea-sured at 760 nm in an F-doped-silica-core Al-jacketed optical fiberas a function of irradiation time at 1 Gys at ambient temperature(sim27 C) in the dark except for sim3 seconds of probe light for eachframe grab The illustrated in situ optical bleach spike was takenfrom a separate experiment at the same dose rate and was ldquograftedrdquoonto the present data for comparison purposes Circled numbers 12 3 and 4 correspond to the numbered spectra of Figure 5(a) Figurefrom [44]

monotonically increasing with increasing wavelength upto maximum value measurable at that time 1000 nm Ispeculated in [45] that the lattermay be the high-energy tail ofChernov et alrsquos LTIRA (cf Section 31)This speculation couldbe tested by repeating this experiment with an instrumentcapable of recording spectra out to sim2000 nm

34 If STHs Are the Problem Accelerated Testing Can EasilyLead to False Positives Figure 7 adapted from [48] exhibitsoptical absorption data picked off at 900 nm from completespectra of the type shown in Figure 5(a) recorded as functionsof 120574-irradiation time for two virgin lengths of fiber takenfrom the same spool of aluminum-clad low-OHlow-ClKS4V pure-silica-core optical fiber subjected to dose rates of015 Gys and 102Gys Note in Figure 7 the confluence of thetwo data sets (solid squares and circles) at times longer thansim106 s The large hollow symbols are not data points ratherthey have been added to connect arbitrarily selected pointson the two curves which share identical radiation dosesClearly if the 102Gys curve had been an accelerated test and015Gys was the anticipated mission dose rate the acceler-ated test would be seriously lying about the vulnerability ofthis fiber to mission conditions

35 Radiation Hardening by the Presence of Hydroxyl Groupsor Interstitial Hydrogen In [33] the influence of pulsed x-irradiation on the optical transmission of a pair of high-purity-silica-core optical fibers was investigated at room tem-perature Transient exposures employed a sim1MeV pulsed X-ray generator with doses varying between 1 and 300Gy(SiO

2)

and dose rates gt1MGys One of these fibers had a highOH content and the other an extremely low OH contentFigure 8 shows the resulting induced absorption in the low-OH-silica-core sample at times 05 and 16 s after that pulseas the black curves with peaks near 16 eV These curves arecompared with the (magnified to fit above 23 eV) spectra of

Indu

ced

loss

(dB

km)

102 103 104 105 106 107

1000

100

Time (s)

Stretched 2nd order = 053Kohlrausch = 06

Stretched 2nd order = 096


102 rads

153 rads

120573

120573

120573

120573120573

Figure 7 Growth and radiation-stimulated destruction of opticalbands sampled at 900 nm for an identical virgin pair of low-OHlow-Cl aluminum-clad pure-silica-core (KS4V) optical fiberscontinuously subjected to two different 120574-ray dose rates Largehollow symbols link points on the two growth curves receiving equalaccumulated doses This is an adaptation of a figure in [48] wherefurther information about the data collection and curve fitting canbe found

014

012

01

008

006

004

002

008 1 12 14 16 18 2 22 24 26 28

Photon energy (eV)

05 s

16 s

(iv)(iii)

(i)(ii)

08 1 12 14 16 18 2 22 24 26 28Photon energy (eV)

RIA

(dBmiddot

mminus1

middotGyminus

1 )

003

0025

002

0015

001

0005

0

RIA

(dB

mminus1G

yminus1)

Figure 8 Pulsed-X-ray-induced spectra of a pair of optical fiberswith pure silica cores one with high-OH and the other with low-OH decomposed to emphasize bands centered near 16 eV uniqueto low-OH fiber [33] Note rapid room-temperature decay of thesemetastable visiblenear-IR bands

the similarly irradiated andmeasured high-OHfibers (curvesi and iii resp) Subtraction of curves i and iii from therespective spectra of the low-OH fiber resulted in curves iiand iv respectively which have been decomposed in the insetinto a pair of bands centered near 163 and 188 eVmdashvirtuallyidentical to the bands that I have assigned to STHs induced inlow-OH-silica-core fibers continuously 120574-irradiated at doserates in the range of sim015 to sim5Gys [44ndash46 48]

In order to better understand the results of Figure 8it should be understood that 120574-rays [49] X-rays [50] and64 eV laser photons [50] have each been shown to create free


hydrogen atoms in OH-containing silica glasses by radiolyticdissociation of hydroxl groups in according to

equivSi-OH 997888rarrequivSi-O∙ + ∙H0 (4)

where ldquoequivSi-O∙rdquo is a nonbridging-oxygen hole center(NBOHC) and the dots ldquo∙rdquo indicate unpaired electronswhich in these particular cases have both been monitoredby ESR When such irradiations are carried out at 100Kor lower the numbers of ∙H0s found in high-OH silicasbefore warming are typically sim2 to 3 times more numerousthan any other paramagnetic defect [25 49 50] Warmingbriefly to sim150K (or sometimes only to sim130K) results inthe disappearance of all ∙H0s due at least partially to theback reaction of (4) Those ∙H0s that neither back react norimmediately react with STHs or defect center precursors inthe glass have been demonstrated to dimerize into ESR-silentH2molecules some of which subsequently diffuse in the

temperature range sim190ndash290K to the sites of NBOHCswhere they are ldquocrackedrdquo according to the reaction [25]

equivSi-O∙ +H2997888rarrequivSi-OH + ∙H0 (5)

The released hydrogen atom ∙H0 commonly reacts withprecursors to form 1198641015840

120573centers [10 25 32] (or formyl radicals

in the rare case of silica glasses containing traces of carbonmonoxide [49])

STHs have never been observed in high-OH glasses pre-sumably because the initially created ∙H0s immediately reactwith STHs to form ESR-silent protons (which in a-SiO

2gate

oxides of MOS structures drift toward the SiO2Si interface

under positive gate bias to form deleterious Pb centers [2])Thus the experiment of [33] becomes additional evidencethat radiation-induced optical bands centered near 163 and188 eV in low-OH pure-silica-core optical fibers are trulyattributable to STHsmdasheven though these optical-fiber STHsdiffer from the bands at 216 and 260 eV that unambiguouslycharacterize STH

2and STH

1 respectively in irradiated bulk

silica [47]

4 Superiority of Fractal Kinetics forAssessing the Kinetics of Radiation-InducedDefects in Glasses

In [48] I reported my derivations of first- and second-orderfractal kinetic processes relevant to radiation-induced defectcreation in glasses and their thermally induced decays atambient temperature These relations cannot be applied tosituations where decays are radiation induced Fortunatelyhowever Vladimir Mashkov has derived the fractal kineticequations for the growth and radiolytic decay of defects inglasses [51] Indeed Vladimirrsquos work preceded mine andinspired and guidedme to domy own derivations for the caseof thermally decaying defects [48]

So why are fractal kinetic formalisms superior to theldquostretched exponentialrdquo Kohlrausch function given that inboth cases the solutions are functions of (119896119905)120573 where 119896 is aneffective rate constant 119905 is time and 0 lt 120573 lt 1 Well my

answer is that the parameterizations of the fractal formalismsthat I obtained by changing the dimensionless variable 119896119905 rarr(119896119905)120573 for both the classical first-order and classical second-

order kinetic equations (i) explicitly pertain to the thermaldecay of the radiation-induced defects (ii) result in solutionsthat have been found to fit the experimental data muchbetter than by any other means and (iii) have also revealedsome striking totally unexpected and potentially valuableempirical rules [48] which the ad hoc parameterizations ofthe strictly first-order Kohlrausch function conceal IndeedKlafter and Shlesinger [52] have shown that three verydifferent theoreticalmodels leading to sameKohlraush law allhave a common underlying mathematical structure whereasin the present case the mathematical structures are particularto the specific models

