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PERTURBED ANGULAR CORRELATIONS
E. Matthias
To cite this version:
E. Matthias. PERTURBED ANGULAR CORRELATIONS. Journal de Physique Colloques, 1974, 35 (C1), pp.C1-1-C1-2. �10.1051/jphyscol:1974101�. �jpa-00215476�
JOURNAL DE PHYSIQUE Colloque C1, suppN~?ler~t au no I, Tome 35, Ja~zuier 1974, page 1
PERTURBED ANGULAR CORRELATIONS
E. MATTHIAS
Fachbereich Physik, Freie Universitat Berlin, West Germany
Resume.
-
L'auteur passe en revue les dkveloppements de la methode de la perturbation des corrklations angulaires depuis sa decouverte en 1951 jusqu'a aujourd'hui. I1 fournit une biblio- graphie substantielle perrnettant d'aborder efficacement ce domaine.Abstract. - A review is given of the method of perturbed angular correlations since its discovery in 1952 up to now. A list of selected references is provided which allows an easy and efficient access to the subject.
In 1952 the Ziirich group [ I ] published a paper in which they measured the magnetic moment of the 4'247 keV-state in "'Cd. This was the first example of the application of perturbed angular correlation (PAC) techniques to the determination of electronia- gnetic moments of nuclear excited states. Now, more than 20 years after that first measuren~ent a large number of moments have been detel-mined by this method which has proved to be most powerful throu- ghout the large lifetime range from l o - " s up to minutes. Several factors have contributed to tlie growing importance of PAC. On the technical side it was the development of nuclear radiation detectors with decent resolution as well as tlie develop~iient of fast pulse electronics. On the physical side, the stilnulus came from three sources :
1) The refinement of nuclear models raised interest in checking predictions about em moments.
2) The discovery of internal fields extended the range t o lifetimes as short as a few picoseconds.
3) The use of C o u l o ~ n b excitation and nuclear reactions to populate and orient the states of interest.
I n which area of physics can tlie PAC method make a contribution ? The major subject of these experi- ments will be ern ~nornents of radioactive ~iuclear states. In-beam measurements, in particular, bring a vast number of isomel.ic states within re:icli. V~II-ious combinations of targets and projectiles will allow us to measure almost any excited state with a reasonable lifetime. This will offer tlie possibility to obtain a better systematic knowledge of ~llr~giirtic. ~ ~ i o i i ~ c i ~ t s than was possible from stable ground statcs only.
Investigations along these lines are pl-esently concentra- ting on high-spin isomers of comparatively well understood struct~tre. This type of experiments led to tlie discovery of anomalous orbital m;tgnetisrii [?]
a n d contributed to the understanding of otlicr magnetic higher order efTects [3]. The situation with rcspcct to nuclear C J I I N ( / I . I I ~ O / C I I I O I I I O I I I . ~ is I'itr less satisfying
since we always have to rely on field &I- a d ' lents in solids o r free atoms. The uncertainty of the effective field gradients limits the accuracy with which quadru- pole moments can be obtained. In an effort to avoid this difficulty PAC measurements have been used to determine ratios of quadrupole moments. An impor- tant recent development in this field was tlic demonstra- tion that quadrupole interaction freq~tencies can bc observed in thick targets, provided that the influence of damage centers is eliminated by wol-king at tempe- ratures close to the melting point [4].
The application of PAC to study extranuclear properties has focused on a manifold of problems : C h e ~ ~ l i c a l qfc~cts have been subject of investigation [5].
Elec~tric ,fic.l(l g~.rrt/iei~/.c have been studied in ~netallic and ionic crystals [5]. [6], and temperaturc [7] as well as pressure [8] were used as paralneters in some investigations. I-lowever. by hl- tlie largest cfthrt has been devoted to measure I~j~l~ei:/ii~e,ficldr in dilutc magneticalloys [L)]. [lo] and other magnetic lattices [I I].
Temperature and concentration dependcnce were the subject of numerous investigations. The latter in particular in connection with a comparison oF hyperfine lields of dissolved and implanted impuri- ties [O]. R~ltr.vu~ioi~ ~ I ~ O C C S S C I . have also been studied by PAC. A l t l i o ~ ~ g h there seems to be limited interest in this problem useful informrttion has been obtained fol- local moments [I 21, diffusion of damage centers [I 31 and correlation times in liquids [14]. Also for these applications there is a clear trend toward in-beam measurements. Classical PAC was always severel) hampered by the fact that only very few convenienl iso~iieric states are populated in radioactive decay.
In-beam experiments olt'er ;I ~ i i ~ ~ c h lasfel- choice of' suitable levels. Also the large recoil energies involveti can be used \villi advantage to implant tlic n u c l e ; ~ ~ . probe into any desired environment. Generally.
howcvcr. r:tdioactivc methods likc PAC cannoi compctc with -nictliods using stable gro~lntl slate<
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1974101
CI-2 E. MATTHIAS
because of inevitable linewidth, radiation damage, and sometimes after-effects. Nevertheless the PAC method has several features which can be of advantage for specific problems. Examples are : extremely low concentration, temperature independent orientation, time scale, possibility of recoil implantation, selection of states with large moments, etc.
A promising development is noticed for PAC experiments in p e e afon7s. A few years ago the strive to measure moments of picosecond states led experi- menters t o use the large hyperfine splitting in free atoms [15]. Obstacles were optical excitations, charge state distributions, and short collision times in gases.
