Sub-MeV Neutrino Technology R. S. Raghavan Virginia Tech NOW-2006 September 10, 2006

R. S. Raghavan NOW 2006 Sep 10, ‘06

Sub-MeV Neutrino Technology

R. S. RaghavanVirginia Tech

NOW-2006September 10, 2006

http://www.phys.vt.edu/


Lo-Nu Low Threshold Nu Reactions30 year Personal Theme

Motivation:• New perspectives for Nu Flavor physics— Lower the nu Energy larger the flavor effects• Powerful tools for frontier new sciences – The most interesting nu sources occur at LO energies— Astro, Geo- Nu Physics

NOT EASY!--- NeedRadically New Ideas and/orFar Out New Technology This Science is coming into vogue and relevance only recently



New Paths in LO-Nu Technology

Four Lo Nu Reactions

• (νe ,p) 1.8 MeV 1956 Reines K’Land

• (νe , 115In) 0.114 MeV 1976 LENS

• (ν , e) 0.020 MeV 1992 CTF, B’xino, K’land, Cryo?

• Recoilless Nu 0.0186 MeV 2006 ??? Res Cap



Reactor Antineutrino Detection—ReinesFirst Breakthrough against LE Bgd Wall

• Source: Reactor produced antineutrinos- 0-8 MeV Major flux < 3 MeV• Proposition unbelievable since terrestrial material bgd formidable below 5 MeV, especially below 3 MeV

How to Proceed:Major Idea: Tag the neutrino reaction: νe+p n+e+

Serendipity: Look at delayed neutron in concidenceIt works because neutron diffusion creates DELAY, thus it gives a “coded” signal that DISCRIMINATES—No tag if delay is too short to

measure Discovery of neutrino Still the most successful idea in Neutrino Physics Only viable way for antineutrino Science Reactor neutrinos, Geoneutrinos, Supernova relic nus ……



LENS—100 keV neutrino detection with tag• Objective: pp neutrinos from Sun—• 0-420 keV—No hope against bgd wall—

UNLESS ….Nu Tag !• 1976—Copy the Master—Can one

invent a delayed coincidence tag for neutrinos by imitating the Reines neutron tag for antinus?

• Problem: Neutrinos can be detected only with inverse beta on nuclei heavier than proton

• Answer: Choose inverse beta to ISOMERIC excited nuclei (not to the ground state as in Cl or Ga)

νe + 115In 115Sn* (τ = ~5 μ s)

+2γ+e-



Indium Tag—Idea great but where is the Technology?30 yr job !!

• Basic Detection technology- In liquid Sciintillator• Background Analysis Insights• Novel Detector Nu Reactions Scintillation Lattice Chamber

Complete Low Energy Solar Nu Spectrum99+% of solar nu output

What Science?•Neutrino Luminosity of Sun•Latest: Measure Gamow Energy of pp fusion via ENERGY of pp nu spectrum temperature profile of energy production in sun (hep-ph/ 0609030)Christian Grieb—Talk tomorrow



ν +e ν +e of < 100 keV neutrinosTechnology, Technology, Technology !

Objective: 7Be nus from sun (861 keV) by nu-e scattering—Signal extends from 0-670 keV “Compton” Edge

No reaction event tag !! But…• Monoenergetic Nusignature recoil electron profile• High Rates 1/r2 oscillation with earth’s rotation• Above all….Brute Force Tech. to suppress radio-bgd

• New Chemical Tech of Ultrahigh Radiopurity (U, Th. K)• and methods to detect such ultrahigh radiopurity Proof CTFhistoric expt of 5 ton detector of 20 keV events Borexino –15yr Research by DEDICATED Group• now setting templates for Kamland, future cryoliq experiments

…. Borexino Now in High Gear –operating detector in 2007 ! Gioacchino Ranucci talk tomorrow



New Perspectives with very low energy neutrinos

• Recoilless Resonant Capture Reactions with Tritium anti-Neutrinos

Very low energy 18.6 keV—current limit 1800 keVVery large enhancement of reaction cross section• 10 orders of magnitude higher than current X-sec

Experiments with kgrams not ktons of material Experimental baselines in cm not km