Figure 9 illustrates the most striking empirical rule thatI discovered [48] by using my new fractal formalisms tofit the growth in optical attenuation at 1300 nm recordedfor four spools each of two sets of Ge-doped-silica-coreoptical fibersmdashone of the sets being multimode (MM) andthe other single-mode (SM)mdashduring 120574-irradiations at 00045017 and 34Gys and either an 88 times 10minus6Gys nuclear-reactor irradiation or a 1 times 10minus4Gys 120574-irradiation All ofthe spectral data that I fitted were acquired by Joe Friebeleand his group at the Naval Research Laboratory and hadbeen previously reported in [53] The stunning features ofFigure 9 are the facts that (i) the fractal rate coefficients 119896in both first- and second-order are essentially coincidentand (ii) they turn out to define a single linear function ofdose rate over six orders of magnitude in dose rate Needlessto say this outcome offers genuine hope that it should bepossible to safely extrapolate these parameters into dose-rateregimes greater than 4Gys (for which sources are generallyunavailable) as well as backwards into the realm of dose rateslower than 10minus5Gys (in which case complete growth curvessuch as those of Figure 10 could not be obtained in practicallaboratory times)

41 There Are Two Other Fractal Kinetic Parameters Besides kFigure 9 is only a part of a much longer story [48] which Iwill attempt only to outline here Most importantly I mustconfess that there are two additional fractal measurablesderivable from the fitting functions which also depend onthe experimental dose rate D

(A) 120573 is the exponent of the dimensionless variable(119896119905) that appears in both the first- and second-order fractal-kinetic differential equations and theirsolutions wherein 119896 is the deduced fractal rate coef-ficient plotted on the ordinate of Figure 9 and 119905 isthe running time of the irradiation in seconds Themaximum irradiation times 119905max were arranged in[53] to achieve as nearly as possible the same totaldoses D

119894times 119905max(119894) for each of the four experimental

dose rates D119894 where 119894 = 1 2 3 or 4 (However

this ideal objective was not quite achieved for the twolowest dose rates in Figure 10) By means of fittingthe experimental growth curves I found 120573 to vary

10 Physics Research InternationalRa

te co

effici

ent (

sminus1) 10minus3

10minus4

10minus5

10minus6

10minus7

10minus8

Classical 1st-order kinetics

Linear

0001 001 01 1 10 100Dose rate (rads)

Classical 2nd-orderkinetics

Figure 9 Fractal-kinetic rate coefficients 119896 determined as functionsof dose rate D by fitting [48] growth curves comprising inducedlosses at 1300 nm as functions of accumulated dose from sim7Gy tosim104 Gy in four virgin samples (one curve for each dose rate) of theMMGe-doped-silica-core fiber of [53]The fractal first-order (opencircles) and second-order (solid squares) fitting functions (describedin detail in [48]) were employed here without taking into accounta small population of dose-rate-independent (nondecaying) defectsinferred to be copresent When corrections were made to accountfor such nondecaying defect populations the data points collapsedonto the slope-1 line almost perfectly (Note that Figure 10 shows thesimilarly fitted curves for the corresponding SMfibers each ofwhichtakes into account the non-decaying components)

(concave downward) from sim10 at the lowest doserates to sim05 at the highest dose rate [48]

(B) 119873sat is the saturation defect concentration at infinitetime (119905 rarr infin) which though formulated differentlyin the two kinetic orders considered was foundto behave nearly identically when each was plottedversus the dose rates D

119894 By means of my fits I found

119873sat to increase by a factor of sim100 as D increased bysim6 orders of magnitude [48] with an average slopesim1205732 (vis-a-vis the slope of 100 determined for 119896 inFigure 9)

42MajorDifferences betweenClassical-Kinetic Constants andFractal-Kinetic Coefficients In my fractal derivations [48]both 119896 and 119873sat are expressed in terms of the dose ratesD in combination with the radiation-induced-creation andthermal-decay-rate coefficients119870 and 119877 respectively whichare constants in the classical rate equations upon which theyare based

In my 1st-order fractal-kinetic rate equation I found that119896 = 119877 (which was no longer a constant see below) while inits solution I found that119873sat = (119870D119877)

120573

In my 2nd-order fractal-kinetic rate equation I found

that 119896 = (119870D119877)12

and in its solution I found that 119873sat =(119870D119877)

1205732

Given these strikingly different formulae for the two

fractal-kinetic orders it was surprising to find that thecalculated values of 119896 (see Figure 9) as well as those of 120573 and119873sat (cf [48]) for each of these two fractal-kinetic orders coin-cided rather accurately for every sampled dose rate Again allvalues of 119896 120573 and119873sat were derived from independent fits ofmy first- and second-order fractal solutions for two sets (MMand SM) of four experimental growth curves corresponding

1 10 100 100001

1

10

100

C

BIndu

ced

loss

(dB

km)

Dose (rad)

120573120573120573

120573340 rads= 052

17 rads045 rads 0011 rads

= 066= 085 = 1

times103

Figure 10 Growth of induced attenuation at 1300 nm in lengthsof Corning single mode (SM) Ge-doped-silica-core optical fibersseparately subjected to 120574-ray irradiations at dose rates of 0011 04517 and 340 rads at 50∘C (continuous solid curves and black squares)[53] The small open circles are best fits to these four data sets basedprimarily on the fractal second-order-kinetic growth solutions givenas (equation (17) of [48]) for defects (termed ldquoPopulation Ardquo) thatthermally decay at ambient temperature However after the best-fitPopulation-A simulations were accomplished and found to be lessthan perfect these fits were improved upon by cut-and-try additionsof first one and finally two nondecaying (dose-rate independent)populations termed B and C The finally optimized Population Band C growth curves are illustrated here by the correspondinglylabeled dotted curves Because these additional populations wereindependent of dose rate by design the very same pair of curveshad to be added to each of the four fractal-kinetic simulationscomprising the dose-rate-dependent parts of the four growth curvesin order to achieve the final fits such as the ones depicted hereFigure from [48]

to four different dose rates D (Figure 10 shows the second-order fits of the SM data)

Another surprising outcome turned out to be the empir-ical rules [48] In the 1st-order case 119877 prop D and 119870 prop D

12

whereas in the 2nd-order case119870119877 is independent of D while119870 times 119877 prop D

43 What Are the Defects Responsible for the Radiation-Induced Losses at 1300 nm After a long period of time think-ing about it I am finally convinced that the ldquoPopulation Ardquoattenuations must be manifestations of the long-wavelengthtails of the optical bands of self-trapped holes which peaknear 163 and 188 eV in low-OH silica-based optical fibers[44ndash46] (see Figure 11) If I am right about this then itshould be possible to radiation harden low-OH pure silica-core optical fibers or fiber devices against photo darkeningat 1300 nm by pre-irradiation at a relatively low dose rate (cfSection 33)

Populations B and C in the Ge-doped-silica fibers dis-cussed above make much smaller (but permanent) contribu-tions to the radiation-induced losses at 1300 nm Clearly they


25

20

15

10

5

0

2500

2000

1500

1000

500

0400 600 800 1000 1200 1400

Indu

ced

abso

rptio

n (d

Bkm

)

Wavelength (nm)

times103

Figure 11 120574-ray-induced optical absorption bands attributable tometastable self-trapped holes in separate lengths of an aluminum-clad low-OH F-doped-silica-core optical fiber at 27∘C in the darkThe short-wavelength spectra were recorded in situ using a 1mlength of fiber and a prism-based CCD-camera spectrometer [48]whereas long-wavelength spectrum was recorded in situ using a10m length and an optical signal analyzer Dose rates in radsand irradiation times in seconds are indicated in the figure Thedose delivered to the 10m length was about the same as for the960 s exposure of the 1m length (note that the right-hand scale isexpanded by a factor of 10) Figure from [48]

must comprise the long-wavelength tails of the nearest (non-STH) bands at shorter wavelengthsThesewould be theGe(1)[5 6] and GeX [54 55] trapped-electron centers centered at44 eV and 26 eV respectively and perhaps also the 20 eVband (eg [56]) due to NBOHCs

