TRN BULE1TIN OF THE ISRAEL PHYSieAL SOCIETY
1979 Annual Meeting PROGRAM and ABSTRACTS -'. ' '•' y -,
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H 1979 i 10 Annual Meeting PROGRAM | } and '\ ABSTRACTS i THE ISRAEL PHYSICAL SOCIETY
Members of the Council for 1978-1979 PRESIDENT C. Kuper Israel Institute of Technology VICE-PRESIDENT M. Luban Bar-IIan University TREASURER B. Arad Soreq Nuclear Research Center SECRETARY J. Felsteiiser Israel Insitute of Technology
Members at Large U. Atzmony Nuclear Research Center-Negev Y. Disatnik Tel-Aviv University M. Gavish Ministry of Defence Armament Development Authority, Haifa A. Gersten Ben-Gurion University n.Z. Frenkel Hebrew University M. Kirson Weizmann Insitute of Science THE ISRAEL PHYSICAL SOCIETY COOPERATE MEMBERS
Ben-Gurion University of the Negev Bar-Ilan University Tel-Aviv University Elscint Ltd. Hebrew University of Jerusalem Technion - Israel Institute of Technology Weizmarm Insitute of Science THE ISRAEL PHYSICAL SOCIETY 1979 ANNUAL MEETING BEN-GURION UNIVERSITY OF THE NEGEV BEER SHEVA, 1-2 APRIL 1979
-iW,: PREAMBLE ?;*•• The 1979 annual meeting of the Israel Physical Society will take ; place at the new campus of the Ben-Gurion University of the Negev, in ;•.; Beer-Sheva, on Sunday and Monday, 1-2 April 1979, I' The plenary sessions will be held in the 06 auditorium, in Alef .',•'. building. The parallel sessions will be held on the third floor of the I;: library. /.;y The registration will begin at 9:45 a.m., Sunday morning. The - registration desk will be located in front of the 06 auditorium. ;"\ In the evening of the first day there will be a banquet at the Neot Midbar Hotel. The banquet will begin at 7:30 p.m. The after dinner speaker will be Professor Oren of the Department of Archeology, Ben-Gurioii university, who will speak about, and show slides of, the recent archeological discoveries in the Sinai desert. The organizing committee wishes to thank Professor V, Volterra, head of the Physics Department, Professor D. Bahat, Dean of the Faculty of Natural Sciences, and Professor M. Rosen, Hector of the University, for financial support.
The Organizing Connittee
S. Malin - Chairman S. Mordechai A. Rabinovitch THE ISRAEL PHYSICAL SOCIETY 1979 ANNUAL .MEETING 1-2 April, 1979 Ben-Gurion University ox the Negev CONDENSED PROGRAM Sunday Morning Alef Building
9:45 Registration 4 10:15 'A'ords of Welcome (06 Auditorium) Mr, Yosef Tekoa, President of the Ben-Gurion University of the Negev A. Shapira 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, 10.45 Plenary Session (06 Auditorium) Y. Ne'eman, Tel-Aviv University - Presiding B. Levich, Tel Aviv University (40 min) The Role Played by Theoretical Physics in Modern Applied Science M. Dresden, Institute for Theoretical Physics, State University of New York at Stony Brook, USA (40 min) On Solitons and Supersymraetry 12:30 Business Meeting of the Israel Physical Society (06 Auditorium) LUNCH Sunday Afternoon 14:30 Parallel Sessions Library Building Room 32S A. General Relativity and Astrophysics Y. Katz, The Hebrew University - Presiding M. Carmeli, Ben Gurion University of the Negev (30 min) Classification of Gauge Fields Contributed Papers B. Lasers and Optics Room 309 A. Levine, Nuclear Research Center, Negev - Presiding S. Yatsiv, The Hebrew University (30 min) The Role of Emission from Metastable States of Free Atoms in Lasers G. Erez, Ben-Gurion University and Nuclear Research Center- Negev (30 min) Experimental Determination of Populations in Copper Vapour Laser t; Contributed Papers I- \ \-& - 5 -
;-'V C. Applied Physics Room 326 >••-• K. Weiser, Israel Institute of Technology, Haifa - Presiding |;" D. Electric and Magnetic Properties of Solids Room 323 ?Vl A.A. Hirsch, Israel Institute of Technology, Haifa - ,{VJ Presiding JfX D. Zamir, Soreq Nuclear Research Center (30 min) g. A Study of the Electronic Structure of Metal Hydrides ''•"•; using NMR Techniques j-v Contributed Papers 'X E. Thin Layers Room 308 ;:'• E. Gruenbaum, Tel-Aviv University - Presiding K. J. Gersten, The Hebrew University (30 min) •:• Interaction and Processes of Semi-Conductor Surfaces p. Z. Weinberg, Israel Institute of Technology, Haifa (30 rain) • . Transport Properties of SiO2 ^ Contributed Papers Business Meeting of the Thin Layers Division F. Atomic and Molecular Physics Room 322 A.S. Kaufman, The Hebrew University - Presiding B. Rosner, The Israel Institute of Technology, Haifa (30 min) Atomic Processes in Heavy Ions Collisions with Small Impact Parameter Contributed Papers
Sunday Evening 19:30 Banquet of the Israel Physical Society at the Neot Midbar Hotel
I''"; Monday Morning Library Building | 9:30 Parallel Sessions t> G. Defects in Solids Room 322 |~ M. Dariel, Ben-Gurion University 3 Nuclear Research Center, : Negev - Presiding ;-., Contributed Papers
•'•'• ;;: ' H. Phase Transitions Room 325 p . R. Thieberger, Ben-Gurion University 6 Nuclear Research i[Z Center, Negev - Presiding ?; Contributed Papers I. Condensed Matter - General Room 323 S. Shtrikman, The Weizmann Institute - Presiding M. Luban. Bar-IIan University, Ramat-Gan (30 rain) Equations of State of Fluids and the Virial Expansion Contributed Papers J. Nuclear Physics Room 309 K. Blueler, University of Bonn - Presiding Y. Eisenberg, Tel Aviv University, Ramat-Aviv, Tel Aviv (30 min) Recent Developments in Meson-Nucleus Interactions E. Friedman, The Hebrew University (30 min) New Results for Pionic Atoms and Applications in Nuclear Physics Contributed Papers K. Plasma and Fusion Room 308 S. Kuperman, Tel Aviv University - Presiding Z. Vager, The Weizaann Institute (30 min) Experimental Study of Electronic Plasma in Solids via the Explosion of Fast Molecular Ions Contributed Papers LUNCH
Monday Afternoon Alef Building 14:30 Plenary Session (06 Auditorium) C. Kuper, Israel Institute of Technology, Haifa - Presiding L.Schulman, Israel Institute of Technology, Haifa (40 min) First Order Phase Transitions: Progress and Problems D. Gill, Ben-Gurion University (40 min} Fluorescent Biophysical Probes Z. Lipkin, The Weizmann Institute (40 min) What is a Quark?
•A I••1 1 7 THE ISRAEL PHYSICAL SOCIETY 1979 ANNUAL MEETING
1-2 April, 1979 Ben-Gurion University of the Ne.gev
COMPLETE PROGRAM
Sunday Morning Alef Building
9:45 Registration 10:IS Words of Welcome (06 Auditorium) Mr.Yosef Tekoa, President of the Ben-Gurion University of the Negev A. Shapira will present the Yon Kippur War Memorial Fund Scholarship, granted by the IPS in memory of the .members of the Society who fell in the Yom Kippur War, 10:45 Plenary Session (06 Auditorium) Y. Ne'eman, Tel Aviv University - Presiding B. Levich, Tel Aviv University (40 nin) The Role Played by Theoretical Physics in Modern Applied Science M. Dresden, Institute for Theoretical Physics, State University of New York at Stony Brook, USA (40 nin) On Solitons and Supersyametry 12:30 Business Meeting of the Israel Physical Society (06 Auditorium)
LUNCH |
;| 'i SUNDAY AFTERNOON, 1 APRIL 1979 LIBRARY BUILDING 14; 30 (Room 325) A. GENERAL RELATIVITY AND ASTROPHYSICS Y. KatE, The Hebrew University, Jerusalem - Presiding A-l CLASSIFICATION OF GAUGE FIELDS C30 min) M. Carmeli, Ben-Gurion University, Beer-Sheva
A-2 THE INFLUENCE OF THE UNIVERSE ON THE PLANET MOTION M. Ya. Azbel Department of Physics and Astronomy, Tel-Aviv University, Ramat-Aviv The influence of the inhomogeneity and non-ftationarity of the Universe on the planet motion is investigated. It is probably below the present experimental accuracy, but when the accuracy increases, it may provide the information about the Universe inhomogeneity.
A-3 CLASSICAL NONLINEAR DYNAMICS OF COUPLED NAVES IN MODEL UNIVERSES Ch. Charach Department of Physics, Ben-Gurion University of the Negev, Beer Sheva Following the approach developed by Gowdy, Berger and Misner we construct closed inhomogeneous cosmological models containing i) gravitational-scalar, ii) gravitational-electromagnetic waves. These models are obtained as a result of homogeneity breaking in the scalar and electromagnetic Bianchi type I models. These cosmological solutions provide exactly solvable examples for the study of nonlinear fully relativistic regime of coupled scalar-gravitational and electromagnetic- gravitational waves in the early universe. The asymptotic behavior is considered in the vicinity of the initial singularity and in the high frequency limit. It is shown that the wave coupling phenomena cause an evolution, which is significantly different from that of the vacuum - 9
model. We suppose that, like the enpty universe, the present solutions can be used as an input for the subsequent quantization program.
1. R. Gowdy, Phys. Rev. Lett. 12, 60 (1971); Ann. Phys. (N.Y.) 83, 203 (1974). — '«••'—• 2. B.K. Berger, Ann. Phys. Oi.Y.) 83, 458 (1974); Phys. Rev. D 11, 2770 (1975). — — 3. C.W. Misner, Phys. Rev. D 8, 3271 (1973). 4. Ch. Charach, S. Malin, ffcys. Rev. D. (in press). 5. Ch. Charach, Phys. Rev. D (in press).
A-4 ON THE DIMENSIONS OF TIE UHVERSE AS LARGE NUMBERS Yigal Ronen Department of Nuclear Engineering, Ben-Gurion University of the Negev, Beer Sheva
The Planck's system of units Lp = (RG/c)"5 = 1.62 x 10"35m. Tp = (fiG/C5)* = 5.39 x lO-^sec, and Up - (ftc/G)-S = 2.18 x io~8kg are the most fundamental ones. This system of units is based on the most univer- sal principles of Physics, sanely, the laws of black body radiation and gravitation. Expressing the dimensions of the universe with Planck's system of units we obtain the following values: the universe mass 1053/2.2 x 10"8 » 1061, the universe age 6.3 * WplfSA x 10"1*1* » 106J, and the universe radius 1026/1.6 x 1O"3S « 10s1. The large numbers obtained seem to support the unlikelihood of their accidental corresponding and seen to agree with Dirac's Large Number hypothesis. 1"lf To maintain the connection between the universe's dimensions during time, either G has to decrease proportionally to t"1 and the universe's mass increased proportionally to* t2 or no mass creation with G increasing proportionally to t. The last conclusion is supported by the use of Mach's principle.* 1. Dirac, P.A.M. Proc. R. Soc. A165, 199 (1938). 2. Dirac, P.A.M. Nature 139, 323 (1937). 3. Dirac, P.A.M. Proc. *. Soc. A333, 403 (1973). j: 4. Dirac, P.A.M. Proc. *.. Soc. A338, 439 (1974). 5. Dicke, R.H., Nature 192, 440 (1961).
K - 10 - A-5 PREFERRED DIRECTIONS IN ISOTROPIC UNIVERSE? Elhanan Leibowitz Department of Mathematics and Department of Physics, Ben-Gurion University of the Negev, Beer Sheva The distribution of galaxies in the three-dimensional curved space is assumed, in the standard cosmological model of general relativity, to be isotropic (and homogeneous). Most of the galaxies, however, reveal in their structure one or more axis of symmetry, and the question arises as to whether the orientation of the galaxies ought to be random, or there are other laws of orientation which do not violate cosmological princi- ples. Deliberations over this question have led recently1 to the intro- duction of the concept of synmetric vector fields in general Riemannian manifolds. The latter are unit vector fields which exhibit local rota- tional symmetry. In this communication, properties of three-dimensional manifolds admitting symmetric vector fields are discussed. In particular, juxtaposition of manifolds of positive and negative constant curvature may have some bearing on the determination of the still undecided sign of the curvature associated with the universe.
1. A.G. Walker, in Topics in Differential"Geometry, edited by H. Rund and W.F. Forbes (Academic Press, N.Y., 1976),
A-6 SECONDARY PEAK IN CLUSTERS OF GALAXIES - A CLUE TO THEIR FORMATION? A. Dekel and J. Shahara The Racah Institute of Physics, The Hebrew University of Jerusalem, Jerusalem The secondary peak in clusters of galaxies is interpreted to reflect the cutoff of adiabatic perturbations at the damping scale at recombi- nation, X_. This cutoff, if sufficiently sharp, leads to the forma- tion of a shell around regions with large perturbations, at a distance of ~ AQ. We obtain good fit to the galaxy count profiles for n ~ - 1/2, where n is the spectral index, but show' that the effective index for masses around Mp can be aore negative. Possible consequences of this interpretation regarding the formation of structure in the Universe are discussed. 1. A. Dekel and J. Shaham, Preprint (1979). A-7 THE INVARIANT NORMALIZED MOMENTUM FLUX OF THE SOLAR WIND
M. Eyni and R. Steinitz Department of Physics, Ben-Gurion University of the Negev, Beer Sheva
The solar wind exhibits relatively stable flow structures, characterized by different flow velocities. High, velocities are accompanied by high proton temperatures, and usually also by low proton densities. Thus, although flow conditions in the solar wind vary, we find from published data measured by Helios that the (distance) normalized momentum flux of the solar wind is invariant. The dispersion in the value of the momentum flux decreases as the sun is approached.
1. H. Rosenbauer, R. Schwenn, E. Marsch, B. Meyer, H, Miggenrieder, M.D. Montgomery, K.H. Mdhlhauser, W. Pilipp, V. Vages, and S.M. Zink, A survey on initial results of the Helios plasma experiment, J. Geophys. 42_, 561 (1977).
