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