The nomenclature ldquoGeXrdquo was introduced by Anoikinand his coworkers [54] to express its unknown place inthe Pantheon of Ge-doped-silica-glass defects Howeverthere was one clue By rerecording the optical spectra oftheir 120574-irradiated polymer-clad Ge-doped-silica-core fibersone year later they found that the number density ofGe(1) centers had diminished by about 70 while GeXhad increased by an amount approximately equal to thenumber of Ge(1) centers lost Accordingly I speculate thatGeX may be a Ge(1) that has reacted with atmospherichydrogen that penetrated their polymer jackets If my guessis right then Ge(2) should have been completely destroyedin less than a yearrsquos time (cf Section 221) However Anoikinet al [54] did not record their spectra to energies higherthan 32 eV so further research will be needed to findout what happens to the 58 eV band (associated withGe(2) see Figure 2) in irradiated polymer-clad fibers subse-quently exposed to the atmosphere for extended periods oftime

44 Fractal-Kinetic Isothermal Decay Curves Postirradiationdecay curves were measured only for the MM and SM Ge-doped fiber coils exposed to the highest dose of 1Mrad at adose rate of 340 rads [53] My study of these curves yieldedsome good news and some bad news

1 10 100 1000 10000 100000 10000000

10

20

30

40

50

60

70

80

90 MM fiber data

Indu

ced

loss

(dB

km)

Time (s)

Naive Kohlrauschprediction fromgrowth-curve fit

( = 071)

Stretched 2nd-orderbest fit ( = 054)

Kohlrauschbest fit

( = 044)SM fiber data


Naive stretched 2nd-orderprediction from growth-curve

fit ( = 062)120573

120573

120573

120573

120573

Figure 12 Thermal decay curves of MM and SM Ge-doped-silica-core optical fibers following a 1-Mrad irradiation at 340 rads (boldblack curves) [53]The SMdata correspond to the upper curve of thegrowth data of Figure 10 Other features are explained in the textFigure from [48] Although virtually impossible to discern in thefigure above the experimental data terminate at 60000 s thus theopen circles at longer times are solely extensions of the fits to thedata at shorter times

The good news is that the existence of nondecaying (dose-rate independent) defect centers was confirmed and theunambiguous numbers of these nondecaying centers werefound to agree rather well with the sum of the high-doseends of the ldquoPopulations B and Crdquo growth curves that I haditerated intomy simulations of the growth curves of Figure 10This verification came in the form of the time-independentinduced losses sim10 dBkm that I was forced to add to myfractal-kinetic decay-equation simulations in order to matchthe actual decay curves shown as the bold black lines inFigure 12

The ldquobad newsrdquo was that the fractal decay-rate constants119877 that I used so successfully to simulate the dose-rate-dependent growth curves of Figure 10 were too large byfactors of sim15 to fit the actual decay curves of Figure 12The naıvete of my notion that they should match exactlyis illustrated by the light dashed curves in Figure 12 Mysuccessful fits using substantially larger values of 119877 in myfractal-kinetic second-order decay solution (Equation (20) of[48]) are shown in Figure 12 as the small hollow circles Myfractal first-order-kinetic best-fit (ldquoKohlrausch best fitrdquo smallhollow triangles) is clearly inferior In fact this bow towardthe second-order solution is good news for my fractal-kineticformalisms given that the recombination of electrons andholes is a second-order kinetic process

Apropos of predicting the decay curve from the param-eters of the growth curve it has been proven possibleto dissect power-law growth curves into a succession ofclassical 119899th-order-kinetic solutions wherein the dominantsubpopulations are characterized by growth and thermaldecay rate constants 119870(D) and 119877(D) respectively both ofwhich decline inmagnitudewith increasing doseD accordingto rigorously derived rules [57] Then for power laws 0 lt 120573 lt1 kinetic orders 119899 and experimental irradiation times 119905irrad


the characteristic postirradiation decay time constants 120591119888are

predicted to be

120591119888=

119905irrad[(119899 minus 1) (1 minus 120573)]

for 119899 gt 1

120591119888=

119905irrad[1 minus 120573]

for 119899 = 1(6)

This prediction has actually worked out nicely in one exper-imental case [57] However the caveat here is that (6) havesucceeded only when applied to pure power-law growthcurves Whether or not an analogous system can ever beworked out for continuously curved growth curves such asthose in Figure 10 is uncertain

5 Conclusions

It is clear that a half century of electron-spin-resonance andoptical studies of radiation-induced point defects in pure anddoped silica glasses has been an immense boon for under-standing the performances of both bulk and fiber-optic formsof thesematerials in radiation environments ranging from theLarge Hadron Collider and the International ThermonuclearExperimental Reactor to outer space Fortunately these stud-ies are continuing given the virtual infinity of trace impuri-ties manufacturing methods environmental conditions andend-user requirements to which these essential materials anddevices will continue to be subjected Hopefully the body ofknowledge incorporated into this paper and the referencesprovidedwill stimulate future studies in areas that still remainunsettled while averting ldquoreinvention of the wheelrdquo in areasthat are solidly established

In particular I hope that the reader will recognizefrom Section 4 that fractal kinetics is much more than justa systematized study of dose-rate-dependent attenuationsinduced in silica-based fiber optics by ionizing radiationsRather it is a rigorous mathematical formalism that perfectlymatches the model pertaining to the experimental data andserendipitously provides a reliable means for extrapolatingthe results of dose-rate-dependence studies backward intotime regimes so extended that the experiments cannot becompleted in practical laboratory times and forward intosuprahigh-dose-rate regimes for which no laboratory sourcesare likely to become available in the near future

Acknowledgments

The author thanks Katsumi Tanimura for kindly providinghis original data and curve fits which he has replotted inFigure 4 and Ed Taylor for inviting him to speak on thistheme at the SPIE 2011 Optics + Photonics Conference 8164thereby inspiring an early version of this paper He composedthis paper without outside funding

References

[1] D L Griscom ldquoNature of defects and defect generation inoptical glassesrdquo Proceedings of SPIE vol 541 pp 38ndash59 1985

[2] D L Griscom ldquoHydrogen model for radiation-induced inter-face states in SiO

2-on-Si Structures a review of the evidencerdquo

Journal of Electronic Materials vol 21 no 7 pp 763ndash767 1992[3] D L Griscom ldquoAmorphousmaterials electron spin resonancerdquo

in Encyclopedia of Materials Science and Technology pp 179ndash186 Elsevier Science 2001

[4] D L Griscom ldquoElectron spin resonancerdquo in Glass Science andTechnology vol 4B of Advances in Structural Analysis pp 151ndash251 Academic Press New York NY USA 1990

[5] E J Friebele and D L Griscom ldquoColor centers in glassoptical fiber waveguidesrdquo in Defects in Glasses vol 61 of MRSProceedings pp 319ndash331 1986

[6] D L Griscom ldquoOn the natures of radiation-induced pointdefects in GeO

2-SiO2glasses reevaluation of a 26-year-old ESR

and optical data setrdquo Optical Materials Express vol 1 pp 400ndash412 2011

[7] D L Griscom ldquoTrapped-electron centers in pure and dopedglassy silica a review and synthesisrdquo Journal of Non-CrystallineSolids vol 357 no 8-9 pp 1945ndash1962 2011

[8] D L Griscom and E J Friebele ldquoFundamental radiation-induced defect centers in synthetic fused silicas atomic chlo-rine delocalized e centers and a triplet staterdquo Physical ReviewB vol 34 no 11 pp 7524ndash7533 1986

[9] R A Weeks ldquoParamagnetic resonance of lattice defects inirradiated quartzrdquo Journal of Applied Physics vol 27 no 11 pp1376ndash1381 1956

