Bulletin of the Israel Physical Society

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BULLETIN OF THE ISRAEL PHYSICAL SOCIETY

H i—t

w 1976

2- Annual Meeting K PROGRAM S . and ^j . • - ABSTRACTS

/"•;•• BULLETIN OF THE

ISRAEL PHYSICAL

SOCIETY tr en o HI

» 1976 o í- Annual Meeting j5* PROGRAM Š and ABSTRACTS THE ISRAEL PHYSICAL SOCIETY

Members of the Council for 1974-1975

PRESIDENT Y. Eisenberg Weizmann Institute of Science VICE-PRESIDENT C. Kuper Israel Institute of Technology TREA5URER A. Krumbein Soreq Nuclear Research Center SECRETARY A. Shapira Weizmann Institute of Science

MEMBER5 AT LARGE:

U. Atzmony Nuclear Research Center-Negev A* Avnir-Wiener Ben Gurion University Y. Barda Hebrew University A. Engelsrat Department of Defence A. Gotesman Tel Aviv University

M. Klein Bar Ilan University PREAMBLE

The 1976 annual meeting of the Israel Physical Society will take place in the Physics Department of the Technion-Israel Institute of Technology, Haifa, on Sunday ana Monday, 11-12 April 1976. The registration will begin at 9 a.m. on Sunday, and the desk will be located in the hall of the Physics Department. The plenary sessions will be held in Room 323 Df the Physics Building, The parallel sessions will be held in the Physics, in the Solid State Institute and in the Electrical Engineering buildings. The meeting program includes 6 invited papers and 1£ sessions of contributed papers. In th»; evening of the first day there will be a symposium en the future of physics teaching in Israel. Exhibitions of laboratory teaching and research equipment, made in Israel, will be open to the participants in the SSI Building during the meeting. The Organizing Committee is grateful to the Technion Department of Physics for financial and technical assistance.

The Organizing Committee S.G. Lipson - Chairman D. Cabib - Secretary 8. Rosner P. Singer R. Weil THE ISRAEL PHYSICAL SOCIETY

1976 ANNUAL MEETING Sunday, April 11 - Monday, April 12 Technion-Israel Institute of Technology, Haifa

CONDENSED PROGRAM

Sunday Morning (Phys., Rm 323) 9.00 Registration • 9.45 Opening Address Y. EISENBERG, President of the Israel Physical Society, will present the Yom Kippur Wur Memorial Fund Scholarship, granted by the IPS in memory of the members of the Society who fell in the Yom Kippur War. 10:15 Plenary Ses3ion (Phys., Rm 323) Y. EISENBtiRG, The Weizmann Institute, Presiding U.P. OPPENHEIM, Technion (45 min) "Laser Isotope Separation" COFFEE BREAK S. SHTRIKMAN, The Weizmann Institute of Science (45 min) "A New Kind of Multicritical Point Associated with a k-Space Instability" 12:00 Business Meeting

Sunday Afternoon 14:00 Parallel Sessions A. Nuclear Physics (Phys., Rm 323) A. MARINCV, The Hebrew University, Presiding Contributed Papers B. Magnetism (Phys., Seminar Rm 1) M. FIBICH, Technion, Presiding Contributed Papers

C. Thin Films {Phys., Seminar Rm 2) 0. BRANDON, Technion, Presiding N. KLEIN, Technion (30 min) "Estimate of the Band Gap of Insulators" Contributed Papers Business Meeting of the Thin Films Division 0. Helium and Superconductors (Sol. St. Inst., Rm 52) 1. PRIVDRQTSKI, Technion, Presiding Contributed Papers

E. Lasers and Plasma Physics (Sol.St.Inst. Rm 58) 6. EREZ, Nuclear Research Center, Beer Sheva, Presiding Contributed Papers

Sunday Evening {Phys., Rm 323) 19:30 Symposium "The Future of Physics Teaching in Israel" Moderator: A.A. HIRSCH, Technion

Monday Morning (Phys., Rm 323) 9:30 Plenary 5«ssion S. ALEXANDER, The Hebrew University, Presiding R. OPHER, Tachnion (45 min) "Study of Electron Momentum Distributions} Theory and Experimental Methods" COFFEE BREAK 10:30-12:45 Parallel Sessions F. Elementary Particles and Fields •i (Phys., Rm 323) Y. GREW, Tel Aviv University, Presiding Contributed Papers

G. Astrophysics (Phys., Seminars. Rm 1) M. CARMELI, Ben Gurion University, Presiding Contributed Papers

H, Phase Transitions (Phys., Seminar Rm 2) M. LUBAN, Bar Ilan University, Presiding Contributed Papers

I. Lasers and Plasma Physics (Sol. St. Inst. , Rm 58) U. GANIEL, The Weizmann Institute, Presiding Contributed Papers

J. Mechanical and Thermal Properties of Solids (Sol. St. Inst., Rm 52) D. GERLICH, Tel Aviv University, Presiding Contributed Papers

K. Atomic and Molecular Phvaica (Sol. St. Inst,, Rm 60) A. BEN-REUVEN, Tel Aviv University, Presiding Contributed Papers

L. Thin Films (Elec. Eng., Rm 413) N. KLEIN, Technion, Presiding Contributed Papers f-'onaav Afternoon

13:45 Parallel Sessions H. Crystal Defects (Phys., Seminar Rm 1) D.S. TANNHAUSER, Technion, Presiding Contributed Papers

N. Holography and Interferometry (Sol. St. Inst., Rm 52)

J. SHAMIR, Technion, Presiding

Contributed Papers

0. Semiconductors (Phys., Ssminar Rm 2] A. HAREL, Tadiran, Presiding Contributed Pe>p8T3

P. Lasers and Plasma Physics (Sol. St. Inst., Rm 58) Y. PAISS, Soreq Nuclear Research Center, Presiding Contributed Papers

15:00 Plenary Session (Phys., Rm 323) N. ROSEN, Technion, Presiding J. GOLDSTEIN, The Hebrew University (45 min) "Some Properties of Quasi Two-Dimensional Electron Gas on ZnO Surfaces"

COFFEE BREAK

S, BLUDMAN, University of Pennsylvania and The Hebrew University (45 min) "Neutrino Dynamics in Stellar Collapse" THE I5RAEL PHYSICAL SOCIETY

1976 ANNUAL MEETING

Sunday, Aoril 11 - Monday, April 12

Tftchnion-Israel Institute of Technology, Haifa

COMPLETE PROGRAM

Sunday f-'orning (Phys., Rm 323)

9:00 Registration

9:45 Opening Address

Y, EISENBERG, President of the Israel Physical Society, will present the Yom Kippur War Memorial Fund Scholarship, granted by the IPS in memory of the members of the Society who fell in the Yom Kippur War.

10:15 Plenary Session

Y. EI5ENUER6, The Weizmann Institute, Presiding

U.P. OŕŕENHEIM, Technion (45 min) "Laser Isotope Separation"

COFFEE BREAK

S. SHTRIKMAN, The Weizmann Institute of Science (45 min) "A New Kind of Multicritical Point Associated with a k-5pace Instability"

12:00 Business Meeting

Sunday Afternoon ' (Phys., Rm 323)

14: DC

A. NUCLEAR PHYSICS - •

A. MARINCV, The Hebrew University, Presiding 11 \

A-l

PROPERTIES OF THE I3QR WITH THE 4°Ca(3He,3He'a)36Ar AND 40ca(3He,3He'p)39K REACTIONS A. Hoalem The Racah Institute of Physics, one Hebrew University, Jerusalem, Israel; and W.Benenson, G.M.Crawley and T.L.Khoo Cyclotron Laboratory and Physics Department,Michigan State University, East Lansing, Michigan 48824. Inelastic scattering of electrons and hadrons has established the concentration of a great E2 strength in resonance-like structure 3-5 MeV wide at E = 63 x A"1/3 MeV. This resonance is now commonly identified with an isosca1er giant quadrupole resonance (GQR) which exhausts some 40\-80% of the isoscaler energy weighted quadrupole sun>(2). Here we report on particle decay properties of this resonance - as obtained from a study of the reactions 40Ca{3He,3He'p)39K and *°Ca(3He,3He'a)3^Ar. Such a measurement is of particular interest since radiative capture experiments suggest that the greatest part of the E2 total decay strength does not lie in the ground state channel'3'. Both processes mentioned above are found to proceed via two intermediate distinct resonances at excitation energies 40 Ex = 14.5 MeV and 18.0 MeV in Ca. The 18.0 MeV resonance, previously identified with the IGQR decays strongly by alpha and proton emission with a ratio rp;ra = 1.0*0.2. Only a small fraction of the total observed strength, * 13% for the 0o mode and

1. G.R. Satchler, Phys. Report 14c (1974) 97. 2. M.Gell-Mann and V.L. Telegdi, Phys. Rev. 91_ (1953) 169. 3. S.S.rianna - private communication. 12

A-2

THE

A-3

ISOBARIC ANALOGUE STATES IN 43Sc STUDIED BY ELASTIC AND INELASTIC PROTON SCATTERING FROM «Ca

E.Navon, A.Marinov, Ch.Drory, J.Burde, M.Paul and A.Ginzburg The Racah Institute of Physics, The Hebrew University, Jerusalem, Israel.

The isobaric analogue states in Sc have been studied using the proton beam from the tandem Van de Graaff accelerator. Exci- tation functions of elastic and inelastic proton scattering leading to the ground state and to the 2+(1.S24 HeV) and 0+(1.838 MeV) excited 3tates of 42Ca were measured at 90°, 122.5° and 160° at bombarding energies from 3.0 to 3.8 MeV. More than 20 resonances were identified and angular distributions of the inelastically scattered protons were measured at bombarding energies corresponding to most of the resonances 13

observed in the excitation curves. The spins of the states in 43Sc and their partial widths for decay to the ground state and to the two excitsd states in ^2Ca were determined in roost of the cases. The results show that although most of the levels have very small partial widths for decay to the ground state of 42Ca, some of them have quite significant :s

A-4 THE USE OF GENERALIZED HAUSER-FESHBACH THEORY FOR REACTIONS THROUGH ISOBARIC ANALOGUE RESONANCES

A. Frenkel, H.M. Hofmann*, Z. Vager, S. Wald, Department of Nuclear Physics, The Weizmann Institute of science, Rhovot,Israel A generalized Hauser-Feshbach theory (GHFT)(1) was used for calculating the energy averaged cross section for reactions via Isobaric Analogue Resonances (IAR). The method is compared to the Agassi- Vager model (AVM)(2). The AVM formulates the S matrix in terms of the background S matrix, and the parameters of the analogue state only. The statistical behaviour of the background is well established, and it is only there where statistical assumptions enter. We generated a set of statistical background S-matrices, and performed ensemble averages of bilinear products of S matrix elements, at different energies. The results were compared to those of the GHFT, where the input was the energy averaged S matrix, taken from the AVM. Both methods coincide within statistical errors. The comparison was carried out for IAR around A=90, where the background has transmission coefficients of the order 10"2, which require the use of large ensembles containing up to 15000 S matrices. Cases with 4,5 and ó open channels were investigated. In our work we demonstrated the consistency of a physical model such as the AVM, with the statistical assumptions underlying the GHFT. We suggest to use the GHFT, together with the average S matrix given by the AVM, for calculating average cross-sections, polarization etc. in reactions via doorway states. 1) H.M. Hofmann et al., Ann. Phys. 90_ (1975) 403. 2) D. Agassi and Z. Vager, Nucl. Phys. A218 (1974) 573. * Present address: Insv" ute for Theoretical Physics, Erlangen, Germany 14

A-.5, EXTRACTION OF SPECTROSCOPIC FACTORS FROM (p.p'y) ANGULAR CORRELA- TIONS AT ANALOGUE RESONANCES C. Abramson, A. Frenkol, I. Plesser and Z. Vager Department of Nuclear Physics, Weizmann Institute of Science, Rehovot Angular correlations between inelastically scattered protons leading to the first excited 2* state of even-even nuclei in the mass 90 region, and subsequent 2+ ->• 0+ y rays were measured. Analogue resonances corresponding to the low-lying 3/2+ and S/2+ ixcited states of the even-odd nuclei were observed. The Agassi-Vager model (1), together with a generalized Hauser- Feshbach theory (2), are used for the analysis of the compound- enhanced cross-section, for resonances below neutron threshold. The applicability of previous methods(3) is discussed. The řpectroscópic factor thus extracted are compared to shell-model calculations. (1) D. Agassi and Z. Vager, Nucl. Phys. A218 (19743 573. (2) H.M. Hofmann et al., Ann. Phys. 9£ (1975) 403. (3) N. Cue et al., Nucl. Phys. A229 (1974) 429.

EFFECT OF MOLECULAR BINDING ON THE RESONANCE SCATTERING OP PHOTONS FROM THE 6.324 MBV LEVEL IN 15H 0. Shahal, Nuclear Research Center-Negey, Beer-Sheva R. Moreh, Nuclear Research Centar-Negev; Ben-Gurion University V. Volterra, Ben-Gurion TJnireroity of the Neger, Beer—Shera

The temperature effect of nuclear resonance acattering froa the 6.324 M«V level in 15.N was studied aa a function of temperature 15. .15. using a gaseous N and a solid Li NO, targets. The Y source was produced by the Cr(n,t) reaction. In order to reproduce the experimental rariation of the scattering cross section versus temperature the lamb treatment for metallic elements was generalised to the case 15

of diatomic and more complicated nolecu.lers. In N sn effective temperature was defined in vhich the zero-point energy of vibration of the diatomic molecule was included. In Li NO,, an effective temperature wa3 defined by introducing a modified Debye temperature and accounting for the normal modes of vibration of N in the NO " molecule. In a way, the prssent experiment measures the total Mletie energy of the scattering nucleus including the zero-poin^ vibrations in molecules.

A-7

THE MAGNETIC MOMENT OF THE 96 keV, 3/2+ LEVEL OF 190

G. Goldring, B. Richter, Z, Shkedi and Y. Kolfson, Department of Nuclear Physics, Weizmann Institute of Science, Rehovot, Israel

The magnetic moment of the first excited 96 keV, 3/2T level of 19O has been determined by an integral perturbed angular correlation measurement in an external transverse magnetic field. The 3/2+ level was populated via the reaction ^o(d,pY)l£>O with deuterons of Ed = 2.0 MeV from the Weizaann Institute Van-de- Graaff accelerator. The target consisted of 93% enriched H?180 water. The 96 keV y-rays were registered in coincidence with the 1.4 MeV y-rays, of the feeding l/2+-<-3/2+ transition. The measured y-y angular correlation for the (l/2+-K5/2+-+5/2+) cascade is presented in fig. i. From the precession angle of the angular correlation in the applied transverse magnetic field of 16.0 kGauss represented by the open circles in fig. 1, a value of g = -0.48(6) was obtained for the g-factor of the first excited 3/2+ level of 190.

fig. 1 The angular correlation 16

ON THE SYSTEMATICS OF NUCLEAR MAGNETIC MOMENTS IN LIGHT s-d SHELL NUCLbl.

Z. Shkedi, Department of Nuclear Physics, Weizmann Institute of Science, Rehovot, Israel.

The values of several recently determined magnetic moments of short-lived states in1°'19>200 and in 18Ne nuclei have been interpreted in terras of a simple Shell-Model structure. These • states are believed to consist mainly of several identical nucleons in the d§/2 configuration. The experimental values of the g-factors generally agree with the pure d{?,9 values i.e. g=+1.89 and g=-0.76 for protons and neutrons respectively. The deviations from the pure configuration values can be attributed entirely to a very small admixture of the (d"-l d_ .„) configuration into the d",., wave function. Upon investigation of all up-to-date reported g-factors of states which are believed to belong to the ds/2 shell in Z,N=8-14 nuclei, another systematic feature is observed. The distribution of the n.-asured g-factors of these states appears to cluster in three groups:

T,/T = +1, "active protons" : = +1.49 T, = 0, N = Z : = +0.55 T„/T = -1, "active neutrons": = -0.40 in standard isospin notation. Isospin symmetry implies:

(0) . , /T. 1(1) g = g + CT3/T) g - where g and g are the isoscalar and isovector terms < > respectively, g( ' can be obtained from these g+1 values by:

gC°) ,>(<»> • ) = +Oľ55 in excellent agreement with the experimental value of for the self conjugate nuclei. Both values are also in excellent agreement with the theoretical value of g(^= +0.57. 17

A-9

MAGNETIC MOMENT OF THE 6+ ISOMERIC STATE IN 1}ltTe+

A. Wolf* and E. Cheifetz, The Weizmann Institute of Science, Rehovot, Israel

+ The magnetic moment of the 6 isomeric state (Tl /2=163nsec) in 1311Te (composed of 2 protons outside the doubly magic core 132Sn) was measured by a time-differential perturbed angular correlation method,?using the alignment produced in the fission process. A thin 10 fissions/min, Cf source plated on a 25 mg/cn>2 copper backing was placed in a magnetic field of (8.08Í0.05) kGauss normal to the fission direction. Gamma-rays emitted by fragments stopped in the copper backing at three angles (45c, 0°, -45°) with respect to the fission axis were detected in a Ge(Li) detector, the fission direction being determined by the complementary fragments which were detected by three surface barrier detectors. The intensity of the 6+-1-4+, 115.3 keV transition in 13United States- Israel Binational Science Foundation (B,S,Ft, Jerusalem, Israel].

*0n leave of absence from the Nuclear Research Center, Negev, P.O.B. 9001, Beer Sheva, Israel.

A PHENOMENOLOGICAL APPROACH TO BACKBENDING

G. Barnea, Solid State Institute, Technion, Haifa, Israel. A. Mann, Department of Physics, Technion, Haifa, Israel.

The phenomenon called "backbending" O»2) suggests a non-analytic dependence of the energy E on the angular quantum number, I, Based on an analogy with the many-body theory of a similar phenomenon in the magnetic susceptibility of {jaramaBiietic metals (3,4)) we propose the following dependence relation 18

for E as a function of I

This formula constitutes a four-parameter fit to the data. It is shown to yield a rather good description of energy levels of backbending nuclei up to the highest spin measured (1=22).

1. R.A. Sorensen, Rev. Mod. Phys. 45, 353 (1973). 2. A. Johnson and A. Szymanski, Phys. Rep. T_, 181 (1973). 3. G. Barnea, J. Phys. C: Solid State Phys. %, L216 (1975). 4. G. Barnea and D.M. Edwards, to be published and this conference, Bl.

A-ll

ANGULAR DISTRIBUTIONS OF SPECIFIC GAMMA RAYS EMITTED IN THE DE-EXCITATION OF PROMPT FISSION PRODUCTS OF ZS2Cf. t

A. Wolf and E. Cheifetz, Weizmann Institute of Science, Rehovot, Israel

Angular distributions of specific y-rays emitted in the de- excitation of prompt fission products of 2StCf were measured with respect to the fission direction. A total of 42 angular distributions were measured, 23 of which were of transitions in even- even fragments. The strong anisotropy (A2=0,4-0.6) measured for 2+ •+ 0+, 4+ -»• 2+, and 6+ •* 4+ transitions in 138>l4°Xe and 11>z'llikBa provides direct evidence that the angular momentum of the primary fragments is completely aligned perpendicular to the fission axis. Most of the results are consistent with the results of a statistical calculation. The anisotropies measured for some transitions in even-odd fragments were combined with information of other authors in an attempt to determine spins of low-lying levels in these fragments. Finally, it is shown that about 60% of the anisotropy of the gross unresolved Y-ray spectrum measured extensively by other authors(l) is due to transitions in the ground state band of even-even fragments.

t This research was supported by a grant from the United States- Israel Binational Science Foundation (B.S.F., Jerusalem, Israel). *0n leave of absence from the Nuclear Research Center, Negev, P.O.B. 9001, Beer Sheva, Israel.