OPENS NEW HORIZONS for NEUTRINO PHYSICS



Neutrino Physics in bench scale baselines1. Gravitational Red Shift: I linewidth in 180 cm fall-line First Direct test of Equivalence Principle for Neutrinos

2. Θ13 flavor oscillations in 10m baseline Implications for CP violation & Baryon Asymmetry

3. New problem: Test of Sterile Neutrinos test LSND resultLSND implies Δm2 ~0.5 to 1 eV2 sin2 2θ = 0.1 to 0.01 ….??Presumed conversion to sterile neutrinosfor THe: Disappearance / oscillations in ~5cm baselines

Major Neutrino Physics Interest !



Detecting AntineutrinosLow energy νe – why ?• Detecting 40K in earth• Short Baseline anti-neutrino oscillations How to lower νe detection threshold below 1.8 MeV?

Basically different from νe detectionνe Reaction Produces e+--not e-

Sets Min.Threshold = 1.022 MeV e.g. νe+pn+ e+ Eν min = 1.022+0.782 = 1.8 MeV

νe+3HeT +e+ Eν min= 1.022+0.0186 = 1.0406 MeV

--No Escape –Some but not much gain in reducing nuclear Q alone



New Idea I: Breakthrough in Threshold ProblemLev Mikaelyan (1968)

Rediscover “New” Idea of LM (Orbital electron + νe) Capture:

νe +3He +e- ( 1s orbital) T Get TWO things:

1. Really low threshold Enu min = 18.6 keV ! Voila!2. All energy except Eν is fixed---Resonant Character !

Eν (res) = Q – B(1s He)+ER

Great but, Not much use for wide band nu spectra from Reactorsbecause neutrino density ρ = (dn/dE)/N is too small Need idea #2



Resonant Source of AntineutrinosJ. Bahcall (1962)

Idea #2:Inverse of Lev Mikaelyan’s reaction:

T 3He + e- (in 1s orbit) + νe “bound State” β-decay—John Bahcall (1962) Theory: 0.69% x0.8 =0.54% Bβ decay goes to ground state of He Eνe = Q + B (1s)+ER

Just what is needed for resonance in LM reaction with extra energy to capture the 1s electron in the He target

The two reactions are exact time reversed processes. Resonance means HIGH XSec Can go to low νe threshold AND enhance Xsec !!

By How much? IDEA # 3



RECOILLESS NEUTRINOS• Idea # 3Recoil energy 2xER spoils Resonance. Get rid of it !Use T and 3He embedded in solids--Under proper conditions -- expect Recoilless Transitions

E R terms that destroy resonance energy balance eliminatedArrange experimental conditions for high spectral density of nuebars narrow

linewidth Γ (not natural LW)

Can one do this?— Deeper understanding of process now New paths visible from technology Progress in Specific Experimental Designs

ΔE thermal linewidth~0.06 eV at T=300K

ER~ 0.05 eV in T



L. Mikaelyan-- Resonant νe Cross section

LM formula FOR RESONANT νe CAPTURE

σ = 4.18x10-41 go2 ρ(E(νe res)/MeV) / ft1/2 cm2

= 4.6x10-49 x ρ go

2 = 1.24x10-5 (1s Electron density)ft1/2 = 1132 s (weak interaction factor- T decay constant)ρ = no. of neutrinos/MeV (in incident neutrino spectrum)



Neutrino Line Width & Resonance X-section

Thermal Motion: Δ = Eν √(kT/Mc2) = 0.08eV; (if T and He are in solids –must include effect of Debye temperatures)

RECOIL ENERGY! :ER = Eν2/ 2Mc2 = 0.061eV

ρ(Eνe res/MeV) = (106/ 2Δ) x overlap emission & abs windows (106 / 0.16) x 0.4 2.5x 106 Resonance Enhancementσ = 10-42 cm2 for 18 keV νe = σ (νe +p) for 3 MeV νe

ROOM FOR IDEA # 3 LINE WIDTH Γ <<< thermal width Δ ? σ increases correspondingly

Must eliminate ER first



Recoilless Resonance X-section1. Recoilless Fraction f f = exp-{4/3 (ER/ Z) (Z= zero point energy ZPE) for low temperatures (T<< Θ = Debye Temp = 8/9 (Z/Mc2)