[10] D L Griscom ldquoCharacterization of three E1015840-center variants inX- and 120574-irradiated high purity a-SiO

2rdquo Nuclear Instruments

and Methods in Physics Research B vol 1 no 2-3 pp 481ndash4881984

[11] D LGriscomandMCook ldquo29Si superhyperfine interactions ofthe E1015840 center a potential probe of range-II order in silica glassrdquoJournal of Non-Crystalline Solids vol 182 no 1-2 pp 119ndash1341995

[12] D L Griscom ldquoThe natures of point defects in amorphoussilicon dioxiderdquo in Defects in SiO

2and Related Dielectrics Sci-

ence and Technology G Pacchioni L Skuja and D L GriscomEds pp 117ndash159 Kluwer Academic Publishers Dordrecht TheNetherlands 2000

[13] G Buscarino S Agnello and F M Gelardi ldquoSi29 hyperfinestructure of the E1015840

120572center in amorphous silicon dioxiderdquo

Physical Review Letters vol 97 no 13 Article ID 135502 2006[14] M Jivanescu andA Stesmans ldquoMulti-frequency ESR analysis of

E1015840120575defect in a-SiO

2rdquo in Proceedings of the 8th Symposium SiO2

Advanced Dielectrics and Related Devices Varenna Italy 2010[15] D L Griscom ldquoElectron spin resonance characterization of

self-trapped holes in amorphous silicon dioxiderdquo Journal ofNon-Crystalline Solids vol 149 no 1-2 pp 137ndash160 1992

[16] D L Griscom ldquoSelf-trapped holes in pure-silica glass a historyof their discovery and characterization and an example oftheir critical significance to industryrdquo Journal of Non-CrystallineSolids vol 352 no 23-25 pp 2601ndash2617 2006

[17] J A Weil ldquoA demi-century of magnetic defects in 120572 quartzrdquo inDefects in SiO

2and Related Dielectrics Science and Technology

pp 197ndash212 Kluwer Academic London UK 2000[18] E J Friebele D L Griscom and G H Sigel ldquoDefect centers in

a germanium-doped silica-core optical fiberrdquo Journal of AppliedPhysics vol 45 no 8 pp 3424ndash3428 1974

[19] J Isoya J A Weil and R F C Claridge ldquoThe dynamicinterchange and relationship between germanium centers in 120572-quartzrdquoThe Journal of Chemical Physics vol 69 no 11 pp 4876ndash4884 1978


[20] R J McEachern and J A Weil ldquo17O hyperfine interactionfor the [GeO

4] IIIminus and [GeO

4Li] AC

0 centers in an enrichedcrystal of 120572-quartzrdquo Physical Review B vol 49 no 10 pp 6698ndash6709 1994

[21] A Alessi S Girard M Cannas S Agnello A Boukenter andY Ouerdane ldquoEvolution of photo-induced defects in Ge-dopedfiberpreform influence of the drawingrdquo Optics Express vol 19no 12 pp 11680ndash11690 2011

[22] K Nagasawa T Fujii Y Ohki and Y Hama ldquoRelation betweenGe(2) center and 119mT hyperfine structure of ESR spectra inGe-doped silica fibersrdquo Japanese Journal of Applied Physics vol27 no 2 pp 240ndash243 1988

[23] A A Bobyshev and V A Radtsig ldquoEPR study of the centers ofchemisorption of certain gases on a GeO

2surfacerdquo Kinetics and

Catalysis vol 22 pp 1229ndash1235 1982[24] T E Tsai and D L Griscom ldquoOn the structures of hydrogen-

associated defect centers in irradiated high-purity a-SiO2OHrdquo

Journal of Non-Crystalline Solids vol 91 no 2 pp 170ndash179 1987[25] D L Griscom ldquoThermal bleaching of x-ray-induced defect

centers in high purity fused silica by diffusion of radiolyticmolecular hydrogenrdquo Journal of Non-Crystalline Solids vol 68no 2-3 pp 301ndash325 1984

[26] D L Griscom G H Sigel and R J Ginther ldquoDefect centers ina pure-silica-core borosilicate-clad optical fiber ESR studiesrdquoJournal of Applied Physics vol 47 no 3 pp 960ndash967 1976

[27] M G Jani R B Bossoli and L E Halliburton ldquoFurthercharacterization of the E1015840

1center in crystalline SiO

2rdquo Physical

Review B vol 27 no 4 pp 2285ndash2293 1983[28] R Schnadt andA Rauber ldquoMotional effects in the trapped-hole

center in smoky quartzrdquo Solid State Communications vol 9 no2 pp 159ndash161 1971

[29] K L Brower ldquoElectron paramagnetic resonance of Al E10158401centers

in vitreous silicardquo Physical Review B vol 20 no 5 pp 1799ndash18111979

[30] A N Trukhin A Sharakovski J Grube and D L GriscomldquoSub-band-gap-excited luminescence of localized states inSiO2-Si and SiO

2-Al glassesrdquo Journal of Non-Crystalline Solids

vol 356 no 20-22 pp 982ndash986 2010[31] D L Griscom ldquo120574 and fission-reactor radiation effects on

the visible-range transparency of aluminum-jacketed all-silicaoptical fibersrdquo Journal of Applied Physics vol 80 no 4 pp 2142ndash2155 1996

[32] D LGriscomD B Brown andN S Saks ldquoNature of radiation-induced point defects in amorphous SiO

2and their role in SiO

2-

on-Si structuresrdquo in The Physics and Chemistry of SiO2and the

Si-SiO2Interface pp 287ndash297 Plenum New York NY USA

1988[33] S Girard D L Griscom J Baggio B Brichard and F Bergh-

mans ldquoTransient optical absorption in pulsed-X-ray-irradiatedpure-silica-core optical fibers influence of self-trapped holesrdquoJournal of Non-Crystalline Solids vol 352 no 23-25 pp 2637ndash2642 2006

[34] J H Konnert P DrsquoAntonio and J Karle ldquoComparison of radialdistribution function for silica glass with those for variousbonding topologies use of correlation functionrdquo Journal ofNon-Crystalline Solids vol 53 no 1-2 pp 135ndash141 1982

[35] G Pacchioni and A Basile ldquoCalculated spectral properties ofself-trapped holes in pure and Ge-doped SiO

2rdquo Physical Review

B vol 60 no 14 pp 9990ndash9998 1999[36] A V Kimmel P V Sushko and A L Shluger ldquoStructure and

spectroscopic properties of trapped holes in silicardquo Journal ofNon-Crystalline Solids vol 353 no 5-7 pp 599ndash604 2007

[37] A C Wright ldquoDefect-free vitreous networks the idealizedstructure of SiO

2and related glassesrdquo in Defects in SiO

2and

Related Dielectrics Science and Technology pp 1ndash35 KluwerAcademic Publishers London UK 2000

[38] A C Wright ldquoNeutron and x-ray amorphographyrdquo in Experi-mental Techniques of Glass Science pp 205ndash314 The AmericanCeramic Society Westerville Ohio USA 1993

[39] D L Griscom ldquoSelf-trapped holes in amorphous silicon diox-iderdquo Physical Review B vol 40 no 6 pp 4224ndash4227 1989

[40] P V Chernov E M Dianov and V N Karpechev ldquoSpectro-scopic manifestations of self-trapped holes in silicardquo PhysicaStatus Solidi B vol 155 pp 633ndash640 1989

[41] E Harari S Wang and B S H Royce ldquoLow-temperatureirradiation effects in SiO

2-insulated MIS devicesrdquo Journal of

Applied Physics vol 46 no 3 pp 1310ndash1317 1975[42] K Nagasawa M Tanabe K Yahagi A Iino and T Kuroha

ldquoGamma-ray induced absorption band at 760 nm in pure silicacore optical fibersrdquo Japanese Journal of Applied Physics vol 23no 5 pp 606ndash611 1984