1) K. Skarsvag and I. Singstad, Nucl. Phys. 62_, 103 (1965). 19

A-12

STUDY OF ACTINIDES PRODUCED BY SECONDARY REACTIONS IH TUNGSTEN TARGET1*' A.Marinov and S.Eshhar KacaRacahn Institutinstitute ofr Physicsťnysics, Thrne Hebreneorew Universityuniversity,, jeJerusalemi ; A.M.Friedman'* ',Argonne National Laboratory,Argonne,.Illinois3 ; C.J.Batty, A.I.Kilvington and J.L.Weil' * ', RutherforRutherfoid Labora- tory, Chilton, Didcot, Berkshire; G.W:A.íJewton and V.J.Robinson, Chemistry Department, University of Manchester, Lancashire; and J.D.Hemingway, Universities Research Reactor, Risley, Lanchashire. In previous papers ' evidence for the possible existence of a superheavy element with Z=112 were presented. These results, if correct;, would indicate that heavy elements may be produced via secondary reactions, in the bombardment of,for instance,tungsten with 24 GeV protons. The aim of the present work was to prove or disprove the validity of the proposed mechanism by studying the production of actinides in a tungsten target that was bombarded with protons of 24 GeV. Actinide fractions from Am up to Lw were separated from our W3 target'*'^'. Fission fragments were found in all the sources from Am to Fra and their intensities in the region of few events per month were followed since 1971. By comparison with die a-spectra that were measured with the same sources for long periods, it was found that the origin of the fission fragments could not come from "^Cf or from any other contamination. It is therefore reasonable to conclude that actinides are produced in the bombardment of tungsten with 24 GeV protons via secondary reactions. Further measurements of ct-X rays coincidences and a-recoil nuclei coincidences'3' were performed. The results that will be presented support the previous conclusion. (*) Work supported in part by the Central Research Fund, Hebrew University. (**} Attached staff at AERE,Harwell, Didcot, Berkshire,England. (***)Present address-University of Kentucky,Lexington,Kentucky. 1) Marinov et al., Nature 229_ (1971) 464 2) Marinov et al.. Nature 23£ (1971) 212 3) Batty et al, Nucl, Instr. and Meth. 99_ (1972) 179 20

A-13 A COMPARATIVE STUDY OF NEUTRON ACTIVATION RESULTS Joseph Yell in institute of Archaeology and Department of Physics Hebrew University Isadore Perlraan Institutes of Archaeology and Chemistry Hebrew University Trace element detection is assuming an increasingly important role in interdisciplinary science. Among the various techniques available neutron activation enjoys certain advantages which make this technique preferable in situations demanding good accuracy on a large number- of elements covering a range 5of chemical behaviourisms, no prior chemical separation or treatment, large volume turnover and compatibility with other laboratories. The last point is extremely important as without it the results of two different laboratories cannot be directly compared. We report here the results of a preliminary study on the compatibility of analysis carried out on the same samples by two laboratories, one in Jerusalem and one in Berkeley, California. Each laboratory employed a different reactor for activation and different y-detectors for analysis. Both ceramic and rock samples were analyzed for trace as well as major elements. Trace elements examined included Ce, Th, Cr, Hf, Ba, Sb, Cs, Ni, Se, Rb, Ta, Co, and Eu and major elements Fe, Na and Ca. The concentration of these and other elements were determined relative to a common standard. The results of this study will be discussed with emphasis on the precision and accuracy attained in each laboratory and the compatibility of the two laboratories. Sunday Afternoon (Phys., Seminar Rm 1) 14:00

B. MAGNETISM M. FIBICH, Technion, Presiding

B-l

ANOMALOUS BEHAVIOR IN THE FIELD DEPENDENCE OF THE MAGNETIZATION OF STRONGLY ENHANCED ITINERANT PARAMAGNETS

G. Barnea, Solid State Institute, Technion, Haifa, Israel. D.M. Edwards, Dept. of Mathematics, Imperial College, Londnn SW7, England.

Microscopic Fermi liquid theory is used to prove that the leading correction to the linear dependence of the magnetization M on the applied magnetic field H is a term proportional to H3 Jln j H j. This result agrees with calculations based on phenomenological Landau theory 00 and like the non-analytic dependence of the susceptibility on the temperature (2.3) is a many-body effect. It is shown that subject to certain assumptions, the coefficient of the H3Jtn|H| term is proportional to the sixth power of the exchange enhancement factor. This non-analytic dependence of the magnetization on the external field leads to features in the Arrott plot (M2 versus H/M) which provides a good fit to the observed low field anomaly in stoichiometric (4) The experimental data is fitted over a wider range of field by introducing a further term proportional to H^Jtn | H| . Other strongly enhanced itinerant paramagnets are discussed. 1. S. Misawa, Phys. Rev. Lett. 26., 1632 (1971). 2. S. Misawa, Phys. Lett., 32A, 153, S41 (1970). 3. G. Barnea, J. Phys. C: Solid State Phys. 8_, L216 (1975). 4. C. J. Schinkel, F.R. de Boer and B. de Hon, J. Phys. F. Metal Phys. 3_, 1463 (1973). ř •

B-2 SPIN CORRELATION AND SPECIFIC HEAT OF THE ONE-DIMENSIONAL

ANTIFERROMAGNET CsNiCl3 D. Moses, H. Shechter and E. Ehrenfreund Physics Department and Solid State Institute, Technion, Haifa J. Makovsky, Nuclear Research Center, Negev, Beer-Sheva CsNiCl, is known to have one-dimensional antiferromagnetic correlations in a wide temperature range above its three- dimensional ordering temperature of 'v* 4.8K. We have measured the specific heat of a single crystal specimen of CsNiClj from 4K to 40K. The magnetic part of the specific heat was found to have a broad maximum at about ^ 22K and a term linear in temperature below

B-3 NUCLEAR RELAXATION STUDIES OF THE ONE-DIMENSIONAL

ANTIFEROMAGNET CsNiCl3 D. Moses, R. Brener and E. Ehrenfreund, Physics Department and Solid State Institute, Technion, Haifa L.S. Smith, Physics Department, University of Pennsylvania, Philadelphia, PA, U.S.A. We have measured the Csl33 spin-lattice relaxation rates as a function of temperature C5¥Til50K) at selected frequencies •ÍV=7, IS and 34 MHz) in the one-dimensional antiferroraagr.et CsNLClj. All the measurements were made on a single crystal at 23

temperatures above.the three-dimensional ordering temperature where one-dimensional correlations are apparent and govern the spin dynamics of this system. At relatively high temperatures CkgT >J, where J is the exchange constant) the relaxation rate can be described by TJ1=a+bv"1/2. jhis indicates that in this temperature range one-dimensional diffusion processes are dominating the spin dynamics. Furthermore, the temperature dependence of the relaxation in this temperature range could also be accounted for by a diffusion process. At low temperatures (k[jT

B-4

CRYSTAL FIELD INDUCED SPIN ROTATION IN g

G. Dublon, M. Kroupp, M. P. Dariel and U. Atzmony Nuclear Research Center-Hegev.P.O.Box 9001,Beer-Sheva

Recent specific heat measurements of ferromagnetic cubic Laves phase HdCop (T =116K), revealed a pronounced anomaly at S2K. The present Mossbauer study of Fe-doped NdCo?, which are supplemented by RSM magnetization measurements of polycrystalline NdCo_, were mare to investigate the thermal anomaly. The Mossbauer results exhibit a spin rotation from a direction close to the [llO] cubic axis below !*2K, to the [100] axis above 1»1*K. This is reconcilable with both the specifiCpheat data and a previous neutron diffraction study of NdCOp, which failed to detect changes in the magnetic ordering or crystalline structure below T . Single ion crystal field calculations reproduced tfie observed spin rotation and crystal field parameters were determined. The magnetization vs temperature curves of NdCo„ exhibit a small maximum around-UOK. This anomaly was reproduced by calculating the Hd moment in the presence of crystalline and exchange fields, using crys+.al field parameters which r

were determined by the Mossbauer results. The combined^

••lossbauer and magnetization data yield a](2.3±0.1pB Na moment in NdCo and we find 25

-0.088

1. 3. Deenadas, R.3. Craig, N. Marzouk and VJ.E. Wall.-.ce J. Solid State Chem. ,4.,1(1972) . 2 R.M. Moan, W.C. Koehler and J. Farrel, J. Appl. Phys.,31,978(1965).

B-5

NEUTRON DIFFRACTION STUDY OF

H. Pinto, M. Melamud and H. Shaked Nuclear Research Center, Negev.

The structure of the compound Fe2wOg is of the Tri-c -PbO2 type, and it belongs to the crystallographic space group D-Ľ4 - Pbcn. The lattice constants are a = 4.576 A, b=16.766 A and c= 4,967 A , with,. 4 formula units per lattice point. Neutron (Á* 2.4 A ) diffraction patterns were taken at 300 °K (RT),170 OK,77OK (LNT), and 4,2 °K (LHeT).Some intensity-temperature curves were also taken. The results may be summarized as iollows: .... 1. The RT pattern agrees with the reported* crystallographic structure and ions positions.

2. Reflections with h+k odd, not allowed by Pbcn,L010~, 03 0" , {100> , £031) appear upon cooling at Ti^240 °K and increase in intensity down to LHeT, 3. Reflections with h+k even, allowed by Pbcn:\020\,021 '110í , llII1- , -JL5Ó' , show upon cooling an increase in intensity, starting at T2~150 °K (as observed with 1.021} and {111' only ) . The first set of lines is consistent with Cz, i.e. ferromagnetic (LOO) planes coupled antiferromagnetically with spin along (po£) . This structure belongs to Pbc'n1. The space group Pbc'n1 , however, allows two structures: Cz and Fx (ferromagnetic with spin along D.OÓJ ) , The second set of lines is consistent with Fx and*'or chances in the ions positions. Preliminary Mossbauer effect afid rotating sample magnetometer measurements, corroborate some of these conclusions. 25

References. 1. Senegas J. and Galy J., Solid State Chera. 1£,5, (74) 2. Atzmony U, and Dublon G.„ to be published.

B-6 INELASTIC NEUTRON SCATTERING STUDY OF ION ENERGY LEVELS SPLIT BY CRYSTAL-ELECTRIC AND MAGNETIC-INTERNAL FIELDS.

N. Shamir, M, Melaraud and H, Snaked Nuclear Research Center, Negev. Direct transitions between ionic states 30 to 1000°K apart are observed in the energy transfer spectra of inelastically scattered neutrons. Spacing between energy levels and relative transition probabilities are determined from the positions and intensities respectively, of the neutron lines. Large (30-50 grams) nontrans- parent powder samples can be studied in this method, which is especially suitable to investigate levels near ground state at low temperatures. Such an investigation may be useful in the study of phase transitions. The measurements are performed on the "recently constructed triple-axis neutron-spectrometer KANDI III, using powder samples, at different temperatures between 1.2 K and room temperature. Energy levels of Pr were recently studied. Work is currently performed on the rare earth ion levels in the orthochromites (RCrO,), 3+ and on the Cr levels in the orthochromites containing a diamagnetic rare-earth. A study of Co energy levels in CoGeO^ at temperatures below and above the transition to antiferromagnetism is being carried out. 26

B-7

THE INTERMEDIATE JAHN-TELLER EFFECT IN Pd3+ IN MgO ^j.

B. Barnet, A. Raizman and J.T. Suss Soreq Nuclear Research Centre, Yavne.

The electron paramagnetic resonance (EPR) of Pd in single crystals of MgO exhibits an intermediate Jahn-Teller effect. A numerical diagonalization of the matrix of random strains and tunneling within the vibronic Ai and 2E manifold_was performed for various ratios of the random strains (6) to the tunneling splitting (3ľ). The corresponding EPR spectra were computed. From the angular variation and the line shape oE the experimental low temperature spectrum at 4.2K the 6/3r ratio for Pd3+ in MgO was estimated to be in the range of 0.3-0.5.

B-a MAGNETIC PROPERTIES OF A DISORDERED 5UBSTITUTI0NAL MAGNETIC ALLOY-HEISENBERG MODEL

H. Dvey-Aharon and M. Fibich Physics Department, Technion-Israel Institute of Technology, Haifa

The magnetic properties of a disordered A B.. ferromagnet, with A-A interactions only, are analyzed in terms of a Heisenberg type Hamiltonian. A Green's function technique is applied to derive the transition temperature Tc(x) and the critical concentration xc , below which no bulk ferromagnetism exists. This is repeated for various ratios of second to nearest neighbor interactions. Kesults for x are shown to agree with the relevant critical site percolation concentration in each case. Dispersion relation and density of states of the spin wave spectrum are calculated and compared with those obtained by other techniques and for different types of disorder. For x < x spin wave excitations exist for wave number k above a certain lower bound k (x). The inverse of k_Cx) is interpreted as the linear dimension of the largest magnetic cluster that the system can sustain at x < xc . Results are compared with those obtained by percolation methods. Magne- tization and heat capacity are also calculated and compared with experimental data. 27

INTERNAL FIELD DISTRIBUTION IN SPIN-GLASSES

Chaim Held and Michael W. Klein, Department of Physics, Bar-Ilan University, Ramat-Gan

Recent progress in -^asuring the internal field distribution of spin glasses using polarized u-mesons has generated a greet deal of interest in the theory of spin-glasses. We perform a selfconsistent calculation of the field distribution of a dilute spin-glass system interacting via a Heisenberg exchange interaction and find that the probability of obtaining zero fields vanishes2 like H^dH for small H, where H is the internal field. As a consequence of this we show that the low T experimental specific heat can not be explained by a simple internal field model. The internal distribution of fields we obtained is consistent with the polarized p-meson experiments.^ Furthermore, the theory gives cusps in the magnetic susceptibility as is found by Riess and Klein.3

1. D.E. Murnick and A.T. Fiory and W.J. Kossler, Phys. Rev. Lett. 36, 100 (1976), Ibid 33, 969 (1974) 2. C. Held and M.W. Klein, Phys. Rev. Letters 35^ 1783 (1975) 3. I. Riess and M.W. Klein, To be published and this conference.

B-1D

THEORY OF CUSPS IN THE SUSCEPTIBILITY OF SPIN GLASSES

Han Riess, Department of Physics, The Technion, Haifa, and Michael W. Klein, Department of Physics, Bar-Ilan University, Ramat-Gan

We develop a selfconsistent theory for the susceptibility of spin-glasses. We show that in this selfconsistent theory two different order-parameters enter: 1) The magnetization M which is in general zero 2) the order-parameter m, (k = 1 or 2 for our systems) which is related to the root mean square of the local magnetization averaged over the whole system. The order parameter m, enters selfconsistently into the width of distribution function P(H) of internal fields H and is 23

nonzero for T < T . The magnetic susceptibility is continuous at T = T andcgives a cusp at T . The theory also gives a different set of concentration-dependent scaling parameters at low T, and'at high T. A comparison of our results with experiment will be made.

1. J.A. Mydosh ar.d V. Canella, Phys. Rev. B6_, 4220 (1972)

COMPETING INTERACTIONS AND THE VERY HIGH FIELD MAGNETIZATION IN SPIN-GLASSES

Baruch Fischer and Michael W. Klein, Department of Physics, Bar-Ilan University, Ramat-Gan, Israel

Spin Glasses are magnetic systems which interact with random "competing-exchange-potentials", (CEP) which results in neither ferro nor antiferromagnetic phase transition, but rather in a spin-glass transition.l>2. The magnetic susceptibility x is continuous at Tc, however the derivative of x diverges at T = Tc. The behaviour of the system is strongly effected by the CEP and it is therefore of interest to obtain this from physically measured quantities. We show that the very high field magnetization of u spin glass system can by expanded in 2 power series of c(l - Acfi(T) + B c f2(T)), where c and T are the magnetic impurity concentration and temperature, respectively A and B are constants. The T dependence of fi(T) agrees with recently measured high field magnetization of Ag-Mn-*. It is shown that the term c-^ÍT) is simply related to the CEP of the spin-glass system.

1. I. Riess and M.W. Klein, To be published and this Conference 2. S.F. Edwards and P.W. Anderson, Ja Phys. F5_, 969 (1975) 3. Pon-Wei Hou and B.R. Coles, Phys. Rev. Lett. 3£, 1655 (1975) 29

B-12.

SPIN GLASS TRANSITION IN A SYSTEM WITH SYMMETRIC-EXCHANGE- INTERACTION

Moshe Gitterman and Michael W. Klein Department of Physics, Bar-Ilan University, Ramat-Gan

In a recent work, Edwards and Anderson and Sherrington and Kirkpatrick^ (SK) developed a new general method for evaluating the average free energy of a system of frozen in and magnet- ically interacting localized spins, by evaluating l*j![(Zn - l)/n, where Z is the partition function. We use this n-expansion of SK2 to evaluate the free energy for a system interacting with a symmetrically distributed random potential of the form of the sum of two Gaussians centered at ± Joand width J. We prove that the system undergoes only a spin glass transition at 2 2 Tc = J{1 + x /2 + x )}, where x = Jo/J. When the width of the distribution J = 0, the system stays paramagnetic down to T = 0. We thus show that the specific sum of two 6-function interactions discussed by Mattis^ gives no transition. Results on the magnetic susceptibility and specific heat near the spin glass transition are given in terms of the parameters entering the system.

1. S.F. Edwards and P.W. Anderson, J. Phys. F:Met. Phys. 5_, 965 (1975) 2. D. Sherrington and S. Kirkpatrick,'Phys. Rev. Letters 35, 1792 (1975) 3. D.C. Mattis, Yeshiva University Preprint, December 1975.

B-13

ABNORMAL RELAXATION OF SUPERPARAMAGNETIC PARTICLES Itamar Eisenstein and Amikaro Ah3roni Electronics Department, Weizmann Institute, Rehovoth

In small enough ferromagnetic particles, the magnetization is uniform, and its direction changes by thermal agitations working against an anisotropy energy barrier which is proportional to the volume, V. In an ensemble of such particles these directions approach a thermal equilibrium with a relaxation time, T, that should thus increase with increasing V. However, experiments on some cubic materials ' have revealed a sáze range in which T abnormally decreases with V. Thir. might be explained by assuming 30

a non-uniform magnetization reversal mcde which makes the barrjer and T decrease in the range of the anomaly. In contradistinction to previous calculations , ours predict the same phenomenon in uniaxial materials, provided their anisotropy is sufficiently small. Computations have been mane for the hexagonal ferrite Fe with x=1 at r0o m BaCo Ni- 16°27 ' temperature, taking for the 4 4 3 4 anisotropy constant K = 1.22x10 erg/cm , and 4TTM = 3500 G for the saturation magnetization. For these values, the theoretical result is that T increases with V for particle diameter of up to ° -5 -8 400 A, then decreases rather steeply from 10 sec to 10" at a diameter of about 600 A. For still larger sizes T increases again 4 and the whole behavior is rather similar to the prediction for BaCo Ti Fe O. at x^l.3, but the present material seems x x iz~^x i.yQ handier for experimental studies.

1. A.M. Afanass'ev e_t al, Sov. Phys. JETP, 31_, 65 (1970). 2. A.P. Amulyavichus et_ a^, Sov. Phys. JETP, 37_, 859 (1973). 3. I. Eisenstein and A. Aharoni, Phys. Rev. B (to be published). 4. Landolt-BOrnstein new series, Group III, vol.4b, Chap.7 (1970). Sunday Afternoon (Phys., Seminar Rm 2)

14:00

C. THIN FILMS

D. BRANDON, Technion, Presiding

C-l

ESTIMATE OF THE BAND GAP OF INSULATORS

N. Klein, Dept. of Electrical Engineering, Technion - Israel Institute of Technology, Haifa, Israel. (invited, 30 mins)

In good insulators ionic, surface, impurity band and intrinsic conductions a.re avoided and the currents are due to injection of carriers at the electrodes. The latter can be small, when either the electrode injection barriers, or the trap depths in the insulator are large both for holes and electrons. For electrode limited currents the band gap accommodating the barriers is smallest, when the electrode Fermi levels fall roughly to the middle of the band gap. The smallest band gap ensuring insulat- ing properties at a given field is calculated by stipulating an upper limit for the current density. An approximate relation is obtained, which is not strongly influenced by the current density limit and by trapping in the insulator. This relation is compared with experimental results.

C-2

THE ELECTRICAL CONDUCTIVITY OF VERY THIN METAL FILMS

0. Gottlieb and V. Halpern Department of Physics, Bar-Han University, Ramat-Gan, Israel. The solution of the Boltzmann transport equation to calculate the electrical conductivity of very thin metal films is a difficult mathematical problem. However, on physical grounds one expects this conductivity to depend on the total rate of scattering of the electrons, and not on the scattering rate weighted in favour if large-angle scattering as for bulk crystals. This hypot'T'sis has been confirmed by analysis of che results of previou ."siculations, and by calculations 3Z

using a new technique that we have developed. Thus, we find that the standard Fuchs-Sondheiiier results are applicable to films whose thickness is less that 1/100 of the electron mean free path 1. , provided that one inserts in this theory the value of 1, appropriate to the total scattering rate.