A-8 RADIATION PRESSURE IN THE ENVELOPES OF LOW MASS RED GIANTS
A. Harpaz Department of Physics and Astronomy, Tel Aviv University, Ramat Aviv
In recent years it became more and jwre evident that the process of mass- loss from stars has an important role in determining the path of stellar evolution. In discussions about the empirical evidence of continuous mass loss from red giant stars, it was suggested that the cause for this phenomenon could be either radiation pressure in the envelope, or acoustic energy from the convection zone. In the discussion on the Creation planetary nebulae, the radiation pressure is considered as one of the possible mechanisms for the mass loss in the fora of the planetary nebulae. We have investigated two sequences of stellar models: the first - a star of 1.2 Mft with different core Masses, The second was obtained from the evolution of a star with continuous aass loss. The overall result was that in the envelopes of all these calculated models, where the circumstances were not suitable yet for the formation of dust grains, the quantity Lj./Lc never exceeded the value of 0.1, and hence we have to look for the probable nechanism for the mass loss process in the other mechanises. There remains the possibility that above the photosphere, where dust grains can be formed, the role of radiation pressure might be more significant.
fk I - 12 - i | THE ROLE OF EQUATION OF STATE IN STELLAR COLLAPSE h | I. Lichtenstadt and N. Sack fe Racah Institute of Physics, The Hebrew University of Jerusalem, f' Jerusalem { A simple Equation of State (EOS), which mokes up more realistic EOSs, { was used to calculate and study the behaviour of collapsing stellar i' cores. In our EOS the pressure consists of two parts: a thermal pres- 4 sure, resembling that of an ideal gas and a cold pressure, with an (•• adiabatic index which goes up from below 4/3 at low densities to about ]., 2.5 at high densities. >: We found tha- a greater adiabatic index of the thermal pressure and * a softer cold pressure at low densities are favourable for mass I' ejection after the collapse halts, At this stage the inner core is T practically separated from the outgoing core envelope and its hydro- ;. dynamical behaviour does not affect the blow-off. [- A-10 i MASSIVE, EXTENDED F.NVELOPES AROUND COLLAPSED STARS r- i- A. Finzi ),- Department of Mathematics, Israel Institute of Technology, Haifa s iiost x-ray sources in population II systems seem to result from [• collisions of collapsed stars with normal stars. After a collision, the ;' material of the normal star evolved into a semi-transparent envelope j, of radius ~ 1017 cm which surrounds the collapsed star.1 The study j of this envelope leads to the following conclusions: ! 1. A static envelope, which contains almost all the mass, surrounds i a comparatively small sphere where matter is steadily flowing into "; \ the compact star. j 1 2. In the static envelope, matter is only very weakly ionized. There, :j f partial absorption of x-rays is balanced by the emission of secondary ?} j; radiation. This secondary radiation, which is partially trapped, .;) !. supports the envelope against collapse. j r'- *' I 3. The radius of the envelope cannot exceed an upper limit propor- >j [ tional to the mass Mc of the compact star. The mass of the envelope .J :- cannot exceed an upper limit, proportional to M^ ; only if M » 3M ;[ ;. the envelope can be sufficiently massive to store matter before1 it ° *.i I accretes onto the compact star. Ne conclude that the compact star • i should be a black hole. ,: )\ 1. A. Finzi, Astron. and Astroph. ftf, 149 (1978). j ; :] I-,r-> Jit- _ | » &''V." A - 11
4v;: VARIABILITY OF G, CONFORMAL INVARIANCE AND ALL THAT ... *:.•: I Amnon Meisels and Jacob Bekenstein i; • • Department of Physics, Ben-Gurion University of the Negev, Beer-Sheva ? V We pose the following questions; t-:.' (a) Can one define in a way which is independent of the choice of a ,;H system of units what is meant by "variable G"1? :? Q>) Can one give the most general theory for such a case which will T;' also be conformally invariant? :'. (c) How does G change within this theory? } In the following we answer the first two questions in the affirmative ':• and we conclude by giving to question (c) a strange answer; •;••• "it doesn't!". SUNDAY AFTERNOON, 1 APRIL, 1979 LIBRARY BUILDING 14:30 (Room 309) B. LASERS AND OPTICS A. Levin, Nuclear Research Center, Negev - Presiding B-l THE ROLE OF EMISSION FROM METASTABLE STATES OF FREE ATOM IN LASERS (30 min) 5. Yatsiv, The Hebrew University, Jerusalem B-2 EXPERIMENTAL DETERMINATION OF POPULATIONS IN COPPER VAPOUR LASER (30 min) 6. £rez, Ben-Gurion University, Beer-Sheva and Nuclear Research Center, Negev
B-5 A GEOMETRICAL CONSTRUCTION FOR SELF-FOCUSING OF RAYS IN HOMOGENEOUS NONLINEAR MEDIA Dan Censor Department of Electrical Engineering, Ben-Gurion university of the Negev, Beer Sheva Recently, a model for ray tracing and self-focusing in weakly nonlinear media has been proposed.1"3 In the present discussion the feasibility of the model is examined for the simplest case of a cylindrical geometry and a homogeneous time invariant and isotropic medium, The formalism leads to a geometrical construction with wave fronts as the orthogonal trajectories of the rays. The graphical solution clearly shows the self- focusing of the rays, due to the gradient of the field intensity and th* nonlinearity of the medium, 1. D. Censor, J. Plasma Phys. 16, 415 (1976), 2. D. Censor, Phys. Rev. A., 1^, 1673 (1977). 3. D. Censor, Phys. Rev, A., to appear (1979), - 15 -
THE OPTOGALVANIC EFFECT G. Erez and E. Miron ;;'V Nuclear Research Center, Negev and Department of Physics, VvJ- Ben-Guiion University of the Negev, Beer Sheva r V; One measures the voltage across a hollow cathode tube. When the tube !*.}•;, is illuminated with a dye laser, pulsed or modulated, a characteristic *<£}, voltage change appears if the light's wavelength corresponds to an U'\ optical transition in the gas or in the material sputtered from the :A7; cathode. The amplitude and shape of the electrical signal depend on the f-'• characteristics of the level in question, atomic concentrations, light ;V' intensity, current, pressure, etc. The spectroscopic resolution is ;; limited only by Doppler width. The system is of extreme instrumental 'r simplicity. The effect can be used for spectroscopic research, investi- {,'• gation of plasma processes in the tube, laser wavelength stabilization, "v. etc. Experimental results are presented for neon and argon as gases, •. and for uranium as a sputtered material. ft''"
B-5 IONIZATION OF ATOMIC GAS BY LASERS G. Erez, J. Oreg, M. Strauss amd L.A. Levin Nuclear Research Center, Negev A model for calculating the ionization of an atomic gas by lasers is described. The model was applied to selective ionization of uranium gas. The atomic gas under investigation is irradiated by N lasers in overlapping beams in the x direction. The laser wave lengths are adjusted for excitation of the atoms along a selected atomic level ladder, up to ionization (level N+l). The model is based on the 'bean approximation1. Line absorption, spontaneous and stimulated emission are considered. The spectral shape of the atomic lines and the laser beams are taken into account. The rate equations (RPA) for the atomic level population densities and the continuity equations for the laser fluxes are given in terms of the variables x (space), t (time) and A (wave length). A multigroup scheme in the A parameter and numerical iterative scheme in the x, 1. variables was developed to solve these equations. The solutions are checked by simple conservation rules. The scheme was applied to a four level system of uranium gas. The effect of the follow- ing factors on the ionization process were investigated: the spectral distributions of the atomic and laser line shapes, the laser energies, spatial distributions and relative delays. - 16 -
B-6 VISCOSITY ESTIMATION AND DIMENSIONAL ANALYSIS OF HOLE FORMATION IN THIN FOILS PRODUCED BY HIGH POWER LASERS B. Arad, S. Eliezer, H.M. Loebenstein, A. Zigler, H. Zmora and S. Zweigenbaun Soreq Nuclear Research Center, Yavne In this paper the gross features of the behavior of a flat target irradi- ated with a high power laser are investigated. We distinguish between three cases: (a) a thin target which is penetrated while the laser is still irradiating the target, (b) a thicker target which is burnt through at some time tb much longer than the laser pulse duration TL, (C) an infinitely thick target in which a crater is formed. Considering the various physical processes, we put the appropriate input data into a dimensional analysis and derive a functional relationship between the radius of the hole or the crater and the laser flux or the laser energy. This relationship is supported by the experimental data. In the second part of this paper, we assume that the velocity profile of the ejected natter has a linear dependence on the radius close to the hole boundary. Following this assumption, we obtain
*T = .2ir: L CD where Mj. is the momentum measured by the target pendulum1, L is the target foil thickness, V(a) is the velocity of the ejected material, S is the scale length over which the velocity changes linearity to zero, T* is the ablation time (approximately twice the laser pulse duration), n is the dynamical viscosity of the "flowing" material and R is the radius of the hole. The experimental results plotted in Fig. 1 for the 25 and 50y« targets support the derivation of Eq. (1) while the 9|im foil results which were penetrated during the laser irradiation time show a different behavior.2 Inserting the experimental data into Eq. (1) together with the assumption of 6 = 50pm and solving for n yields a value of (5-10) x 101* poise in good agreement with Altshuler et al.3 who measured the viscosity of water under high pressure of 80-250 kbar.
The momentum Mj transferred to a flat Al target as a function of the hole radius R, produced by the laser ablation. 17 -
B. Arad, S. Eliezer, Y. Gazit, H.M. Loebenstein, A. Zigler, H. Zmora and S. Zweigenbaua, "Burn-through of tidn aluminum foils by laser driven ablation", submitted for publication. B. Arad and S. Eliezer, "Viscosity estimation of aluminum flowing under pressure of a few megabars", submitted for publication. L.V. Altshuler, G.I. Kanel and B.S. Chekin, Sov. Phys. JETP 45, 348 (1977). —'
B-7 MEASUREMENT OF POPULATION INVERSION KINETICS BY A FAST HOOK SYSTEM I. Smilanski Nuclear Research Center, Negev Although knowledge of the inversion kinetics is vital in pulsed laser research, the inversion has never been directly measured in fast, high gain, pulsed lasers. The relevant lines are either heavily radiating or absorbing and have complicated, time dependent line shapes, making resonant absorption an impractical tool. Self-trapping, superradiance, metastable levels and calibration difficulties limit the usefulness of fluorescence measurements. In the Rozhdestvenskii hook method1, the anomalous dispersion is measured interferometrically in the wings of the absorption line; hence optically thick media can be analyzed, and details of the lineshape and intensity fluctuations in the light source can be ignored. However, conventional white light sources require prolonged exposure times, imposing severe requireaents on the inter- ferometer stability and a prolonged alignment procedure. In the present work these difficulties were pvercone by employing a nitrogen pumped dye laser as the light source2, and a CCTV instead of a photographic plate. Real time microdensitometry3 peraits accurate and fast density measurements. The short dye laser pulses not only give good tine resolution but reduce considerably the stability requirements on the interferometer, since during 5 ns the amplitude of acoustic vibrations is negligible. Using this method the time evolution of the population inversion in a copper vapor laser was studied, with concentration and time resolution of better than 1012 atoms-cm"3 and 20 ns respectively. 1. W.C. Marlow, Applied Optics, 6, 1715 (1967). 2. N. Miyazaki and K. Fukuda, J. Phys. D, 1£, 1905 (1977). 3. S. Lavi, E. Miron and I. Smilanski, Optics Communications, 27_, 117 (1978). - 18 -
B-8 ULTRASHORT LASER PULSE ANALYSIS OF MULTIPHOTON FLUORESCENCE Z. Bauman Soreq Nuclear Research Center, Yavne and Department of Chemistry, Tel-Aviv University, Ramat-Aviv Ultxashort laser pulses e.g. 1-100 psec wide, are commonly used in various physical and chemical studies. Unfortunately those laser pulses are too short to be analyzed with the standard methods. The use of multiphoton fluorescence as a possible tool for their analysis has been introduced by Giordmaine et al.1 using the TPF (two photon fluorescence) method and by Rentzepis et al.2 using the 3PF (three photon fluorescence} method. It was accepted, however, that these methods yielded less information than some alternative ones, e.g., the streak camera or the high order harmonic generation. Nevertheless, because of its low cost, simplicity of operation and the possibility of displaying the whole pulse in one shot, it was widely applied to provide information regarding the state of locking or the pulse width. So far little effort has been made to further develop these methods (for a brief review see Ref. 3). Some progress was made by us1* show- ing that in principle, the asymmetry constraint can be removed from the 3PF display. In this paper an assessment of the theoretical and experimental essentials of the multiphoton fluorescence methods and some of their prospects, as well as, part of our work is described. 1. J.A. Giordmaine, P.M. Rentzepis, S.L. Shapiro and K.N. Wecht, Two Photon Excitation of Fluorescence by Picosecond Light Pulses, Appl. Phys. Lett. U., 216 (1967). 2. P.M. Rentzepis, C.S. Mitchele and A.C. Saxman, Measurement of Ultrashort Laser Pulses by Three Photon Fluorescence, Appl. Phys. Lett. 17., 122 (1970). 3. R.C. Greenhow and A.J. Smith, Picosecond Light Pulses, in Advances in Quantum Electronics, Vol. 2, D.H. Goodwin, ed., London and New York Academic, 1974, pp. 157-286. 4. 2. Bauman, Detection of Laser Pulse Asymmetry by Three Photon Fluorescence, IEEE Journal of Quantum Electronics, QE-13, No. 10, 87S (1977). - 19 -
B-9 OPTICAL ELEMENT FOR RESTORING PICTURES AFTER TRANSMISSION THROUGH AN UNORDERED FIBER-BUNDLE U. Levy and A.A. Friesem Department of Electronics, Weizmann Institute of Science, Rehovot Direct transmission of pictures by optical fibers is usually accomplished by means of a bundle of many flexible fibers, carefully arranged at both ends. These so-called coherent bundles are relatively expensive compared to unordered bundles, and their length is limited because of technical difficulties in the production stage. With the unordered bundles, the problem of course is that a certain input light pattern focused on the input face is completely scrambled when viewed at the output face. We conceived and tested a holographic optical element for unscrambling the transmitted information and restoring the original input pattern. The element consists of small independent holograms - one for each fiber in the bundle. Each hologram, corresponding to one particular fiber, is recorded separately with a reference beam having a certain angular direction. In readout, when light from a given fiber impinges on its corresponding hologram, the diffracted beam propagates in the direction of the particular reference beam used for recording. In essence the hologram serves to direct the light from the fiber to a desired and known position. For imaging, this new relative position is identical to the relative position of the particular fiber at the input face of the bundle. Details of the preparation process will be discussed and experi- mental results illustrating the restoration technique will be presented. COUUStON EFFECTS IN THE MULTlTHOTOM DISSOCIATION OF S G. Koren and U.P. Oppenhein Department of Physics, Israel Institute of Technology, Haifa Measurements of Multiphoton Dissociation CMPD) of 32SFg by irradiation with a single TEA C02 laser pulse as a function of gas pressure are reported. Superexcitation conditions and pulses of different lengths were used in order to investigate collision effects on the MPD of SFg. In addition the energy of the pulses transmitted through the absorption cell was measured to distinguish between optical absorption effects on the MPD and MPD which is affected by collisions. The results using laser pulses of 8J with a duration of 150 ns show that at low gas pressures there is an almost constant MPD yield where 15% of the molecules are dissociated in a single pulse, whereas at pressures higher than 0.1 torr a strong decrease of the MPD yield is found. The transmitted pulse energy in this case follows the MPD behavior as a function of pressure. The results with the stronger laser pulses of 30J and duration of ~ lps show a pressure dependence of the MPD similar to that obtained with the weaker pulses, but with 100% yield at the low gas pressures. The transmitted pulse energy, however, was found to be almost constant at pressures of up to 0.3 torr. The present results indicate that collisions with the photo- fragments provide the most likely channel for the observed decrease of the MPD yield versus pressure. - 20 -
SUNDAY AFTERNOON, 1 APRIL 1979 LIBRARY BUILDING 14:30 (Room 326) C. APPLIED PHYSICS K. Weiser, Israel Institute of Technology, Haifa - Presiding
C-l New Method of Photoconductivity Measurement* S. Mil'shtein and A. Senderichin Department of Physics, Ben Gurion University of the Kegev Beer Sheva, Israel The spectral dependence of photoconductivity Might give detailed infor- mation about the energy gap and the impurity levels within the gap only in the case when the spectral dependence of the absorption coeff- icients a(A) is known. Determination of a(X) from reflectivity and transparency measurements is limited by the accuracy of finding Io • I(l-R), which strongly depends on surface state, since R is the reflectivity coefficient.1 The excess photocondictivity ta also depends on surface parameters as surface recombination velocity s.2 Trying to avoid the difficulties mentioned above we developed a new method of photoconductivity measurements. Taking into account the bulk generation-recombination processes and the surface recombination as well, the excess photoconductivity can be presented CD . where 6 is the quantum efficiency, u - the surface mobility. An (L.,s) - excess concentration on the surface as a function of the diffusion length and the surface recombination velocity. Measuring the transversal photoconductivity AoCx) for three layers lying on different depths we obtain: -OUC- Ao(x2) - -ox. - e C2) AoCx3) - Ao(x1) - e Equation (2) enables us to calculate the absolute value of a(X) from the measured values of the photoconductivities Aoj, Ao«, .-J A03. The derived spectral distribution of a facilitates solving the problem of finding the other parameters of the material. * Supported by US Air Force under grant APOSR-78-3526. J 1. J. Pankove, "Optical processes in semiconductors", (1971). 2. T.S. Moss and T.D.H. Hawkins, Phys. Rev. Letters, Vol. 1, No. 4, 129-130 (19S8). !#f
- 21 -
C-2 IMPROVED FRESNti. SOLAR CONCENTRATORS
E.M. Kritchman, A.A. Friesem and G. Yekutieli Faculty of Physics, Weizmann Institute of Science, Rehovot
A new type of linear concave Fresnel lens for concentrating solar radiation very near the ultimate concentration limit is considered. The differential equations that describe the lens are solved to provide computed solutions which are then checked by ray tracing techniques. The dominant design parameters are the light collection field angle, the refractive index of the lens, the width of the individual grooves, and the overall shape of the lens. The performance of the lens is investigated and compared to that of a flat Fresnel lens, showing that the new lens is preferable for concentrating solar radiation. Specifically, our results show that the concave lens is capable of concentrating solar radiation by a factor of 80 with an efficiency of 88 percent.
