R. Vianden and M. Forker
Helmholtz - Institut für Strahlen- und Kernphysik, Universität Bonn, Germany
XIV International Conference on Hyperfine Interactions
XVIII International Symposium on Nuclear Quadrupole Interactions
Foz do Iguaçu (Brazil)
5 - 10 August 2007
Perturbed angular correlation –
past and future
A. F. Pasquevich and M.S. Castiglioni
Departamento de Física, Universidad Nacional de La Plata, Argentina
Outline
Some historical remarks
Principle of the (Time Differential) PAC technique
Highlights of application
Development of the field in time and space
Analysis of strengths and weaknesses
Suggestions
Outlook
The idea
Maurice H. L. Pryce (1913 -2003) was a theoretical physicist
with very broad interests who had a spectacular early career
at Cambridge, Oxford and Bristol and spent the second half
of his life in the United States and Canada.
First development of theoretical
foundations of angular correlations.
More complete and still up to date
is the article of H. Frauenfelder and R.M. Steffen
In “Alpha, Beta and Gamma ray spectroscopy”
K. Siegbahn ed. 1965
The undisturbed - angular correlation
Parent isotope
I = 1
I = 0
I = 0
1
2
Detector 1
2 1
Detector 2
About 1011
parent isotopes
in a sample
Coincidence
counter
R.M. Steffen, Adv. In Phys. 4 (1955) 293
Dete
cto
r 2
How does Time Differential PAC work in principle?
Parent isotope
I = 1
I = 0
I = 0
1
2
0 2 4 6 8 100.00
0.05
0.10
0.15
0.20
An
iso
tro
py
time in half lifes of intermediate state
Quantity measured:
/HgBL
/zzQ
VQe
zzyyxxVVV /)(
systemEFGofanglesEuler:,,
Magnetic interaction:
Electric quadrupole interaction:
,Q
t1/2
m= +1
m= -1
m= 0
First steps
P. Lehmann + J. Miller, 1955111mCd in CdSO4, 200 Mc/s
R.S. Raghavan et al., 1973111mCd in CdSO4,
Q = 155 MHz, = 0.4
(app. 200 Mc/s for = 0)
111Cd in Indium metal
181Ta in Hafnium metal
1955
1962
1956
P. Lehmann + J. Miller, 1956
Q = 125 MHz
Nuclear moments: g-factors and quadrupole moments
Measured up to now:
420 g – factors, 120 quadrupole moments
by TDPAC or TDPAD
H. H
aa
s a
nd
D.A
. Sh
irley, J
. Ch
em
Ph
ys
. 58
(19
73)3
339
1973
E. M
atth
ias
, D.A
. Sh
irley, J
.S. E
va
ns
an
d R
.A. N
au
ma
nn
, Ph
ys
. Re
v. (1
96
5) B
26
4
1965
Magnetic and electric hyperfine fields in solids
E.N. Kaufmann, K. Krien, J.C. Soares
and K. Freitag, Hyp. Int. 1 (1976) 485
S. Cottenier and H. Haas
Phys. Rev. B 62 (2000) 461
N.P. Barradas, M. Rots,
A.A. Melo and J.C. Soares,
Phys. Rev. B 47 (1993) 8763
181Ta in Be111Cd in Co
Hyperfine fields and local
lattice relaxation at 4d and
5sp impurities in bcc iron
Defects in metals and semiconductors
T. Klas, R. Fink, G. Krausch, R. Platzer, J. Voigt,
R. Wesche and G. Schatz, Surf. Sci. 216 (1989) 270
H. Skudlik, M. Deicher, R. Keller, R.
Magerle, W. Pfeiffer, D. Steiner, and E.
Recknagel, Phys. Rev. B 46 (1992) 2159
111Cd on a Cu surface
111Cd in Si hydrogen
passivated
Diffusion and dynamic processes
A. Weidinger and R. Peichel, PRL 54(1985) 1683
M. Zacate, A. Favrot, G. Collins,
PRL 92 (2004) 225901
Diffusion of H in Ta metal
observed with 181Ta
Reorientation
jumps of 111Cd
in In3La
Development with time
Source: Web of Science, Citation Index, INSPEC
Query: perturbed angular correlation* OR TDPAC
1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010
0
20
40
60
80
100
120
Nu
mb
er
of P
ub
lica
tio
ns/Y
ea
r
Year
Where is it used today?