[43] K Nagasawa M Tanabe and K Yahagi ldquoGamma-ray-inducedabsorption bands in pure-silica-core fibersrdquo Japanese Journal ofApplied Physics vol 23 no 12 pp 1608ndash1613 1984

[44] D L Griscom ldquoVisibleinfra-red absorption study in fibergeometry of metastable defect states in high-purity fusedsilicasrdquoMaterials Science Forum vol 239ndash241 pp 19ndash24 1997

[45] D L Griscom ldquoRadiation hardening of pure-silica-core opticalfibers reduction of induced absorption bands associated withself-trapped holesrdquoApplied Physics Letters vol 71 no 2 pp 175ndash177 1997

[46] D L Griscom ldquo120574-Ray-induced visibleinfrared optical absorp-tion bands in pure and F-doped silica-core fibers are they due toself-trapped holesrdquo Journal of Non-Crystalline Solids vol 349no 1ndash3 pp 139ndash147 2004

[47] Y Sasajima and K Tanimura ldquoOptical transitions of self-trapped holes in amorphous SiO

2rdquo Physical Review B vol 68

no 1 Article ID 014204 pp 142041ndash142047 2003[48] D L Griscom ldquoFractal kinetics of radiation-induced point-

defect formationand decay in amorphous insulators appli-cation to color centers insilica-based optical fibersrdquo PhysicalReview B vol 64 no 17 Article ID 174201 2001

[49] D L Griscom M Stapelbroek and E J Friebele ldquoESR studiesof damage processes in X-irradiated high purity a-SiO

2OH and

characterization of the formyl radical defectrdquo The Journal ofChemical Physics vol 78 no 4 pp 1638ndash1651 1983

[50] D L Griscom ldquoGrowth and decay kinetics of defect centersin high-purity fused silicas irradiated at 77K with X-Rays or64-eV laser lightrdquo Nuclear Instruments and Methods in PhysicsResearch B vol 46 no 1ndash4 pp 12ndash17 1990

[51] V A Mashkov W R Austin L Zhang and R G LeisureldquoFundamental role of creation and activation in radiation-induced defect production in high-purity amorphous SiO

2rdquo

Physical Review Letters vol 76 no 16 pp 2926ndash2929 1996[52] J Klafter andM F Shlesinger ldquoOn the relationship among three

theories of relaxation in disordered systemsrdquo Proceedings of theNational Academy of Sciences of the United States of Americavol 83 pp 848ndash851 1986

[53] E J Friebele G M Williams andW D Mack ldquoQualified partslist optical fibers in radiation environmentsrdquo in Optical FiberReliability and Testing vol 3848 of Proceedings of SPIE pp 232ndash239 September 1999


[54] E V Anoikin V M Mashinsky V B Neustruev and Y SSidorin ldquoEffects of exposure to photons of various energies ontransmission of germanosilicate optical fiber in the visible tonear IR spectral rangerdquo Journal of Non-Crystalline Solids vol179 pp 243ndash253 1994

[55] D LGriscom ldquo120574-ray-induced optical attenuation inGe-doped-silica fiber image guidesrdquo Journal of Applied Physics vol 78 no11 pp 6696ndash6704 1995

[56] L Skuja ldquoSection 1 Defect studies in vitreous silica and relatedmaterials optically active oxygen-deficiency-related centers inamorphous silicon dioxiderdquo Journal of Non-Crystalline Solidsvol 239 no 1ndash3 pp 16ndash48 1998

[57] D L Griscom M E Gingerich and E J Friebele ldquoModel forthe dose dose-rate and temperature dependence of radiation-induced loss in optical fibersrdquo IEEE Transactions on NuclearScience vol 41 no 3 pp 523ndash527 1994

Submit your manuscripts athttpwwwhindawicom

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

High Energy PhysicsAdvances in

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014


FluidsJournal of

Atomic and Molecular Physics

Journal of



Advances in Condensed Matter Physics

OpticsInternational Journal of



AstronomyAdvances in

International Journal of


Superconductivity


Statistical MechanicsInternational Journal of


GravityJournal of


AstrophysicsJournal of


Physics Research International


Solid State PhysicsJournal of

Computational Methods in Physics

Journal of



Soft MatterJournal of

Hindawi Publishing Corporationhttpwwwhindawicom

AerodynamicsJournal of

Volume 2014


PhotonicsJournal of


Journal of

Biophysics


ThermodynamicsJournal of


I II III IV VIrradiation Prompt occurrences Excited state relaxation

recombinationCarrier trappingdefect formation

UV light Photolytic defects

X raysLight emission(Compton electrons) Recombination Radiolytic fragments

(principally H )Transient defectsElectron-hole pairsFast electrons Free carriers Trapping at

radiolytic defects(Secondary electrons)NeutronsTrapping at

preexisting defectsFast ions

Atomic displacementsTrapping atimpuritiesRecombination

Dimerization

Stabilization bydiffusion of charge-compensating ions

Aggregatescolloids bubbles and so forth

Trapping atknock-on damage

Self-trapping

Free vacanciesand interstitials

Furtherdiffusion-limitedreactions

Diffusion-limited reactions

120574-rays

Figure 1 Modes of defect formation in insulators subjected to various types of ionizing radiations andor particles of sufficiently high energyto create ldquoknock-onrdquo damage See [1] for discussions of the indicated processes

100 200 300 400 500 600 700 800 900 100001

1

10

100

Ge(2)

Ge(1)

STH

44 eV58 eV

52 eV shifted

24 eV

Isochronal anneal temperature (K)

Sym

bols

opt

ical

inte

nsity

(eV

cm

)Cu

rves

ESR

spin

den

sitie

s (au

)

Ge 119864prime

Figure 2 ESR-determined number densities (bold curves relative units) and independently determined optical-band intensities (symbolseVcm) for X-ray-induced defect centers in separate samples of a Ge-doped-silica fiber-optic perform following irradiations to the same doseat 100 and 77K respectively and subsequent 5-minute isochronal anneals to the higher temperatures (The ESR data were also recorded atdiscrete temperatures but are displayed here as continuous curves as an aid to the eye) It is seen here that the self-trapped holes (STHs) andthe Ge(1) trapped-electron centers correlate well with optical absorption bands centered near 24 and 44 eV respectively (and have identicaloscillator strengths [5 6]) The upshifted Ge(2) number-density curve (dashed blue curve relating to Ge(2)rsquos higher oscillator strength)strongly matches the 58 eV optical data below 300K and is cryptically correlated with those data above 300KThe diamonds representing a52-eV band not associated with any ESR-detectable defect are shown here displaced upward by a factor of 24 from their originally recordedoptical intensities in order to discover their perfect match with the red curve in the range 200ndash370K which comprises the sum of the changesof the Ge(1) and Ge(2) number densities in the range 200ndash370K multiplied by negative 05 This figuremdashadapted from [5]mdashwas recentlypublished in [6] where full explanations of the meanings and implications of these data can be found

as applied to paramagnetic ions and radiation-induced pointdefects in (mostly silica-based) oxide glasses

The associations of ESR-determined defect-center struc-tures with specific optical absorption bands are generally

established by ESR-optical correlations obtained for exam-ple by means of postirradiation isochronal thermal anneal-ing experiments Figure 2 provides an example of such aparallel set of ESR and optical isochronal anneal sequences




2are often







120572 1198641015840120572119867119879





4tetrahedra linked



120574centers










1and STH









4




4tetrahedron



2-



2




2




[GeOslash4∙]2

minus


4H]2

minus

+ ∙H0 (2)





2than







2O3-3SiO




2O3-3SiO

2glass result from











2O3doping





SiO

Si

119910

119909

119911

(a)

Si

O

O

O

O119910

119909

119911

(b)





2 have been


















1and STH




1 15 2 25 3 35 4 45 5

0

002

004

006

008

Opt

ical

den

sity

Photon energy (eV)

