CONCLUDING REMARKS

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CONCLUDING REMARKS

H. de Waard

To cite this version:

H. de Waard. CONCLUDING REMARKS. Journal de Physique Colloques, 1974, 35 (C6), pp.C6-

697-C6-698. �10.1051/jphyscol:19746156�. �jpa-00215772�

JOURNAL DE PHYSIQUE

Colloque C6, supplment au no 12, Tome 35, Dtcembre 1974, page C6-697

CONCLUDING REMARKS

H. DE WAARD

In summing up [I] the experiences of five days of conference, let me start by giving you some vital statistics. Of the 225 participants from 30 different countries, the largest number, 51, of course came from France

;

Germany followed with 44 and the U. S. A.

with 34. Belgium, Great Britain, Holland, Israel and Italy were each represented by about 10 Mossbauer scientists, the other countries by numbers from 1-5.

The representation of the Soviet Union, by only two physicists, was disappointingly small. Let us hope that it will be higher in next Mossbauer conferences

!

In 94 of the papers presented, Mossbauer effect measurements on 57Fe were reported, 13 papers gave '19Sn results while 12 papers dealt with rare earth isotopes. The other isotopes reported on were

:

lZ5Te (4 papers), 1 9 7 A ~ (3), lS1Ta (3), lZ1Sb (2), lZ9I (2), 61Ni (2), lZ9Xe (I), 13'Xe (I), l17Sn (I), 67Zn (1) and 73Ge (1). In all, 76 % of the papers were about 57Fe and 'l9Sn

;

this number was 67 % for the Ayeleth Hashahar conference in 1972. The increased attention for these two isotopes is not only in relative numbers.

Dr. Stevens [2] found a decrease in the total number of papers per year for most isotopes other than 57Fe and '19Sn from his literature search since 1970. This implies by no means that everything worthwhile has been done already on those other isotopes and in my opinion, research on them should be stimulated.

There are many items of interest that have been insufficiently explored, in particular in the isotopes with very narrow Mossbauer lines. In this respect the recent work of Pfeiffer and Raghavan [3] on 73Ge should be mentioned. Their latest results suggest that room temperature Mossbauer investigations on Ge and its compounds are within reach of a number of laboratories now.

Also 67Zn, reported on at this conference by Perlow [4], still offers tremendously interesting possi- bilities, though in this case experimental problems tend to restrict its use to some more sophisticated labora- tories. Another extension of the number of Mossbauer isotopes is in the direction of higher energy transitions like the 159 keV transition in lt7Sn reported by Gerdau [5]. Here, the effect of course becomes very small but the internal conversion also becomes small and if it is possible to make a strong enough source very small effects can be seen. The method of fast

photo-multiplier current integration mentioned by Viegers [6] offers interesting possibilities for coping with very high count rates.

In reviewing conference highlights I will restrict myself to mentioning some developments since the Ayeleth Hashahar meeting that have struck me in particular. The considerations of Kagan and Goldan- skii on the feasability of a gamma laser or gaser certainly deserve a high place in my little list. Even though the realization of a gamma laser appears to be remote with presently available means, several propositions have emerged that deserve experimental effort.

In the field of after-eflects, that I long considered to be rather unphysical, two interesting new ideas have been launched

:

(a) a possible slow rearrangement of the Kondo cloud after a nuclear decay [7] and (b) a slow relaxation of the electronic states after nuclear decay of certain rare earths impurities in metals [a].

The experimental verification of these phenomena is as yet incomplete.

A next item of interest is the strongly temperature dependent isomer shift of the 22 keV line in 15'Eu observed by Bauminger et al. [9] in some intermetallic europium compounds and tentatively explained as the result of a mixed valency state (2 + ^<

^-+

3

+)

of the Eu-ion caused by rapid transitions of an electron between the conduction band and the 4f shell of the ion.

Microscopic radiation damage studies were helped forward by Vogl's [lo] observation of trapping and detrapping of A1 interstitials in a dilute Co-A1 alloy irradiated by neutrons at 4 K. The use of conversion electrons emitted after recoilless resonance absorption still offers interesting new possibilities.

Weyer and others [ll], for instance demonstrated the sensitivity and time resolution of resonant detectors in their investigations on implanted sources of '19Te, lt9Sb and lt9Sn in semiconductors and of the time distributions of resonantly scattered 14.4 keV radiation from 57Fe.

Depth selective Mossbauer spectroscopy, analyzing the conversion spectrum to derive depth information, was developed into a more quantitative direction by Baverstam et al. [12].

Further, I would like to point out once again that combination of Mossbauer results with results of other

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19746156

C6-698 H.

DE

WAARD

hyperfine investigations, in particular time differential perturbed angular correlation (TDPAC) and nuclear orientation (NO) measurements can improve our understanding of certain problems. At small hyperfine interaction strengths, where Mossbauer lines are only slightly broadened, TDPAC measurements, pursued over, say, 10 half lives of a nuclear state may provide much more accurate information

[13].