C-3

iIÍITIOAli CUiUÍJJJT DENSITIES IS SUHätOONDĽCTJ.« GliANiULAR

AI-A12O rll/IS

D. Abraham, S. Alterovitz, and R. Kosenbaum Department of Physics and Astronomy, Tel-Aviv University, Tel-Aviv Measurements of the critical current densities in thin granular superconducting A1-A1„O films have Heen nade as a function of the normal state resistivity of the granular material ar.d a3 a function of the surfaae preparation. It is observed that the 2 2 Al-AlpO films exhibit critical current densities of 10 A/cm to 3 2 10 A/cm over a broad range of normal state resistivities ranging from 10 uň cm to 10,000 jjil cm; materials such as these having low critical current densities are suitable for quantum device applications. The effect of the aluminum oxide barrier on the critical current densities and the effect of vortex pinning at the edges upon the critical current densities will be discussed*

C-4

ENHANCEMENT OF THE SUPERCONDUCTING CRITICAL TEMPERATURE OF THIN METAL FILM EVAPORATED IN THE PRESENCE OF HYDROGEN OR HELIUM.

Y. Villaret and M. Pasternak, Dept. of Physics,Tel-Aviv University.

Superconducting properties of thin Aluminium films with absorbed H, and He are being studied. It is found that'condensed

Al at 6°K substrates in the presence of H2 He substantially enhances the critical temperature -T - up to 5.0°K and 4.5K respectively. These values can be cSmpared to a typical TC=3.2K 33

obtained for Al - evaporated under the same conditions in vacuum. Typical evaporation rates are 30 8 s" and gas pressures are around 10"^ torr. Experiments performed with Sn films show

similar trends in Tc. Interpretation concerning these results are presently explained in terms of new phonon modes created by the interstitial H. or He atoms. We are facing now the problem of proving the existence of these modes, their characterization and the mechanism by which they interact with the superconducting electrons.

C-5 SU'PERCOroUCTING PROXIMITY EFFECT BET'EIT TIÍC AľT1 PALLA- DIUM LAYERS G. Ueutacher and T. Duby, Department of Physics ar.n Astronomy, Tel-Aviv University, Hamat Aviv, Tel-Aviv Pd-3n and 3n-Pd double layers were prepared by ev°- poration from V.' boats in vacuum (p "5x10 torr) onto glass substrates held at 77 or 300K=through suitable masks that enabled four terminal measurements of electrical resistivity of the double layers as well as of adjecent Pd and 3n single layers. The superconducting trasition temperatures were determined from the resistivity data. A number of samples were prepared keeping

äSn- 500 or 1000A, while dp, varied between 50 and 500Ä. Taking into account only good double layers, i.e. those which had the superconducting transition width of the same order as that of the adjecent Sn single layer, it was found that the transition temperature of the double layers T„ was independent i) of the order of evaporation of Pd and Sn, ii) of the substrate tempemture, and iii) it did not vary with aging. Consequently the inter/netallic boundary between Pd and Sn was reproducib- le. From the obtained values of T as a function of d^- c f -i \ Pd using the empirical formula of Hilsctr ' a value of the penetration depth of Cooper pairs into palladium kD, = (56-10)A was found. Applying the de Gennes model in thick limit' ' values of kp^"1 were calculated, which did not agree with the empirical result. This may be explained by ths fact that the assumptions of the model were not necessarr.'1..- fulfilled in our case. 1. P. Hilsch, Z, ^rysik 167, 511 (1962); 2. P. 3. de Gennes. ?ev. Mod. Phys. ?ř,, 251 34

C-6

PLANAR HALL EFFECT IN GADOLINIUM THIN FILMS NEAR THE CURIE POINT

M. Safrai, R.A. Buckwald and A.A. Hirsch Department of Physics, Technion-Israel Institute of Technology, Haifa

The planar Hall field in Gd thin films exhibits the sinusoidal orientational dependence well known in other ferromagnetic metals. The ferromagnetic resistivity anisotropy (Ap ) near the Curie point (T ) is found proportional to PQ(1-T/T ) ^suggesting a critical exponent of 1/3 for the magnetization. No anomalities were observed in the thickness dependence of resistivity (p()).

C-7

ELECTRONIC TRANSPORT NEAR THE SURFACE OF InSb FILMS

A. Zemel*, Colorado State Univ., Fort Collins.

Galvanomagnetic measurements were made on n-type InSb films between 5 to 20 pra thick, at temperatures from 4.2 to 300K and in magnetic fields up to 60kG. The films were formed by transient crystalization CO 1 —1 and typically had peak mobilities around lO-'cm ,v~ . s and low temperature carrier concentrations of 5x10 ^cm~^. The values of the layer carrier concentrations and mobilities were separated from those of the bulk film by Hall coefficient measurements coupled with the conventional galvanomagnetic measurements. This tachnique yield a surface electron density for the top plus bottom of the film of S-SxlO^cm*"^ and a surface layer mobility of 15OO-2OOOcm .v-i.s"1, both largely independent of temperature. The surface density is found to decrease when the free surface is anodized.

* Present address: Soreq Nuclear Research Center, Yavne, Israel. 35

c-a THE HETERO-EPITAXIAL GROWTH OF GERMANIUM FILMS IN ULTRA- HIGH VACUUM.

M. Barkai and E. Grtinbaum School of Engineering, Tel-Aviv University, Ramat Aviv G. Deutscher and M. Meidan Department of Physics, Tel-Aviv University, Ramat Aviv.

The oriented growth of germanium thin films onto (111) oriented mono-crystalline NaCl substrates has been studied. This substrate, about 400 ft thick, was formed by evaporation in ultra- high vacuum onto air-cleaved mica at 25°C. Without exposing it to air, germanium was deposited onto it at a rate of 15 8/min from an electron bombardment source. Tne film could easily be removed from the substrate by dissolving the NaCl in water, and was analysed by transmission electron diffraction and microscopy. Studies by in situ high energy reflection electron diffraction are also in progress presently. Nearly single-crystal films with (111) orientation could be formed at a substrate temperature of 340°C and a pressure of 2xl0~°torr during evaporation. As the substrate temperature was increased the amount of (111) oriented grains decreased and at 380°C the film had a random poly-crystalline structure. This behaviour, which is contrary to that observed normally in epitaxial growth, where the degree of orientation increases with temperature!, is explained by the high vapour pressure of NaCl at those temperatures (relative to 2xlO"^torr ) As the NaCl sublimes it presumably interferes with the reorientation of nuclei which normally takes place during the coalescence process. For comparison evaporation at a higher pressure (2 x 10 torr) was also performed: it lead to relatively less weil oriented films at substrate temperatures of 300° - 340°C, but the film orientation continued improving for higher substrate temperatures, as usual.

1 E. GrUnbaum, Vacuum 24_, 153 (1975). 36

PRODUCTION OF VERY THIN EPITAXIAL GOLD FILMS M. Talianker and L. Patlajan Department of Materials Engineering, Technion, Haifa, Israel

Epitaxial gold films grown by evaporation in vacuum on rock salt usually contain a rather high density (approximately 1010 cm 2) of planar defects (twins and stacking faults). In addition, at thicknesses below 40 nm the films lack continuity. The present contribution describes a technique for producing continuous, {100} oriented films at thicknesses down to 4 nm with low planar defect densities (approximately 10s to 107 cm 2). These films were deposited under a continuous flux of low energy (300 eV) electrons onto an epitaxial layer of silver on rock salt. Optimum conditions for depositing the films were as follows: 1. The y-irradiated rock salt crystals were cleaved and annealed at 400°C in air. 2. The salt substrate was pumped to 10~7 torr and heated to between 280-290°C. 3. Electron bombardment was initiated and a 0.15 ym layer of silver was deposited epitaxially at a rate of 0.2-0.5 nm sec"1. 4. The silver layer was then annealed for 15 minutes in situ at 290-300°C. 5. The gold film was then deposited at a rate of 0.1 nm sec"1 at the annealing temperature. The silver-gold films were then floated off onto water, rinsed and the silver then dissolved in dilute nitric acid. These films were found to be both thinner, of lower defect density, and to have better continuity than those which have been prepared by previous workers.

Business Meeting of the Thin Films Division Afternoon (Sol. St. Inst. . Rm 52)

14:00 D. HELIUM AND SUPERCONDUCTORS I. PRIV0R0T5KI, Technion, Presiding

D-l EFFECTIVE HEAT CONDUCTION IN DILUTE 3He-4He SOLUTIONS V. Disatnik and A. Yaniv Department of Physics and Astronomy, Tel-Aviv University, Tel-Aviv The effective heat conduction in dilute superfluid 3He -4 He solutions is studied. It is found that, at very low temperatures, the effective heat conductivity (Keff) is determined by four momentum dependent relaxation times. However, by using the appropriate Onsager relation, it is shown that when this momentum dependence is disregarded, Keff depends on only two relaxation times. Within this framework, it turns out that in the regime where the ^He quasiparticles behave like a classical gas and the transport of heat is dominated by scattering from these excitations, Keff is linear in the inverse ^He concentration. This observation is found to be in a good agreement with the experiment (1-2). The analysis of the basic elements of the theory suggests that non-linear effects will tend to increase the heat conduction. Some features of this "heat flush" were observed experimentally and seem to conform with the theoretical predictions (1)• 1. W.R. Abel and J.C. Wheatley, Phys. Rev. Letters 21, 1231 (1968) 2. R.L. Rosenbaum, J. Landau and Y. Eckstein, J. Low Temp. Phys. 1±, 131 (1974).

D-2

DILUTE He- He SOLUTIONS: RAYLEIGH AND BRILLOUIN SCATTERING Y. Disatnik, R. Meyuhas and H. Brucker* Department of Physics and Astronomy, Tel-Aviv University, Tei-Aviv 38

3 4 The scattering of light from the dilute superfluid He- He solutions, at very low temperatures, is considered. Following Rockwell et al.(l) expressions for the relative intensities of the Rayleigh and Brillouin lines are obtained from the hydro- dynamic equations and a set of "compressibility" type sum-rules. The thermodynamic functions appearing in these expressions are then parametrized within the framework of the semimicroscopic equilibrium theory suggested by two of us several years ago (2). The final expressions are easy to apply in calculations of the relative intensities. Tne application of the theory in the analysis of experimental data is discussed and a comparison with other theories is made.

*Killed in action, 16 October, 1973. 1. D.A. Rockwell, R.F. Benjamin, and T.J. Greytak, J. Low Temp. Phys. 18, 389 (197S). 2. Y. Disatnik and H. Brucker, J. Low Temp., Phys. 7, 491 (1972).

D-3 A NEW APPLICATION FOR HOLOGRAPHIC INTERFEROMETRY - STUDIES OF PHASE CHANGES IN ISOTOPIC MIXTURES OF HELIUM NEAR THE ABSOLUTE ZERO Jacob Pipman and S.G. Lipson, Technion, Haifa, Israel Holographic interferometry combines sensitivity and ease of application in the study of density changes in transparent materials. We have used this technique to study phase equilibrium in He3/He4 solid and liquid mixtures, as well as dynamic effects associated with changes in the equilibrium conditions. In particular two types of phenomenon have been studied: interracial surface tension between the Bose quantum liquid (He'* rich phase) and the Fermi quantum liquid (He^ rich phase) and the propagation of a very slow concentration wave produced during the mixing of the two phases. Interfacial surface tension is measured by observing the detailed shape of the meniscus between the phases at temperatures down to 0.4°K and pressures up to 30 atm. The mixing wave is conveniently followed by the use of real-time holography and has apparently never been observed before. We shall discuss its interpretation and its relationship to inter- diffusion of the two isotopes. 39

JL-J.

FIFTH SOUND

CG. Kuper, Physics Department, Technion, Haifa.

A new mode of wave propagation is proposed, associated with an interface between liquid and solid helium. In He, the solidus curve is flat over a wide temperature range (0 to 1.6K), and in 3He there is a flat region around 0.3K. In these regions, although the phase transition is of first order, there is no latent heat. A wave of melting and freezing ("fifth sound") is predicted; in the limit of long waves the velocity is given by 2 cv ^gfPss + PL*)/(PS - PL),

where Ps and p. are the densities, and s and Jl are the thicknesses, of the solid and liquid layers, and where g is the body force per unit mass. If i, "v s "\» 5Ä and g is the van der Waals attraction of the external wall, we might expect Cy ^ 150 m s

D-S PRASE TRANSITIONS IN n-VECTOR MODEL WITH A NONOKPERING PARAMETER WITH AN APPLICATION TO LIGHT SCATTERING IN He3-Hes MIXTURES

Ya'akov Achiam, Yoseph Imry, and David J. Bergman Department of Physics and Astronomy, Tel-Aviv University, Ramat-Aviv

The renormalization-group method is applied to the analysis of phase transitions where the n-vector order parameter is coupled to a nonordering parameter. A variety of critical and tricritical behaviors are found as a function of the physical variables, the specific heat exponent a of the system and external conditions. Relations between the critical indices which characterize the nonordering parameter correlation function are found. These relations are applied to analyze a light scattering experiment in He -He mixtures near its tricritical point of separation. The tricritical behavior is found to be character- ized by a = -0.9. The critical behavior on the X-line near the tricritical point which was found is probably a crossover behavior to the tricritical one. 40

D-6

CALIBRATION OF A LONDON OSMOTIC PRESSUEE THERMOMETEH USING MOSSBÄDER ABSORBER THERMOMETRY J.Hess and A.Levy, Racah Institute of Physics, Hebrew University, Jerusalem, Israel. A London type osmotic pressure thermometer (OPT) connected directly to the dilute phase in the mixing chamber of our new dilution refrigerator has been operated. Construction methods described by Bloyet et al. (2) were used and the thermometer was calibrated in situ using the central doublet of the Mossbauer absorption spectrum of l*>lDy in dysprosium metal power.

For liquid temperatures lower than 50 mk difficulties were encountered with both the OPT and the Mossbauer effect (ME) thermometer although in principle we see no reason why the calibration cannot be extended below 50 mk, given the high sensitivity of the ME thermometer in this region.

A brief description of our new dilution refrigerator will also be given.

í H.London, D.Phillips and G.P.Thomas, Proč. LT11 St. Andrews (1968) p. 649.

1. D.Bloyet, A.C.Ghozlan, P.Piejus, M.Sudraud and E, J-A Varoquauz, preprint intended for publication in Proč. LT13 Bolder, Colorado (1972).

D-7

CRYOGENIC REFRIGERATION UTILIZING THE ELECTROCALORIC EFFECT IN PYROELECTRIC LITHIUM SULFÁTE MONOHYDRATE

Sidney B. Lang Department of Chemical Engineering, Ben-Gurion University of the Negev, Beersheva, Israel

A cryogenic refrigeration cycle based on the (linear) electrocaloric effect in single crystals of lithium sulfáte 41 roonohydrate (LSM) is proposed. The phenomenology of the electrocaloric effect is developed and expressions for the low-temperature heat capacity and pyroelectric coefficient are derived. A Camot cycle consisting of two isothermal and two isentropic steps is proposed and extensions are made to multi-stage refrigerators. Refrigerators operating with a high-temperature reservoir at 1.25 K have a maximum refrigeration capacity of 3.84 yj per cycle per cubic cm of working material (maximum electric field = 100 kV per cm). However, the minimum temperature achievable with one-stage of refrigeration is 0.875 K and with three-stages, 0.047 K. Three-stage refrigerators operating with 1 K reservoirs can theoretically reach temperatures less than 1 mK.

p-a

BREAKDOWN OF THE SEMICLASSICAL CONCENTRATION-POTENTIAL RELATION OF A NONDEGENERATE FREE CHARGE CARRIER GAS IN HIGH EXTERNAL FIELDS AND LOW TEMPERATURES

Y. Weissman Dept. of Theoretical Plysics and Applied Mathematics, Soreq Nuclear Research Centre, Yavne, Israel

We present a set of approximations which allow the derivation of the semiclassical formula n(x) = N(T)-exp[-(eV(x)-Ep)/kTj (and the corresponding formula for p(x)) from the one particle Schroedinger equation using Boltzmann statistics. Inspection of certain approximations involved reveals that the semiclassical formula is valid only when the main contribution to n(x) comes from the oscillating part of the wave functions. At high electric fields and low £emperatures it can happen that the main contribution to n(x) will come from the exponentially decaying part of the wave functions; in this case the semiclassical formula breaks down and should be replaced by a quantum formula, which differs from it considerably. 42

D-9

LXACT CURRENT DENSITY IN LARGE SQUARE-SHAPED JOSEPHSON JUNCTIONS

M. Rosenkrantz and S.I. Ben-Abraham Department of Physics, Ben-Gurion University of the Negev, S4 120 Be'er-Sheva1 The phase difference 5 across a Josephson barrier satisfies the sine-Gordon equation in the barrier plane. For a square-shaped harrier uf side 21- we find an exact solution J in terms of elliptic functions:

2 2 li 5 = arccos{2kXY/[l+(kXY) ]}, Z A sn[(l+k ) z/XJ,k]. Cl) The boundary conditions imply that the modulus k is a solution of the equation

j (2)

For the current density j we find í (3)

For a rectangular junction with Ly = 2LX the total current vanishes. Generalizations to rectangular junctions and lattices of junctions will be discussed. 1 lien-Abraham, S.I., Phys. Lett. A (in press); also abstract at t:i i s ;r- acting.

D-10

MAGNETIC CURRENT MODULATION IN LARGE RECTANGULAR JOSEPHSON JUNCTIONS

S.I. Ben-Abraham and M. Rosenkrantz Department of Physics, Ben-Gurion University of the Ne«ev, 84 120 Be'er-Sheva1 We consider a rectangular Josephson junction in the (xy) -plane with an applied magnetic field H . We find an exact solution to the problem 3. The phase difference 6 and the current density j across the barrier are doubly periodic functions of x and y. The phase and current pattern splits into N alternating square- 43

Jomains. Tlie fluxons sit in the node lines. When the boundary conditions are exactly met the total current is zero when N is oven and maximum when \i is odd.

1 Rosenkrantz, M., and Ben-Abraham, S.I., preceding abstract.

D-U

NONTRIVIAI. SPACE-TIME DEPENDENT PHASE IN LONG JOSEPIiSOX JUNCTIONS

S.I. Ben-Abraliam and M. Rosenkrantz Department of Physics, Ben-Gurion University of the Negev, 84 120 Be'er-Sheva1

An exact nontrivial solution to the sine-Gordon equation is 1

6 = 2

X = dii^3 i- . K,k , T' - en .V1^ > i£- K'.k' . (1)

Hence, the pha.<=e difference 6 across the barrier is a monotonie quasi-periodic function of x and t with wavelength 2 2 2 A = 2>JK(l-2k )' /Cl-k ) and frequency v = c/A. The modulus k is determined from the boundary condition L = nA, where L is the length of the barrier. Since d<5/dt s 0, the junction current displays periodic peaks of like signs and has a nonvanishing mean value. Calculations of current-voltage characteristics are in progress.

1 Ben-Abraham, S.I., Phys. Lett. A (in piess); also abstract of this meeting. Sunday Afternoon (5ol. St. lost., Rm 58)

14:00 E. LASERS AND PLASMA PHYSICS G. EREZ, Nuclear Research Center, Beer Sheva, Presiding

THE INTENSITY DISTRIBUTION OF A TRANSVERSE FLOW CO, LASER AND THE DEPENDENCE OF ITS OUTPUT POWER ON THE CAVITY WIDTH.

0. Eidelman, E. Bin-Nun and M. Rokni, The Racah Institute of Physics, The Hebrew University of Jerusalem.

;,'e have measured the intensity distribution of a transverse flow CO2 laser along the flow direction, and the dependence of its output power on the cavity width. The experiments were performed with a transverse flow COT laser chemically excited by the reaction of nitric oxide with atomic nitrogen(1). The intensity distribution is found to be of a multi-mode structure fairly symmmetrical about the optical axis. The overall output power is found to increase with increasing cavity width up to an optimum value and then it decreases with any further increase of the cavity width. These results do not agree with those expected from Cool's model^. We believe that this is due to the fact that Cool's model neglects any correlation between the radiation intensities at different points across the width of the cavity. Our results qualitatively conform with those expected from the model of Tulip et al.(3), which assumes total correlation between the radiation intensities at different points across the width of the cavity.