C-3 THE dc-SQUID RESPONSE TIMES AND CHARACTERISTICS
E. Ben-Jacob and Y. Imry Department of Physics and Astronomy, Tel-Aviv University, Tel-Aviv
1 1 The response times and characteristics of the dc-SQUID driven by external current source and magnetic flux were studied, we used the lumped circuit model for the junctions (Fig. 1). According to this model there are three independent characteristic times in the problem. The ratio of those times defines two parameters G = 1_ (U>T is the UjRC J Josephson plasma frequency) and K = jeXf" ' whlch govern both the response times and the device characteristics. Conditions on G and K for optimizing the response, stability and sensitivity of the dc-SQUID were obtained. The model of Fig. 1 was also used as a model for a junction with length of the order of Xj (Josephson's penetration depth) in a magnetic field. The results were found to be in agreement with experiment,2
I V \7 i •j 22 -
t FIG: 1 1. L.D. Jackel, T.D. Clark, Rev. Sci. Inst, 46, 1249 (1975) 2. W.C. Stewart, Appl. Phys. Lett. 14_, 392 (1969).
C-4 RESPONSE TIMES AND THE I-V CHARACTERISTICS OF SHORT JOSEPHSON JUNCTION* E. Ben-Jacob and Y. Imry Department of Physics and Astronomy, Tel-Aviv University, Ranat Aviv The response times and the nature of the I-V characteristics of short Josephson junction driven by a current source were studied. Approximate analytical arguments and numerical simulations were used for the lumped circuit model of the junction (Tig. 1). According to this model there are two independent characteristic times in the problem, RC and l/u>j (uij is the Josephson plasma frequency], The ratio of those times, 6 = —jL- , governs both the response times and the nature of the I-V characteristics. The lumped circuit model1»2 in which R is voltage independent is appropriate for the "shunted" junction, We also extended the calculation for the more general case in which R is voltage dependent, as appropriate for T « Tc. -ir —i—c T Fig: 1 23 -
1. W.C. Stewart, Appl, Phys. Lett. 12, 277 (1968), 2. D.E. McCumber, J. Appl. Phys. 32_, 3113 (1968). ,%:•-', •Supported by a grant from the Israeli Academy of Sciences,
C-5 fe. APPLICATIONS OF THE SHORT JOSEPHSON JUNCTIONS RESPONSE TIMES ON THE rf-SQUID OPERATION E. Ben-Jacob and Y. Imry I Department of Physics and Astronomy, Tel-Aviv University, Ramat-Aviv The dynamics of a SQUID ring driven by external flux were studied. We used the lumped circuit model for the junction which is the weak-link element of the ring (Fig. 1). The characteristic entry and exit times for the cases of linear and oscillatory time changes of the external flux were treated. It was found that the condition for quasistationary behaviour of the SQUID is not only a low enough frequency, but also a small enough amplitude of the AC external flux. These studies were used for analysing the rf-SQUID1 (the SQUID coupled with rf-circuit). Conditions for optimizing the response, stability and sensitivity of the device were obtained. M'
ex
_T C I
Fig: 1 1. R.A. Buhrman, SQUIDs and their Applications, Walter de Gruyter and Co., Berlin, New York, 1977. C-6 CHARACTERISTICS OF THE LONG JOSEPHSON JUNCTION P. Marcus IBM Research and ETH Zurich Y. Imry Tel-Aviv University, Ramat Aviv Periodic solutions of the equation for the long tunnel junction with constant uniform current feed and a dissipation tern proportional to 34>/3t have been found under the assumption that the solutiois have the form of travelling waves $(x-ut) where u is a velocity. The partial differential equation reduces to the usual one-parameter equation for a point junction with lumped capacitance and resistance, but now the parameter depends on u. Current-voltage characteristics of the point junction can then be used to find the characteristics of the long junction for any given length. A series Of characteristic modes is found each of which starts at the origin, follows the ohmic line (or lies slightly above it) to a resonant voltage at which the current rises abruptly to large values. The lower node solutions in long ; junctions are kinks in
Zone plates have been used as an X-ray microscope in the 10-100A -: region.1 The resolution is limited by the chronate aberration of a 'i single zone plate. .••? The using of two zone plates in tandem was suggested by Young.2 He *f found the conditions for the total power of the two zone plates l| combination at two different wavelengths to be equal. This condition I is found to be not practical because the corresponding back focal 1 lengths (BFL) differ appreciably. The condition for equal BFL is v found. The axial color is eliminated in first order while t;.*>. residual j lateral color is practically unnoticeable, A three zone plate lens is j also introduced. The chromate correction is now very satisfactory. ? *€t - 25 - 1 §•
Development in zone plate fabrication, and the use of phase and blazed zone plates will enable constructing multielement zone plate lenses. 1. B. Nieman, D. Rudolf and G. Schnuihl, X-Ray Microscopy with Synchxontron Radiation, Appl. Opt. 15_, 1883 (1976). 2. M. Young, Zone Plates and their Aberrations, J. of Opt. Soc. of Amer. 62, 972 (1972).
I; PSEUDOHOLOGRAPHY USING ZONE PLATES ||.; Joshua Gur |j The University of Rochester, The Institute of Optics, Rochester, NY
: Pseudoholography is a method for recording the information about an >• object by recording a coded version of the image in the first step. In the second step the processed piece of film is laser illuminated -• and the object is reconstructed. This method, using zone plates as ;•/ masks, is being used as a powerful diagnostic tool for laser produced ':• plasma investigations.1 It has been recently shown that an improved -; resolution can be achieved in higher order reconstructions.2 Several '; configurations are explored as well as special zone plate designs, v;> that improve significantly the efficiency at high order reconstructions. •'-." . I. N.M. Ceglio, X-Ray Microscopy of Laser Fusion Plasmas Using coded ?•• Imaging Techniques, SPIE 106, X-Ray Imaging 55 (1977) . [\ 2. Joshua Gur and J.M. Forsyth, Optical Simulation of a technique ;:'; for Obtaining Submicron Resolution X-Ray Images in Laser Pellet S Compression Experiments, Appl. Opt. 14, 1 (1978).
p] THERMOPLASTIC RECORDING WITH CAPACITIVE CHARGING
H; Z. Hirshfeld, Z. Rav-Noy, and A.A. Friesem j^ Department of Electronics, The Weizmann Institute of Science, f\ Rehovot ;•;•' A conventional photoconductor-thermoplastic (PC-TP) device for real- 1% time, in-situ, write-read-erase holographic recording consists of a ii glass substrate, a transparent conductive electrode of InO, a thin [;; organic photoconductive layer, and a thin deformable thermoplastic f;. layer. By adding a flexible netallie layer, it is possible to conven- \'j. iently sensitize the device by aeans of capacitive charging rather 3 than the usual awkward corona charging. We have considered this vl composite structure in some detail and developed a model which >:Y partially explains the storage Mechanism, particularly the dependence F" of the holographic response on charge potential and spatial frequency |;,; of the recording. Several devices were fabricated and tested, showing J;:' that their resolution capabilities are 500 lines/mm, but the record- !'; erase cycles are so far limited to about twenty. The development of fi\ the model along with experimental results will be presented. - 26 -
C-10 ANALYZING THE OPTICAL AND GEOMETRICAL PROPERTIES OF THE ANTERIOR SEGMENT OF THE EYE BY HOLOGRAPHY M. Segal and J. Politch Department of Physics, Israel Institute of Technology, Haifa We consider a new method of recording and identifying refractive index changes of birefringent materials. This method was of great help to our work on geometrical and physical properties of the anterior segaent of the human's eye. Three types of holograms are recorded simultaneously, on the same holographic plate, which was placed perpendicularly to the Bye's optical axis. Two of these holograas are reconstructed with a monochromatic source, as during the recording stage (off-axis and on- axis holograms), and the third, which is a shadow hologram, can he reconstructed with white light source. Simultaneously we can record the geometrical shape of the cornea by aeans of an off-axis holography, in which the recording plane is parallel to the optical axis of the eye. All the recordings were achieved in one step, applying an unpolarized continuous wave He-Ne laser, operating in the TEMOO mode.
C-ll MEASUREMENTS OF THICKNESS AND REFRACTIVE INDICES OF TRANSPARENT MULTILAYER M. Oren and J. Politch Department of Physics, Israel Institute of Technology, Haifa We describe a method of measuring the thicknesses and refractive indices of transparent multilayer, based on the reflected light only. A Michelson interferometer is applied in this measurement. It contains a convex lens in every arm, and instead of one of the mirrors the examined multilayer is placed. The theory shows, that if the thicknesses arc of the order of a fraction of a millimeter, the number of layers, their thicknesses and uieir refractive indices can be calculated from the measurements. The measurements are based solidly on geometrical optics. The method works well for plane layers, however, when the surfaces of the layers are curved the mathematical expressions are more complicated. This may be partially overcome by using a point light source and measuring also the refracted beam. - 27 -
C-12 A Ca F2: Dy THERMOLUMINESCENT DOSIMETER FOR ENVIRONMENTAL MONITORING Ben Shachar Barak and German Uzi Nuclear Research Center, Negev One of the nost modern and developing methods for accurate dosiaetric measurements is the thermoluminescent (TL) process. This method is used for personel and environmental monitoring as well as for research in nuclear medicine. For accurate environmental measurements around nuclear facilities, the most useful dosimeter is the sensitive and accurate, Ca F2: Dy phosphor.1'2'3 After calibrating the measuring instrumentation (Harshaw Thermoluminescence Detector, Model 2000-C with Automatic Integrating picampermeter Model 2000 B), we checked the reproducibility and linearity of some dosimeters, as well as their sensitivities for low exposures. We received good reproducibility even for low doses (about 4-7% standard deviation for 10 mR, without annealing), as well a good linear response for a 10 mR - 1R range. There are two aain advantages in the ase of Ca F2; Dy dosimeter: its pronounced energy dependence for low energy x-rays (below 100 Rev)1'2'*5 and its significant fading, depending mainly on the storage temperature. The first effect can be corrected by accurate measure- ment of the energy dependence of Ca F2: Dy for an energy range of 50-1250 KeV and shielding it to make the energy dependence as flat as possible. The second effect may be diminished by waiting at least 24 hours between the exposure and the reading and if possible, perform- ing a thermal treatment (pre-irradiation and post-irradiation anneal- ing).1'5
1. D.H. Denham, Katren, Corlay-BNWL-SA-4191, 1972. 2. E. Piesch, Kerntechnik, 19_ (1), 27 (1977). 3. K.E. Duftschmid, ST-45/75 (1975). 4. J.E. Hoy, Health Physics, 21_ 0-971). 5. B. Burgkhard, Herera, piesch, Nuclear Instruments and Methods 155, 293 (1978). - 28 -
SUNDAY AFTERNOON, 1 APRIL 1979 LIBRARY BUILDING 14:30 (ROOM 323) D. ELECTRIC AND MAGNETIC PROPERTIES OF SOLIDS A.A Hirsch, Israel Institute of Technology, Haifa - Presiding D-l A STUDY OF THE ELECTRONIC STRUCTURE OF METAL HYDRIDES USING THE NMR TECHNIQUE D. Zamir, Soreq Nuclear Research Center, Yavne
D-2 THE CRITICAL RELAXATION OF A 1-D CONSERVED MAGNETISATION ISING MODEL Y. Achian Nuclear Research Center, Negev The critical relaxation of the one-dimensional Ising spin system with conserved magnetisation is studied using the real space renormalization- group (R.G.) approach.1 The result shows that the relaxation mechanism proposed by Kawasaki2 is irrelevant in the R.G, sense, The slowest dynamic node is the energy mode. The relaxation of an antiferromagnetic node is faster, even though slowed down at T • 0. The dynamic exponent is z * 3. This is the value proposed by the conventional theory, and by the continuum spin R.G, study of similar conserving systems. 1. Y. Achiam and J.M. Kosterlitz, Phys, Rev, Lett, 41_, 128 (1978). 2. K. Kawasaki, Phys. Rev. 145, 224 (1966).
D-3 ROLE OF DISLOCATION SCATTERING FOR THE LOW-TEMPERATURE ELECTRICAL RESISTIVITY A. Bergmann, M. Kaveh and N. Wiser Department of Physics, Bar-1 Ian University, Rama't-Gan Recent ultra-high-resolution resistivity measurements1'2 at low temper- atures have revealed several puzzling features of the temperature- dependent part of the electrical resistivity p(T) for pure Ag and AC and their dilute alloys. These include (i) negative deviations from Mattiessen's rule for both Ag and At, (ii) an unexpected Th behavior for p(T) for a large class of dilute Ag alloys, (iii) the apparent complete absence for Ag of the predicted T2 term due to electron- electron scattering3, and (iv) the markedly different temperature dependences observed for p(T) for apparently similar samples of Ag. - 29 -
Our analysis of p(T) shows that all the above features of the resis- tivity data can be explained quantitatively if one includes the coupling between electron-dislocatiom scattering and all the other scattering •echanisms. The basic idea is the following. Electron-impurity scatter- ing is isotropic and hence leads to an isotropic electron distribution function +00, corresponding to the relaxation-tine approximation. By contrast, because dislocation lines are highly anisotropic entities, electron-dislocation scattering leads to a >(k) that is anisotropic over the Fermi surface. At low temperatures, tKe relative strength of electron-impurity scatterimg and electron-dislocation scattering determines the functional form of *CjO • At somewhat higher tempera- tures, electron-phonon scattering must also be taken into account. The interplay between these tkr** scattering mechanisms (electron-impurity, electron-dislocation and electron-phonon) in determining the functional form of #(k) leads to the rich variety of results observed1*2 for p(T) for and Ag and their dilute alloys. 1. B.R. Barnard and D. Caplin, J. Phys. (Paris) 39, Suppl. C6-1050 (1978), (Proc. 15th Iat. Conf. Low-Temp. PhysTJ". 2. J.A. Rowlands and S.B. Moods, J. Phys. F8, 1929 (1978). 3. W.E. Lawrence, Phys. Rev. » 13, 5316 (1976). D-4 FAULTED ZnS SINGLE CRYSTALS AS QUASI ONE-DIMENSIONAL CONDUCTIVE SYSTEMS
Y. Brada Racah Institute of Physics, Hebrew University of Jerusalem, Jerusalem The conductivity in one-dimensional ionic conducting systems has shown an exponential frequency dependence.1 A similar frequency dependence is reported here for an electronic conductor, i.e., faulted single crystals of ZnS. In these crystals, which grow as hexagonal structures at elevated temperatures, there occur slips in the basal planes during the cooling down to room temperature, at which the 3C structure is stable.2 These slips generate various structures which are homogeneous in the direction perpendicular to the c-axis Cor < 111 > axis in the cubic case). The misfit in the prismatic planes creates charged layers3 I:, and barriers.1* The DC conductance along the c-axis is negligible (~10-11 mhos) while across the c-axis it is about 10"1* mhos. As in the case of one-dimensional ionic conductors, this electronic conductor can be described as a disordered one-dimensional system. The theoretical approach5 developed for the ionic case can also be applied here. 1. A. BystriSm and A.M. BystrSm, Acta Crystal log. 3_, 146 (1950). 2. I.T. Steinberger, E. Alexander, Y. Brada, Z.H. Kalman, I. Kiflawi and S. Mardix, J. Cryst. Growth 13/14, 285 (1972). 3. B.G. Yacobi and Y. Brada, Phys. Rev. B, W.» 66S (1974). 4. G. Shachar and Y. Brada, J, Appl. Phys. 41, 3127 (1970). 5. J. Bernasconi, H.U. Beyeler, S. StrSssler and S. Alexander, to be published.
ic^c^.'C-c?-'-rrii-! »-^*~-s**.a3. - 30 -
CRITICAL FIELD MEASUREMENTS OF I.i-Ge SUPEHCONDUCTING ALLOYS* ' I. Grave1 and G. Deutscher Department of Physics and Astronomy, Tel-Aviv University, Ramat-Aviv We have Measured the electrical resistivity and the upper critical -.; field Hc2(6) for In-Ge sables coevaporated onto room temperature ; substrates. The values of the coherence length £(T) are calculated -i from both electrical and magnetic measurements in different regions • of 5(T)/d (d being the thickness of the sample), and so are the ; values of the anisotropy ratio Hl9 /Hj_ . The shapes of the curves H(, (T), Hj^(T) are studied to reveal a special behavior in terms of i strength and slope: this behavior is interpreted as that of an : extreme type superconductor in which the "dirtiness" is not due to r point defects but rather by the embedding of superconducting paths in an insulating matrix. A criterion to obtain information about the structure of metal- insulator alloys from critical field measurements is sought in terms of the behavior of different-systems. The critical field at fixed temperatures as a function of the sample resistivity (and metal , volume ratio) reveals a net change in slope around a critical resis- i tivity of about 25 yft cm. The possibility of connecting results to '; percolation behavior of the metal insulator system axound the percolation threshold is looked for. -, * '•' Research supported in part by the Israeli National Council for •; Research and Development and by the Karlsruhe Nuclear Research Center. • i D-6 -i MEASUREMENT OF THE TEMPERATURE DEPENDENCE 1 OF THE ELECTRICAL RESISTIVITY OF SODIW AND POTASSIUM BELOW 4.2 K j B. Levy and A.J. Greenfield -\ Department of Physics, Bar-Ilan University, Ramat-Gan » Measurements have been made of the temperature dependence of the I electrical conductivity p(T) for sodium and potassium in the temperature -v range 1.1-4.2 K. According to the standard theory1, at sufficiently A low temperatures the functional dependence is p(T) = p0 + ATn, where J p0 is the residual resistivity, A is a sample-independent coefficient i of the contribution to p(T) arising from electron-electron scattering | and n is 2. Our measurements confirm this functional dependence | with n « 2.00 ± 0.02 for both metals. However, we find that A is not ! sample independent but depends on the ratio Pj/Pj where p^ and pd ;' are the contributions to PO x Pj + Pd arising from impurity and dis- I location scattering, respectively. An experimental apparatus was built i to measure p(T) with a resolution of 1 ppm in this temperature range. ]
•t j r 31 -
Also, a. new sample preparation system was devised whereby samples are produced having PQ an order of magnitude smaller than previously. This very-small-pn sample is used to establish the ratio PJ/PJ in subsequent measurements. Similarly, a procedure was devised for chang- ing p£ and Pd separately in order to obtain samples with different, known values of the ratio Pj/Pd- P(T) has been measured for a series of samples having 16 different values of Pj/pj and A has been calcu- lated for each sample. These results for A vs. Pj/pa are in full agreement with a recently proposed theory.2 1. J.M. Ziman, Electrons and Phonons (Oxford University Press, London, 1960), Chapter IX, Section 9.14. 2. M. Kaveh and N. Wiser, submitted to Phys. Rev. Lett.