STH2

STH1





2and STH







1









18000

16000

14000

12000

10000

8000

6000

4000

2000

0400 500 600 700 800 900 1000

Dose [Gy(Si)]In

duce

d lo

ss (d

Bkm

)

Wavelength (nm)

(1) 34(2) 244

(1)

(2)

(3)

(4)

(3) 17 times 105(4) 25 times 106

(1)

(2)

(3)

(4)

(a)


3000

2000

1000

0

1 2

Indu

ced

loss

(dB

km)

(b)




Radiationbleaching

1

23

4

Indu

ced

loss

(dB

km)

102 103 104 105 106

104

103

Growth Recoveries


Steady state


Time (s)





2)


Indu

ced

loss

(dB

km)

102 103 104 105 106 107

1000

100

Time (s)




102 rads

153 rads

120573

120573

120573

120573120573


014

012

01

008

006

004

002

008 1 12 14 16 18 2 22 24 26 28

Photon energy (eV)

05 s

16 s

(iv)(iii)

(i)(ii)

08 1 12 14 16 18 2 22 24 26 28Photon energy (eV)

RIA

(dBmiddot

mminus1

middotGyminus

1 )

003

0025

002

0015

001

0005

0

RIA

(dB

mminus1G

yminus1)














2gate



2and STH


silica [47]













te co

effici

ent (

sminus1) 10minus3

10minus4

10minus5

10minus6

10minus7

10minus8


Linear

0001 001 01 1 10 100Dose rate (rads)









120573


that 119896 = (119870D119877)12


1205732



1 10 100 100001

1

10

100

C

BIndu

ced

loss

(dB

km)

Dose (rad)

120573120573120573

120573340 rads= 052


= 066= 085 = 1

times103




12





25

20

15

10

5

0

2500

2000

1500

1000

500

0400 600 800 1000 1200 1400

Indu

ced

abso

rptio

n (d

Bkm

)

Wavelength (nm)

times103





1 10 100 1000 10000 100000 10000000

10

20

30

40

50

60

70

80

90 MM fiber data

Indu

ced

loss

(dB

km)

Time (s)


( = 071)


Kohlrauschbest fit




fit ( = 062)120573

120573

120573

120573

120573







predicted to be

120591119888=


for 119899 gt 1

120591119888=

119905irrad[1 minus 120573]

for 119899 = 1(6)


5 Conclusions



Acknowledgments


References





































4Li] AC













2rdquo Physical











2-












2and


















2OH and




2rdquo














FluidsJournal of


Journal of










Superconductivity




GravityJournal of








Journal of






Volume 2014


PhotonicsJournal of


Journal of

Biophysics






2are often







120572 1198641015840120572119867119879





4tetrahedra linked



120574centers










1and STH









4




4tetrahedron



2-



2




2




[GeOslash4∙]2

minus


4H]2

minus

+ ∙H0 (2)





2than







2O3-3SiO




2O3-3SiO

2glass result from











2O3doping





SiO

Si

119910

119909

119911

(a)

Si

O

O

O

O119910

119909

119911

(b)





2 have been


















1and STH




1 15 2 25 3 35 4 45 5

0

002

004

006

008

Opt

ical

den

sity

Photon energy (eV)

STH2

STH1





2and STH







1









18000

16000

14000

12000

10000

8000

6000

4000

2000

0400 500 600 700 800 900 1000

Dose [Gy(Si)]In

duce

d lo

ss (d

Bkm

)

Wavelength (nm)

(1) 34(2) 244

(1)

(2)

(3)

(4)

(3) 17 times 105(4) 25 times 106

(1)

(2)

(3)

(4)

(a)


3000

2000

1000

0

1 2

Indu

ced

loss

(dB

km)

(b)




Radiationbleaching

1

23

4

Indu

ced

loss

(dB

km)

102 103 104 105 106

104

103

Growth Recoveries


Steady state


Time (s)





2)


Indu

ced

loss

(dB

km)

102 103 104 105 106 107

1000

100

Time (s)




102 rads

153 rads

120573

120573

120573

120573120573


014

012

01

008

006

004

002

008 1 12 14 16 18 2 22 24 26 28

Photon energy (eV)

05 s

16 s

(iv)(iii)

(i)(ii)

08 1 12 14 16 18 2 22 24 26 28Photon energy (eV)

RIA

(dBmiddot

mminus1

middotGyminus

1 )

003

0025

002

0015

001

0005

0

RIA

(dB

mminus1G

yminus1)














2gate



2and STH


silica [47]













te co

effici

ent (

sminus1) 10minus3

10minus4

10minus5

10minus6

10minus7

10minus8


Linear

0001 001 01 1 10 100Dose rate (rads)









120573


that 119896 = (119870D119877)12


1205732



1 10 100 100001

1

10

100

C

BIndu

ced

loss

(dB

km)

Dose (rad)

120573120573120573

120573340 rads= 052


= 066= 085 = 1

times103




12





25

20

15

10

5

0

2500

2000

1500

1000

500

0400 600 800 1000 1200 1400

Indu

ced

abso

rptio

n (d

Bkm

)

Wavelength (nm)

times103





1 10 100 1000 10000 100000 10000000

10

20

30

40

50

60

70

80

90 MM fiber data

Indu

ced

loss

(dB

km)

Time (s)


( = 071)


Kohlrauschbest fit




fit ( = 062)120573

120573

120573

120573

120573







predicted to be

120591119888=


for 119899 gt 1

120591119888=

119905irrad[1 minus 120573]

for 119899 = 1(6)


5 Conclusions



Acknowledgments


References





































4Li] AC













2rdquo Physical











2-












2and


















2OH and




2rdquo














FluidsJournal of


Journal of










Superconductivity




GravityJournal of








Journal of






Volume 2014


PhotonicsJournal of


Journal of

Biophysics






4tetrahedron



2-



2




2




[GeOslash4∙]2

minus


4H]2

minus

+ ∙H0 (2)





2than







2O3-3SiO




2O3-3SiO

2glass result from











2O3doping





SiO

Si

119910

119909

119911

(a)

Si

O

O

O

O119910

119909

119911

(b)





2 have been


















1and STH




1 15 2 25 3 35 4 45 5

0

002

004

006

008

Opt

ical

den

sity

Photon energy (eV)

STH2

STH1





2and STH







1









18000

16000

14000

12000

10000

8000

6000

4000

2000

0400 500 600 700 800 900 1000

Dose [Gy(Si)]In

duce

d lo

ss (d

Bkm

)

Wavelength (nm)

(1) 34(2) 244

(1)

(2)

(3)

(4)

(3) 17 times 105(4) 25 times 106

(1)

(2)

(3)

(4)

(a)


3000

2000

1000

0

1 2

Indu

ced

loss

(dB

km)

(b)




Radiationbleaching

1

23

4

Indu

ced

loss

(dB

km)

102 103 104 105 106

104

103

Growth Recoveries


Steady state


Time (s)





2)


Indu

ced

loss

(dB

km)

102 103 104 105 106 107

1000

100

Time (s)




102 rads

153 rads

120573

120573

120573

120573120573


014

012

01

008

006

004

002

008 1 12 14 16 18 2 22 24 26 28

Photon energy (eV)

05 s

16 s

(iv)(iii)

(i)(ii)

08 1 12 14 16 18 2 22 24 26 28Photon energy (eV)

RIA

(dBmiddot

mminus1

middotGyminus

1 )

003

0025

002

0015

001

0005

0

RIA

(dB

mminus1G

yminus1)














2gate



2and STH


silica [47]













te co

effici

ent (

sminus1) 10minus3

10minus4

10minus5

10minus6

10minus7

10minus8


Linear

0001 001 01 1 10 100Dose rate (rads)









120573


that 119896 = (119870D119877)12


1205732



1 10 100 100001

1

10

100

C

BIndu

ced

loss

(dB

km)

Dose (rad)