2. Line Width Γ –Determines resonance density, Xsec (not natural lw but experimental energy fluctuation width) practical

parameter from magnetic spin-spin relaxation time T2

3. Effective σ(res) (LM formula): σ(res) = f(s)f(a) 4.6x10-49 x ρ/MeV cm2

= f(s)f(a) 4.6x10-49 x 106 / Γ (eV)T

Anticipate: f(s)f(a) ~0.1; T2~100 μs Γ~ 6x10-12 eV

σ(res) ~ 1032 cm2

10 orders of magnitude larger than σ (νe + p)



Emitter-Target Energy Balance in Solids

Look at energy balance of T-He reaction in solids Crucial for ultra sharp ResonancePerturbing Energies that affect the resonance: • Atomic (B’s already considered)• Chemical bonding (T but not He)• Lattice vibrational energy, at T≠ 0 second order Doppler shift Zero Point Energy even at T=0 • Dipolar interaction in rigid lattice of spins• Magnetic shielding-- Site dependent “chemical” /other shifts

Can the strict Energy Matching of Resonance (to 10-16 ) Survive?



Self Compensation of perturbing Energies in THe system Nu Resonance Involves two time reversed processes

Source: Initial State: Chemically bonded T Final State: νe + 3He No recoil-No lattice phonons emittedTarget: Initial State: νe + 3He Final State: Chemically bonded T No recoil-No lattice phonons emitted

Total Perturbing Energy Tritium = ET

Total Perturbing Energy Helium = EH

ET ≠ EHe in generalEmission : E (νe res) + (ET –EHe) Absorption: E (νe res) + (EHe-ET) = E (νe res) - (ET –EHe)

Energy gain in Emission is COMPENSATED EXACTLY in absorptionResonance condition maintained STRICTLY

νeT

He He

TB β-decay Nu+e capture



Self-Compensation Conditions

Conditions on ET , EHe for self-compensation:1) Unique energies 2) Identity of ET EHe each in Source and Absorber3) Static Perturbation—no relaxation Conceptual Framework SAFE

What about effects in Practice?Sources of breakdown in energy balance: • Distribution of E’s Inhomogeneous broadening• Relaxation homogeneous broadening• Non indentity of E’s in source/absorberLine Shift



Basic Experimental Conditions• Source and Absorber prepared identically• Engineer T sites and He sites identical and unique• Identical temperatures of source/absorber eliminate second order Doppler shift• Spin ½ i.e. Zero Quadrupole moments of T and 3He No electric perturbations due to random strain fields

Residual Major Non-compensatable effects:• Variation of ZPE from site to site- inhomog. broadening• Spin-spin magnetic relaxation— homog. Broadening

Final line width determined by larger of above two broadenings



Tritium and He sites in metals

TInterstitial SitesOctahedral – fcc metalsTetrahedral—bcc metals

HeMicrobubbles:1-2nm diam; 4000 atomsSolid under pressure ~10 GPa at <100KHe atoms closer than in IS sites

T He



Search for Resonance-Viable T-He Matrix• Quest for matrix and conditions where• IS sites dominant –not bubbles• T and He will occupy Same type of INTERSTITIAL SitesTall Order?

• Search for metal matrix and conditions published data on:• EST = self trapping energies determines mobilities site choices for He• ZPE = to estimate recoil free fractions



Niobium?Parameters of T and He in Nb

• Find site choice (EST= self-trapping energies) and ZPE (for recoil free fractions) from theoretical study of H, D, T in Nb

Theoretical EST & ZPE for T and 3He in Nb interstitial sites (IS)

SiteEST (eV) ZPE (eV)

T He T He

TIS -0.133 -0.906 0.071 0.093OIS -0.113 -0.903 0.063 0.082

Choice for T & He

•M. J. Puska & R. M. Nieminen, Phys. Rev. B10 (1983) 5382



How to make Unique, Identical IS for He Niobium !