From this brief, subjective and incomplete summary of developments I now turn to some comments about the structure of this conference. In these idyllic sur- roundings we would have been happy even if the program were badly organized, but it was not. On the contrary, thanks to the unrelenting efforts of the program coordinators the preparation and execution of the program were excellent. True, many of us have had to work hard during what we thought would be a well earned siesta, preparing the jam sessions (rap- porteur sessions). I have found this act of preparation in a small group one of the best features of the rappor- teur system

:

the material to be presented is discussed intensively among those very people that are most interested and that know most about it.

It is too much to expect that the rapporteur system would be perfect the first time it is tried

;

I feel it must be used with discretion. In the following I have for- mulated some recommendations for future Mossbauer conferences, convinced as I am that it is useful to have such conferences.

-

Review papers should cater for a wide audience

;

they should be allowed sufficient time.

-

Rapporteur sessions should fulfill the following requirements

:

a) Only seasoned rapporteurs should be chosen.

b) Only papers with a clear logical connection should be included. Borderline papers can be presented separately in other sessions.

-

The duration of conference sessions should not exceed

6

hours per day (real time).

-

Parallel sessions should be held on

⁽⁽

intensive

⁾⁾

subjects with little overlap, preceded and followed by joint sessions.

-

Joint sessions should be held on special subjects (novel and exotic applications, instrumentation).

-

A viewgraph should not contain more than 90 words.

At the end of these brief remarks I wish to thank above all Dr. Shenoy, Dr. Friedt and Dr. Janot for programming and materially organizing this confe- rence in such an excellent and thorough manner. Our thanks are also due to Mr. Poinsot, our p~ojectionist, to Dr. Richard and Dr. Scherrer for taking such good care of transportation and to Mme Adloff for organizing a much appreciated ladies program as well as for performing so well the always thankless job of taking care of reservations.

Notw and references

[I] Before summing up, I attempted to report on section 13 of the conference (irreproducible and unwanted results) for which I had selected such intriguing subjects as :

Speculations on the Ruby Gazer !! with unmentio- nable sources ? Emotional narrowing )) ; (( De Unzu- langlichkeit des Spinhamiltonians bei der Erklarung von Erscheinungen in eisenhaltigen biochemischen Systemen (Jugenderinnerungen, H. Eicher, ohne Figuren) ⁾⁾ ; <( The measurement of the size of particles in a liquid from its undercooling (Ulrich) ⁾⁾ and ^<( Eli- mination of Mossbauer data by erasing Stevens tapes ^)).

Since Dr. Shenoy pointed out to me that this session had to be kept very short my report of it was limited to showing a viewgraph of some of the most important conclusions and some references. This viewgraph was shown for the standard time that had been set as a norm by other rapporteurs. It was handed to Professor Goldanskii for future use.

[2] Remark during dinner.

[3]

PFEIFFER, L.

and

RAGHAVAN,

R. S., Scientific Program Abstract, J. Physique Colloq. 35 (1974) C 6-203.

[4]

PERLOW, G.,

Scientific Program Abstract, J. Physique Colloq. 35 (1974) C 6-197.

[5]

MIJLLER, W., WINKLER,

H. and

GERDAU,

E., Scientific Program Abstract, J. Physique 35 (1974) C 6-375.

[6]

VIEGERS,

M. P. A. and

TROOSTER,

^{J. M.,} Scientific Program Abstract, J. Physique Colloq. 35 (1974) C 6 and Nucl.

Instrum. Meth. 118 (1974) 257.

[7]

HIRST,

L. L., Review paper, J. Physique Colloq. 35 (1974) C 6-21.

181

STOHR,

J.,

KALVIUS,

G. M.,

SHENOY, G.

K. and

HIRST, L.

L., Contributed papers, Intern. Conf. on hyperfine interac- tions studied in nuclear reactions and decay (Uppsala, Sweden) p. 80.

[9]

BAUMINGER,

E. R.,

FELNER,

I.,

FROINDLICH, D., LEVRON,

D.,

NOWIK,

I.,

OFER,

S. and

YANOVSKY,

R., Scientific Program Abstract, J. Physique Colloq. 35 (1974) C6-61.

[lo]

VOGL, G.,

Scientific Program Abstract, J. Physique Colloq.

35 ₍₁₉₇₄₎ C _6-165.

[ l l ]

WEYER,

G.,

DEUTCH,

^{B. I.,}

NYLANDSTED-LARSEN,

^A.,

ANDERSEN,

J. U. and

NIELSEN,

H.

L.,

Scientific Program Abstract, J. Physique Colloq. 35 (1974) C 6-297.

DROST,

H.,

PALOW,

K. and

WEYER, G.,

Scientific Program Abstract, J. Physique Colloq. 35 (1974) C 6-679.

1121

BLVERSTAM,

U.,

EKDAHL,

T. and

RINGSIROM, B.,

Scientific Program Abstract, J. Physique Colloq. 35 (1974) C 6-685.

[13] An example of this is the TDPAC measurement on the 23.8 keV level of 119Sn by

SOARES,

J. C., KRIEN, K.,

BIBILONI,

A.

G., FREITAG, K.

and

VIANDEN,

R., Phys.

Lett. 45A (1973) 465.