Rio de Janeiro
Sao Paulo
La Plata
Pullman
Penn state
Lisbon
Kopenhagen
LeuvenCracow
Germany
Bonn
Göttingen
Leipzig
Saarbrücken
(Konstanz)
(Berlin)
Moscow
Canberra
Kyoto
Dehli, Chandigar
BeijingBelgrade
South Africa
Israel
Mumbai
ISOLDE/CERN
Strengths of the PAC technique
tracer amounts allow observation of undisturbed systems
applicable at all temperatures
applicable at high pressures
dynamic processes observable
(fast: ns scale, slow: phase transitions, chemical reactions etc.)
sub-nano resolution of lattice structures
affordable price for a complete set-up: 100 – 150 k$
Weaknesses
I-131Hg-199Cu-62
Re-187Pb-204m
Ru-99Yb-172
Se-77Mo-99Pd-100In-117Ce-140
F-19 Coul. exc.Ta-181Cd-111
0 100 200 300 400
0 100 200 300 400
PAPER
Basis: ~ 1500 papers
1960 - 2007
Limited number of probes
Probe mostly
an impurity in the sample
Source preparation
Legal constraints
Complex electronic set-up
Limited access to ISOLDE/CERN
Opportunities: Synchrotron radiation PAC
Sergueev, U. van Bürck, A. I. Chumakov, T. Asthalter, G. V. Smirnov, H. Franz, R. Rüffer, and W. Petry,
Phys. Rev. B 73 (2006) 024203
57Fe in the molecular glass former dibutyl phthalate DBP
doped with 5% mol of ferrocene FC enriched to 95% in 57Fe.
Opportunities: Improved detectors
Ideal detector:
Ge-detector energy resolution
BaF2 time resolution
LSO efficiency
(Non hygroscopic)
Limits today:
Max frequency 2 GHz
time resolution with BaF2
app. 100 ps FWHM at 60Co energies
100 200
0
10000
20000
30000
40000
50000
Co
un
ts
Energy [keV]
Diploma thesis, Leipzig
LaBr3 BaF2
Opportunities: Improved Hardware
PAC goes digital:
PK-3: Actual Concepts of Digital PAC-Spectroscopy
J. Röder, C. Herden, J.A. Gardner, K.D. Becker, M. Uhrmacher, H. Hofsäss
Opportunities: Density functional theory
H. Haas and D.A. Shirley, 1973
It took a bit longer. But now:
Success for pure systems and
Increasingly also for impurities
in elements and compounds.
H. Haas, S. Cottenier, L.A. Errico, P.H. Dederichs,
M. Akai, H. Akai, and J. Kanamori ….
L. A. Errico, G. Fabricius, M. Renteria, P. de la Presa,
and M. Forker, Phys. Rev. Lett. 89 (2002) 55503-1
Opportunities: DFT theory temperature dependence
Taking into account the
influence of phonons the
temperature dependence
could be described
for the first time starting
from basic principles
calculations.
D. Torumba et al., Phys. Rev. B 74 (2006) 144304
and contributions here
Contributions S. Cottenier, H. Haas
111Cd in hcp Cd metal
Threats
Loss of knowledge on the technical application
Loss of facilities for the production of samples
Suggestion: An international PAC network
Information on new developments
Relevant data on PAC isotopes, suppliers
Typical set – up, detectors, electronics
Evaluation programs, Fit programs + advice
DFT theory, contacts
Exchange of students
Support for developing and new, problem oriented groups
PAC Web site:
Suggestions: An international PAC network
Facilitate sample preparation
International cooperation on implantation
Funding seems possible through the
7th framework program of the European Community
Transport costs, Travel etc.
PAC, Radio Hall, Radio-DLTS, Diffusion
Contact us if you are interested!
Possible new directions
Investigation of sub-nano structures
The EFG is influenced only by the nearest neighborhood of the
probe. Even if relaxations are taken into account the important
volume has a diameter of 2 – 3 lattice constants, i.e. typically < 1
nm!
Typical applications:
•Local order in amorphous alloys
•Ordering processes in alloys
•Influence of particle size on magnetic and electric hyperfine fields
Possible new directions
Defects and impurities in modern semiconductor technology
group III-Nitrides, ZnO,
magnetic effects in semiconductors, HfO2 etc.
Biology
Time dependence of the interaction
through fluctuation fields due to jumps of the probe or
other constituents of the material.
Time dependence of the interaction
due to recovery (after) effects in the electron shell of the
probe. Could be linked to conductivity of the material:
conductivity of insulators free of surface effects etc.
coherent electron tunneling at low temperatures etc.
Conclusion
Problem oriented instead of technique oriented
Collaboration with specialized group
Help to create the WW - PAC - Network
Discussion during and after this conference
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