(1) E. Bin-Nun and M. Rokni, IEEE. J. Quant. Elect. QE-10, 89 (1973). (2) T.A. Cool, J. Appl. Phys. 40,, 3563 Q969). (3) J. Tulip and H. Seguin, J. Appl. Phys. 42, 3393 (1971). 45

E-2 DEUTERIUM SEPARATION IN FORMALDEHYDE BY AN INTENSE PULSED CO^ LASER

G. Kořen, U.P. Oppenheim, D. Tal, M. Okon and R. Weil Solid State Institute and Department of Physics, Technion-Israel Institute of Technology, Haifa, Israel

ABSTRACT

Following reports ' of laser separation of deuterium in formaldehyde using UV light sources, we present the first COT laser enrichment of deuterium ir formaldehyde gas, using a "~-20 MW CO? TEA laser operated at 10.59u. Strong focusing of pulses onto the sample yields highly efficient selective ihotodissociation of the formaldehyde molecule. An enrichment factor of approximately 40 is found for the gas at an initial pressure of 20 torr, after irradiation with 300 laser pulses. No such effect is found when the pulses are only slightly focused. Since the dissociation energy is over 3 eV, many infrared photons participate in the dissociation of one molecule i.e. - we are dealing with a multiphoton process C3) . The method described here offers the prospect of reducing the cost of deuterium production.

1) E.S. Yeung and C. Bradley Moore, Appl. Phys. Lett. 2\_, 109 (19?-). 2) Laser Focus, June 1975, p. 16. 3) R.V. Ambartzumiai , N.V. Chekalin, Yu.A. Gorokhov, V.S. Letokhov, G.N. Makarov and E.A. Ryabov. Laser Notes in Physics, Vol. 43, Laser Spectroscopy, Proc. of the Second Int. Conf., Megěve, June 23-27, 1975, page 121 Springer - Verlag, Berlin 1975.

E-3

'SIMULTANEOUS TWO WAVELENGTH AMPLIFICATION IN DYE LASER AMPLIFIERS' U. Ganiel, M. Nagler and D. Treves Department of Electronics, Weizmann Institute of Science, Rehovot

In previous studies of multiple wavelength, tunable dye lasers,1 competition effects between the two spectral components, 46

were found to limit the control one has on their relative intensities. We performed a set of experiments aimed at a better under- standing of these competition effects in an amplifying dye laser medium. The system consisted of a pulsed, dual-channel Nitrogen laser (8 n.sec, 100 kw pulse per channel), which was used to pump two Rhodamine 6G (R6G) narrow-band laser oscillators (wavelength Xi and A2) and a R6G amplifier. The oscillators were independently tunable and their output were fed into the amplifier. Special care was taken to insure spatial overlap of the excited region in the amplifier and the two input beams. We measured the small signal gain of X2, over a range of 25 nm for a number of saturating input signals at constant \\. A comparison of the experimental results with an idealized model of a homogeneously broadened dye laser amplifier2 does not give a satisfactory fit. Possible explanations for the discrepancy will be discussed.

1. A.A. Friesem et al., Appl. Phys. Lett. 23_, 249 (1973) 2. U. Ganiel et al. I.E.E.E. J. Quan. Elect. GE-11, 881 (1975).

E-4

CHEMIEXCITATION OF IffiTASTABLE STATES OF LEAD ATOMS

A. Gabai, M. Rokni, Y. Shmuelovitz and S. Yatsiv The Racah Institute of Physics, The Hebrew University of Jerusalem, Israel.

2 The chemiexcitation of the Pj 2 metastable states of the 6p configuration in Pb in the coméustion of C2H2 + 02 is reported. The atoms are produced by doping the reactants mixture with 3 Tetra-Methyl-Lead. The population of the Pj,2 states is monitored by time-resolved absorption spectroscopy. The relative population of the excited states is found to exceed a few percent of the T.M.L. dopant number density. Evidence is given for the chemica'. rather than "thermal" nature of the population of the metastable states. Assessment of this method for establishing population inversion and laser operation between metastable atomic levels will be discussed. 47

E-5

INJECTION LOCKING OF THE SPECTRUM OF PULSF.D DYE LASERS I. ANALYSIS

U. Ganiel, A. Hardy, and D. Treves - Department of Electronics, The Weizmann Institute of Science, Rehovot, Tsrael.

Injection locking can be a very efficient method for channeling the output of a high power dye laser system into a tunable, narrow band portion of the spectrum, determined by an injected signal. The behavior of such systems is analyzed in detail. The analysis is based on a set of coupled integro-differential rate equations introduced previously, l which are solved subject to appropriate boundary conditions. Both a straight, two mirror cavity, and a ring cavity, are considered. It is found that after the initial transients, there is a quasi steady state period (the first plateau) , during which the laser radiation is completely locked to the wavelength A^ of the injected radiation, and the intensity Ij at X^ is proportional to the pumping rate W, During the first plateau tne intensity If, of the radiation at the free oscillation wavelength X^, grows exponentially in time. The duration of the first plateau fT ) depends, apart from the material parameters and cavity losses, on the proximity of A. to A and on the intensity of the injection Ijn. It is shown that T scales linearly with the cavity length but only logarithmically with I. . Once I approa- ches Ij, there is a transition period, after which a new steady state (the second plateau) is established, and most of the output is included in I,, while 1^ becomes proportional to Iin, with a gain factor determined by the material parameters, X^ and X^.

Although the problem must be solved numerically in general, all the features described above can be deduced by various analytical approximations, which are in excellent agreement with the exact numerical results. The application of the results to practical systems will be discussed.

(1) U. Ganiel et al., IEEE J. Quantum Elec, QE-11, 881 (1975). 48

E-6

INJECTION LOCKING OF THE SPECTRUM OF PULSED DYE LASERS. II. EXPERIMENTAL

S. Blit, U. Ganiel and D. Treves - Department of Electronics, The Weizmann Institute of Science, Rehovot.

Injection locked dye laser systems are described. Flashlamp pumped (FLF) and laser pumped (LP) systems were constructed. The source of the narrow-band injection was a single-mode CW dye laser. Attempts were made to minimize thermal anJ shock-wave induced inhomogeneities in the pulsed laser. Special care was taken to match the mode of the injected radiation to an eigenmode of the pulsed laser c.ivity.

Our measurements consisted of simultaneous recording of the power, spectral and temporal features of the laser output. The performance of the systems was evaluated at various injection intensities, wavelengths and pumping rates. We have found that the total output power can be locked into a single longitudinal mode, which is continuously tunable over more than 50A°. Partial locking can be achieved over a wider range, up to ^200A°, but at the extremes of this range the locking lasts only during part of the laser pulse, so that the energy content of the narrow-band portion is smaller than that of the free running laser. The efficiency of the I.P system was ^10% (pump light to laser output) while the FLP system had about 0.1% overall efficiency. With a Rhodamine 6fi solution, energies of up to 50mj of single-mode, tunable radiation in 0.3psec pulses were obtained.

Details of the experimental set up will be described.

E-7

THE POPULATION AND KINETICS OF OPTICALLY EXCITED 3p STATES OF Hg ATOMS

Y. Degani, E. Rosenfeld, M. Rokni and S. Yatsiv The Racah Institute of Physics, The Hebrew University of Jerusalem, Israel.

3 The population kinetics of the metastable P0 level of mercury was studied. The excitation was performed by irradiating a mixture of Hg and N2 with intense pulsed mercury light. This pulse had a square wave shape and its duration could be varied between 0.1-20 msec. The density of metastables was monitored by the time-resolved absorption of the 4047 A° transition of Hg. We found that the decay time of the Po population becomes shorter with increasing duration of the pumping pulse. This 49

effect was pronounced at hg vapour pressure of about 2 mtorr

(corresponding to room temperature) and at N2 pressure of about

20 torrs. Upon lowering the Hg vapour pressure, or the N2 density, this effect Mas markedly reduced. Our observations indicate thai, this effect could be attributed to interaction J of atoms at the P0 state with an excited species of Hg. The nature of this species and the mechanism of this effect are

investigated. The population density achieved in the ~P0 level is sufficient for possible excitation of laser transitions 3 3 3 fiom the Sa to the P2 and P3 levels.

E-3

TIE EXCITATION OF ONE SINGLE VIBKATIONAL MODE OF A MOLECULAR SPECIES bY MĽAÄS OF SELECTIVE ENHANCEMENT OF THE CORRESPONDING STIMULATED RAMAN SCATTERING STOKES INTENSITY.

S. Kimel and R. Schatzberger, Chemistry Department,'Technion- Israel Institute of Technology, Haifa.

The relative intensities of different Stokes lines in a stimulated Ranan scattering (SRS) spectrum, of a pure compound or of a mixture, may serve as a measure for the transient distribution of the excited molecular population over the vibrational levels.

We have investigated the increase of the intensity of a certain chosen SRS line, or the appearance of a new line, by the use of an appropriate field at the corresponding Stokes frequency. In a previous study this additional field was provided by a fluor- escent dye in the optical path.

In the present study a Raman cell containing a binary mixture was pumped by a ruby laser, and simultaneously by SRS produced in a separate cell. This cell contained only one component of tiie mixture, and was placed in front of the Raman cell. Results will oe presented for the SRS spectra from benzene/nitrobenzene mixtures of different compositions as a function of the ruby laser intensity and of the intensity of an additional SRS Stokes field either from benzene or from nitrobenzene. The measurements snow the possibility of a controlled increase of one Stokes field in the mixture and a .corresponding depletion of the other-fields. Tlie implications of the SRS method for isotope enrichment will be mentioned. 50

1. S. Kimel and R. Schatzberger, in "Lasers in Physical Chemis- try and Biophysics", Ed. J. Joussot-Dubien, Elsevier, Amsterdam, (1975] 143. 2. S. Kimel, A. Ron, and S. Speiser, Chem. Phys. Letters 28 (19 74) 109.

E-9 INTERACTION BETWEEN A SPATIALLY EXTENDED COLLECTION OF TOO-LEVEL SYSTEMS AND A SINGLE MODE FIELD

Abraham Shalom, Technion - Israel Institute of Technology, Haifa

The interaction between a collection of two-level systems (TLS's) and a resonant mode of the electromagnetic field inside a cavity is investigated, the model being an idealization (that ignores losses) of the resonant interaction between a large number of molecules and a cavity mode. The new feature of the analysis is the consideration of different strengths of coupling between different molecules and the mode (due to the variation of the field intensity inside the cavity). The main question under investigation is the temporal behavior of both the molecules and the field for initial conditions that are of particular interest, complete molecular excitation and absence of field excitation. The equations of motion are integrated numerically. The results are displayed graphically. The number of photons in the cavity rises (from zero) to an initial maximum and then shows a series of (unequal) peaks. The results are qualitatively different from those obtained under the assumption of equal coupling for all molecules 1. They are also different from previous work in which the variation of coupling strength was considered^.

1. I.R. Senitzky, Phys. Rev. A 3., 421 (1971). 2. C.S. Chang and P. Stehle, in Coherence and Quantum Optics, ed- ited by L. Mandel and E. Wolf (Plenum, New York, 1973). 51

E-10

ARE SOME OSCILLATOR QUANTUM STATES MORE "CLASSICAL" THAN OTHERS?

David Agmon, Technion-Israel Institute of Technology, Haifa

The frequently-occurring statement that coherent states describe most closely the classical harmonic oscillator is found to be an oversimplification and misleading. In view of the fact that the most general classical description (and the one most suitable for application) is statistical, the following era' cria are suggested for setting up and examining the classical analog of a quantum mechanical oscillator state: 1) íq(ť)} = 2) {E} = - (•fiw/2) 3) [SqCtiSp(t)]2 í [Aq(t)Ap(t)]* - &2/4) 4) 6E« AE 5) |{(qCt] - {q(t)})n}| í ]<{q(t) -)">l where { } indicates the classical averzie and ô indicates the classical P..M.S. devintion. The classical analog of various types of states, including the coherent states are exhibited. It is concluded that other states may be regarded as being as close to their respective classical analogs as the coherent states. Sunday Evening (Phys., Rm 323) 19:30 Symposium

"The Future of Physics Teaching in Israel"

Moderator:

A.A. HIRSCH, Technion Monday Morning (Phys., fim 323)

9:30 Plenary Session

S. ALEXANDER, The Hebrew University, Presiding

R. OPHER, Technion (45 min) "Study of Electron Momentum Distributions: Theory and Experimental Methods" 13:30

F. ELEMENTARY PARTICLES Al\ifl FIELDS (Phys., Rm 323) Y. QREN, Tel Aviv University, Presiding

F-l AZIMUTHAL ASYMMETRY IN PION PRODUCTION, AND THE HEAT CONDUCTIVITY OF I1ADR0NIC MATTER J. Goldberg, Department of Physics, Technion, Haifa An asymmetry is observed in the azimuthal distribution of pions in the reaction K-p -»• K-ir+Trp at 14 GeV/c. It is related to the model of pion production by heating the hadronic matter, with finite heat conductivity.

F-2 SLOW PARTICLE INCLUSIVE SPECTRA AND CHARGED PARTICLE MULTIPLICITY DISTRIBUTIONS IN pd AND ir+d COLLISIONS AT 195 GeV/c B. Haber, Y. Eisenberg, D. Hochman, U. Karshon, E.E. Ronat, A. Shapira, J. Schultz, R. Yaari and G. Yekutieli The Weizmann Institute of Science, Rehovot, Israel and H. Braun, D. Brick, F. Etienne, A. Fridraan, E. Jagham, P. Juillot, G. Maurer and A. Michalon, Centre de Recherches Nucleaires, Strasbourg4 France Using the NAL 30" proportional wire chamber-bubble chamber hybrid system we have measured pd and ir+d interactions -t 195 GeV/c. The average multiplicity of negative particles in pn reactions is 54

larger than that of pp. This negative excess may be related to the neutron fragmentation in TT" mesons. A measurement of all particles emi'tted in the backward hemisphere reveals that the excess is due to low multiplicities but it includes also considerable contributions from topologies up to 11 prongs.

The pn distributions are affected by double scattering in the deuteron. Results of a model which takes into account the strong correlation of particles in the forward jet will be presented and the effects on the distributions will be discussed.

F-3

DECAY OF K*C1420) INTO K*(890) AND TWO PIONS

J. Goldberg, Department of Physics, Technion, Haifa

Following the theoretical work of Levy, Singer and Toaff, the decay of K*(1420) into %*{ 890) and two pions, comprising TW coupling, has been investigated and found in the reaction K-p -»• K°Tr+TT-!T-p at 3 GeV/c. The width obtained is 9 ± 3 MeV, ;ind it is shown that the ir+7T pair associated to K*(890) is mainly in the T=l state.

L',•!-DIMENSIONAL DOUBLY PERIODIC SOLUTION TO THE SINE-GORDON EQUATION

S.I. Ben-Abraham Department of Physics, Ben-Gurion University of the Negev, 84 120 Be'er-Sheva'

The two-dimensional sine-Gordon equation can be written in the form

3* 3é —- + —- = 2 sin$ cos* , fii 352 3n2 where all valuables are dimensionless. An exact, doubly periodic and finite solution is

sins«, 55

With real k, the solution describes an NaCl lattice of two- dimensional solitons and antisolitons, with pure imaginary k a square lattice of imaginary solitons or antisolitons; b. —> 0 yields small linear oscillations, while fe = 1 corresponds to a single two-dimensional soliton. With both k and n imaginary we have real nonlinear standing waves. Since k is equal for boih £ and n, quantization on £ implies quantization on o. For tj> interpreted as an order parameter the theory predicts a weakly first order transition. Applications are to liquid crystals, quantum optics, superconductivity, crystal defects, and, of course, field theory.

F-5 NULL-PLANE CHARGES AND FOURIER TRAKSFOHKS, AI.D THE ASYMPTOTIC BEHAVIOUR OF SCATTERING AMPLITUDES

Eldad Gal-Ezer and Lawrence P. Horwitz Department of Physics and Astronou'.y, Tel Aviv University, Raaat Aviv, Israel

It is shown that the existence of null plane charges and null plane Fourier transforms (which enter into the discussion of current algebra at infinite momentum) depends on the high energy asymptotic behaviour of scattering amplitudes; s In s behaviour is the maximum growth allowed. The possibility of defining charges for the case of spontaneously broken symmetry is also discussed. 56

INTERACTIVE COMPUTES GRAPHICS IN THE PHYSICS LABORATORY

D.C. Rapaport, Physics Department, Bar-Ilan University, Ramat-Gan

A PDP 11/40 minicomputer with a refreshed graphic display is being used to collect and display x-ray scattering data in a real-time environment. The goal of the project is to simulate in software the functions of a well-endowed multi- channel analyzer.. Using a lightpen the experimenter can expand, roll and.smooth the spectrum and identify features vith a movabie cursor without interfering with the data collection. Other features include timed runs, automatic storage of spectra in a disk-based library, and retrieval of spectra from the library by name. Monday Morning (Phys., Seminar Rm 1)

10:30

G. ASTROPHYSICS

H. CARMELI, Ben Gurion University, Presiding

6. CONFIRMATION OF KNOWN NUMERICAL SOLUTIONS FOR THE QUIET SOUR WIND EQUATIOMS

S. Cunerman, N. Metzler * and M. Spici^elj;lass Dept. of Physics and Astronomy, Tel-Av:v University Tel-Aviv

A detailed comparison of two integration methods for the quiet solnr wind, namely, starting at the "sinotilar critical r>omt" and nroceedin^ outward and then inward (Method I) and starting at "infinity" and nroceeding inward (Method n) is j;iven. No consideration is riven to interaction with interstellar ^as.

It is found that (i) in the domain where both methods provide physical solutions (e.g., from 1 Kg to a few AU heliocentric distance) the results coincide within less than 1 percent (this confirms the validity of the results obtained so far by the authors using Method I); (ii) Method II provides nhysical solutions over all the interplanetary ranj»e, which represents an advantage over Method I; and (iii) while for solutions within 1-2 AU heliocentric distance the two methods consume comparable computer tine, for solutions up to very large heliocentric distances, Method II is preferable.

Subject headings: nlasnas - solar wind

will present the paner 58

G-2 A THIRD.STAR IN HER X-l SYSTEM?

Tsevi .""azeh and Jacob Shaham Racah Institute of Physics Hebrew University, Jerusalem

A third distant star is proposed to exist in the Her X-l system. Moving in an eccentric orbit around the center of mass of the close pair with a period of 35 days,the third small star modulates the mass flow from Hz-Her into the disk around the neutron star. Priodic changes in the disk structure are caused, resulting in the mysterious 35 day on-off period. The observed long-term behaviour of Hz-Her-1 is explained by a precession of the nodes, brought about by the small angle (^15°) between the two planes of motion. Definite predictions, which may soon become observationally measurable, are made.

1Jones, CA., Forman, W., and Liller, W., Ap.J.L.182, L109

£-3

HD 108 AS A BINARY WITH A COLLAPSED COMPONENT

Jacob D. 3ekenstein Physics Department, Ben Gurion University

The high velocity single-lined binary HD 108 is regarded as having been accelerated by the supernova explosion of one of its components which then turned into a collapsed object. Simple estimates show that the effects of momentum transfer by the supernova shell to the companion are far more important than those of mass loss in determining the post-explosion parameters of the system. We obtain a model-independent relation between the system's peculiar velocity, excentricity, and mass ratio, which was heretofore* nelieved valid only for the case that momentům transfer is negligible. From it it follows that the mass of the presumed collapsed object cannot exceed 5 !•:,_. 3y using reasonable novels for the momentum transfer

it can DS shown that the supernova ejected some 6 ns, a value wnich accords with what is known aaout type II sunernovae.

• Hutchings, J. B. 1975> Ap. J., 200, 122.

Gott, J. R. 1971, Nature, 23^,

G-4 CARBON, NITROGEN AND OXYGEN ABUNDANCES IN PIANEĽARY NEBUIňS: OBSERVATIONS AND THEORY.

A. Finzi Department of Mathematics, Technion - Israel Institute of Technology.

R. Yahel Theoretical Physics Department, Hebrew University, Jerusalem. Solar abundances of C,N,0 are beleived to be in the approximate ratio 3:1:10. In general, measurments of the abundances of these elements in HII regions seems to conform these values. However, there is an important exception: in planetary nebulae Carbon abundances are below normal while Nitrogen is overabundent (1). Qualitatively, at least, these results seem to agree with the theoretical prediction made on the assumption that the ejected matter underwent partial hydrogen burning through the CNO bicycle during the ejection process and that this burning provided the energy needed to eject the nebulae (2,3). Theoreticaly, the expected enrichment of Nitrogen is more pronounced the heavier the mass of the central star. Results in reasonable agreement with observations can be obtained by assuming a low stellar mass, around 0.5 Mg.