120573120573120573

120573340 rads= 052


= 066= 085 = 1

times103




12





25

20

15

10

5

0

2500

2000

1500

1000

500

0400 600 800 1000 1200 1400

Indu

ced

abso

rptio

n (d

Bkm

)

Wavelength (nm)

times103





1 10 100 1000 10000 100000 10000000

10

20

30

40

50

60

70

80

90 MM fiber data

Indu

ced

loss

(dB

km)

Time (s)


( = 071)


Kohlrauschbest fit




fit ( = 062)120573

120573

120573

120573

120573







predicted to be

120591119888=


for 119899 gt 1

120591119888=

119905irrad[1 minus 120573]

for 119899 = 1(6)


5 Conclusions



Acknowledgments


References





































4Li] AC













2rdquo Physical











2-












2and


















2OH and




2rdquo














FluidsJournal of


Journal of










Superconductivity




GravityJournal of








Journal of






Volume 2014


PhotonicsJournal of


Journal of

Biophysics











2O3doping





SiO

Si

119910

119909

119911

(a)

Si

O

O

O

O119910

119909

119911

(b)





2 have been


















1and STH




1 15 2 25 3 35 4 45 5

0

002

004

006

008

Opt

ical

den

sity

Photon energy (eV)

STH2

STH1





2and STH







1









18000

16000

14000

12000

10000

8000

6000

4000

2000

0400 500 600 700 800 900 1000

Dose [Gy(Si)]In

duce

d lo

ss (d

Bkm

)

Wavelength (nm)

(1) 34(2) 244

(1)

(2)

(3)

(4)

(3) 17 times 105(4) 25 times 106

(1)

(2)

(3)

(4)

(a)


3000

2000

1000

0

1 2

Indu

ced

loss

(dB

km)

(b)




Radiationbleaching

1

23

4

Indu

ced

loss

(dB

km)

102 103 104 105 106

104

103

Growth Recoveries


Steady state


Time (s)





2)


Indu

ced

loss

(dB

km)

102 103 104 105 106 107

1000

100

Time (s)




102 rads

153 rads

120573

120573

120573

120573120573


014

012

01

008

006

004

002

008 1 12 14 16 18 2 22 24 26 28

Photon energy (eV)

05 s

16 s

(iv)(iii)

(i)(ii)

08 1 12 14 16 18 2 22 24 26 28Photon energy (eV)

RIA

(dBmiddot

mminus1

middotGyminus

1 )

003

0025

002

0015

001

0005

0

RIA

(dB

mminus1G

yminus1)














2gate



2and STH


silica [47]













te co

effici

ent (

sminus1) 10minus3

10minus4

10minus5

10minus6

10minus7

10minus8


Linear

0001 001 01 1 10 100Dose rate (rads)









120573


that 119896 = (119870D119877)12


1205732



1 10 100 100001

1

10

100

C

BIndu

ced

loss

(dB

km)

Dose (rad)

120573120573120573

120573340 rads= 052


= 066= 085 = 1

times103




12





25

20

15

10

5

0

2500

2000

1500

1000

500

0400 600 800 1000 1200 1400

Indu

ced

abso

rptio

n (d

Bkm

)

Wavelength (nm)

times103





1 10 100 1000 10000 100000 10000000

10

20

30

40

50

60

70

80

90 MM fiber data

Indu

ced

loss

(dB

km)

Time (s)


( = 071)


Kohlrauschbest fit




fit ( = 062)120573

120573

120573

120573

120573







predicted to be

120591119888=


for 119899 gt 1

120591119888=

119905irrad[1 minus 120573]

for 119899 = 1(6)


5 Conclusions



Acknowledgments


References





































4Li] AC













2rdquo Physical











2-












2and


















2OH and




2rdquo














FluidsJournal of


Journal of










Superconductivity




GravityJournal of








Journal of






Volume 2014


PhotonicsJournal of


Journal of

Biophysics













1and STH




1 15 2 25 3 35 4 45 5

0

002

004

006

008

Opt

ical

den

sity

Photon energy (eV)

STH2

STH1





2and STH







1









18000

16000

14000

12000

10000

8000

6000

4000

2000

0400 500 600 700 800 900 1000

Dose [Gy(Si)]In

duce

d lo

ss (d

Bkm

)

Wavelength (nm)

(1) 34(2) 244

(1)

(2)

(3)

(4)

(3) 17 times 105(4) 25 times 106

(1)

(2)

(3)

(4)

(a)


3000

2000

1000

0

1 2

Indu

ced

loss

(dB

km)

(b)




Radiationbleaching

1

23

4

Indu

ced

loss

(dB

km)

102 103 104 105 106

104

103

Growth Recoveries


Steady state


Time (s)





2)


Indu

ced

loss

(dB

km)

102 103 104 105 106 107

1000

100

Time (s)




102 rads

153 rads

120573

120573

120573

120573120573


014

012

01

008

006

004

002

008 1 12 14 16 18 2 22 24 26 28

Photon energy (eV)

05 s

16 s

(iv)(iii)

(i)(ii)

08 1 12 14 16 18 2 22 24 26 28Photon energy (eV)

RIA

(dBmiddot

mminus1

middotGyminus

1 )

003

0025

002

0015

001

0005

0

RIA

(dB

mminus1G

yminus1)














2gate



2and STH


silica [47]













te co

effici

ent (

sminus1) 10minus3

10minus4

10minus5

10minus6

10minus7

10minus8


Linear

0001 001 01 1 10 100Dose rate (rads)









120573


that 119896 = (119870D119877)12


1205732



1 10 100 100001

1

10

100

C

BIndu

ced

loss

(dB

km)

Dose (rad)

120573120573120573

120573340 rads= 052


= 066= 085 = 1

times103




12





25

20

15

10

5

0

2500

2000

1500

1000

500

0400 600 800 1000 1200 1400

Indu

ced

abso

rptio

n (d

Bkm

)

Wavelength (nm)

times103





1 10 100 1000 10000 100000 10000000

10

20

30

40

50

60

70

80

90 MM fiber data

Indu

ced

loss

(dB

km)

Time (s)


( = 071)


Kohlrauschbest fit




fit ( = 062)120573

120573

120573

120573

120573







predicted to be

120591119888=


for 119899 gt 1

120591119888=

119905irrad[1 minus 120573]

for 119899 = 1(6)


5 Conclusions



Acknowledgments


References





































4Li] AC













2rdquo Physical











2-












2and


















2OH and




2rdquo














FluidsJournal of


Journal of










Superconductivity




GravityJournal of








Journal of






Volume 2014


PhotonicsJournal of


Journal of

Biophysics










18000

16000

14000

12000

10000

8000

6000

4000

2000

0400 500 600 700 800 900 1000

Dose [Gy(Si)]In

duce

d lo

ss (d

Bkm

)

Wavelength (nm)

(1) 34(2) 244

(1)

(2)

(3)

(4)

(3) 17 times 105(4) 25 times 106

(1)

(2)

(3)

(4)

(a)


3000

2000

1000

0

1 2

Indu

ced

loss

(dB

km)

(b)




Radiationbleaching

1

23

4

Indu

ced

loss

(dB

km)

102 103 104 105 106

104

103

Growth Recoveries


Steady state


Time (s)





2)


Indu

ced

loss

(dB

km)

102 103 104 105 106 107

1000

100

Time (s)




102 rads

153 rads

120573

120573

120573

120573120573


014

012

01

008

006

004

002

008 1 12 14 16 18 2 22 24 26 28

Photon energy (eV)

05 s

16 s

(iv)(iii)

(i)(ii)

08 1 12 14 16 18 2 22 24 26 28Photon energy (eV)

RIA

(dBmiddot

mminus1

middotGyminus

1 )

003

0025

002

0015

001

0005

0

RIA

(dB

mminus1G

yminus1)