D-7 AN EFFECTIVE MEDIUM CALCULATION OF THE BROKEN STRAND MODEL
S. Marianer and M. Weger The Racah Institute of Physics, The Hebrew University of Jerusalem, Jerusalem The broken strand model introduced by Weger and Kaveh1 is used to calculate the dielectric constant and electrical conductivity of quasi one-dimensional conductors. The quasi one-dimensional conductor is replaced by a network of resistors and the broken bonds are replaced by capacitors. Effective medium theory is then applied to obtain the variation of electrical conductivity and dielectric constant with frequency and fraction of broken bonds. 1. M. Keger and M. Kaveh (to be published in J. Phys. C).
D-8 EXPERIMENTAL EVIDENCE FOR A SUPERCONDUCTING CONTRIBUTION TO THE ELECTRICAL CONDUCTIVITY OF BULK At AT TEMPERATURES WELL ABOVE T
M. Sinvani and A.J. Greenfield Department of Physics, Bar-IIan University, Ramat-Gan Measurements of the temperature dependence of the electrical resis- tivity p(T) of bulk A£ in the temperature region above the super- conducting transition temperature Tc have been performed on three samples having residual resistance ratios (RRR) 62, 66 and 380. The two samples with the lower RRR values both exhibited a detectable decrease in the measured p(T) at temperatures up to about 0.S K above the transition temperature Tc * 1,163 K. The decrease Ap(T) - 32 -
was shown to be associated with the superconducting state by the application and renoval of a magnetic field of 5-10 G at each tempera- ture. The temperature dependence of Ap(T) fits a plot of flp(T) - n A[CT/Tc)-l] with A = 0.1 pficm and n = 3/4. For the sample with RRR = 380, ApCT) could not be observed to within the sensitivity of our apparatus, which has a noise level of 5 ppm. There are theories1'2 which predict such an effect due to fluctuations of the order para- meter of the superconducting state. These predictions have been veri- fied for thin films3, but not for pure bulk metals. Our measured value for A is about 4 orders of magnitude above that predicted by these theories. Also, our Measured value of n * 3/4 lies halfway between the value of n« 1 predicted for thin film samples and the value of n * 1/2 predicted for bulk saaples. 1. L.S. Aslaaazov and A.I. Larkin, Sov. Phys. Solid State JLO_, 875 (1968). 2. K. Maki, Prog, in Physics 40, 193 (1968). 3. K. Aoi and M.A. Klenin, J. Phys. C. 6, L316 (1973). I — V STUSTUDIE1 S OF ANTIFERROMAGNETISM IN Dy2Ge207 SINGLE CRYSTALS I. Yaeger Department of Physics and Astronomy, University of Georgia, Athens, Georgia and Department of Physics, Ben-Gurion University of the Negev*, Beer Sheva B.M. Nanklyn Clarendon Laboratory, University of Oxford, Oxford, England The a.c. Magnetic susceptibility at 40 Hz of flux grown single crystals 1 of Dy2Ge207 has been Measured from 4.2 K down to 0,39 K in external Magnetic fields up to 40 kOe. An antiferromagnetic ordering was observed at TN » 1,97 ± 0.03 K. The Maximal symmetry of the tetra- gonal crystallographic space group P4j2i2 of this material2 allows for an eight-sublattice configuration of the Dy3 spins. From the zero- field a.c. susceptibility it is deduced that these spins lie in the (001) plane and possess highly anisotropic g-tensors. The experimental results are analyzed in the nean field approximation and the tempera- ture dependence of the zero-field a.c, susceptibility is accounted for in terms of the spin-spin interactions between the Dy3+ ions occupying the lowest lying Kramers' doublet. •Present address 1. B.M. Wanklyn, J. Materials Science £, 649 (1973). 2. Yu. I. Snolin, Sov. Phys. Crystallogr. IS, 36 (1970). - 33 - ;
D - 10 i ;:>;': CURIE TEMPERATURE AND ATOMIC VOLUME EFFECT G. Galeczki and A.A. Hirsch, Department of Physics, Technion, Haifa v. • The existence of a paramagnetic Curie-Weiss temperature above the ' ; ferromagnetic Curie temperature is usually ascribed to inhonogeneities ; .. in the spontaneous magnetization. However, we suggested recently1 a j I'if phenomenological model leading to a bi-transition, i.e. a discontinuous ff[ order-order transition at some temperature TQQ followed by a dis- ; f~\ continous order-disorder transition at Ton- Neglecting fluctuations, |;J the model assumes an intrinsic magnetostrictive mechanism, undetectable •Vi- by macroscopic (strain-gauge) measurements. A non-quadratic magneto- s l; volume equation of state: fts = Qon is postulated, where fls denotes £•:••" the intrinsic volume magnetostriction whil<: n the reduced spontan- '•'!:• eous magnetization. The exponent "s" is shown to be close to 3/2 for '•;<• ferromagnetic transition metals. The model shows a formal analogy t..'; with cation-disordered superionic crystals2 when non-quadratic ;~ effective attraction between an interstitial cation and the vacancy is assumed. 1. A.A. Hirsch and G. Galeczki, (submitted for publication to J. : Magn. and Magn. Mater.). 2. Yu. I. Kharkats, Phys. Stat. Sol. (b) «§_ (1978) 371.
D-ll ELECTRICAL PROPERTIES OF INDIUM DOPED LEAD TIN TELLURIDE i
K. Weiser, A. Klein and M. Ainhora, Solid State Institute, Institute of 1 Technology, Haifa ; ,;:v Doping lead tin telluride (LTT) of composition 0.2 SnTe, 0.8 PbTe with j 'i indium (In) produces essentially intrinsic material in the temperature ",{ ;.: range from 300 K down to 50 K. At lower temperature the carrier 'I • concentration begins to rise and eventually flattens out below 20 K. .' [ Put differently, the Hall constant rises sharply, then falls and ", eventually becomes constant below 20°K. j We explain these results on the basis of an auto-compensation i model and the positive temperature dependence of the bandgap. We ' believe that two neutral In atoms produce one donor and one acceptor 1 f and thus fix the Fermi level at an energy within the forbidden gap ,' '•• which depends on the energy of the neutral atom and the negative f- •.'•• correlation energy which causes the auto-compensation1. Because of the j •' positive temperature dependence of the bandgap, however, the Fermi } '{. level eventually moves into one of the bands so that the material j -: becomes degenerate, with a large and temperature independent carrier ] concentration. j 1. D. Adler and E.J. Yoffa, Phys. Rev. Lett. 36, 1197 (1976). ! i F I r i' [ SUNDAY AFTERNOON, 1 APRIL 1979 LIBRARY BUILDING I 14:30 [Room 308) E. THIN FILMS E. Gruenbaun, Tel-Aviv University - Presiding E-l I INTERACTION AND PROCESSES ON SEMI-CONDUCTOR SURFACES (30 Bin) [. J.I. Gersten, The Hebrew University, Jerusalem f E-2
TRANSPORT PROPERTIES OF SiO2 Z. Hteinberg, Israel Institute of Technology, Haifa
E-3 A NEW THEORY OF INELASTIC ELECTRON TUNNELING T.E. Feuchtwang Department of Physics, Israel Institute of Technology, Haifa and The Pennsylvania State University, University Park, PA. The currently accepted theories of inelastic electron tunneling spectra are phenoaenological and invoke either the golden rule or the transfer Hamiltonian formalism. These are Manifestly equivalent at zero tempera- ture. A generalization of the golden-rule analysis of inelastic tunnel- ing to finite temperatures is presented and used to demonstrate the formal equivalence of both, theories. A new many body formulation of inelastic tunneling is developed applying Feuchtwang's tunneling theory1, to a one-dimensional junction. The new theory leads to a precise interpretation of the phemmenological parameters in the current theories. The new theory identifies the ordinary nonresonant impurity induced inelastic tunneling and a resonant inelastic tunnel- ing channel. The latter cannot be accounted for by the current theories.
1. T.E. Feuchtwang, Phys. Rev. BIO, 4135 (1974); ibid B12, 3979 (1975); ibid B13, 517 (1976). 35 -
E-4 ELECTRON-SURFACE EFFECTS OK IONIC CRYSTALS A. Friedenberg and Y. Shapira School of Engineering, Tel-Aviv University, Ramat Aviv Ionic crystals are known to be instable under irradiation by electron beans. We bombarded the surface of several ionic crystals, prepared by thin-film evaporation under high vacuum, with medium energy electrons. The effects of the electron-surface interaction were analysed using Auger electron spectroscopy, quadrupole mass spectrometry and high energy electron diffraction. Combining the results of time-resolved analyses by these methods, we propose a mechanism for the electron- surface interaction and its effects on the various surface constituents. The interaction will be described in terms of surface dissociation by neutralization of the ionic species and their partial desorption. The dependence on electron current density, on substrate type and tempera- ture and on the vacuum conditions will be discussed. The implications to hetero-epitaxial growth on electron bombarded surfaces will also be described. E-5 MICROWAVE TRANSITION THROUGH THIN METAL FILMS M. Ya. Azbel Department of Physics and Astronomy, Tel-Aviv University, Ramat-Aviv The transmission of microwaves through thin metal films is evaluated. It is proved to be anomalously large, in particular, in the vicinity of cyclotron resonance and static skin-effect. The theory is in agreenent^ with experiments.1"3 1. J. Lebech et al., Phys. Letts. 54A, 211 C1975). 2. M. Surma et al., Solid State Comun. 17, 1359 (1975); 20, 493 (1976).
E-6 ELECTRICAL MEASUREMENTS OF At-Ge SUPER-CONDUCTING MIXTURES* Y. Shapira and G. Deutscher Department of Physics and Astronomy, Tel Aviv University, Ramat-Aviv We have measured the properties of thin films obtained by co-evapora- tion of A£ and Ge. The samples were studied by electrical measurements, electron microscopy and magnetic critical field. The range of At concentration varied from 50% to 85%, I
i
I Electron microscopy revealed that the system is composed of poly- ;- crystalline A£ grains imbedded in a Ge matrix. The size of the grains f was measured and was considered in relation with Tc enhancement and !• varying concentration. The system exhibits three different ranges of r behaviour. At very low concentrations of (JL the samples are semi- [ conductor. At moderate concentrations the samples are super-conductor, I but weakly semiconducting in the normal state, and the influence of : the magnetic field on Tc cannot be characterized by the normal resistivity. The transition between these two regions is sharp (less than 2% ratio of A£ volume). In the third region the samples are metallic superconductors and the normal resistivity does characterize the samples. This change of behaviour is spread over 5% ratio of A£ volume. In this transition region the dependence of Tc on magnetic field exhibits an upper curvature. * Research supported in part by the Israeli National Council for Research and Development and by the Karlsruhe Nuclear Research Center.
E-7 PHASE SENSITIVE DETECTION OF ELECTRON-INDUCED DESORPTION FROM ZnO
Y. Shapira and A. Friedenberg School of Engineering, Tel Aviv University, Ramat-Aviv
Surfaces of ZnO powders and single crystals are known to be sensitive to UV illumination and to oxygen adsorption which affect their conduc- tivity. Recent works have shown that CO2 is the dominant desorbing species from such surfaces while irradiated by UV photons. We report here a system for phase sensitive detection (PSD) of desorption from ZnO samples bombarded by a properly modulated electron beam. The PSD of a mass spectrometer signal assumes the high sensitivity and selec- tivity of the results. We find that CO2 is the dominant species in this case too. We followed the desorption kinetics under various experimental conditions such as electron energy, current density and surface temperature. We relate the results to photodesorption studies and provide a mechanism for this process. This mechanism will be discussed with supporting experimental evidence obtained by Auger electron spectroscopy. 37 -
E-8 EPITAXIAL GROWTH OF Ag ON ELECTRON-BOMBARDMENT NaCl (111) SURFACE M. Barkai, Y. Shapira and E. Grunbaum School of Engineering, Tel-Aviv University, Ramat-Aviv Effects of electron bombardment on NaCl (111) surfaces, obtained by deposition in UHV, and on subsequent epitaxial growth of Ag on such V surfaces were studied using reflection high energy electron diffraction (RHEED) and Auger electron spectroscopy (AES). Electron bombardment is shown to have a strong effect on the epitaxy if employed for a suffi- ciently short time. In this case, the metallic Na neutralized in the process seems to offer a better substrate especially for metal epitaxy. Otherwise fast oxidation and disordering of the NaCl surface occurs, eliminating the possibility of obtaining an oriented Ag film'. A mechan- ism of the electron bombardment effects will be discussed.
E-9 C-V STUDY OF METAL - ZnO - SiO2 - Si STRUCTURES H. Gilboa and Z. Kalahora Ministry of Defense Arnavent Development Authority, Haifa The monolithic surface acoustic wave (SAW) convolver based on the MIS structure of Si/SiO2/ZnO/Al, requires rf sputtering of ZnO on SiO2 such that the electrical characteristics of the Si/SiCb system remain unchanged after the deposition of the ZnO film. Two main problems arise during the preparation of the structure. During the prebake or the vacuum thermal etch preceding the actual rf sputtering, tied-up surface states bonds are broken thereby increasing the surface states density. During the rf sputtering deterioration is caused by radiation damage associated with heavy ions, electrons, and ultraviolet-light bombard- ment of the substrate.
C-V curves are used to detect the deterioration of the Si/SiO2 structure, and a modified fabrication process is used to minimize the damage. Specifically, the time and temperature of the prebake is reduced, and thinner SiO2 films are used. It is shown that by this process the C-V characteristic of the Si/SiOj system is almost unchanged by the deposi- tion of the ZnO films. 38 -
E-10 THE INFLUENCE OF IONIC TRAPS ON CURRENT INJECTION INTO THIN INSULATORS
L. Ziph-Schatzberg and N. Klein Department of Electrical Engineering, Israel Institute of Technology, Haifa
Insulators, such as silicon nitride, are assumed to contain equal densities of positive and negative ionic traps.1 Owing to distortions of the electric field in the vicinity of the traps, currents injected into an insulator are enhanced, when the traps are unoccupied. This can be found at low and at very high fields. In contrast, when traps of one polarity are occupied at medium fields by injected carriers, the current is diminished. Accounting for these effects and assuming current injection by Fowler-Nordheim tunneling, I-V characteristics were calculated and compared with measurements on silicon-nitride and aluminum oxide films.
1. P.C. Arnett, J. Appl. Phys. 46, 5236 (197S).
BUSINESS MEETING OF THE THIN LAYERS DIVISION - 39 -
SUNDAY AFTERNOON, 1 APRIL 1979 LIBRARY BUILDING 14:30 (Room 322) F. ATOMIC AND MOLECULAR PHYSICS A.S. Kaufman, The Hebrew University, Jerusalem - Presiding F-l ATOMIC PROCESSES IN HEAVY IONS COLLISIONS WITH SMALL IMPACT PARAMETER (30 min) B. Rosner, Israel Institute of Technology, Haifa F-2 THE DEPENDENCE OF THE CHARGE STATES OF H£ FRAGMENTS ON THE GAS TARGET PRESSURE E. Navon and D. Nir Department of Physics, Israel Institute of Technology, Haifa An accurate measurement of the dependence of the charge states on the target gas pressure in dissociative collision of Hj ions has been performed. Various projectile energies and various target gasses have been used. The charge states of both fragments have been measured by a set of detectors and coincidences between their signals. The equations of the processes are similar to those of radioactive decay and the behaviour depends on the ratios of the charge exchange cross sections to the dissociation cross section.