1. M. Peinibert, S. Torres - Peiiribert, Ap. J., 168_, 413 (1971). 2. A. Finzi, R. A. Wolf, Astron. and Astrophys., 11 418 (1971). 3. A. Finzi, R. Finzi, G. Shaviv, Astron. and Astrophys., 37_ 325 (1974). 60

G-5 X-kAY JOURCES AND COMPACT OBJECTS IN GLOBULAR CLUSTERS AND IN THE GALACTIC BULGE.

A. Finzi Department of Mathematics, Technion -Israel Institute of Technology.

'Je suggest ihat the x-ray sources in globular clusters and in the bulge are created in the close encounters of compact objects ( neutron stars and, perhaps, black holes) and main sequence stars. According to our suggestion, no binary is formed in a close encounter, but the envelope of the main sequence star is dis- rupted and a cloud of matter from this envelope is captured in a close orbit in the field of the compact object and later evolves into a thin extended envelope, x-ray emission takes place as matter from the envelope is accreted onto the compact object.

The total mass of the compact objects needed to JJ.plain the observed number of x-ray sources in globular clusters corresponds to a few thousandths of the mass of the clusters. In the bulge, on the other hand, the total :r.ass of the compact objects must be roughly comparable to the mass of the bulge itself.

f,-6

HOMOGENEOUS COSMOLOGICAL MODEL IN BIMETRIC THEORY OF GRAVITATION

Itzhak Goldman and Nathan Rosen Department of Physics, Technion, Haifa

Cosraological models have been recently constructed in the framework of the bimetric theory of gravitationl»2. These are homogeneous isotropic models with zero spatial curvature (k = 0). A typical example corresponds to a universe which expands from some non-singular state after a previous contraction. In the present work the effects of introducing a cosmological terni into the field equations are investigated. It is found, for example, that a universe filled with radiation can expand from an initial state of finite density to a final state of finite density. 61

XK. Rosen, Gen. Rel. and Grav. 4_, 435 (1973). 2D. Babala, J. Phys. A (Loud.) 8., 1409 (19"5)

LIMITS ON THE VARIABILITY OF REST MASS

Jacoc D. B^enstein Physics Department, Ben Gurion University The possibility that rest mass of particles varies over cosmological times cannot be ruled out by direct experiment. However, the -Lotvos-Dicke-Braginsky experiments do show that if rest masses vary, they all vary in the same way. It is thus permissible to treat rest mass as a dynamical scalar field, tie write down the most general (not necessarily quadratic) Lagrangian for this field including a direct coupling to curvature for generality. Consideration of the scaling properties of the various particle Lagrangians known shows that the scalar field Lagran- gian can be put into a quadratic form depending on only two parameters. We then regard the scalar field as a source of the gravitational field on the sams footing with all other fields. We assume that general relativity describes gravitation correctly. It is then possible to show that when units are used for which rest masses of particles are constant (but G and h are not), the theory is equivalent to a sub- set of the scalar-tensor theories with constant rest masses. Comparison of the predictions of the theory of variable rest masses with the results of experiments originally designed to test general relativity thus becomes possible and permits one to set limits on the values the two parameters that determine the theory can assume. f-'.onday Morning (Phys., Seminar Rm 2)

10:30

H. PHASE TRANSITIONS

M. LUBAN, Bar Ilan University, Presiding

THE COMPETITION BETWEEN SUPERCONDUCTIVITY AND PEIERLS INSTABILITY IN COUPLED LINEAR CHAIN SYSTEMS B. Horovitz The Racah Institute of Physics, The Hebrew University,Jerusalem The superconducting transition temperature (T ) and the Peierls instability temperature (T ) are evaluated using the Eliashberj equation. A finite and even large interchain coupling helps to raise both temperatures to their Mean Field values due to the special role of the phonon with momentum T below a critical electron-phonon coupling constant which depends on the bare phonon frequency. This determines an upper bound on T so that for higher transition temperatures T > T and superconductivity is unlikely. Higher values of T are possible if the interchain coupling is increased above critical value where the Peierls instability is supp- ressed.

H-2

FERROELECTRICITY IN (Ba,Sr)";iO3 SOLID SOLUTIONS

L. Benguigui, Solid State Institute, Haifa, Technion, Israel

K. Bethe, Philips Laboratory, Hamburg, Germany

The variation of the ferroelectric transition temperature was studied in the solid solutions (Ba,Sr)Ti03, in which BaTiO3 exhibits-a ferroelectric transition but SrTiOj does not. From the measurements of the dielectric constant, we deducted the variation with the percentage of Sr of the microscopic parameters which characterize a structural ferroelectric transition. We conclude rhat the reason for the non occurence of ferroelectricity in SrTiO^ is the relative importance of Che anharmonic force constants. 63

H-3

STUDIES OF PHASE TRANSFORMATIONS IN Fe-Mn ALLOYS SUBJECTED TO HIGH PRESSURE A. Rabinkin, M.M. Stupel and B.Z. Weiss Department of Materials Engineering, Technion - Israel Institute of Technology, Haifa.

Mossbauer spectroscopy and X-ray diffraction analysis were used to study some peculiarities of phase transformations in Fe-Mn alloys (20^C,. ^32 at%) . Heat treatment, plastic deformation and high pressure were used in order to obtain various fractions of the h.c.p. e-phase. It was found than an almost pure e-phase state could only be obtained by plastic deformation (up to 60% thickness reduction) of specimens initially in the y-phase state. In contrast to this, the application of 90 kbar pressure under pseudo hydrostatic cc .•'.- itions, resulted in two phase y+e mixture, where the maximum volume fraction of e-phase is about 50%. These results differ from the theoretical prediction (1) of the influence of high pressure on phase equilibria in Fe-Mn alloys. The effect of varying amounts of e-phase (obtained by differ- ing degrees of plastic deformation) on the y-*z phase transformation subsequently induced by high pressures, was studied. Possible mechanisms to explain the influence of different treatments will be discussed.

(1) T. Erschova, E. Ponjatovsky, I. Aptecer, J. of Phys. Chem., 43, 748 (1968).

H-4

SOUND VELOCITY AND DIELECTRIC LOSSES OF Ag,HgI4 IN THE VICINITY OF THE PHASE TRANSITION.

L. Benguigui and R. Weil, Solid State Institute, Technion, Haifa

We have measured the sound velocity of longitudinal haves in polycrystalline samples of Ag^Hg^ and í-he dielectric losses between 0.25 and 50 MHz. This compound exhibits at 51°C an order-disorder transition associated with a high ionic conductivity in the high temperature phase. l\'c observed 64

significant discontinuity of the sound velocity at the phase change indicating that a least cne elastic constant becomes low. The dielectric losses shows two peaks in the low temperature phase but four peaks in the high temperature phase. These features can be related to the release of the Ag and Hg ions in the high conductivity phase.

i- J

EXACTLY SOLVABLE MODEL EXHIBITING A MULTICRITICAL POINT

R.M. Hornreich and S. Shtrikman, Department of Electronics, The Weizmann Institute of Science, Rehovot, Israel Marshall Luban, Department of Physics, Bar-Ilan University, Raiuai-Gaii, Israel and Department óf Electronics, The Keizmann Institute of Science, Rehovot, Israel

A hypercubic d-dimensional lattice of spins with nearest neighbor ferromagnetic coupl'irg and next nearest neighbor anti-ferromagnetic coupling along a single axis is studied in the spherical model limit (n -*•M ) and is found to exhibit a multi-critical point of the uniaxial Lifshitz type. The shape of the \ line is calculated•explicitly in the vicinity of the multi-critical point, and analytic expressions are -iiven for the shift exponentty(.d) and its amplitudes A+(d) . iiie amplitude A (d) changes sign for d = 3. For several rare earth alloy systems which appear to display a uniaxial Lifshitz point, the measured X line is suggestive of that calculated here for d = 3.

H-6

THE SMECTIC C PHASE OF LIQUID CRYSTALS

D. Cabib, Physics Department, Technion, Haifa

L. Benguigui, Solid State Institute, Technion, Haifa

We consider the interaction between two neighboring molecules in a sraectic layer (TBBA and similar materials) as arising from the electrostatic force between their polar bonds. In view of recent experimental evidence that the molecules rotate freely around their long axis, we assume that the component of the dipóle 65

moments along this axis gives the only contribution to the interaction. We show that, given the measured average nearest neighbor distance and the molecular geometry, the sweetie C phase is stable with rrspect to the smectic A and the maximum tilt angle is <\» 60°. This does not agree with experiment, and therefore suggests that Priest's model for the A-C transition is not sufficient. If we consider the molecules as hard rods, we find a maximum tilt angle of ^ 30° in good agreement with experiment. A model which takes into account the finite volume of the molecules is discussed.

CUTOFF EFFECT OX THE SPIN LATTICE RELAXATION TIME IN LIQUID CRYSTALS

S.L). Goren* and C. Korn Department of Physics, Ben Gurion University of the Negev, Beer Sheva

S.B. Marks** Department of Chemistry, Ben Gurion University of the Negev, Beer Sheva

The proton spin lattice relaxation time in APAPA, PAA and ĽBBA was measured as a function of temperature over an extended temperature range by supercooling. The proton spin lattice relaxation time of UBPA was also measured as a function of temperature for various frequencies near the cutoff frequency. The results are interpreted in terms of the Doane, Tarr and Nickerson model whereby a cutoff frequency is introduced in the theory of relaxation via fluctuations of the order parameter.

* On leave at Clarendon Laboratory, Oxford University, Oxford, England. **Present address: Dead Sea Bromine Co. Ltd., Beer Sheva 66

H-a

ON THE STABILITY OF CHEMICAL EQUILIBRIUM

V. Steinberg, Department of Mathematics, Tel-Aviv University M. Gitterman, Department of Physics, Bar-Han University

The general conditions of stability of a system in which a chemical reaction occurs are presented. Although the conditions of the chemical stability are the same as for diffusional stability, the fora of chemical instability lines, the corre- spondent critical parameters etc. depend not only on the interactions between particles but also on the intermolecular interactions. As examples we considered the ionization and isomerisation reactions. The stability of three-component Debye-Huckel's plasma was analysed. We found that the diffussional instability leads to the instability of an ionization reaction, i.e. the system divides into two phases with different degree of ionization. This phase transition is first order and is accompanied by the dielectric-metal transition, which was observed in cesium and mercury vapor. For certain ratio of the characteristic energy of isomers and the heat of mixing an instability of the mixture of isomers is possible. We present numerical calculations of isomer phase diagram. 67

2:2

UNIVERSALITY OF MELTING AND FREEZING INDICATORS AND

ADDITIVITY OF MELTING CURVES.

Yaakov Rosenfeld, Nuclear Research Center-Negev

P.O.B. 9001, Beer-Sheva, Israel.

The assumption of universality of some melting and freezing indicators, in the context of approximate models of the liquid and the solid, gives rise to simple semiempirical melting equations, that describe additivity of melting curves. The melting equations are exact in the high temperature limit and give reasonably accurate results also near the triple point

They find many applications including quantum corrections to the melting curve.

1. Y. Rosenfeld, J. Chem. Phys. 6^, 2769 (1975)

2. Y. Rosenfeld, Chem. Phys. Lett. In Print. Monday Morninfl (Sol. St. last,, Rm 56)

ID: 30

I. LASERS AND PLASMA PHYSICS

U. GANIEL, The Weizmann Institute of Science, Presiding

1-1

MOMENTUM MEASUREMENTS OF LASER PRODUCED PLASMA

S. Zweigenbaum and Y. Gazit Dept, of Plasma Physics, Soreq Nuclear Research Centre, Yavne.

Measurements of the total recoil momentum of the target and the angular distribution o.'. momentum of a laser-produced plasma are important in understating beam-target interaction. Sensitive devices for taking such measurements were developed, based on the principle of the physical ballistic pendulum, which are capable o£ detecting plasma momentum as small as 2.5xlO~5 dyne sec. ľv.o different types of devices were developed: a) a target ' r.Julum which measures the recoil momentum of a target as a r.-.iult of the blow-off of plasma created by the laser irradiation, -.-..I b) a pendulum for measuring the momentum of the expanding ;>L.uraa in a given direction. Measurements were made with a :,'d: glass laser system consisting of five amplifying stages which delivers 2 joules at 0.5 nsec. The light intensity on the target is lQl^ watt cm~^. Using Al targets on the target pendulum we found the recoil momentum and the laser energy to be linearly dependent with a constant cf proportionality of 0.9 dyne sec joule"!' in the energy range 0.1 to 2 joules. A pendulum c f the second type was placed 30° from the laser beam at a distance of 27 cm. Also in this case we found a linear dependence between the momentum of the expanding plasma and the laser energy. The proportionality constant was 1.3 dyne sec~l joule.

The angular distribution of the olow-off products will be. measured by placing several such pendulums in different directions around the laser beam. 69

TAPE-BASED DATA-ACQUISITION SYSTEM FOR LASER-PRODUCED PLASMA RESEARCH

H. Szichman Soreq Nuclear Research Centre, Yavne, Israel.

Recently a magnetic tape drive ires incorporated into our compu- terized plasma diagnostic system. The first version of the hard- ware configuration has been reported elsewhere (1,2). This new facility permits us to operate our data acquisition system composed of a HP-2100A mini-computer with standard peripherals, in a so-called magnetic tape system (MTS). In the magnetic tape environment, the diagnostic program is initiated by a supervisory program which operates in response to usar requests transmitted to the system through the teletype keyboard and also automatically loads the overlay program into the memory core according to software programming. The >ITS also includes a second file with a table of experimental parameters which is constantly updated during experiments. Hence- forth, tape is reserved for recording the laser shot data, each shot forming a separate file. This new arrangement has the following advantages: a. System is easily restarted after a system fail. b. Data recorded on the magnetic tape may then be read in a larger computer (IBM 165'370) for further processing. c. More memory is now available for diagnostic programming, since only the active subprogram is resident at a given time in the compute! memory. REFERENCES: 1. Siichman, H. and Ramigolski, B., J. Phys. E8, 742 (1975) 2. Pa.Lss. Y., Szichman, H. and Rosmann, M., Nucl. Instrum. Mpthods, in press.

1. NOÍJ-SYřPIHTRIC TWO-STRI-AM INSTAUILITY

S. Cuperman? L. fiomberoff, I. Roth and K. Bernstein Department of Physics and Astronomy, Tel-Aviv University Tel-Aviv t

The recent ľlun Ľ rook - NASA exnerinants on counterstreanin" nlasna instabilities (ľirnstein et al., 1975) in which electric field omissions n- fro((uencies £(n + 'í) ± cTj:v. '-n = lj 2' 3,...i), a < 0,5) have been observeJ, raised the theoretical proólen of the non-synnetric two stream instability. This is the case in which the counterstreamng beams have different velocities in the directions parallel anil perpendicular to the static magnetic fields as well as different particle density.

This paper investigates theoretically the aforementioned problen. Thus, the instability of quasi-eiectrostatic wives at shifted half odd integer mul- tnlcs of the cyclotron frequency due to two non-synmntric counterstrc-anini; electron beans is considered. The beam velocities parallel and perpendicular to the static magnetic field are represented by different double Dirac delta functions; no parameter limitation is imposed. A systematic investigation of (i) the coupling between plasma modes and cyclotron modes and (ii) the coupling between cyclotron modes (beam 1) and cyclotron modes fiicnn 2) resulting in shifted half odd integer multiples of the cyclotron frequency is carried out.

The results include approximate but sinple analytical expressions for rauxinum growth rates and for-marginal stability as well as exact numerical solutions for the detailed unstable spectra fl <_ an <_ 20) in both u> and }: -space. The relative weakening or suppression of certain modes is also oredieted.

* will present the paper

2. MODIFICATIONS TN THE MAXIMUM CONVnCTIVIi GROWTH RATE OF TIIE EIJiCTRO- •IAG.VETIC PROTON-CYCLOTRON INSTABILITY DUH TO THE PRESENCE OF TilERMU IONS

I. Gorheroff* and S. Cuperman Department of Physics and Astronomy, Tel-Aviv University Tel-Aviv

The effect of thermal ions on the convective properties of the electromagnetic proton cyclotron instability is investigated. It is shown that when the proton anisotropy, Ap, is smaller than one, cold ions, with relative specific charge m^/Z- nip i 1, stabilize the convective growth of the instability. Wnen Ap > 1, the effect of thermal ions is to enhance the convective growth of the instability in the range where the real part of the frequency, «r, is smaller than the ion gyro- frequency, fij^. The maximum enhancement„ corresponding to an optimum concentration ot heavy ions, is shown to be a constant independent of the species. However, for eacu species, even for /\_ > 1, (except for protons), there is always a range of ^-values such that tne soecies will stabilize the system.

heavier ions are shon to he more effective in enhancing the convective growth of the instability, in the sense that tne heavier they are, smaller relative concentrations are required to reach the constant value mentioned above.

For sufficiently heavy species, the required concentration to optimize the convective growth, is indepenuent of the species.

* will present the paper

1-5

3. NONLINEAR DEVELOPMENT OF THE ION-CYCLOTr i INSTABILITY.

S. Cuperman, A. Sternlieb and D.J. Williams Department of Physics and Astronomy, Tel-Aviv University Tel-Aviv

Cornwall et al (1970) suggested that if the ring current protons penetrated the plasmapause, intense resonant electroraagnetic ion cyclotron turbulence would lead to their rapid precipitation loss.

In this paper we present a computer simulation study of the electromagnetic ion-cyclotron instability in a homogeneous plasna consisting of protons and electrons embedded in a static magnetic inc field, Box- plasma parameters used are Kfp = 25 keV, 8Tm KT 1 = ar 1 T T = 5- Bp> = p p,:i/' ox * ' " P,J/ P»:I Effects such as sources: and losses or .<=pace non-uniformities are not considered here.

The predictions of the linear theory for the fast build-up ^ unstable left-hand (proton-like) electromagnetic ion-cyclotron waves are fullv confirmed. The quasi-linear and non-linear developments of the instability are followed in tine to a state of quasi-e(|uilibrium (from a collective point of view) in which Tn ( /Tp = 1,3. The nonlinear analysis includes th:_ correlation between the relative energy density in the electromagnetic waves, thermal anisotronv, narallel and perpendicular velocity distribution functions and the pitch-angle distribution function.

* will present the paner 72

1-6

•J. .\U\XI.VJ-AR OSCILLATIONS IN WARM PLASMAS WITH INITIAL VELOCITY rr.RTUItilATIONS * S. Cunernan and M. Mond Dopt. of Physics and Astronomy, Tel Aviv University Tel Aviv \ 'ihase-snace boundarv intenration method of the Vlasov equation is •iscJ in order to investigate the nonlinear frequency o* an electron plasma mode. Unlike the familiar discrete particle sinulation codes in i.liich a United number of particles may be considered, the present model represents a more realistic plasma case in which a very large number (•".racticallv unlimited) or plasma particles evolving in their self-consistent collective field is investigated.

The unnerturbed collisionless, one-'dimensional plasma system consists of -..am electrons having a water bag equilibrium-distribution function shape and of ions at rest, which provide a fixed, homopenecus neutralizing background. The initial perturbation is introduced bv changing the

boundaries of the electron plasma such that vu = v0 (1 + a sin kx) and

v, = -v0 (1 - a sin kx), vu and vj representing the upper and the lower Iioundary, respectively. This corresponds to a standing wave perturbation.

Tie results obtained for different wavelength perturbations \ H 2ir/k -.1 For several perturbation amplitudes, a are presented and discussed.

• :. Ĺ J1 nresent the naner

1-7

5. TKRHE-COMPONENT NON-SY!(METRIC COUNTER-STREAMING INSTABILITIES. I. LONGITUDINAL ELECTRON PLASMA MODES.

S. Cunerman, L. fľomberoff and I. Roth !)ept. oc Physics and Astronomy, Tel fv iv University • Tel Aviv

The counter-streaming instabilities arising in a three-component electron plasma are investigated analytically and numerically in the

general non-symmetric case, i.e. when e = n2/ni j I, a 5 -U2/U1 j 1 and n ?, = na/ l Ý 0. Here nj, n2 and na represent the electron particle density in the first and second beam and in the background (ambient) .-stationary plasma, respectively; U^ and 1)3 represent tne streaming velocities of the two counterstreaming electron beams. No magnetic 73

or temperature effects are considered; consequently t!ie t'iree components interact only through the collective electric fields and only longitudinal modes are present. Tiie positive ions here represent a stationary neutralizing background.