• He transport in Nb : T in Nb for 200 days• Remove T and monitor He for 200 d

time(days)

0

0.005

0.01

0.015

0.02

0.025

0.03

0.035

0 50 100 150 200 250 300 350 400

He3

/Nb

(ato

mic

frac

tion)

250K c1

235K c1

220Kc1215Kc1200Kc1

225K c1

Tritium Desorbed Tritium in NbT

235K c2+c3250K c2+c3



Niobium- Unique Discovery• Conclusions on Niobium as Matrix choice:• Calculations show that at <200K He is ONLY in IS sites• No bubbles are formed indefinitely• The EST of Tetra and Octa sites are nearly degenerate He sits randomly in either site• Available: 6 Tetra and 3 Octo sites/bcc unit cell 67% He in Tetra IS site All T in Tetra IS site Uniqueness and identical site requirement satisfiedNb is unique in providing these featuresKey Discovery



Line widths --Homog and Inhomg• Homog caused by spin-spin relaxationtake T2 data• Inhomog site to site variation of ZPE (no electric perturbations) Unknown. Guidance from successful observation of ultra sharp 67Zn γ resonance (ΔE/E ~ 5x10-16) (W. Potzel et al, Hyp. Int. 72 (1992) 191)

Observation of resonance despite ZPE and electric perturb. Hope that inhomg in THe within 10 times that of Zn

Homog

Inhomog



Homogeneous Broadening: Dipolar LinewidthH NMR in NbH 300Kx

13 kHz

Dipolar Interaction of T, 3He nuclear spinswith spins in the vicinity:nuclear spins H (or D) , T, 93Nb andelectron paramagnetism of the lattice

NMR measurement on H In NbHx (300K)(Stoll & Majors Phys Rev B 24 (1981) 2859 ).Applies closely to our case since nuclearmoments of T, 3He and H are very similar~2.9 (H), 2.8 (T), 2.1 (3He) nm

Experimental line width ~13 kHzΔE = 8.5x10-12 eVΔE/E = 4.6 x 10-16

NMR-MASS resolves the two NMR lines (αo βo with different chemical shifts)and the sidebands introduced by MASS(magic angle sample spinning)

Homog. Broad

Rigid spinSplitting resolvedVia magic angle spinning



Preliminary estimate of X-sec

• ZPE (T—Nb TIS): 0.071 eV• ZPE He--Nb TIS): 0.093 eV• f(T) f(He) = 0.076• T2 = 0.2x10-4 s• Γ = 8.6x10-12 eV• He TIS site fraction = 2/3

σ (res) = 0.3x10-32 cm2



Detection of Nu Resonance• Two (Default) Methods in T-free target

1. Nubar Activation —Capture Rates N• Mass Spectrometry of “milked Tritium” and measure

Number N of T produced in given time by Us-MS N grows (linearly with t) –signature• Typical activation time 65 d = 0.01 of 1/tau of T

2 Reverse C-beta decay of signal T (a la Ray Davis)3 involves a reduction from N by factor 6500 (1/τau of T)4 in situ by heat produced5 in MS T sample by counting C-betas



Nu Resonance in Practice—Target Questions• He target is prepared by TT method• This implies target has active T• How to cope with enormouos T (~1017)• vs tiny amounts of “signal” T produced in resonance? Biggest Practical Problem to be Solved

• Best solution visible at present:• TD exchange; or TH exchange? Exchange energy small ~0.04 eV for HD; smaller for TD, TH T limit set only by dilution factor Multiple exchanges with D2 gas at 35 torr demonstrated in practice

—Mass spectrometry of exchange gas showed no T ; also no He (Abell & Cowgill, Phys. Rev. B44 (1991)44)

Must be revisited and quantified with ultrasensitive MS



Preliminary Estimates of RatesRec. Resonance Capture Rates for Close (~5cm) and far (~10 m)

geometries• Rates in close geometries can be high (~0.1 Hz !)• offers safety margins vs dilution by unknown broadening effects• Initial priority: feasibility studies at close geometries



Conclusions & Outlook

• Conclusions:• NbT(He) major discovery—sets firm conceptual basis for ultra high resolution recoilless nu resonance• Line width problems may be accommodatable• Technical road map to experiment emerging

• To do:• Investigate and nail down TD (H) exchange in Target • Experimental determination of basic parameters (ZPE, site

preference… via n, X-ray diffraction, NMR in actual NbT sample prepared below 200K—no such data yet

• Invent Real time signal methods ???• ……….