F-3 THE DEPENDENCE OF THE CHARGE STATES ON THE IMPACT PARAMETER OF A HEAVY ION IN A SINGLE COLLISION M. Meron, B. Rosner, D. Maor and I. Gertner Department of Physics, Israel Institute of Technology, Haifa The charge states of several heavy ions, He, C, N and Ne scattered from gaseous targets in the single collision region have been measured. The ; bombarding energy was in the range of 0,4-1 MeV and various gases, He, >j N2, Ne and Ar have bsen used as targets. The dependence of the outgoing ;'| charge states spectrum on the incoming projectile charge state and on :i the impact parameter of the collision has been determined. The charge •; states have been separated by an electrostatic deflector and position ^ sensitive detector. Analysis of the data shows an increase in the i average charge states when the impact parameter decreases towards the = t projectile K shell radius, going through a maximum and then decreasing. I The gross features can be explained by the statistical model1*2, while I- a refinement of the theory and inclusion of electron promotion3 is ;. needed to explain the decrease of the average charge state around the I K sheel. r- I. 1. A. Russek and M. Tom Thomas, Phys. Rev. 109, 2015 (1958). I 2. A. Russek and J. Meli, Physica 46_, 222 (1970) and references ( therein. | 3. K. Taulbjeng et al., J. Phys. B, Vol. 9, 1351 (1976). "f i. hi I NEGATIVELY CHARGED FRAGMENTS IN THE DISSOCIATION OF Hj AND H3 IONS v D. Nir and A. Ginzburg t Department of Physics, Israel Institute of Technology, Haifa l' b The probabilities for H" production in single dissociative collisions ! of H£ and H| ions have been measured for various bombarding energies I in the 1 meV region with various pressures of the gas target. Using I deflectors, a set of detectors and electronic coincidences, the proba- |, bilities for the dissociation channels containing H" and any comple- j mentary fragments have been determined. All the possible dissociation
G. DEFECTS IN SOLIDS M. Dariel, Ben-Gurion University, Beer-Sheva -
G1 Nuclear Research Center - Presiding
REQUIREMENTS AND APPARATUS FOR DIFFUSION STUDIES IN SUPERIONIC CONDUCTORS
Raoul Weil Department of Physics and Solid State Institute, Israel Institute of Technology, Haifa* David Lazarus Department of Physics and Materials Research Laboratory, University of Illinois, Urbana
Diffusion in solids is usually studied by radioactive tracer methods. Normally diffusion proceeds at a truly negligible rate at room temper- ature. However, when diffusion in superionic conductors is studied a difficulty arises due to the fact that these materials haye diffusion coefficients which are orders of magnitude higher than those of other solids at room temperature. Because of this, and because some super- ionic conductors have interesting transitions at low temperatures, sectioning of the diffused saaples must be done at cryogenic tempera- "X," tures. The principle of the apparatus used is that sample sections are obtained by controlled abrasion of the specimen against emery paper under liquid nitrogen. *The work described was performed while this author was on sabbatical leave at the University of Illinois.
G-2 THE KEY ROLE OF THE FINITENESS OF THE PROPAGATION VELOCITY OF COLLECTIVE ADVANCED INTERACTIONS IN LARGE ENERGY FLUCTUATIONS AND RATE PROCESSES IN DENSE SYSTEMS
Y. Khait Solid State Institute, Israel Institute of Technology, Haifa Formation of short-lived energy fluctuations (SLEFs) of some particles in and on solids and other dense matter, up to UQ » U- taking the central role in many phenomena in physics, chemistry, etc. is a collec- tive space-non-uniform very non-stationary non-local phenomena with a memoTy.1'2 The SLEF is caused by advanced short-term collective high- frequency interactions (ASMI) propagating with the finite (e.g., sound) velocity c0 toward the fluctuating particles (F.P.) and transferring to them, from Jhe surroundings, the transferable thermal fluctuation energy UQ » UQ.1'2 The ASMI are absorbed for a short while by F.P. which can participate in observable SLEF-induced rate processes. The relativistic-like 4-dimensional space-tiae SLEF treataent and the SLEF causality conditions and also their connections with large observable effects are discussed.
1. Y. Khait, Inter. J. Heat § Mass Transfer, 16, 1329 (1973); Phys. Stat. Sol. (b), 86_, 409 (1978); Phys. Stat7"Bol. (b), 89, K III (1978). 2. Y. Khait, Proc. 13th IUAP Conf. Statistical Phys,, Adaa Higler, Bristol (1978), p. 722.
G-3 EPR SPECTRUM OF COPPER ION PAIRS IN CaO
J. Barak, A. Raizaan and J.T. Suss Solid State Physics Department, Soreq Nuclear Research Center, Yavne
The electron paraaagnetic resonance (EPR) spectrua of nonidentical Cu ion pairs incorporated by diffusion into single crystals of CaO was studied. The fine structure of the spectrua is consistent with an S * 1 state with an isotropic g-factor, g = 2.21, and a zero field splitting D • (702 ± 6) x lO'Va"1. The spectrua is attributed to nonidentical next nearest neighbor [100] Cu pairs. The hyperfine structure for pairs with an axis parallel to the Magnetic field con- sists of ten equally separated lines (for each isotope) with relative intensities of 1:1:2:2:2:2:2:2:1:1, while for pairs with an axis perpendicular to the Magnetic field it consists of four linss (for each isotope) of equal intensities and separations. The hyperfine structure can be fitted to the haniltonian H = — 63 63 with S = 1, Ii = I2 = 3/2, Ai,, = 2, A2|, •• 63 1 63 Ai, = 21 x Kr^uT and AO, = 0. - *3 -
G-4 AN EPR STUDY OF DEFECTS IN DILUTE Au:Er ALLOYS*
A. Raizman and J.T. Suss Solid State Physics D<- .tment, Soreq Nuclear Research Center, Yavne D.N. Seidaan Department of Materials Science and Engineering, Cornell University, Ithaca, NY D. Shaltiel and V. Zevin The Racah Institute of Physics, The Hebrew University, Jerusalem R. Orbach Department of Physics, University of California, Los Angeles, Calif. The electron paramagnetic resonance (EPR) spectrun of Er was used as a probe to study the behaviour of defects produced by cold working (rolling and polishing) of dilute Au:Er alloys. It is known that the predominant defects produced by cold working of aetals are dislocat- ions. Heating of the alloys produces the following changes in the characteristic features of the EPR spectrum: a decrease in the intensity, a decrease in the linewidth and an increase in the A/B ratio (the asymmetry parameter of the first derivative of the absorpt- ion line). The Korringa relaxation rate did not change throughout our experiments. Our results indicate, that the EPR technique is a promis- ing tool for the study of defects in metals. * This research was supported by a grant from the United States- Israel Binational Science Foundation (8SF), Jerusalem, Israel.
'(',{ QUADRUPOLE INTERACTION OF V IN ZrV2H p' M. Peretz and J. Barak -; Soreq Nuclear Research Center, Yavne )'•". J. Shinar | The Hebrew University, Jerusalem
The NMR spectra of V in ZrV2H has been measured as a function of X. Using the Quadrupole echo technique spectra with well resolved Quadrupole Satellites have been obtained. The Quadrupole interaction of V was found to depend on hydrogen concentration, with v » 320 KHz for x = 4, and v = 17 KHz for x = 0. H H Calculation of eqQ assuming a screened point charge have been performed and compared to the experimental results. -h A correlation between (T,T) which is proportional to the conduc- tion electrons density of states and eqQ - has been found. G-6 NEUTRON DIFFRACTION STUDY OF HYDROGEN IN o-TITANIUM
H. Pinto,a C. Korn,fc S. Goren,6 and H. Shakeda* "^Nuclear Research Center, Negev ^Department of Physics, Ben-Gurion University of the Negev, Beer Sheva
The lattice site of hydrogen dissolved in o C.HCP) phase of titanium, has been determined by neutron diffraction. The structure factors and line intensities were calculated for o-TiH^ (0 < x < 0.1) with the hydrogen randomly distributed over the (i) tetrahedral positions, (ii) octahedral positions. By comparing observed with calculated relative line inten- sities for a polycrystalline sample of TiHx (x ~ 0.04), it was found that the hydrogen occupies the tetrahedral site of the HCP lattice. The hydrogen was then driven out by heating up the sample. The changes in the observed line intensities were compared with the changes calculated by assuming that the sample had been completely dehydrogenized. It was found again that the hydrogen had occupied the tetrahedral site. Hence, a-TiHx is isostructural with ot-ZrH, where it had been reported that hydrogen occupies the tetrahedral site.
G-7 NMR STUDIES OF THE DIFFUSION OF Li IN GLASSES
S. Goren, C. Korn and V. Volterra Department of Physics, Ben-Gurion University of the Negev, Beer Sheva
The spin lattice relaxation times in the laboratory frame, Tj, of Li in SiO2 and SiO2 (5% Al) has been measured in the temperature range of 100-850 K and at frequencies of 14.5 and 22.5 MHz. In addition, the spin lattice relaxation in the rotating frame, T, , has been measured for these samples in the temperature range of 35&!-850 K with an r-f field of 25 gauss. The results are interpreted in terms of diffusion with a distribution of correlation times, and correlated with data known from dielectric measurements.
* Research supported by Binational Science Foundation Grant No. 943 • MS -
/ THE ANOMALOUS LOW-T PROPERTIES OF GLASSES AND CN' DEFECTS IN ALKALI HALIDES i • • i t Baruch Fischer and Michael W. Klein* ;; Department of Physics, Bar-1 Ian University, Ramat-Gan ir ' We have shown that a system of CN~ molecules dissolved in alkali •;S halides (NaCl, KC1), possesses most of the low temperature properties y of glasses. Thus by using the CN~ system as a model for glasses, we are :Jv able to explain the linear T-dependence of the specific heat, the T2- y • dependence of the thermal conductivity and other thermal properties of '• glasses, as well as the similar behavior of these properties for differ- £, ent amorphous systems. h- * !' Present address: Dept. of Physics and Materials Research Lab., V University of Illinois, Urbana, Illinois 61801, USA
G-9 i EFFECTS OF X-IRRADIATION ON RbMgFj CRYSTALS : B. Trieman and N. Kristianpoller - Department of Physics and Astronomy, Tel Aviv University, Ramat-Aviv 5-J ! Single RbMgF3 crystals which are known to have the hexagonal BaTiO3 ; type structure1, were X-irradiated at various temperatures from 77°K to 600°K. Effects of X-irradiation were investigated by optical •' methods. A strong X-luminescence appeared during the irradiation. ] Emission spectra showed main bands at 305, 335, 410, 430 and 560 nm. -j The temperature dependence of the emission was investigated. Prolonged I X-irradiation resulted also in the production of point defects and • the appearance of characteristic absorption bands. Absorption spectra were measured from the VUV to the IR. The pure untreated crystal is ' transparent from about 120 nm to 10|i* Additional absorption appearing after X-irradiation at 330 nm, 315 nm and 280 nm is attributed to ' VK, F and F2 centers respectively. Thermal stability of the radiat- ! ion induced defects was also investigated. Correlation was found j between the spectral composition of the TL, emitted during thermal 1 annealing of the radiation induced defects and the mentioned bands '\ of the X-luminescence. Our results are in agreement with those previ- ] ously obtained for electron-irradiated crystals2 and conclusions are ;j drawn regarding the processes responsible for the radiation damage. • i 1. M.W. Shafer and T.R. McGuire, J. Phys. Chem. Solids, 30, 1989 (1969). — i 2. N. Koumvakalis and W.A. Sibley, Phys, Rev. B 13, 4509 (1976). '\ MONDAY MORNING, 2 APRIL 1979 LIBRARY BUILDING 9:30 (ROOM 325) H. PHASE TRANSITIONS R. Thieberger, Ben-Gurion University, Beer-Sheva - Nuclear Research Center, - Presiding
H-l A POSSIBLE NEW PHASE IN CHOLESTERIC LIQUID CRYSTALS* R.M. Hornreich and S. Shtriknan Department of Electronics, Weizmann Institute of Science, Rehovot Using Landau's theory, we have investigated the phase transition which occurs in cholesteric-type liquid crystals when the unifom isotropic phase becomes thermodynamically unstable. In addition to the well- known cholesteric phase (phase I), two other states are possible, characterized by hexagonal (phase II) and body-centered cubic (phase III) symmetry, respectively. Within the framework of Landau theory, we find that the ordered phase with lowest free energy is either state I or III, with the latter predicted to occur when the coefficient of the cubic invariant in the free energy density is sufficiently large in comparison with that of the Lifshitz invariant (i.e., the term bilinear in the order parameter and its spatial derivitive responsible for chirality in cholesterics). Our results thus differ from.those of Brazovskii and Dmitriev.1 We believe that this theoretically predicted cubic phase may be relevant to understanding the so-called blue phase2, which is known to occur in certain cholesterics upon cooling from the isotropic state. Experimentally, this phase is known to be optically isotropic, but nothing is known regarding its structure. Possible experiments to clarify the nature of this little understood phase will be discussed. * Supported in part by a grant from the U.S.-Israel Binational Science Foundation (BSF), Jerusalem, Israel. 1. S.A. Brazovskii and S.G. Dmitriev, Sov. Phys.-JETP 42, 497 (1976). 2. P.J. Collings and J.R. McCall, J. Chem. Phys. 69, 3371 (1978) and references cited therein.
I V •' - *7 -
y H-2 PHASE TRANSITIONS IN DNA, THEIR KINETICS, AND DNA SEQUENCING M. Ya. Azbel < , Department of Physics and Astronomy, Tel Aviv University, Ramat Aviv DNA consists of two bounded strands. Their unbinding is denoted as helix-coil transition and is described by the one-dimensional two- component Ising model with the long-range interaction.1 The theory of DNA coiling is constructed. It is proved the coiling may be a phase transition of the nature, strongly depending on the component sequence. The theory allows one to obtain certain information about the DNA se- quence from experimental data. The agreement between theory and experi- ments with natural DNAs is surprisingly good. The kinetics of the un- binding of DNA strands is described by the inhomogeneous Glauber-Ising model.' The relaxation to the equilibrium state is the "step-by-step" one rather continuous, described by the set of certain discrete relaxa- tion times. In general, when the degeneracy of the lower energy level exceeds the degeneracy of the higher energy level, this implies the phase transi- tion, related to the change in the ground state of the effective Hamiltonian (which is in fact a free energy for a certain nonequilibrium state) of the system. Certain examples of such one- and two-component 1, 2 and 3-dimensional systems are investigated. 1. R.W. Kartell and E.N. Montroll, Adv. Chen. Phys. 22, 129 (1972). 2. K. Binder et al., Phys. Rev. B12, 5261 (1975).
H-5 DILUTE SPIN GLASSES AT ZERO TEWERATURE* Amnon Aharony Department of Physics and Astronomy, Tel-Aviv University, Ramat-Aviv The zero temperature phase diagram of a random Ising system with the nearest-neighbor exchange coupling having probabilities p, q and r of being positive, negative or zero exhibits paramagnetic (PM), ferromagnetic (FM), antiferroaagnetic (AFM) and spin-glass (SG) phases (see figure). The s-state Potts model describes the usual percolation point P when s + 1, The limit s -»• 1/2 describes the spin glass percolation point G and an Ising model describes the point I if no frustrated plaquettes are included.1»z Otherwise, these models give lower bounds for G and I. In addition, prelim- inary numerical calculations of the phase diagram will be discussed.3 Supported by a grant from the U.S.-Israel Binational Science Foundation (BSF), Jerusalem. 1. A. Aharony, J. Phys. CU, L4S7 U978). 2. A. Aharony and P. Pfeuty, J, Phys. C12_, L125 (1979). 3. A. Aharony and K. Binder, to be published.