* will present tiie paper

1-8

A QUANTITATIVE EVALUATION OF N.D.T. METHODS

E. Segal, Y. Segal, A. Notea, Department of Nuclear Engi- neering, T--1 'on - Israel Institute of Technology, Haifa Israel.

A procedure has been developed for characterization and optimization of N.D.T. methods.

It provides a logical and organized method to obtain the optimal design parameters of the N.D.T. methods, limits of detection, resolving power etc. The dominant concept in the procedure is a characterization function F(x., a., R, 3R/3x., ba) which correlates the variables that have to be measured (x.), the design parameters (a.), the response function that is measured R(x.,a.) and the uncertainty o(R).

Gama rays and ultrasonic methods were analyzed and compared to demonstrate the generality of the approach and the use of the concepts. 74

1-9

GAS GUN FOR IMPACT STUDIES

Y. Porat, University of Tel-Aviv

M. Gvishi

Armament Development Authority

Gas gun for impact studies, designed and installed at the laboratory of the Armament Development Authority, is described. The major parameters of the gas gun performance - projectile velocity and tilt of the projectile face - are examined. The measured projectile velocity as a function of the driver gas pressure per projectile mass is compared with theoretically predicted curve. The target asbciiibiy is designed for using shock reverberation techniques with manganin gauge pressure transducers. A present purpose of the system is the measurements of the ferroelectric - paralectric: phase transition in PZT ceramics under shock - waves.

CO Graduate student at University of Tel - Aviv. Monday Morning (Sol. St. Inst., H- -a

10:30

J. MECHANICAL AND THERMAL PROPERTIES OF 5OLID5

D. GERLICH, Tel Aviv University, Presiding

J-l

PHONON-PHONON SCATTERING RELAXATION TIMES FOR ALKALI METALS

M. Kaveh, Department of Physics, Bar-Ilan University, Ramat-Gan

A method will be presented for obtaining the temperature dependence of the phonon-phonon scattering relaxation time Tph-nh(T) for the alkali metals from the measured values of the low-temperature electrical resistivity p(T). Phonon—phonon scattering enters the theoretical expression for p(T) through its effect on phonon drag. As the temperature increases, phonon- phonon scattering tends to equilibrate the phonon system, thus gradually eliminating the dramatic low-temperature effect of phonon drag on p(T). The central result of the analysis is the derivation of the following expression for the ratio W(T) of the phonon-electron to the phonon-phonon scattering relaxation time

W(T> - {>expt " >calc}^eouil(T> " «W

T is tne T is where pexpt( ) experimental resistivity, Pequil( ) the value calculated without phonon drag, and Pcaic(T) is the value calculated with phonon drag but without phonon-phonon scattering. The analysis is applied to the highly accurate Pexpt(T) data for potassium. We find that below 6 K, phonon scattering is negligible compared with phonon-electron scattering (W = 0.01 at 6 K), whereas above 30 K, phonon-phonon scattering dominates phonon-electron scattering (W = 10 at 30 K). Since TPh-el is independent of temperature and can be calculated explicitly, we are able to obtain numerical values for Tph_ph(T). Our results for Tph_pf,(T) exhibit the exponential temperature dependence required by the general theory of the phonon-phonon interaction. Comparison will be made between our experimental determination of Tp^j-hCT) for potassium and recent calculations by Albers, Wilkins ana co-workers.1,2 A discussion of these calculations will also be given.

1. 31.C. Albers and J.W. Wilkins, Proc. LT 14, Vol. 3, 59 (1975). 2. R.C. Albers, L. Jiohlin, M. Roy, and J.W. Wilkins, Phys. Rev. B (to be published). 76

SPECIFIC HEATS AND LATTICE DYNAMICS OF CUPROUS HALIDES

Z. Vardeny, G. Gilat and D. Hoses Technion-Israel Institute of Technology, Haifa

The specific heats of CuCl, CuBr and Cul were measured in the temperature range of 5°K to 200°K. Their room-temperature phonon spectra were fitted by a nine-parameter shell model.Comparison between the lattice dynamical properties of the various cuprous halides are drawn; CuCl is the most anharmonic among them. The specific heats were calculated from'the lattice dynamical models ..:.! compared with the measured specific heats. Comparison is also made between experimental and calculated Debye temperatures - 6D(T) , as well as between other moments of the phonon densities of states - g(v) , obtained experimentally and theoretically. There is an excellent agreement for CuCl below 95*K , although the calculations were based on the room-temperatUxe phonon spectrum. A fair agreement is observed also for CuBr and Cul .

J-3

PiiONON DISPERSION RELATIONS IN LEAD

\. Talmi, Department of Physics, Technion, Haifa

<•;. Gilat, Department of Physics, Technion, Haifa

A method that enables the calculation of phonon dispersion relation;; to a high accuracy from a relatively small number of data points has been developed. The method has been applied to lead which has a complex phonon spectrum and the overall fit is about 5%. It was also found that at some points the neutron scattering results are inconsistent with elastic constants data. The method is based on smooth and three dimensional interpolation of the dynamical matrix given at a few high symmetry points. Although the method is not based on the ordinary Born - von-Karman model it enables the calculation of force constants. The method guarantees that the calculated g(v) does not include spurious singularities. The method is very general and will be soon applied to the phonon spectrum of transition metals and also to r<-Ga. 77

J-4 ON LARGE THERMAL ENERGY FLUCTUATIONS IN SOLIDS Y. Khait, Solid State Institute, Technion, Haifa, Israel The method of calculation of the probability of a large short- lived (of the life-time AT) thermal energy fluctuation up to dE»kT of heavy particles (atom, etc.) of solids is suggested. Each of A=V/Va identical quasiclosed (for the time 3 TI»AT/2) subsystems having the volumes Va=4/3ir(aTiC) and the. energies UOj may have one of the two states: a) The state "B" with the entropy Sa(B) and with the equilibrium distribution of the energy Uav among Na particles of the volume Va; b) The short-lived non-equilibrium state "R" with the entropy SO(R), when the fluctuational thermal energy e%E»kT is acquired and accumulated by a particle inside Va. Hore "C" is the energy transfer velocity- V is the volume of the solid, a is equal to a few units, v is a number of energy states. The numbers aav(B) and aav(R) of the subsystems in the states "B" and "R" are respectively aav(B)=Aexp[Fa-Uav)/kT]; a (R)=exp(Sa(R)-S01(B))/% N *SXp[CFa-Uav)/kT] ' " Hence one can obtain the Arrhenius expressions for the rate coefficients. For the classical approximation if the condit- 3 ions tiC&(E/k9)l/2h/xefk8, VI=4W/3(TIC) , and n1=yVi/Q are satisfied, the preexponential factors in the Arrhenius expressions are in proportion to the value exp[n^''] 0), i.e. they depend exponentially on E, on the Debye temperature 6, on the effective coordinational number Xef> and on tne number Y of degrees of freedom in the elementary volume Q. 1. Y.L. Khait, J. Heat S Mass Transfer, 16, 1329 (1973); Bull. Israel Phys. Soc. 21,91 (197S).

J-5 FLUCTUATION SHORT-LIVED STATES OF CARRIERS IN NON-METALS AND ELECTRON EMISSION FROM THEIR SURFACES Y. Khait, Solid State Institute, Technion, Haifa, Israel A mechanism taking into account the following two kinds of processes is considered: a) Short-lived thermal energy fluctuation of heavy particles (atoms, etc.) up to e%E»kT occurring with the probability W Cl>2), They can form non- stationary defects and fluctuational short-time local states of carriers (flucstrons). b) Transition of carriers (tunnell- ing, Auger transitions, etc.} with the participation of the flucstrons. The rate of the processes is >j>e=W-fe(q/E), where W is determined in d»2)j but fe(q/E) is a conditional probability of the carrier transitions with the participation of the flucstrons. The application of the approach to the electron emission when W can be calculated classically and 1 2 3 when the conditions r^ h/kexs(Eg/keg) / ; Vls=£2{Tlscs) ; n]s=YsVls/Q»l are satisfied, leads to the Arrhenius expression for es, in which the preexponential factor is in 2 propotion to fe(q/Es)exp(nJ/ ) and depends exponentially on the surface parameters: on §s, on the Debye temperature 9S, on the coordination number Xs> on the number ys of degrees of freedom in the elementary volume Q; Cs is approximately the

sound velocity, CS"Ř fl. Such an approach has been applied to cxoelectron emission from irradiated dielectric surfaces (.3). The thermodynamic pert irbation theory can be applied to the volume V± to take into account an external electrical fild

1. Y.L. Khait, Int. J. Heat § Mass Transfer1 L6, 132* (1973); Bulletin of the Israel Phys. Soc. 21_, 91 (1975). 2. Y.L. Khait previous report in this colU-ction. 3. Y.A. Kolbanovskii, Y.L. Khait, L.S. Poiak, V.P. Shifrin, Kinetica i Cataliz, 4 702 (1973) Moscow, U.S.S.R.

J-6

OV THE INFLUENCE OF MECHANICAL STRESSES ON LARGE THERMAL ENERGY FLUCTUATIONS AND ON THE KINETICS OF BRITTAL FAILURE OF SOLIDS

Y. Khait, Solid State Institute, Technion, Haifa, Israel.

The approach suggested in (1»2) was modified to consider the influence.of external mechanical stresses a. on the probability W of large thermal energy fluctuations up ,to e;tE»kT of the heavy particles (atoms, etc.) at the' end f of the cracks,'where

local stresses are. aL. These fluctuations can cause breaks in the bonds between the particles, the' growth of cracks and the fructure of solids (3). The following expressions for the probability W(a) and for the life-time x (a) of the solids with growing cracks can be obtained with the help of the above 5 approach: W(.o)=\iOQexp[6(E/W) /*]eXpl-(E-!iVioWKT]; T(a)~l/W(o) 3 5 1 3 W0O=3Q/2T1V1Y;6 2(2Y* /xe : Q) '. V^^/SXCXÍ) ,

Here a=

above formulas enable us to explain and predict better experimental data (3j. The value aVj depends on the local parameters of solids(i?, xef> etc.) near the ends of the cracks. \s the volume Vj is much larger than the atomic volume d5, the value "a" becomes smaller and has a more reasonable magnitude. rhc relations o«E/aVj and cj» E/aVj determine the magnitude of the stress o and ao, which cause very slow and quick crack growth regimes respectively. The preexponential factor of the H f c-time is equal to x^i^'U, exp[-ô(E/k6)3/4] and depends exponentially on the parameters E, Xef> e> etc-

1. Y.L. Khait, Heat g Mass Transfer, 16_, 1329 (1973); Bull. Israel Phys. Soc. U_, 91 (1975). 2. The first author's report in this collection. 3. V.R. Regel, A.U. Slutzker, E.I. Tomashevskii, Úspechy Phvsitzeskich Nauk 106. 193 (1972), Moscow, U.S.S.R.

J-7

THERMOELASTIC PROPERTIES OF ULE^R' TITANIUM SILICATE GLASS

D. Gerlich, M. Wolf, 1. Yaacov and B. Nissenson Department of Physics and Astronomy, Tel-Aviv University

The elastic moduli, as well as their temperature and pressure derivatives, for ULE titanium silicate glass, have been measured by the ultrasonic pulse superposition technique. From the extrapolated 0°K values of the elastic moduli and their pressure derivatives, the elastic 0°K Debye temperature and GrUneisen constant have been evaluated, and compared with the thermally measured values. The same anomalies in the dynamic, properties, as found in other glasses, i.e. positive temperature an.l negative pressure derivative?, are also found for ULE glass. The correlation between the changes in the bulk modulus and additive in silica rich glasses is discussed.

Registered trade name of Corning Glass Works.

J-t

THERMAL EXPANSION OF CADMIUM FLUORIDE*

D. Shaharabany, M. Wolf and D. Gerlich Department of Physics and Astronomy, Tel-Aviv University 80

The thermal expansion of CdF- single crystal has been measured over the temperature range 80-300°K. From the latter data, the thermal Grllneisen constant as a function of temperature has been evaluated, and compared with the elastic Grllneisen constant. The correlation between the two sets of data, and with possible lattice interactions is discussed.

Excerpts from a thesis to be submitted by D. Shaharabany to the Tel-Aviv University, in partial fulfilment of the requirements for an M.Sc. degree.

STABILITY OF CRYSTAL LATTICES SUBJECTED TO EXTERNAL FORCES

F. Milsteiní Department of Electronics, IVeizmann Institute of Science, Rehovot. K. Huang, University of California, Santa Barbara, CA. 93106, U.S.A.

Lattice stability of cubic crystals, subjected to external forces, is studied theoretically. Stability is assessed according to the positive definiteness of the quadratic form I. . B. . 6b. 6b.', where the B. . represent the second partial derivatives of (internal) lattice energy with respect to lattice parameters, and the 6b. are arbitrary, incremental lattice deformations. (1,2) Two-body, exponentially attractive and repulsive interatomic interactions (3) have been used in the initial studies, and explicit, large strain, theoretical force vs deformation curves have been determined. Numerical values of stress and strain at the onset of instability compare reasonably well with experimental values of maximum stresses and strains observed for fine metallic whiskers.

*Permanent address: University of California, Santa Barbara, CA. 93106, USA. Part of this work was completed while one of us (F.M.) held a John Simon Guggenheim Memorial Fellowship.

U) F. Milstein. Phys. Rev. B _3> 1130 (1971) (2) K. Huang, F. Milstein, and J.A. Baldwin, Phys. Rev. B KJ_, 3635 (1974). (3) F. Milstein, J. Appl. Phys. JJ, 3825 (I9"3;. Monday Hornino (5ol. 5t. Inst. , Rm 6D)

10:30 K. ATOMIC AND MOLECULAR PHYSICS A. BEN-REUVEN, Tel Aviv University, Presiding

K-l RADIATIVE EFFECTS IN CYCLOTRON RESONANCE

David Schmeltzer, Technion-Israel Institute of Technology, Haifa A charged particle in a D.C. magnetic field is analyzed in terras of two harmonic oscillators coupled to the radiation field. For an electron, the cyclotron frequency is found to have a first order shift caused by the reactive power and given by Au - (e2tu An c2R)Lri(w ./

1) A. Rich and J.C. Wesley, Rev. Mod. Phys. 44_, 250 (1972) 2) F.L. Walls and T.S. Stein, Phys. Rev. Lett, jtó, 975 (1973)

K-2

CONTINUUM X-RAY RAMAN SCATTERING

Y.B. Bannett, D. Rapaport, Y. Schlesinger and I. Freund Department of Physics, Bar-Ilan University, Ramat Gan

The spectrum of 8 KeV (Cu-Ka) x-rays scattered from the series of elements Ni through Ge has been measured and found co contain in addition to the resonance Raman peak an intense continuum extending to below 2 KeV. This continuum scattering appears to arise from the infrared divergence of the Compton effect recently predicted by Cavrila-, as well as from Bremsstrahlung radiation due to 82

photoelectrons ejected into the crystal. Comparison of the theoretical predictions with our experimental results will be presented.

1. M. Gavrila and M.N. Tugulea, Rev. Roum. Phys. 2£, 209 (1975).

K-3

T.-j£ciZt<)3 -COi.TRIB'JTIOH TO THE EK5RGY IAVELS OF MJOFIC ATOI.TS AID 11T3 EFFECTS OF •••UCL3AR SIZ3

J. Cr.net G.i:.i!.S. .Centre do Physique Th§oricue,K?irseille, France O.A. Oven -"hysics Denaxtnent, Ben Ouricn University of the Kcer :: have used our previously ciloulntsií, vscuun nolnrisrtion -•-it^ntial to calculated the.'(Zrf) -contribution nr.ift in the •: ir.ic r-toy. eve.vy lovel? usin<- (n) rs point nuclouf, jb) r> Vu':-"-,"; cř.rjr^e rtistriVution, {c)' nô -n ex-v)nfnti">l ch-ír^-é •' .-'."ibuxicn. Cur uoint ehr>r«e revolt is in ^-p"-G-'<.-r.t v-itl> rr-l-.'tic crlcul"t.ion of V/iclv"pnn 'nn Kroil'.' The finite

...... I-..-r(,i.;. F^erl -t0 ^,e insensitive to t""e details of 'be • ••• distribution. C-ar results "re co'""--jred vith the -; -r.ťl r-.-- Rure:r.onts and the .TT?enc-nt vith QÍ2) is .. -cv.-irri. In the context of this nroblen, the renornalization ••jftior. is discussed.

1. J. Calmet nnd D.A. 0";sn, Physics Letters, 533, 67 (1974) D.A. Ov/en, Phys. Rev. JÍS, 4"4 (19'S) •:. E.H. V/ichPwnn'and N.?.:. Troll, Fhys. Hev. JL01, 843 (1956)

K-4

T}£E FOURTH-ORDER VACUUM POLÄRlzuilION DIAfflAI.! AND POSITROKTUi!

n, Department, Ben Gurioa University of tne Ne»ev The ?.no:".?lcup contribution of the fourth- rder vpcuun rolprizp tion to the hypcrfine splitting in -nositroniu"; i.-. resilvea by •;tilisiii^ the radiation cnwe in conjunction \-iir i.^e Bet>"?- 83

• r.T b&uní st?te serturh-ticn theory. Furthermore, p

rule is proposed for Seternti.Bínp: the lovest-order to which r: cli?T:iri contributes, .řrom this we see thot there in still another diarra"n vrhich is a candidate for producing: en •*iJn

1. D.A. Ovren, Phys. Rev. Letters, j^0_, F87

K-5

COľMCK 5CjOT.rESD:G ÍROL: BCUI-D STJII'KS

D.A. Owen ftysics Den?rtnent, Ben Our ion University of ťbc Iľer-pv

V.'e calculate the differential cross section for t 'ohoton sc.-ttered by an electron v;hose st;:te ccn be chyT^ctc.yiac^ by the quantuin numbers n,j r-rd m-- , rnd thereby o^-t^r1': tv.~ vork of Casiľir-'-to excited stitcs. It ÍF fonr.d ťi--t t'--- resultin™ differential cross sections are- in'.e^nniert of electron's initi?l ac^ulni" vare function ?nri thus tie crcr.r sectionr -orovide e direct v.'ay of nc.?.surin~ the rrs:lir>l vsve function of the bouud electron. A rmraber of pr>plic?tion:r. ore considered.

1. H. CBsiialr, Kelv. Phyr. Acta. £, 267 (19?:?)

K-6.

MOSSBAUER STUDIES OF ISOLATED ALKALI-IODIDE MOLECULES. S. Shamay and M. Pasternak

Physics Department - University of Tel-Aviv and T. Sonnino - lioreq Nuclear Research Establishment, Yavne.

129 Mossbauer studies using the I nucleus were conducted in Lil, KI and Csl molecules isolated in solid Argon matrix at 4.2 K. Values of [¥ (o)]*1 - the -s- electron density at the nucleus- were compared with those obtained in policrystallme samples from which the role of nearest (NN) and next nearest neighbours (NNN) on deforming the outer T orbital could he deduced. s 84

1 results are discussed in view of calculated values of N'.V and :.N'N overlap integrals for isolated molecules and crystallites. The experimental set-up is fully described.

PHRTURBATION THEORY FOR PROJECTED STATES AND SHORT-RANGE ATCMIC INTERACTIONS

A. Mann, Department of Physics, Technion, Haifa

V. Privman, Department of Physics, Technion, Haifa

When the distance between two atoms in a di-atomic molecule is small, the united-atom approximation* may séčm a sensible zero order approximation. However, this approximation neglects an important symmetry of the problem. This symmetry-breaking is related to the fact that the united-atom wave function violates the cusp conditions, which the proper wave-function should sat- isfy2. Hence the perturbation series based on the united-atom is not very useful2. Tho application of the perturbation theory for projected states3>4 to the united-atom expansion is shown to yield useful perturbation series. The method of a similarity transformation put forward in Ref. 2 is shown to be a particular case of the perturbation theory for projected states.

1. See, e.g. W.A. B-.ngel, Z. Naturfoxsch. 12, 59 (1957), or ref. 2. 2. W. Byers-Brown and J.D. Power, Proc. Roy. Soc. A317, 545 (1970). 3. R.E. Peierls, Proc. Roy. Soc. A333, 157 (1973) . 4. B. Atalay, A. Mann and R.E. Peierls, Proc. Roy. Soc. A335, 251 (1973).