2gate



2and STH


silica [47]













te co

effici

ent (

sminus1) 10minus3

10minus4

10minus5

10minus6

10minus7

10minus8


Linear

0001 001 01 1 10 100Dose rate (rads)









120573


that 119896 = (119870D119877)12


1205732



1 10 100 100001

1

10

100

C

BIndu

ced

loss

(dB

km)

Dose (rad)

120573120573120573

120573340 rads= 052


= 066= 085 = 1

times103




12





25

20

15

10

5

0

2500

2000

1500

1000

500

0400 600 800 1000 1200 1400

Indu

ced

abso

rptio

n (d

Bkm

)

Wavelength (nm)

times103





1 10 100 1000 10000 100000 10000000

10

20

30

40

50

60

70

80

90 MM fiber data

Indu

ced

loss

(dB

km)

Time (s)


( = 071)


Kohlrauschbest fit




fit ( = 062)120573

120573

120573

120573

120573







predicted to be

120591119888=


for 119899 gt 1

120591119888=

119905irrad[1 minus 120573]

for 119899 = 1(6)


5 Conclusions



Acknowledgments


References





































4Li] AC













2rdquo Physical











2-












2and


















2OH and




2rdquo














FluidsJournal of


Journal of










Superconductivity




GravityJournal of








Journal of






Volume 2014


PhotonicsJournal of


Journal of

Biophysics




Radiationbleaching

1

23

4

Indu

ced

loss

(dB

km)

102 103 104 105 106

104

103

Growth Recoveries


Steady state


Time (s)





2)


Indu

ced

loss

(dB

km)

102 103 104 105 106 107

1000

100

Time (s)




102 rads

153 rads

120573

120573

120573

120573120573


014

012

01

008

006

004

002

008 1 12 14 16 18 2 22 24 26 28

Photon energy (eV)

05 s

16 s

(iv)(iii)

(i)(ii)

08 1 12 14 16 18 2 22 24 26 28Photon energy (eV)

RIA

(dBmiddot

mminus1

middotGyminus

1 )

003

0025

002

0015

001

0005

0

RIA

(dB

mminus1G

yminus1)














2gate



2and STH


silica [47]













te co

effici

ent (

sminus1) 10minus3

10minus4

10minus5

10minus6

10minus7

10minus8


Linear

0001 001 01 1 10 100Dose rate (rads)









120573


that 119896 = (119870D119877)12


1205732



1 10 100 100001

1

10

100

C

BIndu

ced

loss

(dB

km)

Dose (rad)

120573120573120573

120573340 rads= 052


= 066= 085 = 1

times103




12





25

20

15

10

5

0

2500

2000

1500

1000

500

0400 600 800 1000 1200 1400

Indu

ced

abso

rptio

n (d

Bkm

)

Wavelength (nm)

times103





1 10 100 1000 10000 100000 10000000

10

20

30

40

50

60

70

80

90 MM fiber data

Indu

ced

loss

(dB

km)

Time (s)


( = 071)


Kohlrauschbest fit




fit ( = 062)120573

120573

120573

120573

120573







predicted to be

120591119888=


for 119899 gt 1

120591119888=

119905irrad[1 minus 120573]

for 119899 = 1(6)


5 Conclusions



Acknowledgments


References





































4Li] AC













2rdquo Physical











2-












2and


















2OH and




2rdquo














FluidsJournal of


Journal of










Superconductivity




GravityJournal of








Journal of






Volume 2014


PhotonicsJournal of


Journal of

Biophysics













2gate



2and STH


silica [47]













te co

effici

ent (

sminus1) 10minus3

10minus4

10minus5

10minus6

10minus7

10minus8


Linear

0001 001 01 1 10 100Dose rate (rads)









120573


that 119896 = (119870D119877)12


1205732



1 10 100 100001

1

10

100

C

BIndu

ced

loss

(dB

km)

Dose (rad)

120573120573120573

120573340 rads= 052


= 066= 085 = 1

times103




12





25

20

15

10

5

0

2500

2000

1500

1000

500

0400 600 800 1000 1200 1400

Indu

ced

abso

rptio

n (d

Bkm

)

Wavelength (nm)

times103





1 10 100 1000 10000 100000 10000000

10

20

30

40

50

60

70

80

90 MM fiber data

Indu

ced

loss

(dB

km)

Time (s)


( = 071)


Kohlrauschbest fit




fit ( = 062)120573

120573

120573

120573

120573







predicted to be

120591119888=


for 119899 gt 1

120591119888=

119905irrad[1 minus 120573]

for 119899 = 1(6)


5 Conclusions



Acknowledgments


References





































4Li] AC













2rdquo Physical











2-












2and


















2OH and




2rdquo














FluidsJournal of


Journal of










Superconductivity




GravityJournal of








Journal of






Volume 2014


PhotonicsJournal of


Journal of

Biophysics




te co

effici

ent (

sminus1) 10minus3

10minus4

10minus5

10minus6

10minus7

10minus8


Linear

0001 001 01 1 10 100Dose rate (rads)









120573


that 119896 = (119870D119877)12


1205732



1 10 100 100001

1

10

100

C

BIndu

ced

loss

(dB

km)

Dose (rad)

120573120573120573

120573340 rads= 052


= 066= 085 = 1

times103




12





25

20

15

10

5

0

2500

2000

1500

1000

500

0400 600 800 1000 1200 1400

Indu

ced

abso

rptio

n (d

Bkm

)

Wavelength (nm)

times103





1 10 100 1000 10000 100000 10000000

10

20

30

40

50

60

70

80

90 MM fiber data

Indu

ced

loss

(dB

km)

Time (s)


( = 071)


Kohlrauschbest fit




fit ( = 062)120573

120573

120573

120573

120573







predicted to be

120591119888=


for 119899 gt 1

120591119888=

119905irrad[1 minus 120573]

for 119899 = 1(6)


5 Conclusions



Acknowledgments


References





































4Li] AC













2rdquo Physical











2-












2and


















2OH and




2rdquo














FluidsJournal of


Journal of










Superconductivity




GravityJournal of








Journal of






Volume 2014


PhotonicsJournal of


Journal of

Biophysics




25

20

15

10

5

0

2500

2000

1500

1000

500

0400 600 800 1000 1200 1400

Indu

ced

abso

rptio

n (d

Bkm

)

Wavelength (nm)

times103





1 10 100 1000 10000 100000 10000000

10

20

30

40

50

60

70

80

90 MM fiber data

Indu

ced

loss

(dB

km)

Time (s)


( = 071)


Kohlrauschbest fit




fit ( = 062)120573

120573

120573

120573

120573







predicted to be

120591119888=


for 119899 gt 1

120591119888=

119905irrad[1 minus 120573]

for 119899 = 1(6)


5 Conclusions



Acknowledgments


References





































4Li] AC













2rdquo Physical











2-












2and


















2OH and




2rdquo














FluidsJournal of


Journal of










Superconductivity




GravityJournal of








Journal of






Volume 2014


PhotonicsJournal of


Journal of

Biophysics





predicted to be

120591119888=


for 119899 gt 1

120591119888=

119905irrad[1 minus 120573]

for 119899 = 1(6)


5 Conclusions



Acknowledgments


References





































4Li] AC













2rdquo Physical











2-












2and


















2OH and




2rdquo














FluidsJournal of


Journal of










Superconductivity




GravityJournal of








Journal of






Volume 2014


PhotonicsJournal of


Journal of

Biophysics






4Li] AC













2rdquo Physical











2-












2and


















2OH and




2rdquo














FluidsJournal of


Journal of










Superconductivity




GravityJournal of








Journal of






Volume 2014


PhotonicsJournal of


Journal of

Biophysics













FluidsJournal of


Journal of










Superconductivity




GravityJournal of








Journal of






Volume 2014


PhotonicsJournal of


Journal of

Biophysics



Review Article A Minireview of the Natures of Radiation...

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Transcript of Review Article A Minireview of the Natures of Radiation...