H-4 HIGH TEMPERATURE SERIES FOR AN ISING MODEL IN A RANDOM FIELD* Yonathan Shapir and Aanon Aharony Department of Physics and Astronomy, Tel-Aviv University, Ramat-Aviv A random magnetic field applied on a ferromagnetic system induces a new critical behaviour.1 Long range order is destroyed for d $ 4 when the or.'er parameter is continuous and for d j 2 in the Ising case. Mean field theory results are correct above dc • 6, and d « 3 is probably out of the radii of convergence of the expansion in e * 6 - d. We therefore study the critical behaviour of 3D Ising model in a random quenched field using high temperature series. For an uncorrelated Gaussian distribution of the fields, with zero mean and variance a, the coefficients are polynomials in A * c2/J2, where J is the nearest neighbour exchange. From the series for the susceptibility on an f.c.c. lattice we confira that T« decreases and Y increases as function of X, but we cannot yet distinguish a new critical behaviour. The series for dx/dA and (dx/dA)/x in the limit A •*• 0 behave regularly and the numerical result for the crossover exponent + confirms the earlier prediction derived from RG recursion relations2, i.e., • • Y. 1. Y. Imry and S.K. Ma, Phys. Rev. Lett. 35, 1399 (1975). 2. A. Aharony, Phys. Rev. Bl£, 3318, 3328 (1978). Supported by a grant from the U.S.-Israel Binational Science Foundation (BSF), Jerusalem.
H-5 RANDOM ANTIFERROMAGNET IN A UNIFORM FIELD: A REALIZATION OF A RANDOM FIELD* Shauel Fishman and Amnon Aharony Department of Physics and Astronomy, Tel Aviv University, Ramat-Aviv It is shown that a quenched randomness in the exchange coefficients of a uniaxial antiferromsgnet (AFM) in a uniform magnetic field along the anisotropy axis generates critical properties identical to those of an Ising ferromagnet in a random field. This is the first reali- zation of a random field in Mhich the strength of the field can be experimentally controlled. In particular, the following predictions are derived: a) The critical exponents for the antiferromagnetic transition in finite uniform field will be considerably different than those of a pure AFM. (Deviations from mean field theory start at six dimensions2). b) Even at zero field, the susceptibility of the random AFM will exhibit a sharper cusp compared to the pure AFM. c) The tricritical and bicritical points resulting from strong fields will also exhibit new critical properties.2 Supported by a grant from the U,S.-Israel Binational Science Foundation (BSF), Jerusalem. 1. A. Aharony, Y, Imry and S.K. Ma, Phys. Rev. Lett, 37, 1364 (1976)j A.P. Young, J. Phys. CIO, L2S7 (1977). 2. A. Aharony, Phys. Rev. B18, 3318, 3328 (1978). 1 Ihi MULTICRITICAL POINTS GENERATED BY SYMMETRY BREAKING OF THE THREE-STATE POTTS MODEL* Daniel Blankschtein and Amnon Aharony Department of Physics and Astronomy, Tel Aviv University, Ramat-Aviv Adding a uniaxial symmetry breaking term g(sf - s£) and a magnetic field term - hsj to the continuous version of the three-state Potts model, characterized by the Potts term w(sf - 3sis§), generates critical (CP) and tricritical (TCP) points. A typical cut (with I - so - i [ constant g < 0) of the calculated T-g-h phase diagram is shown in • the figure. Universal ratios characterizing the multicritical points : are obtained using mean field theory and renormalization group ; analysis. The results are used to predict the locations of these multicritical points in SrTiO stressed along [1+6, 1+6, 1-26].x I !* 3 J"
Ii'
:. Supported by a grant from the U.S.-Israel Binational Science )• Foundation (BSF), Jerusalem. i 1. A. Aharony, K.A. MUller and t». Berlinger, Phys. Rev. Lett. 38, f 33 (1977). t ! ZERO TEMPERATURE BEHAVIOUR OF A FERROMAGNET IN A RANDOM SKEW FIELD • Serge Gala* and Amnon Aharony Department of Physics and Astronomy, Tel-Aviv University, Ramat-Aviv The critical behaviour of a uniaxially anisotropic ferromagnet in a random field, exhibiting the new multicritical point studied earlier for the field parallel to the anisotropy axis only1, is now general- ized adding a perpendicular field component. The different kinds of global phase diagrams, for characteristic ranges of anisotropies as functions of the strengths of the two field components, at T = 0, exhibited in the figure, are presented. On the basis of this work and of the previous one^, the full phase diagram in the four dimensional space-strength of the parallel field H(| -strength of the perpendicular field Hj_-temperature T - anisotropy a - will be constructed. - 51
AS: O. t,
CLIO. I
Supported by a grant from the U.S.-Israel Binational Science Foundation (BSF), Jerusalem 1. Serge Galam and Amnon Aharony, to be published, H-8 ELECTRONS IN RANDOM POTENTIALS: A RENORMALIZATION GROUP APPROACH* Reli Rosman and Amnon Aharony Department of Physics and Astronomy, Tel Aviv University, Ramat-Aviv The renormalization Group (RG) technique is applied to the problem of electrons in a random potential. It is shown, that if proper care is I- \ taken of the imaginary part of the self-energy of the averaged Green's function, In G~1Cp,E), a stable fixed point can be reached. Nearly free electrons are used as a basis for the perturbation series. After some resumaation, recursion relations are derived, containing the dressed Green's function G(p,E) rather than the bare one. When the RG analysis is started with a complex propagator, it results in the flow of the interaction parameter, v, and the energy, E, through 1 k complex values. Provided that lim G~ (p lE) = 0, the flow ends at the p+0 E4Ec fixed point of the n * 0 components Ginzburg-Landau model.1 i 1 - 52 -
The results are applied to calculate the "critical indices" which characterize the behavior of the density of states and the d.c. - and a.c. - conductivities near the mobility edge, E . * Supported by a grant from the U.S.-Israel Binational Science Foundation (BSF), Jerusalem 1. S.K. Ma, Modern Theory of Critical Phenomena (Benjamin, Reading, Mass., 1976), pp. 411-414. H-9 THE INTERCHAIN INTERACTION PARAMETERS AND THEIR INFLUENCE ON THE 53K and 48K PHASE TRANSITIONS IN TTF-TCNQ Claudio Hartzstein, Vilen Zevin and Meir Weger The Racah Institute of Physics, The Hebrew University of Jerusalem, Jerusalem The parameters of the Coulomb interaction between Charge Density Waves (CDNj on nearest neighbour chains and on next nearest neighbour chains and the CDW-Libron interaction are.calculated and compared for various charge distributions over the TTF and TCNQ molecules. The importance of the temperature dependence of the CDW-Libron para- meters in the determination of the renormalization of the one chain transition temperature is emphasized. The influence of this transition temperature renormalization on the specific heat jump at the Peierls transition is studied and quantitative agreement is shown. H-10 LANDAU-GINZBURG MODEL FOR ROUGHENING PHASE TRANSITIONS M. Kerszberg and D. Mukamel Department of Electronics, The Keiznann Institute of Science, Rehovot It has been argued1 that, under certain conditions, the surface of a crystal may undergo a change in structure known as the roughening transition. At the transition temperature TR the width of the inter- face profile diverges. The existence of Tg < Tc has been conjec- tured* on the basis of low-temperature series expansions for the Ising model, and proved rigorously3 for a particular type of solid-on-solid (SOS) model. The SOS model neglects, however, configurations which might be important for crystal growth. We have introduced a Landau- Ginzburg model taking these configurations into account, and used renormalization-group methods to study its critical behavior. The critical dimensionality, above which the behavior is classical, is found to be dc = 3. In d = 3 dimensions, the critical behavior is classical with logarithmic corrections. In particular, we find that the specific heat should diverge as C ~ (-I^T-TRI)1'9. The behavior is very different from the one expected from analyses of the various SOS models.1* The relation between these models and the Landau-Ginzburg model is discussed. - 53 -
1. W.K. Burton, N. Cabrera and F.C. Franck, Phil. Trans. Roy. Soc. A243, 299 (1951). 2. J.D. Weeks, G.H. Gilmer and H.J. Leamy, Phys. Rev. Lett. 31^, 549 (1973). 3. H. Van Beijeren, Phys. Rev. Lett. 38, 993 (1977)• 4. See e.g., H. MUller-Krumbhaar, in Crystal Growth and Materials, Eds., E. Kaldis and H.J. Scheel (North Holland, 1977).
H-ll INFLUENCE OF QUENCHED IMPURITIES ON FIRST-ORDER PHASE TRANSITIONS Y. Imry Department of Physics and Astronomy, Tel-Aviv University, Ramat Aviv M. Wortis Department of Physics, University of Illinois, Urbana-Champaign Microscopic, random, quenched impurities may or may not produce round- ing of a first-order phase transition. We derive1 a criterion for the v. appearance of rounding due to fluctuations in the thermodynamic phase 'if. of small clusters within the sample. Such fluctuations occur when the free-energy lowering due to taking advantage of local fluctuations in impurity density more than offsets thi free-energy cost of the interface produced. The argument also predicts the spatial scale of such phase fluctuations, when they occur. In some situations this scale is just the coherence length £; in others, the inhomogeneity develops over "domains", which may be ouch larger than £. Near a second-order transition our criterion reduces to the one due to A.B. Harris,2 We specifically discuss what happens when a first-order transition becomes second-order as an external parameter is varied.
1. Y. Imry and M. Wortis, Phys. Rev. B (in press). 2. A.B. Harris, J. Phys. C7, 1671 (1974). - 54 - H-12 SURFACE ACOUSTIC WAVE PROPAGATION NEAR THE SPIN REORIENTATION PHASE TRANSITION OF ErFeO3 G. Gorodetsky and S. Shaft Department of Physics, Ben Gurion University of the Negev, Beer Sheva Measurements of surface acoustic wave CSAW) propagation were carried out near the spin reorientation region of ErFeO3> Velocity shifts due to a coupling of the SAW longitudinal strain conponent and the antiferro- magnetic spins were observed at the lower and upper transition tempera- tures, Tj and Tu respectively, of the spin reorientation. It was found that AT = Tu - T and the relative velocity change, as measured by the SAW, are slightly* smaller than those observed in the bulk wave experiment. Theoretical calculations show that the shift in the transi- tion temperatures may be attributed to this effect of the surface boundary on the magnetic anisotropy. It was also found that an applied magnetic field shifts and suppresses the transitions. The results observed are similar to those of the Bulk wave experiment.1 1. G. Gorodetsky, B. Luthi and T.J. Moran, Inter. J. Mag. 1_, 295 (1971). - 55
MONDAY MORNING, 2 APRIL 1979 LIBRARY BUILDING 9:30 (Room 323) I. CONDENSED MATTER - GENERAL S. Shtrikman, The Hfeizmann Institute of Science - Presiding 1-1 EQUATIONS OF STATE OF FLUIDS AND THE VIRIAL EXPANSION C30 min) M. Luban, Bar-IIan University, Ramat-Gan 1-2
THE PUZZLE OF MAGNETISM IN Fe2TiO5 E. Gurewitz , H. Pinto , M. Melamud , U. Atzmony , H. Shaked ' , G. Gorodetzky , E. Hermone, R.M. Hornreich0, S. Shtrikman0 and B. Wanklynd Nuclear Research Center, Negev Ben-Gurion University of the Negev, Beer Sheva cWeizmann Institute of Science, Rehovot university of Oxford, Clarendon Laboratory The crystallographic structure of Fe2TiOs was reported1 as ortho- rhombic, space group-Cmcm, with Fe3+ and Ti1|+ ions at the 8f and 4c sites, respectively. Mossbauer spectroscopy at 4K and SOK, revealed absorption lines due to hyperfine splitting. We have studied this compound with several techniques. Magnetic susceptibility measurements on powder samples exhibited a weak, antiferromagnetic-like anomaly at ~ S5K. MSssbauer effect measurements confirmed this trans- ition temperature. Sound velocity and specific heat measurements did not exhibit any anomaly at 4.2 < T < 300K. Neutron diffraction of a powder sanple at 4.2K has not showr any evidence for an ordered magnetic structure. In magnetic susceptibility studies of single crystals we have observed an antiferromagnetic-like anomaly along the <| direction and a smooth paramagnetic-like behaviour along the 1 and b directions. Due to talks of spin glass transition, we have analysed the room temperature neutron diffraction pattern and found that Fe and Ti are randomly distributed on the 8f and 4c sites in disagreement with the previously reported structure.1 This result may make a spin glass possible. MOssbauer effect measurements on single crystals are being carried out in a search for a magnetic axis.
1. R.W.G. Wyckoff, Crys. Str., Vol. 3, 2nd Ed., John Wiley, New York, 1964, pp. 247-258. 2. S. Muranaka, T. Shinjo, Y. Bando and T. Takada, J, Phys. Sci. Japan 30 (1971) 890. 56 -
1-3
STATIC AND DYNAMIC PYROELECTRIC COEFFICIENTS OF POLYVINYLIDENE FLUORIDE OVER A 90-370 K TEWERATURE RANGE
Sidney B. Lang Department of Chemical Engineering, Ben-Gurion University of the Negev, Beer Sheva
The static and the real and imaginary components of the dynamic pyro- electric coefficients were measured on a film of polyvinylidene fluoride CPVFj) over a 90-370 K temperature range. These are the first pyroelectric coefficients of PVF2 measured at extremely low tempera- tures, and the first complex dynamic pyroelectric coefficients reported in the literature. The static coefficient was saall and constant below the glass transition temperature Tg, but increased very rapidly above Tg. The real dynamic coefficient was in good qualitative agreement with tne static value. The imaginary dynamic coefficient had a complicated frequency dependence which can be used to examine elastic and piezo- electric relaxation processes.
1-4 STUDY OF SQUINT IN NEMATICS
S.I. Ben-Abraham Department of Physics, Ben Gurion University, Beer Sheva and Department of Physics, Kent State University, Kent E. Gelerinter, Department of Physics and Liquid Crystal Institute, Kent State University, Kent
We discuss some theoretical and experimental aspects of squint, a novel, intrinsically nonlinear feature of flow patterns in nematics,1 The curvature of a roll flow pattern can be approximately described by the equation
1. S.I. Ben-Abraham, J. Physique (in press). - 57 -
1-5 EFFECTS IN NEMATICS SUPPRESSED BY THE ONE-CONSTANT. APPROXIMATION S.I. Ben-Abraham Department of Physics, Ben-Gurion University, Beer Sheva and Department of Physics, Kent State University, Kent In the one-constant approximation, all elastic moduli of a nematic are assumed equal, although their differences are, in fact, comparable to their values. Keeping the splay, twist, and bend moduli (kj, k2, k3, respectively) apart, does not significantly complicate the mathematics, tdiile.it reveals some phenomena that crucially depend on 6 • k3 - ki. The most significant part of squint1 is proportional to 6. By changing the boundary conditions from parallel to perpendicular and by controlling the tendency of the nematic to smectic ordering it is possible to vary 6 from very large negative to very large positive values. It is suggested to use this to measure squint in a wide range.
1. S.I. Ben*Abraham and E. Gelerinter, preceding abstract. 1-6 ATTENUATION OF SOUND IN He" AND He3-He" SUPERFLUID MIXTURES i- R. Kleiner, Y. Eckstein, Y. Lahav and J. Landau Department of Physics, Israel Institute of Technology, Haifa Measurements of the attenuation of sound in superfluid He4 are presented. The attenuation was measured at f « 10 MHz, pressures 0-21.1 Atm., and temperatures 30-600 mK. Other measurements had suggested that the dispersion of the phonons becomes convex at pres- sures above 18-19 Atm. The present experiment is very sensitive to the dispersion curve and we find that the dispersion remains concave up to at least 21.1 Atn. Measurements were also taken in nixtures of x « 0.07%, 0.14% and 0.44%. The aim was to study the influence of the He3 excitation on the thermal phonons via the attenuation of acoustical phonons. The attenuation was expected to increase in the mixtures because of additional absorption by the He3 impurities. The attenuation actually decreased. A possible mechanism for this will be presented.
1-7 LOW TEMPERATURE SPECIFIC HEAT OF He3 - He" SOLUTIONS*
Emil Polturak and Ralph Rosenbaw Department of Physics and Astronomy, Tel Aviv University, Ramat-Aviv The specific heat of a 5% He3 in He* solution was measured between 10 and 60 mk. Preliminary analysis of the data yields a specific heat effective mass of 2.45 m3, 2.85 m3 and 3.05 *3 at s.v.p., 10 and 20 atmospheres, respectively C"3 is the mass of a He3 atom).