J<=! THEORETICAL CALCULATIONS OF SPECTRAL LINE PROFILES OF GASEOUS CESIUM BY USING THE BORN APPROXIMATION Ľ. Weissmann, Y. Ben-Aryeh and A. Postan Department of Physics Technion-Israel Institute of Technology, Haifa, Israel 85

In applying the Bom approximation in the Green's function method a new formula £or the line broadening is obtained. We develop tin; result by using a perturbation theory, which includes the .square of an effective interaction potential. Using the new method, theoretical calculations of line^ profiles of gaseous cesium are made. The theoretical calculations are compared with experiments^'^ and a-quite good agreement is obtained

1. C.L. Chen and A.V. Phelps, Phys. Rev. A ]_, 470 C1973) . 2. J.F. Kielpopf, J.K. Davies and J.A. Gwinn, J. Chem. Phys. 53, 2605 (1970) .

Mr.2 APPLICATION OF GREEN'S FUNCTION METHODS TO SPECTRAL LIME BROADENING

A. Postan, Y. Ben-Aryeh and E. Weissraann Department of Physics Technion-Israel Institute of Technology, Haifa, Israel lve treat, the problem of spectral line broadening in a system of absorbing atoms immersed in a bath of foreign gas perturbers. Ignoring the internal degrees of freedom of the perturbers, we consider three types vt one-particle Green's functions corresponding respectively to the translation of the absorber, to the translation of the perturber and to the internal excitation of the absorber. A periodicity relationl •for the internal excitation Green's function in the complex plane is proved. Using variational methods* we get a Lorentzian f'iape for the line profile in which the width and shift are .oraplicated functions of frequency. In this work we develop a new quantum statistical approach to the problem of spectral line broadening2.

1. L.P. Kadancff and G. Baym, "Quantum Statistical Mechanics", Benjamin, Menlo-Park, California (1962),

2. Y. Ben-Aryeh and A. Sorgen, Phys. Rev. 4, 2170,2178 (Iy71). Monday Morning (Elec. Eng., Rm 413)

10:30

L. THIN FILMS

N. KLEIN, Technion, Presiding

L-l

CONVERSION ELECTRON MOSSBAUER SPECTROSCOPY OF THIN FILMS M. Ohring and R. Oswald Stevens Institute o£ Technology, Hoboken, N.J. U.S.A.

Mossbauer spectra of thin unenriched Fe and Fe-Si films were obtained by counting conversion electrons in a backscatter geometry. The electron detector was a windowless, channel electron multiplier which was fabricated in our laboratory. It operates in vacuum with a relatively high efficiency for counting electrons enabling the measurement of spectra from thin films deposited on conventional thick substrates and eliminating the necessity to employ thin transparen* absorbers. A comparison between common transmission Mossbauer spectroscopy and the more rarely employed backscatter methods shows that, under certain conditions, backscatter conversion electron Mossbauer spectroscopy results in larger signal to noise ratios as well as significant reduction in counting times when thin films are involved. The magnitude of the effects, theoretically expected in films, will be discussed and compared with that measured experimentally.

L-2

COMPACT INTERFEROMETER FOR ACCURATE DETERMINATION ^F OPTICAL CONSTANTS OF THIN FILMS

J. Shamir, Dept. of Electrical Engineering, Technion - Israel Institute of Technology, Haifa, Israel.

An interferometer, based on the Rosters prism is described. The interferometer is highly stable due to the symmetry between the 87

two interfering beams, and a very high accuracy is achieved by {.he incorporation of a high sensitivity fringe detection system. The sensitivity is better than 10"^ of the measuring wavelength, but the present accuracy is limited to 10~3 by environmental and system noise.

The interferometer is best suited for the analysis of thin transparent fil.ns and the determination of the thickness of reflecting films.

L-3

PHOTODEPOŠITED THIN SELENIUM FILMS*

M. Perakh and A. Peled School of Applied Science and Technology, Hebrew University, Jerusalem, Israel

1. A process enabling one to obtain uniform homogeneous selenium films has been developed (patent pending). This process consists of the following stages: A. Chemical reaction (reduction of selenium] stipulating the creation of a colloidal solution of selenium. B. Quenching procedure. C. Photophoresis and adsorption of colloidal particles on a substrate + growth of the film. The thicknesses of the films obtained are in the range of 0.1-2u. The important feature of the process is the strong influence of light on the rate of film growth and its quality. This de- sirable influence of light is attained only when the light pene- trates into the solution through the substrate. The rate of ijru'1-.th strongly increases with an increase of light intensity and depends as well on the wavelength. (Red border was observed at approx. 6155±20 X.) 2. Stiuctures of the films were investigated using SĽM techniques, as well as X-ray techniques and by measuring certain optical characteristics. The films were found to be amorphous at deposition temperatures up to M5°C. Four stages of (film) growth were discovered: A. Creation of separated spheroidal particles of selenium. B. Partial merging of the spherules (creation of a laby- rinth structure). C. Transition from the B stage to the platelet structure. D. The final stage of a plate-like structure. 88

3. Certain optical and electrical investigations were carried out. *Dr. H. GinsbuTg also took part in this work.

1-4

DETERMINATION OF PREFERRED ORIENTATION OF ZnO SPUTTERED FILMS bY A SIMPLE X-RAY TECHNIQUE

S. Maniv and A. Shaulov Department of Physics, Ben Gurion University of the Negev, Beer Sheva

Thin films of sputtered ZnO 1-10 u thick, consist of hexagonal crystallites of about 1 u size. The degree of preferred orientation of the hexagonal axis of these crystallites, is an important parameter in determining the performance of the film as an ultrasonic surface waves transducer on nonpiezoelectric substrates. For this purpose we built a X-ray camera in which the sample is mounted on a goniometer and may be continuously rotated in its own plane. The diffraction pattern is recorded on a flat film perpendicular to the incident monochromatic beam, lne intensity of the diffraction arcs is nonuniform and yields quantitative information on the degree of preferred orientatioľi. •'.e made experiments on thin films of ZnO sputtered on glass substrates and found that the (002) planes are parallel within "' ů° to the substrate surface.

L-5

KLECTROMIGRATION IN THIN COLD FILMS ON MOLYBDENUM

E. Kinsbron, Department of Materials Engineering, Technion - Israel Institute of Technology, Haifa, Israel

Current densities of 10 -10 A/cm~ -.-ere passed through thin gold film deposited onto a molybdenum surface. lioth film were P.F sputtered to a thickness of about 1000 A and were photolithogra- puically etched to Eorm tvo short edges of the gold film on the molybdenum substrate. Due to the discountinuity of the gold material in the flla edge next to the cathode, gold atoms 39

niigraced towards the anode leaving a free molybdenum surface an a result of the high current density. The gold atans v.ove'l by electroraigration towards the anode and agglomerated at the gold film edge next to the anode in the form of extensive hillocks or crystallites. The velocity of the filra was assumed to represent the average drift velocity for electroraigration. In ;he temperature range 260 C-500 C the velocity of the gold edge was found to be constant at any given temperature and current density. At any constant temperature, the velocity was proportional to the current density^ Finally, the velocity depended exponentially on the temperature.

The gold motion was always in the direction of electron flor r.n>l the drift velocity per unit current density between 10 -10 cm /A.S. The activation energy for the drift velocity w;as found to be 0.6 eV.

L-6

PREPARATION OF THIN FILMS OF SULFIDES OF CERTAIN METALS RY CHEMICAL DEPOSITION

M. Perakh and H. Ginsburg Graduate School of Applied Science; The Hebrew University of Jerusalem, Jerusalem, Israel

1. As a continuation of the investigations previously performed in our laboratory (which related to selenium films), a process enabling one to obtain homogeneous uniform films of several sul- rides, e.g. iigS, has been developed. The process in its main features is similar to that relating to deposition of S-.-. It also includes the stages 1) of chemical reactions in solutions (in tills case, of the exchange reaction rather than of reduction) and 2) of transport of colloidal particles, followed first by their adsorption on the substrate surface and then by film growth. 'The prin- ciples, of the process, previously established for the Se- Jupositisn, turned out to be very fruitful in cases of certain 'ns.-tal-rii f jde films as well. 90

2. A correlation between optical density of films investigated and their thicknesses, as well as between the above properties and operating conditions (i.e. concentrations of the reajjenf.s, temperatures of reduction and of quenching, intensity of light, and its wavelengths, etc.) have been established. 3. The films' structures .have been investigated using the SEM technique. In particular, these investigations, along with study of optical absorption, have shown that in certain regions of operating conditions the films are amorphous. This is important for the supposed utilization of films as elements of special transducers possessing sensitivity to the light wavelength.

SOME EXPERIMENTAL POINTS CONCERNING METALIZED SUBSTÍÍATES PRODUCTION

Samuel Chervinsky Microelectronic circuits are produced from inetalized substrates. The three main microelectronic tvechnologies used today are: thick film hybrid, thin film hybrid and monolytic integrated circuitry. In thin-film hybrid circuitry, vacuum evaporation, chemical vapor deposition, or sputtering are used with photolythographic processes to lay down conductors, resistoTS, capacitors and insulators. Two processes are followed: 'i. Additive - in which the film layer are deposited through masks. 2. Substractive - in which, all th. layers are deposited and then patterns are selectively etched. In our production line we produced the film layers first, and et- ching it after, with thehelp of masks and chemicals. The common metalized substrate is the 'iCr, Ni, Au substrate which can be produced with electron-beam gun. The results of the guiding research necessary for the production of NiCr, Ni, Au substrates with E.B. gun will be presented. The me'calurgical, chemical and the kinetic of the NiCr layer oxidation will be given. Monday Afternoon jPhys., Seminar Rm 1)

13 s 45

M. CRYSTAL DEFECTS

í). TANNHAU5ER, Technion, Presiding

M-l

RELATION BETWEEN VACANCY FORMATION AND MIGRATION ENERGIES

S.I. Gén-Abraham, A. Rabinovitch Department of Physics, Ben-Curion University of the Negev, 84 120 Be'er-Sheva'

J. Pelleg Eepartment of Materials Engineering, Ben-Gurion University of the Negev, 84 120 Be'er-Sheva' The Frenkel-Kontorova model is modified to provide an adequate general description of a vacancy, independent of the knowledge of the atomic interactions in the crystal. The migration energy of a vacancy appears to be twice its relaxation energy. We show ".hat the migration energy em is related to its formation energy s:f by ein/ef = expO/2.r) - 1, where r is the relaxation radius. According to experimental and numerical results, we assume that, along the migration axis, uhe vacancy's nearest neighbors are certainly within the relaxation radius, whereas the fourth neighbors are certainly not. Hence we have 2 < r < 4, and 1.20 > em/ef :• 0.48. This includes virtually all known cases. With the second-neighbor value r = 5/2, we obtain em = 0.87 ef. This should be interpreted as a universal scaling law to zeroth order and subject to modifications by the crystal structure and the nature of the atomic interactions. For FCC metals, i» _• put r between the 5th and 7th shell (r f» 2.5). This includes second neighbors but excludes third neighbors along < 1M) >. Thus we obtain 1.02 > em/Ef > C.81. For BCC metals, we put r between the 10 h and 12th shell, including third neighbors along < 11.' :•. We obtain 0.69 > EP,/ef > 0.S8. Empirical --verag- valu..; are em/ef = 0.94, 0.90, 0.62', 0.88 for FCC, HCPj BCC, ai'.i' '• Metals, respectively. The agreement is sejn to be 92

K-2

RELATION BETWEEN DEBYE TEMPERATURE, MELTING POINT AND VACANCY MIGRATION ENERGY

S.I. Ben-Abraham, A. iiabinovitch Department of Physics, Ben-Gurion University of the Negev, 84 120 Be'er-Sheva1

J. Pelleg Department of .Materials Engineering, Ben-Gurion University of the Negev, 84 120 Be'er-Sheva'

Tewary l derived theoretically the empirically found relation B2my23/ef = constant, and also calculated the constant. (Q - Debye temperature, m and v mass and volume per atom, Ef - vacancy formation energy). Similar empirical laws are known to hold for the vacancy diffusion energy Ed and hence for the vacancy migration energy cm. Likewise, these energies are empirically known to be related to the melting point 27' by Tľ'/c = const. We have derived a relation between em and ef 2. Thus, via Tewary, we provide a theoretical justification for all three E'S to be related to 0. The relations TM = 27-/(e) are a consequence of the Linderaann melting formula. We interpret these relationships as universal scaling laws valid to zeroth order. In first order, deviations occur due to the peculiarities of the crystal structure and of the interatomic interactions.

1 Tewary, V.K., J. Phys. F - Metal Phys. _3, 704 (1973). 2 Ben-Abraham, S.I., ľelleg, J., and Rabinovitch, A., preceding abstract.

M-3

INFLUENCE OF VANADIUM ON HYDROGEN DIFFUSION IN TITANIUM*

C. Korn and D. Teitel Department of Physics, Ben Gurion University of the Nt ^ev, Beer Sheva L). Zamir Soreq Nuclrar Research Centre, Yavne

Z. Hadari Department of Nuclear Engineering, Ben Gurion University of the Negev, Beer Sliev 93

Room temperature proton NMR absorption traces and the temperature dependence of the proton spin lattice relaxation time were obtained for samples of Ti-V-II containing various concentrations of V and H, in order to determine the influence of V on the dis- position and diffusion, of hydrogen in titanium. The results show that for low hydrogen concentrations ("" Tiil + V) the hydrogen accumulates preferentially in regions associated witn vanadium where the hydrogen diffuses more readily. For hiij'i hydropen concentrations (••>• Tiläj^ 7 + V) two different activation energies for hydrogen diffusion are discerned: for one, tne activation energy is the same as that for vanadium free titanium hydride, while for the other it is lower. This is in contrast to the case of aluminum alloyed Ti-ll where it is found that tne aZunsimin creates an environment wherein the activation energy for hydrogen diffusion is raised. These phenomena have a beaiinj; cm tiie hydropen embrittlement of titanium alloys.

* This research has been i.upported by the National Coui.cii t'or Research and Development in Cooperation with the Isr.i-.1! Aircraft Industry.

TUNNELING EFFECTS AND THE DIPÓLE INTERACTIONS AMONG POLAR DEFECTS IN KC1

Michael W. Klein, Baruch Fischer and Chaim Held Department of Physics, Bar-Ilan University, Ramat-Gan, Israel

OH impurities dissolved in KC1 dissolve substitutionally and are found experimentally to have six possible dipóle orienta- tions. The energies of the six dipolear states of a single dipóle are degenerate and the degeneracy is removed by the tunneling-potentials connecting the different states, fonting a singlet ground state, a triplet and doublet. For this reason the low temperature specific heat and dialectric- constant of a single dipóle is expected to exhibit the usual Shottky type behaviour. As the number of dipoles in the system increases the dipole-dipole interaction increases in Importance relative to the level splitting of the tunneling states. We study the behaviour of the dialectric constant as a function of the dipole-dipole interaction and the temperature in the limit as the dipole-dipole. interaction is large and small compared to the tunnel splitting energy A. Monday Afternoon (Sol. St. Inst., PTI 52)

13:45

M. HOLOGRAPHY AND INTERFEROMETRY

J. SHAMIR, Technian, Presiding

i'KOTOUIELIiCTKIL POLYMER SYSTEM !:0H VOLUME PHASE HOLOGRAMS ". Rav Noi, A. A. Kriesení Department of Electronics, Weiim;>nn Institute of Science, Rehovot S. Reich Polymer Department, Weizmann Institute of Science, Rehovot

Novel photodielectric polymer systems for the fabrication of high resolution volume phase holograms are described. Highly reactive monomers which polymerize rapidly when inserted between two substrates allow for simple and convenient preparation of recording layers with thicknesses ranging from 10 microns to 3 mm. During recording the po.ymer crosslinks in the irradiated regions causing changes in index of refraction. The refrac.ive- index differentials achieved in our system, which were as high as 0.5 percent, result in diffraction efficiencies of about 100 percent. Experimental measurements reveal that the noise characteristics are comparable to those of high quality photographic emulsions, that the resolution is in excess of 2500 lines/mm, and that angular selectivity may be as high as several minutes of arc. Along with their excellent chemical and dimensional stability and self developing capabilities, the above characteristics make these materials attractive for a number of holographic applications such as high density storage and fabrication of optical elements. The exact hologram formation mechanism along with experimental results of exposure sensitivities, diffraction efficiencies, and signal-to-noise ratios will be presented. 95

äzl A SIMPLE METHOD OF DETERMINING DIFFUSION CONSTANTS BY HOLOGRAPHIC INTERFEROMETRY

Jacob Pipraan and Norberto Bochner, Technion, Haifa, Israel

A method is developed for measuring diffusion constants in transparent mixtures by means of double exposure holographic interferometry. The diffusion constant is deduced by a simple and direct measurement of the inteTferograms. The method was checked with sugar solution and water and gives reasonable agreement with other methods.

N-3

HOLOGRAPHIC NON-DESTRUCTIVE TESTING OF HONEYCOMB PANELS Y. Katzir, A.A. Friesem and D. Peri Department of Electronics, Weizmann Institute of Science, Rehovot

Holographic interferometry permits accurate evaluation of three dimensional diffuse objects. This extremely sensitive technique, which is particularly well suited to the detection of displacements as minute as. 0.1 microns, was used to identify sraalj defects and anomalies in objects subjected to suitable stress conditions. We will present specific examples where the holographic interferometry technique is used in a nondestructive test of honeycomb panels to detect flaws of areas ranging from several square millimeters to several square centimeters. The samples tested include aluminum and composites adhesively bonded panels, as well as stainless steel brazed aircraft parts. The most crucial factor in the tests was the selection of stress conditions to introduce displacements, and in our experiments we deal with pressure,heat, vacuum and vibration, Finally, experimental results demonstrating that both large and single cell disbonds can be easily detected will be presented. 96

INTERFEROMETRIC METHODS FOR MEASURING THE DISTRIBUTION OF CURVATURE \\D TWIST OF PLATES

\. Assa, Formerly a graduate student at the Dept. of Aeronautical ling., Technion I.I.T.

1. Politch, Dept. of Physics, Technion I.I.T.

\. Hetser, On leave from the Dept. of Aeronautical Eng. Technion L.I.T., now at the Dept. of Theoretical f, Appl, Mech., University of Illinois at Urbana, Urbana, Illinois 61801.

Here'.'ith are described several methods concerned with the application of shearing interferometry to the measurement of curvatures and twist of statically loaJed plane reflecting models. The diffraction gratings are applied as the shearing interferometric beam splitter. In the general system a piano light wave is reflected from the model's surface. The curvatures of the rorlected (distort- ed) wave are then deteimined and related to the curvatures of the Model. In che small deflection theory of thin plates under lateral loading, there wore found direct relations between the "moment per unit length"' - m, and the second derivative of the deflection - iV. A pure second derivative of the deflection represents a curvature component, while a mixed one - twist. Two curvature measuring methods are presented, which employ non-focal plane set-ups, using either single or double-frequency grating. These methods require a double exposure recording, followed by spatipl filtering. It was found that the single frequency grating system has lower resolution. A thirJ curvature measuring technique is demonstrated, in which only a single exposure recording is required. The resulting inter- ferogram is then spatially filtered in an arrangement, which places a shearing intorferometric beam splitter at the location of one of the first OTder diffraction spectra. A fourth curvature measuring method is presented, based on Fourior imaging. This technique re- quires a single exposure, followed by optical spatial filtering. The method is also capable of yielding results in real-time. Monday Afternoon (Phys., Seminar Rm 2)

13:45 0. SEMICONDUCTORS A. HAREL, Tadiran, Presiding

0-1 "SECOND BREAKDOWN" IN P-N JUNCTIONS

H. Aharoni Microelectronics Laboratory, Electrical Engineering Dept., Ben-Gurion University of the Negev, Beer-Sheva, Israel. A "second breakdown" in P-N junctions takes place after the occurrence of an avalanche breakdown (first breakdown) when the junction is biased in the reverse direction at high voltage and current. On the reverse characteristics, it can be seen that as the current reaches a certain critical value, a sudden large voltage drop occur;, after which the characteristics stabilize iv. a lo,*, somewhat constant voltage region together with a further increase in the current. A simultaneous event takes place internally within the device. The current leaves the cross-section of the junction and flows mostly in a narrow region and as a result, a ''hot spot" is created.

In this work, experimental results of the "second breakdown" point (current and voltage) in epitaxial P-N junctions are qiven. A series of junctions were built for research purposes with various parameters in order to investigate their influence on the' breakdown current and voltage. It appears that there sre specific factors characterizing the second breakdown process in epitaxial junctions with respect to other types of P-N junctions.