Additional slides



Fast bubble growth –Palladium TritideHopeless!

Cowgill Reproduction of Bubble nucleation in PdT(0.6)

0

0.000005

0.00001

0.000015

0.00002

0.000025

0 1 2 3 4 5 6 7 8

Time (days)

Con

cent

ratio

n

C1C2CB

E(act)eV = 0.13a0 = 3.88E-08g = 1.074E-09

Temperature = 300 K

Calculations verify Experimental dataBubble nucleation essentially complete in a few days;Long term He ONLY in bubbles (red curve)not in Interstitial sites (blue curve )



Basic Embedding Technique Tritides and the “Tritium Trick”

How to embed T and He in solids Metal tritides —Best approach visible

Tritium gas reacts with metals and alloys and forms metal tritides –(PdT, TiT, NbT...)

embeds T in lattice uniformly in the bulk Tritium decays and He grows—distributed uniformly (Tritium Trick (TT))

Problems:1. T and He lattice Sites in TT—Unique? Identical for T, He?2. Must Remove T from absorber to detect resonance New Issue? What effect does this have on identity of T and He

in source and absober?



Resonance – neutrino microspectra

Example: Gas T source and gas He targetDoppler widths and Recoil Shifts of neutrino lines 2Δ is the full width due to thermal motion

Δ

ER



T and He sites in Metal TritidesGreat Deal of Data AvailableFusion and Fuel tech—Sandia-- prime source! Basic Problem of TT T• Reactive-- forms chemical bond-unique sites• Sits in tetrahedral interstitial sites (T) in bcc metals in octahedral interstitial sites (O) in fcc metals He• Noble gas—insoluble in metals• High mobility• Forms pairs quickly and nucleates in microbubbles• Non-unique, distribution of ZPE• Unacceptably large inhomogeneous broadening



He growth in metals-Model calculations

Basic equations: Coupled non-linear diff. eqns. Numerical solution (at VT: thanks to Prof K. Park, Mr D. Rountree) dc1/dt = g - 2p1s1c12 + 2q2c2 - p1s2c1c2 - p1sBc1cB

dc2/dt = p1s1c12 - p1s2c1c2 - q2c2 dcB/dt = p1s2c1c2.

ParametersC1 = mobile C2 = pair C3 = bubbleP1, 2, 3 jump frequencies depending on activation energiesE1,2,3

He transport parameters in NbT at 200KM1.0 T1.0 E1 eV E2 eV E3 eV D/cm2 M=Nb 0.9 0.13 0.43 1.1E-26cD. F. Cowgill, Sandia National Laboratory Report 2004-1739 (2004)



NbT(He) vs NbD(He)--Asymmetry ?• Is source target asymmetry an ISSUE? Diff. ZPE?

Displacements(%) and measured6 activation energies (eV) for H, D & T in Nb IS

•M. J. Puska & R. M. Nieminen, Phys. Rev. B10 (1983) 5382

1st NN Displacement2nd NN Displacement.

H D T H D T

TIS 4.1 3.9 3.9 -0.37 -0.36 -0.35

OIS 7.7 7.5 7.4 0.2 0.19 0.19

Eac6 0.106 0.127 0.135

TD exchange makes little difference in Lattice distortionDo not expect substantial line shifts—can be compensatedWith external Doppler Drive



Real time Resonance Detection?• Invention of real-time detection method of Great Interest• Rudimentary Ideas

1. Spin flip in HeT : μ (He) = -2.1 nm; μ (T) = +2.79 nm Transient (0.2 ms) magnetic field generated Hyperfine coupling to T electron Can response of electron moment be detected by ultrasensitive

SQUID magnetometers?2. Creation of T (partially) inserts electron in d band of metal Extra electrons (after activation for a time) create extra electronic specific heat enough electrons for detectable Bolometric signal?


Sub-MeV Neutrino Technology R. S. Raghavan Virginia Tech NOW-2006 September 10, 2006

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Transcript of Sub-MeV Neutrino Technology R. S. Raghavan Virginia Tech NOW-2006 September 10, 2006