This research was partially supported by BSF, Jerusalem, Israel and by the ONR through a supply of Helium gas. - 58 -
1-8 HIGH-TEMPERATURE THERMOELECTRIC POUTER OF SOLID AND LIQUID ALKALI METALS M. Danino, M. Kaveh and N. Niser Department of Physics, Bar-Ilan University, Ramat-Gan A calculation is presented of the thermoelectric power Q of the alkali metals at high temperatures, both for the solid phase and for the liquid phase. In addition to the value of Q itself, other quantities of interest are the change in Q upon melting and the pressure dependence of Q. Uniformly good agreement with experiment is obtained. The calculation is based on an empirical form factor and the experimental structure factors for both the solid and liquid phases. A simple procedure is introduced, based on a phase-shift analysis, for obtaining the energy dependence of the form factor. This avoids entirely the difficult calculation of the energy dependence of the matrix elements of the screened electron-ion nonlocal pseudopotential operator. One makes the traditional separation of Q * Qc5 • Qp(3 - 2q + j" r), where QF is a known constant independent of the form factor, q is a positive quantity dependent on the form factor and r arises from the energy dependence of the form factor. The term i r, commonly ignored because of calculational difficulties, is shown to be important in almost all cases. In particular, the inclusion of the term 1 r explains the 2 previously puzzling experimental result £exBt>3 for potassium. More- over, we also explain the change in sign " of Q upon melting for cesium. 1-9 ELECTRON MOMENTUM DISTRIBUTION IN MAGNESIUM HYDRIDE
M. Heilper, I. Gertner, A.C. Tanner, J. Felsteiner and R. Opher Department of Physics, Israel Institute of Technology, Haifa K.-F. Berggren Department of Physics and Measurement Technology, Linktfping University, Linkgping, Sweden The electron momentum distribution of polycrystalline Magnesium Hydride (MgH2) has been investigated by measuring its Compton profile, using the 59.54-keV gamma rays froa a 300-mCi 2 The Acr(TCNQ)2 [acridinium-tetracyanoquinodimenthane] salt is a pseudo one-dimensional (Id) charge transfer compound, with metallic like conductivity (200 C"1 cm"1) at ambient temperature. We report the temperature dependence (Fig- 1) and the frequency dependence (Fig. 2) of the proton spin-lattice relaxation tines in both Acr(TCNQ)2 [TJ and Acr(TCNQ-Dlf)2 [Iw] in which the TCNQ protons were replaced bydeuterons. Analysis of the results shows that in the range above ~ 100K the source of the nuclear relaxation is provided by the TCNQ electronic spins and that the acridinium protons relax via dipolar cross coupling with the TCNQ electrons. This is consistent with (nearly) complete charge transfer which leaves the acridinium chain with no net spin while the TCNQ chain is the metallic one. The observed frequency dependence (Fig. 2) gives an indication for a Id diffusive behavior of the spin fluctuations in the metallic TCNQ chains. This diffusive behavior is observed at proton frequencies down to 7 MHz which gives an upper bound for the interchain hopping 10 1 rate of l/xc « 3 x 10 sec" . As the temperature is reduced below ~ 100K an additional relaxation source via the acridinium chain becomes apparent and at 1.5K the two relaxation sources are of the same magnitude as can be seen from Fig. 1. We believe that this additional source originates from localized electrons on the acridinium 1 chain due to some back-charge transfer or external impurities. 1-11 THE SHOTTKY HEAT CAPACITY OF THE VAN-VLECK PARAMAGNETS IN THE PRESENCE OF THE EXCHANGE INTERACTION I. Galili and V. Zevin The Racah Institute of Physics, The Hebrew University of Jerusalem, Jerusalem* The standard basis operators1 Green function technique is used to calculate the contributions to the specific heat from the exchange interacting Rare Earth ions in the Van-Vleck paramagnets. In the case of the singlet-singlet system the general expression for the Shottky heat capacity which is valid up to the first order in the expansion over the reciprocal density of particles is obtained. The numerical . calculations for the RK1CY type of the exchange in the RPA approximation shows considerable influence of the exchange in the paramagnetic phase on the position of the Shottky peak. The spectroscopic data on the crystalline field parameters should be corrected in the case when the exchange coupling constant J(q-O) is comparable with single ion crystal field splitting. 1. D.H.-Y. Yang and Y.-L. Hang, Phys. Rev. BIO, 4714 (1974), 'Supported by the U.S.-Israel Binational Science Foundation, - 60 - 1-12 HYDRODYNAMICS OF WEAKLY INTERACTING VORTICES M. Ya. Azbel Department of Physics and Astronomy, Tel-Aviv University, Ramat-Aviv The hydrodynamics of a stationary planar flow of an incompressible Stokes fluid is investigated, and a general form of the total integral is presented. It is applied to the system of far-off vortex dipoles, where explicit formulas are obtained, A set of such dipoles provides an ascensional force. When the number of vortices goes to infinity, this force nay remain finite though the power, which creates it, goes to zero. 1-13 A NEW THEORY OF SIMPLE CLASSICAL FLUIDS: UNIVERSALITY IN THE SHORT RANGE STRUCTURE Yaakov Rosenfeld Nuclear Research Center, Negev N.W. Ashcroft Laboratory of Atomic and Solid State Physics, Cornel University, Ithaca, N.Y. A theory of simple classical fluids is presented1 in which both the static structure (on the pair level) and the thermodynamics, of all systems describable by spheric lly symmetric pair potentials (e.g., from the hard-spheres to the Coulomb plasma), can be calculated by a unified approach, which yields an accuracy comparable with that of the best computer simulation studies. The theory is based on the diagramatic expansion of the pair distribution function that leads to a modified HNC equation, the key point being the observation that the sum of all elementary graphs can be chosen from a universal set, appropriate to any one simple potential. 1. Y. Rosenfeld and N.W. Ashcroft, submitted to Phys, Rev. Letters and to Phys. Re-. 1-14 THE ANOMALOUS LOW-T PROPERTIES OF GLASSES AND CN" DEFECTS IN ALKALI HALIDES B. Fischer and M.W. Klein*, Department of Physics, Bar-Ilan University, Ramat-Gan We show that CN~ molecules dissolved in alkali halides (NaCl, KC1) crystals possess a number of low temperature properties similar to glasses. In particular we find a low temperature region in which the specific heat is linear in T and the thermal conductivity is proportional to T2. It is suggested that the understanding of glasses may be advanced by studying the properties of interacting strain dipoles in alkali halides. * Present .address: Department of Physics and Materials Research Laboratory, University of Illinois, Irbana, Illinois 61801, USA - 61 - MONDAY MORNING, 2 APRIL 1979 LIBRARY BUILDING 9:30 (Room 309) J. NUCLEAR PHYSICS K. Bleuler, University of Bonn - Presiding J-l RECENT DEVELOPMENTS IN MESON-NUCLEUS INTERACTIONS (30 min) Y. Eisenberg, Tel-Aviv University, Ramat-Aviv J-2 NEW RESULTS FOR PIONIC ATOMS AND APPLICATIONS IN NUCLEAR PHYSICS (30 Mill) E. Friedman, The Hebrew University, Jerusalem J-3 MEASUREMENT OF Tn/Tf FROM PHOTOFISSION OF 23SU WITH NEUTRON CAPTURE Y RAYS A. Wolf Nuclear Research Center, Negev An experimental technique is presented by which rn/Tf from photofission of 23°U can be determined froa a combination of activation and direct fission yield measurements. The activity of 237U after irradiation of an uranium target in the photon beam was Measured with a Ge(Li) detector. The fission yield was determined with, a solid state detector. The photon beam was obtained from thermal neutron capture on iron. The main advan- tage of this technique is that no direct neutron measurements are necessary and therefore rather large errors due to the determination of efficiency of neutron detectors and subtraction of fission neutrons are eliminated. The result obtained is rn/r£ « 3.0 ± 0,3, at an average excitation energy of 7.8 MeV, It is estimated that the same technique may be employed for photon beam 5 intensities of about 10 photons/a^/sec. The value of rn/rf is compared with the results of other authors1 •* and with, theoretical calculations.3 1. O.Y. Mafra et al., Nucl. Phys. A186, 110 (1972). 2. P.A. Dickey and P. Axel, Phys. Rev, Letters 35, 501 (1975). 3. A. Gavron et al., Phys. lev. Letters 38, 1457 (1977). - 62 - J-4 E2-E1 INTERFERENCE FROM ANGULAR DISTRIBUTIONS OF PHOTONEUTRONS FROM LEAD ISOTOPES Y. Birenbaum, Z. Berant, R. Moreh and A. Wolf Nuclear Research Center, Negev The reactions 206,207,208p|, (y>n) were studied using y rays with energies 7-11.4 NeV obtained by thermal neutron capture on chromium and nickel. The neutron spectrum was Measured with a high resolution 3He spectrometer. Angular distributions of neutron groups leading to specific final states were measured and found to be asymmetric around 90s. This asymmetry is probably due to E2-E1 interference, and can be explained by a direct-semidirect Model1'2, in which the reaction is considered to proceed through intermediate giant dipole and quadrupole states. The results are compared with detailed theoretical calculations2 which assume the existence of a giant E2 isoscalar resonance in lead at 10.5 NeV. 1. G.E. Brown, Nucl. Phys. 57, 339 (1964). 2. G. Longo, F, Saporetti and R.- Guidotti, Nuovo Cim. 46A, 509 (1978). J-5 MEASUREMENT OF ABSOLUTE YIELDS FROM PHOTOFISSION OF 238U S. Kahaneand A. Wolf Nuclear Research Center, Negev The yields of the various mass chains formed in photofission are usually determined1 by measuring the relative yields of a number of isotopes, and then extra - or interpolating for the other masses. In this work we have measured directly the absolute yield of 135Xe, formed in photo- fission of 238U. The incident y beam was obtained from thermal neutron capture in iron disks placed near the core of the IRR-2 reactor. The fission yield was measured with a solid state detector, and the yield of 135Xe was determined from the activity of the 249.8 keV line after irradiation of an uranium sample in the y beam. The absolute yield of 135Xe was found to be 0.069 ± 0.005, The yields of several other masi chains were obtained relatively to mass 135. The results are discussed in relation to the dependence of the mass distribution on excitation energy, and the existence of fine structure2 around A * 134. 1. H. Thierens et al., Phys. Rev. Cl£, 1058 (1976). 2. J.L. Meason and P.K. Kuroda, Phys. Rev, 142, 691 (1966). - 63 - J-6 ON THE PROPERTIES OF CHARMED TENSOR MESONS V. Privman and P. Singer Department of Physics, Israel Institute of Technology, Haifa After the discovery of charred particles of low spins, tensor (2+) mesons are also expected and it is of interest to consider theiT expected decays and production cross sections in e*e- collisions. The two-body decays have already been considered.1 In this work we calculate the expected widths for the three-body decays Modes T •* Pirn and T •+ Vit» in a scheme of effective Lagrangians. We consider different models for the TW vertex2'3, propose a new one and compare between them. One of our main conclusions is that the three body decays (T •* Virir) play an important role in the decay of non-strange charmed tensor mesons. We consider also the radiative decays T •* Vy and find our new model for the TW vertex to give the most plausible results. We identify the most important decays and discuss their dependence on the mr ses of charmc' tcnsoi mesons. Finally, we calculate the production cross sections of VT and PT pairs in e+e" collisions. The angular distribution in VT production is very sensitive to the fora of the TW vertex. The production of PT and VT pairs nay contribute up to 20% of o(e+e" + hadrons) at energies of 5*6 GeV. 1. J. Randa and A. Donnachie, MC/T/77/8. 2. N. Levy, P. Singer and S, Toaff, Phys. Rev. D13, 2662 (1976); ibidem Dl£, 1403 (1977). 3. B. Renner, Nucl. Phys. B30_, 634 C1971). V THE COMPTON PROFILE DEPENDENCE ON D.A. Owen Department of Physics, Ben-Gurion University of the Negev, Beer Sheva The Coapton cross section for bound electrons was recently obtained by Owen.1 That work, based on q.ed is extended and an expression for the Coapton profile is derived froa it.2 Froa it the profiles for a hydrogen- like atoa is calculated with and without binding and bff-aass shell' correction (for both s- and p- electrons). It is found that the penalty for ignoring these corrections for s-electrons is to induce an artificial infrared divergence in the calculated profile rendering thea useless, thus these corrections must be included in the calculated profiles. 1. D.A. Owen, Phys. Rev. A16, 1594 0977). 2. D.A. Owen, Phys. Letters 69A, 177 (1978), - 64 - J-8 EXCITED ROTATIONAL BANDS IN 72Ge AND 74Ge S. Mordechai Department of Physics, Ben Gurion University of the Negev, Beer Sheva and University of Pennsylvania, Phila., Pa. H.T. Fortune and S. Lafrance Department of Physics, University of Pennsylvania, Phila., Pa. Several discontinuities observed recently in the structure of the low lying states of nuclei in the mass range A = 70 ~ 80 a as well as theoretical calculations2 have been interpreted as indicating that nuclei in this region undergo a shape transition fro* oblate to prolate deformation with increasing the neutron number. We have studied the (t,p) reaction on all the stable Ge isotopes at a bombarding energy of 15 MeV.3'1* The outgoing protons were measured in the angular range 3.75#-86.25* in 7.5* steps, using the University of Pennsylvania multi- angle spectrograph. Evidence is found for the possible existence of three excited rotational bands in 7ZGe and 7HGe. The proposed bands are based on the excited 0+ states at 1.913 and 2.164 MeV in 74Ge and the 0+ state at 0.688 MeV in 72Ge. The J* of the states and the energy spacings are proper for k • 0 rotational bands. The (t,p) and (p,t) cross sections and the anomalous L « 0 shapes of the 0* members give further support for this structure. 1. M.N. Vergnes, G. Rotbard, F, Guilbant, D. Ardouin, C. Lebrun, E.R. Flynn, D.L. Hanson and S.D. Orbesen, Phys. Lett, 72B, 447 (1978). 2. K. Kumar, J. Phys. G4, 849 (1978). 3. S. Lafrance, S. Mordechai, H.T. Fortune and R. Middleton, Nucl. Phys. A307. 52 (1978). 4. S. Mordechai, H.T. Fortune and S. Lafrance, to be published. - 65 - J-9 THE ORIENTATION OF NITROGEN ADSORBED ON ORIENTED GRAPHITE USING NUCLEAR RESONANCE PHOTON SCATTERING 0. Shahal, R. Moreh Nuclear Research Center, Negev Resonance scattering of 6.324 MeV photons from 15N has been used to investigate the orientation of nitrogen molecules adsorbed on oriented graphite. Scans were Bade at coverage between submonolayer region up to above complete monolayer at 78°K, The maximum orientation of the nitrogen is achieved when the monolayer is completed, In that case the molecules are parallel to the basal plane of the graphite. The vibration energy of the nitrogen atoms parallel and perpendicular to this plane were deduced. Recently some investigations were performed-1 •2 with gas N2 adsorbed on partially oriented graphite foils known commercially as Grafoil*. The nitrogen nolecule is linear, with the two atoms vibrating along the line joining then. This vibration contributed a dominant part of the atomic velocity, due to the Zero-point vibration of the N atom along the molec- ular axis. So the N atom has an anisotropic motion along the molecular axis. The nuclear resonance scattering cross section is strongly dependent on the anisotropic motion.3 This anisotropic motion causes a different Doppler broadening to the nuclear resonance level relative to the incident beam. *Grafoil is the trade name of a product marketed by the Union Carbide Corp., 270 Park Ave., New York, N.Y. 1. J.K. Kjems, L. Passell, H. Taub and J.G. Dash, Phys. Rev. Lett. 32, 724 (1974). ~ 2. J.K. Kjems, L. Passell, H, Taub, J.G. Dash and A,D. Nevaco, Phys. Rev. B13, 1446 (1974). 3. 