0-2

COUPLING BETWEEN THE IMPURITY ACTIVATED ONE PHONON DENSITY OF STATES ANO THE NORMAL MODES OF VIBRATION IN MIXED HI-V SEMICONDUCTORS

R. Beserman, E. Finknian, R.Weil, Solid State Institute, Technion, Haifa, Israel. 93

The vibrational properties of mixed Gallium-Phosphide- Gallium- Arsenide, have been studied using the Raman scattering technique. Ivhen a small concentration of As is introduced in Gallium Phosphide, the impurity gap mode appears, and in the vicinity of the GaP zone center modes additional structues can be seen. With increasing impurity concentration, this additional structure spreads out. The Raman spectra can be interpreted in terra of a coupling betwcvn a continuum and the zone center normal modes of vibrations. The continuum is the one phonon density of states which has been projected in the center of the Brillouin zone and rendered Raman active by the presence of impurities. The one phonon density of states is not only Ramar. active, but interacts strongly with the zone center phonons, this interact:.on gives rise to the Raman active additional structure, and is interpreted using the Ruvalds and Zawadowski formalism tlj.

1. J. Ruvalds and A. Zawadowski, Phys. Rev. B2, 1172 (1970).

0-.3

STUDY OF HIGH FREQUENCY PHONONS IN n-GaAs BY X-RAY BRILLOUIN SCATTERING

M. Eizenberg, Physics Department, Technion, Haifa.

B. Fisher, Physics Department, Technion, Haifa.

Acoustic flux in the range of frequencies ?5-50 GHz was generated by the acoustoelectric effect and investigated in various samples of epitaxial GaAs at 77°K. In this region the frequencies of the phonons axe beyond the limit (y 5 GHz) for the optical Brillouin scattering technique in GaAs, and therefore the more complicated technique of X-ray Brillouin scattering had to be employed. This technique is based on the increase in X-ray scattering near a Bragg angle in the presence of high frequency acoustic phonons. Differential photon counting was used to determine the excess scattering as a function of the angular deviation from the Bragg angle. This measurement yields the dependence of the acoustic intensity on frequency. Combined measurements of t^e spectrum of the phonons and of the acoustoelectric field accompanying the am- plified acoustic flux enabled study of the space and time development of this flux as well as determination of its acoustoelectric gain and lattice attenuation. Mosekilde's quantum theory foi- small signal acoustoelectric amplification in a semidegenerate 99 semiconductor is in satisfactory agreement with our results. The lattice attenuation factors for this range of frequencies, obtained for the first time in these measurements, seem to show a linear dependence on frequency, as expected from Landau and Rumer's theory2. However, more experimental data ars needed for comparison with theory.

1. E. Mosekilde: Phys. Rev. B. 9_, 682 (1974). 2. L. Landau, G. Rumer: Phys. Z. Sowjetunion H_, 18 (1937).

D-d

HOPPING CONDUCTION IN AMORPHOUS SEMICONDUCTORS AT HIGH ELECTRIC FIELDS

Ilan Riess, Department of Physics, Technion, Haifa, Israel

Michael Poliak, Department of Physics, U.C.R., Riverside, California 92502, U.S.A.

Percolation theory for hopping conduction is extended to high. electric fields, F, and applied specifically to the Mott model (a constant density of states). The main difference between the high and low field cases is the large changes in the local chemical potentials at high fields. These changes account for the J deviations from the exp(-(T0/T) i) law for the current, I, that is obtained when F -*• o. For large F one cannot regard the system as a network of resistors since the latter become field dependent. The percolation path is therefore chosen according to the current and is the path that carries the highest possible current. Nearest neighbour pair correlations1 which were introduced first for the F -i- o case are most important for large F and are also included in our treatment. The results are, that for intermediate fields i.nrvfa|e|F/KT while for large F, ÄnI^-(F /F)"*.

1) M. Poliak, J. Non-Cryst. Solids 11, 1 (J.972). 100

PHOTOCHEMICAL ENERGY CONVERSION AND STORAGE USING POLYCKYSTALLIN'E CKALCCGENIDE SEMICONDUCTORS. G. Hodesj J. Manas sen and D. Cahen, V.'eizinann Institute of Science, Renovot, Israel, The performance of a stable photochemical cell (P.E.C.), which uses low band gap chalcogenide semiconductors, such as CdS, CdSe, CdTe, BÍ2S3 cr ZnSe, in a polycrystalline form, as photoelectrcde, will be described. The simplicity of preparation of the photoelectrode will be stressed and illus- trated. The long term stability of both the electrodes and the solution of such a P.E.C. which uses the S=/S redox couple under exclusion of oxygen and large surface area counterelectrodes, will be discussed. It will be shown that it is possible to store, in a controlled manner, part of, or all the conver- ted energy in such a cell, when storage electrodes, such as Ag/AgjS, FeS/FeiSj or Sn/SnS are used or added. Then electricity is obtained both in the light and during dark periods. Conversion efficiencies of 90% and more can be obtained when the storage electrode is separated from the solution by a cation specific membrane. Various configurations of P.E.C.'s using nwo or three electrodes, such as cells with two photoactive electrodes of the same type (e.g. n and n) or of different type (n and p) will be discussed. Monday Afternoon fSol. St. Inst., Rm 58)

13:45

P. LASERS AND PLASMA PHY5IC5

V. PAISS, Soreq Nuclear Research Center, Presiding

P-l

CALCULATION OF X-RAY PRODUCTION RATE AND IONIZATION STATE DENSITY IN HOT ALUMINUM PLASMA

D. S3lzmann Plasma Physics Dept., Soreq Nuclear Research Centre, Yavne

A computer program (XRAY) was written to study the ionizatior. state iunsity and radiation rate from hot dense plasmas. Tlio plasma is assumed to be ! omogeneous and isotropic with constant temperature and ion numL_, density. The results refer to aluminum plasmas only, but the code is general enough also to treat other elements for which a complete set of atomic data is available. The main aim of the program was to make an off-line study of a simplified problem of X-ray radiation. The program calculates the following quantities as a function of electron temperature and total ion number density: distribution of the charge states, average charge, average ionization energy, free- free radiation, free-bound recombination spectrum, total free- bound radiation rate, line spectrum from various charge states, and total line radiation rate.

P-2

EIGK ENERGY FF.OTON SCACT3REIG ON A HAS.'Ji

D.A. Oven >-ní R. Steinitz irhysios De^-rt-fir.t, Ben tturion University of the Ke"ev

'./e investigate the feasiMlit" of usine M."fc enerrv nhoton scattering on electron!! ,«p r T\1.9S»ÍP Trobe to determine,the ioni^tion '-.r.d excitation st^te of the PPP. Ch-en has nhovT.l t!'f>t the er.—-'rrsion entering the different inl crosr. fseotion for scattering on free elpotrons ind on bound' electrons ev? not the sale, "..'e evDÍunte -hether this difference :".? nesisurnble.

1. This conference, jC^J,. 102

P-3 QUANTUM BEATS I.R. Senitzky, Technion-Israel Institute of Technology,Haifa The recent theoretical interest in quantum beats ' ' is reviewed. An analysis of quantum beats in the radiation from a number of three-level atoms is performed using a boson-type second-quantization method which exhibits the collective behavior of n-levei systems and displays both quantum mechanical and classical (or semiclassical) results. The conditions for which this theory predicts the presence and absence of beats, respectively, are found, and differ from those in recent literature. The reasoning behind suggested experiments on quantum beats for testing the "neoclassical" theory is questioned.

1) W.W. Chow, M.O. Scully, and J.O. Stoner, Phys. Rev. A 1_1, 1380 (1975) 2) R.M. Herman, H. Grotch, R. Kornblith, and J.H. Eberly, Phys. Rev. A U., 1389 (1975) 3) I.R. Senitzky, Phys. Rev. Lett. 35, 1755 (19/5)

P-d STATISTICAL PROPERTIES OF A TWO-LEVEL SYSTEM COUPLED TO A RADIATION FIELD R. Gelbard, Physics Department, Technion - Israel Institute of Technology. The decay of a two-level system (TLS) coupled to a radiation field is investigated with emphasis on the statistical properties of the dynamical variables. Langevin equations of motion for the TLS operators are derived. Correlation functions of the Langevin forces are obtained for arbitrary temperature of the radiation field. It is shown that these forces are not Gaussian, in contrast to the case of linear systems coupled to a radiation field.' A technique is developed for finding higher order correlation functions of TLS dynamical variables. The temperature dependence of the decay constant is exhibited. 103

URUĽRED MOTION Uí: A PUSMA UNDP.R APPROPIATE •EOMETRY AND EXTERNAL MAGNETIC FIELD

I. Bcrgťľ. Kibbutz Fvron

ľlic mo1 ion of charged particles in a ring is considered under the influence of a permanent magnetic field paralleľ to the ring axis. It is assumed that collisions occur only at the walls and that they are diffuse. Since particles moving in one sense collide more often than those moving in the other sense, there will be a net current. This state seems not to be the one of higo.est entropy. Monday Afternoon (Phys., Rm 323) 15:00 Plenary Session

N. ROSEN, Technion, Presiding J. GOLDSTEIN, The Hebrew University (45 min) "Some Properties of Quasi Two-Dimensional Electron Gas on ZnO Surfaces"

CL1FFEE BREAK S. BlUDMAN, University of Pennsylvania and The Hebrew University (45 min) "Neutrino Dynamics in Stellar Collapse" AUTHOR INDEX P. Abraham, C~3 D, Cabib, H-6 E. Abramaon, A-5 D. Cahen, 0-5 Y. Achiam, D-5 J . Camet, K-3 D. Agnion, E-10 M, Carmeli, G-Pr, A. Aharoni, B-13 E, Cheifetz, A-9, A-ll H. Aharoni, 0-1 S , Chervinsky, L-7 S. Alexander, Monday Mor. G ,M. Crawley, A-l Plenátry-Pr. S > Cuperman, G-l, 1-3, 1-4, S. Alterovitz, C-3 1-5, 1-6, 1-7 A. Assa, N-4 U. Atzmony, B-4 M.P. Dariel, B-4 Y. Degani, E-7 Y.B. Bannett, K-2 G. Deutscher, C-5, C-8 M. Barkai, C-8 Y. Disatnik, D-l, D-2 G. Barnea, A-10, B-l Ch. Drory, A-3 B. Barnet, B-7 G. Dublon, B-4 C,J, Batty, A-12 T. Duby, C-5 J.D. Bekenstein, G-3, G-7 H. Dvey-Aharon, B-8 S.I. Ben-Abraham, D-9, D-1D, D-ll, F-4, D.M. Edwards, B-l M-l, M-2 E. Ehrenfreund, B-2, B Y* Ben-Arieh, K-8, K-9 0. Eidelman, E-1 W. Benenson, A-l Y. Eisenberg, Sunday L. Benguigui, H~2, H-4, Plenary-Pr., F-2 H-6 1. Eisenstein, B-13 A. Ben-Reuven, K-Pr. K.,. Eizenberg, 0-3 D.J. Bergman, D-5 EV Erez, E-Pr. W. Bernstein, 1-3 S, Eshhar, A-12 R. Beserman, 0-2 F, Etienne, F-2 K. Bethe, H-2 A. Betser, N-4 M. Fibich, B-Pr., B-B E. Bin-Nun, E-1 E. Finkman, 0-2 S. Blit, E-6 A. Finzi, G-4, G-5 S. Bludman, Monday Aft. B. Fischer, B-ll, M-4 Plenary B. Fisher, 0-3 N. Bochner, N-2 A, Frenkel, A-4, A-5 D. Brandon, C-Fr. I. Freund, K-2 H. Braun, F-2 A. Fridman, F-2 R. Brener, B-3 A.M. Friedman, A-12 D. Brick, F-2 A.A. Friesem, N-l, N-3 H. Brucker, D-2 R.A. Buckwald, C-6 A. Gabai, E-4 J. Burde, A-2, A-3 E. Gal-Ezer, F-5 U. Ganiel, I-Pr., £-3, P. Juíllot, F-2 E-5, E-6 Y. Gazit, 1-1 U Karshon, F-2 R. Gelbard, P-4 Y Katzir, N-3 D. Gerlich, J-Pr., J-7, J-8 M Kaveh, J-l G. Gilat, J-2, J-3 Y Khait, J-4, J-5y J-6 H. Ginsburg, L-6 T.L . Khoo, A-l A. Ginzburg, A-3 A.I . Kilvington, A-12 M. Gitterman, B-12, H-8 S. MmexKimel,, c-oE-B J. Goldberg, F-l, F-3 E. Kinsbron, L-5 I. Goldman, G-6 M.WJ. Klein, B-9, B-1D, G. Goldring, A-7 B-ll, B-12, M-4 J. Goldstein, Monday Aft. N. Klein, L-Pr., C-l Plenary G. Kořen, E-2 L. Gomberoff, 1-3, 1-4, C Korn, H-7, M-3 1-7 M. Kroupp, B-4 S.D. Goren, H-7 C.Gí. Kuper, D-4 0. Gottlieb, C-2 E. Grunbaum, C-B 5.B. Lang, D-7 M. Gvishi, 1-9 A. Levy, D-6 J. Lichtenstadt, A-2 B. Haber, F-2 S.G. Lipson, D-3 Z. Hadari, M-3 M. Luban, H-Pr., H-5 V. Halpern, C-2 A. Hardy, E-5 J. Makovsky, B~2 A. Harel, N-Pr. J. Manassen, 0-5 C. Held, B-9, M-4 S. Maniv, L-4 J.D. Hemingway, A-12 A. Mann, A-1D, K-7 J. Hess, D-6 A. Marinov, A~Pr., A-2, A-3, A.A. Hirsch, Sunday A-12 Evening Symposium, B. Marks, H-7 C-6 G. MaureMaurerr , F-F2 D. Hochman, F-2 T. Mazeh, G-2 G. Hodes, 0-5 M. Meidan, C-8 H.M. Hofmann, A-4 Melamud, B-5, B-6 R.M. Hornreich, H-5 Metzler, G-l B. Horowitz, H-1 Meyuhaá, 0-2 L.P. Horwitz, F-5 Michalon, F-2 K. Huang, J-9 Milatein, J-9 Moalem, A-l Y. Imry, D-5 Mond, 1-6 i. Mordehai, A-2 E. Jaglom,o F-2 Moreh;, A-6 D. Moses, B-2, B-3, J-2 I. Riess, B-10, 0-4 V.J. Robinson, A-12 M. hlagler, E-3 M. Rokni, E-l, E-4, E-7 F . Navop, A-3 E.E. Ronat, F-2 G.W.A. Newton, A-12 N. Rosen, Monday Afternoun B. Nissenson, J-7 Plenary-Pr., A. Notca, I-B G-6 • R. Rosenbaurn, C-3 M. Ohring, L-l E. Rosenfeld, E-7 M. Okon, E-2 Y. Rosenfeld, H-9 R. Ooher, Monday Mor. M. Rosenkrantz, D-9, D-10, Plenary D-11 U,.P. Dppenheim, Sunday I. Roth, 1-3, 1-7 Plenary, E-2 Y,. Oren, F-Pr. M. Safrai, C-6 R.. Oswald, L-l D. Saltzmann, P-l D..A. Owen, K-3, K-4, R. Schatzberger, E-8 K-5, P-2 Y. Schlesincjer, K-2 D. 5chmeltzer, K-l Y,, Paiss, P-Pr. J. Schulz, F-2 M,. Pasternak, C-4, K-o E. Seqal, I-S L,, Patlajan, C-y Y. 5eqal, I-a M., Paul, A-2, A-3 I.R. Šenitzki, P-3 A,, Peled, L-3 D. 5hahal, A-6 J., Pelleg, M-l, M-2 J. Shaham, G-2 M., Per&kh, L-3, L-6 Ľ. Shaharabany, J-B D., Peri, N-3 H. Shaked, E-5, B-6 I., Perlman, A-13 A. 5h3lom, E-9 H.. Pinto, B-5 5. Shamay, K—6 J. Pipman, D-3, N-2 J. Shamir, O-Pr., L-2 I., Plesser, A-5 N. 5hamir, B-6 J. Politch, N-4 A. Shapira, F-2 M. Pollack, 0-4 A. 5haulov, L-4 Y. Porat, 1-9 H. Shechter, B-2 A. Postan, K-8, K-9 Z. Shkedi, A-7, A-B V. Privman, K-7 Y, Shmuelovitz, E-4 I. Privorotski, D-Pr. S. Shtrikman, Sunday Plenary, H-5 A. Rabinkin, H-3 L.S. Smith, B-3 A. Rabinovitch, M-l, M-2 T. Sonnino, K-6 A. Raizman, B-7 M. Spiegelglass, G-l D.C. Rapaport, F-ó, K-2 V. 5teinberg, H-8 Z. Rav Noi, W-l R. Steinitz, P-2 S. Reich, N»l A. Sternlieb B. Richter, A-7 M.M. Stupal J.T. Suss, B-7 H. Szichman, 1-2

D, Tal, E-2 M. Taliankerf C-9 A. Talmi, J-3 D. Tannhauser, M-Pr. D. Teitel, M-3 D. Treves, E-3, E-5, E-6 Z. Vager, A-4, A-5 Z. Vardeny, J-2 Y. Villaret, C-4 V. Volterra, A-6 5. Wald, A-4 J.L. Weil, A-12 R. Weil, E-2, H-4, 0-2 B.Z. Weiss, H-3 £. Weissman, K-8, K-9 Y. Weissman, D-8 D.J, .villiams, 1-5 A. VJolf, A-9, A-Xl M. Wolf, J-7, J-8 Y. Wolfson, A-7 I, Yaacov, J-7 R. Yaari, F~2 R. Yahel, 6-4 A. Yaniv, D-l S. Yataiv, E-4, E-7 G, Yekutieli, F-2

J. Yellin, A~13

0. Zatnir, M-3 A. Žemel, C-7 S. Zweigenbaum, 1-1 Directions for Submission of Abstracts

to the 1976 Annual Meeting of the

Israel Physical Society

Abstracts of paperi to be contributed to the 1976 Annual Meeting of the Israel Physical Society must be prepared and sent for direct photo- reproduction in accordance with the following rules.

1. Who may submit an abstract. The Annual Meeting of the Israel Physical Society is open to sll scientists active in physics. When two or more papers are offered by the same author, the second and additional papers will be assigned a place in the program, hut will be presented only if time permits. The subject classification according to the new APS list*1, the signature, name and address of the author to whom correspondence is to be directed must appear at the bottom of the abstract page.

2. Size. The abstract should be typed in english in a space 14cm wide and 16cm long. This space includes title, authors and their affiliations, footnote, references, etc., in the format shown on the accompanying example. To serve ÔS a guide to your typist, an outline of the 14cm x 16cm rectangle may be drawn in light blue pencil, since the blue lines will not be reproduced in photographic copying. Do not exceed these margins.

3. Content. Within the allotted space, you may place tables, equations, line draw- ings (lettering must be as large as elite type), etc.

4 Style. Type the title all in capital letters, without indentation. Skip one line and type in the author's nar-e(s), capitalizing only first letters and initials. On the following line, type the author's affiliation, capitalizing only significant words. Do not indent. If there are additional authors, with a different affiliation, skip one line and repeat as above Following this, skip one line and type the body of the abstract without indenting. Type single space.

* Physics and Astronomy Classification scheme - 1976, issued by the American Institute of Physics. (To help us choose your session usa the p.euoral subject heading only.) 5. Special symbols. If not available on the typewriter, they must be clearly written in black ink.

6. Footnotes. Skip one line between the body of the abstract and the footnotes. , Footnotes to the title and byline are indicated by superscript symbols ' t t nnd footnotes to ťhe text of the abstract bý superscript numerals.

7. Reproducibility. The abstract should be typed on good quality white paper using a carbon ribbon. If a carbon ribbon typewriter is not available please use a fresh black ribbon with a dark setting. Remember that errors, smudges, etc., will be reproduced.

8. Author's instructions. All instructions regarding your abstract must appear at the top or bottom of the abstract itself, not in a covering letter. If you want your abstiact to precede or follow another, instructions to this effect must appear on both.

9. Submission. Send the abstract and two duplicates to the address shown at the bottom of the announcement letter.

Compliance with the above rules will result in speedy publication of your abstract and permit the Bulletin of the Israel Physical Society to fulfill its dual function as the annual meeting program and summary of current research activity in Israel. Nomcompliance will result in the return of the abstract for corrections or in its rejection. a1