Progress was made for static hyperfine interaction in free atoms when a particular charge state corresponding to a Is1 configuration was selected [16]. Recently, time-of-flight and plunger techniques have been employed to measure beats caused by the hyperfine splitting [17]. For large recoil velocities in light atoms it was demonstrated that the time resolution can be improved to better than one picosecond which makes time-differential investigations of static liyper- fine interactions feasible [I 81.
Two conditions characterize the nature of the PAC method [I91 :
1) t o show a measurable anisotropy the nuclear state must be oriented to a certain degree ; and 2) a perturbation can only be observed if the n7-states of the emitting level are coherently populated. The method depends basically on the interference between coherent radiation components emitted from neigh- bouring nz-states [20]. In its time-integral form PAC is analogous to level-crossing in optics, while optical quantum beats correspond to time-differential PAC.
In general any PAC of radiation can be represented by the formula [I91
W k I , k,, wt) =
C
B,(I) A1.(R) r ) . ( k l , k2, w t )1.
where k t is the symmetry axis of the oriented ensemble and k, the emission direction of the radiation. B,(I) describes the degree of orientation, A,(R) is the radia- tion parameter, and the response function defined by
The summation index 1 is odd for
P-
and even for y-radiation.Subject of PAC is the measurement of the perturba- tion factor
tot).
It contains the interaction fre- quency fro111 which the information about moment and field can be derived. Depending on the lifetime of the oriented state we can use different techniques to measure the perturbation factor. Accordingly, this paper will be divided into three sections :1) time-integral PAC, range 10- 1 2 s < z, < lo-' s ;
2) time-differential and stroboscopic observation, range lo-' s s z~ < s ;
3) NMR-tec!iniques, range s, > s.
The form of the perturbation factor will be given for these three types of experiment and illustrated by typical results which, at the same time, are charac- teristic for some of the activities mentioned above.
Limitations on the shortlived and long-lived side on the scale will be discussed.
References
(The followi~lg list of references is selected with the intention to give a few typical examples of the most recent work with PAC in various fields. It is not complete and many important contribu- tions are not mentioned here.)
[I] A E P P L ~ et a/., Helv. P/zj*s. Actn 25 (1952) 339.
[2] YAMAZAKI, T. et al., Plr)ss. Rev. Lrrt. 25 (1970) 547.
131 Nirclear Motiients atrd Nrrclrcir Strrrctrrr.c~. editors H. Horie and K. Sugimoto, J. Pltj~s. Soc. J~rptrtt Suppl. 34 ( 1973).
(1973).
[4] BLECK, J. et al., Pllys. Rev. Lett. 29 (1972) 1371.
HAAS, H. et a/., PIrys. Rev. Left. 30 (1973) 656.
151 SHIRLEY. D. A. and HAAS. H.. Atltr. Rev. Pltvs. Cl~rtrr. 23
- -
RAGHAVAN, R . S. et ;I., ~ b s . Rev. ~c.tt. 30 '(1973) 10 f
HAAS, H. and SHIRLEY, D. A,, J. C/I(,III. PIrys. 58 ( 1973) 3339 ; KLEPPER, 0. et al., Pltys. Rev. C 7 (1973) 1691 ;
GRODZINS, L. et a/., Plrys. Rev. Lett. 30 (1973) 453.
[7] FORKER, M. et al., Plrys. Rev. B 7 (1973) 1039 ; BRANDT, D. and ROSENBLUM, S. S. p. 178 in reference [3].
[8] RAGHAVAN, P. et al., Phys. Rev. Left. 28 (1972) 903.
[9] Hyperfine Irrferactiorrs it1 Escitrri Nlrclei, editors G . Goldring
and R. Kalish (Gordon and Breach Science Publishers lnc.. New York) 1971.
[lo] KRANE, K. S. C I el/., PIrjls. Rev. Lett. 30 (1973) 321.
[ L I] R I N N E I ~ C I I C ~ , H. H. and SHIRLEY, D. A,, Plrjv. Rcv. Lett. 30 (1973) 1147.
[I?] BERNAS, H. and G A B R I E L , H., PIrys. RCIJ. B 7 (1973) 468.
[I31 BEIITSCHAT, H. rt nl., Plrys. Rev. Lett. 25 (1970) 102.
[I41 RIEGEL, D. el ell., P/~J's. Lett. 41A (1972) 459.
[I51 NORDHAGEN, R., p. 893 in reference [9] : SPROUSE, G., 13. 93 1 in reference [9].
[I61 GOLDRING, G. C I el/., PIrj's. RPIJ. Left. 28 (1972) 763.
[I71 DAII, Y. et crl., Z. Ntrlrrrjursclt., 27a (1972) 562 ; SPIIOUSE, G. D. ct NI., PIrj~s. Rev. Lett. 30 (1973) 419.
[IS] RANDOLPH, W. L. ~ ' t n/., preprint 1973.
[19] FRAUENFELDEII, H. and STEFFEN, R. M., Chap. XIX in c( A l l ~ l ~ n , Beta, ~ t r d Catiitira Ruy Spectro.~co[~~ )),
vol. 11, editor K. Siegbahn (North Holland Publishing Company. Amsterdam) 1965. p. 997.
[ZO] PODGORECKI;, M. I. and CHIIUSTALEV, 0 . A,, F ~ r t s ~ l t r i f t e CIL'Y P l t ~ ~ i l i 12 ( 1964) 235.
LElsl, H. J., in ;( Attgrtlnt. Correlrrtia~u Or Nitcl~~ar Disitrte- grntion D, editors H . van Krugten and B. van Nooijen,
(Rotterdam University Press) 1971, p. 375.