0. Shahal, R. Moreh, Phys. Rev. Lett. 40, 1714 (1978), I 66 - MONDAY MORNING, 2 APRIL 1979 LIBRARY BUILDING 9:30 (Room 308) K. PLASMA AND FUSION S. Kuperman, Tel-Aviv University - Presiding K-l EXPERIMENTAL STUDY OF ELECTRONIC PLASMA IN SOLIDS VIA THE EXPLOSION OF FAST MOLECULAR IONS C30 min) Z. Vager, The Weizmann Institute of Science, Rehovot K-2 A MODEL OF COMPLETE STEADY STATE IN HOT HOMOGENEOUS PLASMA David Salzmann Soreq Nuclear Research Center, Yavne A model of Complete-Steady-State (.CSS) in homogeneous optically thin plasma is described. Explicit expressions are obtained for the ion- ization state distribution and the population probabilities of the excited states. It is shown that the results of the model reproduce the Local Thermodynamic Equilibrium and Corona Equilibrium in the. high and low electron densities respectively, but has specific predictions at intermediate densities as well, A comparison is drawn between CSS and the Quasi-Steady-State1, particularly regarding thsir predictions of the population probabilities of the excited ionic states in a hot plasma. 1. R.W.P. McWhirter and A,G. Hearn, Proc, Phys, Soc. 82, 641 (1963). K-3 HIGH COMPRESSION OF PELLETS VIA A VOLTAGE-SHAPED ELECTRON BEAM T. Bar-Noy and M. Sapir Nuclear Research Center, Negev The available power for pellet implosion via an electron beam rises at least as the square of the voltage. This advantage is however- accompanied by a higher penetration depth of high energy electrons which is apt to preheat the fuel at the center and prevent efficient compression. Lately1 it was suggested to circumvent this difficulty by voltage programming. The idea is to start the implosion by a moderate voltage, and then while the density and also the stopping power (because of convergence) are increasing, to increase appropri- ately the voltage. If the matching is adequate, high voltages might - 67 - be applied without excessive heating of the pellet. At the same time the bremsstrahlung preheating effect can be reduced by considering low Z materials for the outer part of the pellet. We report here about calculations of the optimal voltage shapes for compressing solid and hollow boron spheres, and compare them with the theory of isentropic compression.2 1. R. Burke, M. Sapir, Improving the efficiency of electron and ion beam pellet implosions by energy programming, submitted to Nucl. Fusion. 2. R.E. Kidder, Theory of homogeneous isentropic compression and its application to laser fusion, Nucl. Fus. ]A, 53 {1914). K-4 MOMENTUM MEASUREMENTS AND NONLINEAR EFFECTS IN LASER PRODUCED PLASMAS B. Arad, S. Eliezer, S. Jackel, H.M. Loebenstein, I. Pelah, A. Zigler, H. Zmora and S. Zweigenbaum Soreq Nuclear Research Center, Yavne In inertial confinement laser fusion schemes, hot plasma generated from the outer layers of a spherical shell target produces an inward directed momentum in the remainder of the target. This momentum is employed to compress and heat the fusion fuel. We deal here with the experimental determination of inward momentum imparted to a target irradiated by a high power laser. The target was a 1 mm thick Al slab target with polished surface and it was irradiated with the single beam 60 psec duration output of a Nd:glass laser. The scaling law for momentum transfer as a function of focused laser inten- sity was determined using a torsion pendulum. Within the regime of 1 15 2 interest to laser fusion studies (10 ** s Imax £ S x io W/cm ) the momentum was found to vary linearly with laser intensity. The contribu- tion of resonant absorption was determined by irradiating the target with ir and o polarized light and setting the angle of incidence at 17". Momentum transferred to the target was found to be 35% greater for it polarization than for o polarization. Charged particle collector results indicated that the increased momentum was due to an increased amount of material ablation and not due to an increased corona temperature. A simple model was developed to describe the experimental results. The IT - o scaling data was analyzed in terms of the action of pondero- motive forces. This yielded a lower limit to the collision frequency (v/« > .02). 'ft- >'•'. - 68 - 1 SOME LARGE OBSERVABLE EFFECTS OF THE INFLUENCE OF TURBULENCE I ON GAS DIFFUSE DISCHARGES I Y. Khait ;; Solid State Institute, Israel Institute of Technology, Haifa 0. Biblarz ; Naval Postgraduate School, Montrey, California Results of recent studies of the influence of turbulence on diffuse gas discharges (coronas, etc.)1 are considered. This problem represents an . extension of the already complicated situation of discharges in very nonuniform electric fields but in nonmoving gases. Our approach provides a qualitative and semi-quantitative description of some important phenomena occurring in plasmas formed in a turbulent gas which is speedily passing through the strong nonuniform electric field present in the small corona region. These phenomena lead to interesting experimen- tally observable effects; in particular, they allow a substantial increase of current and power consumption (of the order of 102 to 103 times of the nonflow values) in the diffuse discharge prearcing mode. These effects are associated with a sharp enhancement of transport coefficients in the hydrodynamicalLy turbulent plasma. Estimates of the relative current increase and power consumption, turbulent-to-laminar made with the information given herein are in agreement with observa- tions. The obtained results can have various applications in the plasma technology and laser technique. A pulse discharge approach earlier applied to powerful microwave discharges2 can be fruitful in the considered case. 1. Y. Khait and 0. Biblarz, to be published in J. Appl. Phys. 2. Y.L. Khait, Non-Stationary Heat and Mass Transfer in Plasma Chemical Processes, Moscow (1972), Chapter 8. K-6 ', A COLLECTIVE NON-EQUILIBRIUM MULTISTAGE MODEL OF PLASMA - WALL INTERACTION ' Y. Khait ': Solid State Institute, Israel Institute of Technology, Haifa \ The new kinetic many-body semi-phenomenological treatment of the plasma- x wall interaction suggested earlier by the present author1 is considered. } . This approach is a certain combination of correspondingly modified ideas j J used for the collective kinetic treatment of the phenomena caused in and ; I on solids by short-lived large energy fluctuations (SLEFs)2, by recoils3 •: ' and high-energy radiation.1* Short term phenomena (micro-phase transi- ; tions, electron emission, micro-sputtering, etc.) occurring in short- ; lived three-dimensional hot spots (SLHS) caused in the bulk and on the ; surface (and adjacent volume) of the solid by energetic particles imping- '{ ing the wall are considered. The SLHS lifetime tn = tg + ti,ts includes ^ - 69 - ; lifetimes: tg, of the quasi-gas stage; t^, of the quasi-liquid stage and,; to, of the high temperature solid stage. Space and time scales of these ; phenomena and other characteristic parameters and their dependences on ' properties of the solid (structure, anisotropy, etc.) and on energy of j impinging particles are discussed. Differences between the suggested {. approach and the theory based on the binary collision approximation and :v some experimentally observable consequences of the kinetic collective SLHS treatment are discussed. ; 1. Y. Khait, papers of the 4th European Sectional Conf. on Atomic and -. Molecular Physics of Ionized Gases, Sept. C1978) Essen, p. 59. ". 2. Y. Khait, Phys. Stat. Solidi (b) 86, 409 (1978); Phys. Stat. Sol. (b), 89, N2, (1978); Proc. 7th Inter. Vac. Congr. and 3rd Inter. Conf. Solid Surfaces, Vienna (1977), v. 1, p. 711. ; 3. B.N. Finkelstein and Y. Khait, Doclady Academii Nauk SSSR 144, 85, (1962). 4. Y. Khait, in the book: "Radiolysis of Hydrocarbons", Ed. by A.V. Topchiev and L.S. Polak, Moscow (1962). Chapt. 6 (English Translation, Elsevier (1964)), Doclady Academii Nauk SSSR 134, 883 (1960). K-7 PLASMA-WALL COUPLING BY EXCITED NEAR-SURFACE PLASMA REGION Y.L. Khait Solid State Institute, Israel Institute of Technology, Haifa A. Inspektor and R. Avni Nuclear Research Center, Negev The plasma wall interaction is associated with two groups of inter- connected phenomena; a) Processes occurring on the surface and in the adjacent solid material layer (S.L.) under influence of the ion bombardment and other impinging particles. b) Processes taking place in the plasma layer (P.L.) adjacent to the surface under influence of fast electrons, ions, neutral excited particles and photons emitted fron the surface. Thus emitted particles form specific changes of plasaa properties like higher concentration of excited particles near the surface. The phenomena in the S.L. was discussed earlier1, in this paper we ] consider formation and properties of the plasna layer. ;; 70 - This layer is effected by electron fluxes accelerated in the near surface electrical field and serves as a source of ions and excited particles impinging the surface. When ions can be accelerated towards the surface by the local electrical fields. Parameters of this layer depending on plasma conditions and properties of the surface are discussed 1. Y.L. Khait, 4th Europhysics Sect. Conf. on Atomic and Molecular Physics of Ionized Gases, Essen FRG (1978), p. 59. K-8 TWO-DIMENSIONAL EFFECTS IN THE ION-BEAM WET-WOOD-BURNER A. Birnboin, E. Greenspan and D. Shvarts Nuclear Research Center, Negev The ion beam wet-wood-burner (IWWB) concept, which is based on a direct interaction between a deuterium beam and a tritium target, was proposed1 as a possible neutron source for hybrid reactors and other applications. The assessment of the scientific feasibility of this concept was based1 on a one-dimensional model. The feasibility of the concept is reassessed using a two-dimensional model which accounts for energy losses in both the forward (i.e., beam) direction and the trans- verse direction. Desirable working conditions for the ion energy, beam energy density and target density, and the corresponding optimal performance characteristics of the INWB are estimated. 1. A. Birnboim, E. Greenspan and D. Shvarts, Israel AEC Research Laboratories Annual Report, IA-1348, p. 45 (1977). K-9 THE SENSITIVITY OF A GLOW DISCHARGE PLASMA TO MILLIMETER-WAVE RADIATION AT CYCLOTRON RESONANCE A. Rosenberg, J. Politch, J, Felsteiner and R. Opher Department of Physics, Israel Institute of Technology, Haifa The sensitivity of a miniature glow discharge tube to electromagnetic millimeter-wave radiation (70 GHz) was investigated when the tube was placed in magnetic fields near the cyclotron resonance. About 100-fold increase in the detection voltage was obtained at the cyclotron resonance, while the noise voltage was not affected by the magnetic field; the signal to noise ratio (SNR) was improved by more than two orders of magnitude. The SNR at cyclotron resonance was better than that of a commonly used crystal detector (1NS3D) measured under identical conditions. This effect has implications on the understand- ing of the interaction between millimeter-wave radiation and glow discharge plasma. - 71 - K-10 IDENTIFICATION OF MAGNETIC QUADRUPOLE LINES OF HIGHLY IONIZED Ni, Cr, Fe IN THE TFR 600-TOKAMAK M. Klapisch, A. Bar Shalom, J.L. f •* and B.S. Fraenkel Racah Institute of Physics, The V. ' .. University of Jerusalem, Jerusalem TFR Group, EuratOH-CEA Association, Fontenay-aux-Roses, France Three lines at 21.163A, 17.100A and 14.063A appearing in the spectrum of the TFR 600 are identified as Magnetic quadrupole (M2) transitions 6 3 2p ^Q-apS 3s P2 of the ions Cr XIV, Fe XVII, Ni XIX. This identi- fication is based on computations of wavelengths using relativistic wavefunctions and on evaluation of the intensities in the Tokamak plasma conditions.1>2 1. M. Klapisch, J.L. Schwob, M. Finkenthal, B.S. Fraenkel, S. Egert, A. Bar-Shalom, C. Breton, C. DeMichelis and M. Mattioli, Phys. Rev. Lett. 41_, 403 0978). 2. M. Klapisch, A. Bar-Shalom, J.L. Schwob, B.S. Fraenkel, C. Breton, C. DeMichelis, M. Finkenthal and M. Mattioli, Phys. Lett. 69A, 34 (1978). K-ll ANGULAR SCATTERING EFFECT ON FAST IONS ENERGY DEPOSITION IN PLASMAS D. Shvarts Nuclear Research Center, Negev A common approach1 to describe the spatial transport of energetic ions in plasma is to assume that the ions are Moving in straight lines, ignoring any ion deflection. In this work we study the effect of both saali-angle coulomb scattering and large-angle nuclear scat- ,5 tering, which accounts for ion deflection, on the spatial energy :i deposition of fast ions. A comparison between both scattering • mechanisms for various types of ions and plasmas will be discussed. ; 1. G.A. Moses, Nucl. Sci. Eng. 64, 49 (1977). j i - 72 - K-12 RECENT OBSERVATIONS AND CLASSIFICATIONS OF IRON GROUP SPECTRA AT llX IN LASER PRODUCED PLASMA Nissan Spector, Arie Zigler and Hagai Zmora Department of Plasma Physics, Soreq Research Center, Yavne As part of a continuous spectroscopic investigation of laser produced plasma we bring here some new results on isoelectronic spectra of four iron group elements: Cr, Fe, Co and Ni. These spectra were produced and compiled by using the following experimental set-up: a) A Nd:glass laser given a pulse of 2-5 joules, 500ps and power density around 10* W/cm2 on target. One such pulse produced a well exposed spectrogram. b) A flat KAP crystal spectrometer of 80* with respect to the laser axis, the target plane being normal to the laser axis. Wavelengths are observed between 8.5A and 1S.SX and reduced on a Kodak SC7 film, with resolving power around 2000 and reciprocal dispersion of about 0.055X/mm. c) A grant comparator having an overall accuracy of ±1 on a line setting. Many lines were observed, recorded and measured in the above wavelength region. Using previous observations and isoelectronic extrapolations along with theoretical calculations we were able to classify most of the observed lines of Cr, Co and Ni and assign them to their known iron counterparts. Such a comparison permits the tracing of a particular ionization stage along the iron sequence from Cr (24) to Ni (28) *nd provides information on the excitation conditions in the plasma. Typical results of the present work will be discussed. - 73 - Monday Afternoon Alef Building 14:30 Plenary Session (06 Auditorium) C. Kuper, Israel Insitute of Technology, Haifa - Presiding L.Schulman, Israel Insitute of Technology, Haifa (40 min) First Order Phase Transitions: Progress and Problems D. Gill, 3en-Gurion University (40 min) Fluorescent Biophysical Probes Z. Lipkin, The Weizmann Insitute (40 min) What is a Quark? I- 4 - 74 - AUTHOR INDEX ACHIAM Y.: D-2 FISHMAN S.: H-S AHARONY A.: H-3, H-4, H-S, H-6, FORTUNE H.T.: J-8 H-7, H-8 FRAENKEL B.S.: K-10 AINHORN M.: D-ll FRIEDMAN E.: J-2 ARAD B.: B-6, K-4 FRIEDENBERG A.: E-4, E-7 ASHCROFT N.W.: 1-13 FRIESEH A.A.: B-9, C-2, C-9 ATZMONY U.: 1-2 AVNI R.: K-7 GALAM S.: H-7 AZBEL M. Ya.: A-2, E-5, H-2, 1-12 GALACZKI G.: D-10 GALILI I.: 1-11 BARAK B.S.: C-12 GELERINTER E.: 1-4 BARAK J.: G-3, G-S GERSTEN J.I.: E-l BARKAI M.: E-8 GERTNER I.: F-3, F-5, 1-9 BAR-NOY T.: K-3 GILL D.: MONDAY PLENARY BAR SHALOM A.: K-1O GILBOA H.: E-9 BAUMAN Z.: B-8 GINZBURG A.: F-4 BEN-ABRAHAM S.I.: 1-4, 1-5 GOREN S.: G-6, G-7 BEN-JACOB E.: C-3, C-4, C-S GORODETSKY G.: H-12, 1-2 BERANT Z.: J-4 GRAVE I.: D-5 BERGGREN K.-F.: 1-9 GREENFIELD A.J.: D-6, D-8 BERGMANN A.: D-3 GREENSPAN E.: K-8 BIBLARZ.O.: K-S GRUNBAUM E.: E-8 BIRENBA1M Y.: J-4 GUR J.: C-7. C-8 BIRNBOIM A.: K-8 GUREWITZ E.: 1-2 BLANKSCHTEIN D.: H-6 BRADA Y.: D-4 HARPAZ A.: A-8 HARTZSTEIN C: H-9 CAR1CLI H.: A-l HEILPER M.: 1-9 CENSOR D.: B-3 HERMON E.: 1-2 CHARACH CH.: A-3 HIRSCH A.A.: D-10 HIRSHFELD Z.: C-9 DANINO M.: 1-8 HORNREICH R.M.: H-l, 1-2 DEKEL A.: A-6 IMRY Y.: C-3, C-4, C-5, C-6, H-ll DEUTSCHER G.: D-5, E-6 INSPECTOR A.: K-7 DRESDEN M.: SUNDAY PLENARY JACKEL S.: K-4 KAHANE S.: J-5 ECKSTEIN Y.: 1-6 EHRENFREUND E.: 1-10 KALAHORA Z.: E-9 EISENBERG Y.: J-l KAVEH M.: D-3, 1-8 ELIEZER S.: B-6, K-4 KERZBERG M.: H-10 EREZ G.: B-2, B-4, B-S KHAIT Y.: G-2, K-5, IC-6, K-7 EYNI M.: A-7 KLAPISCH M.: K-10 KLEIN A.: 0-11 KLEIN M.W.: G-8, 1-14 FELSTEINER J.: 1-9, K-9 KLEIN N.: E-10 FEUCHTHANG T.E.: E-3 KLEINER R.: 1-6 FINZI A.: A-10 KOREN G.: B-10 FISCHER B.: G-8, 1-14 KORN C.: G-6, G-7 - 75 - KRISTIANPOLLER N.: G-9 ROSENBAUM R.: 1-7 KRITCHMAN E.M.: C-2 ROSENBERG A.: K-9 ROSENFELD Y.: 1-13 ROSMAN R.: H-8 LAFRANCE S.: J-8 ROSNER B.: F-l, F-3 LAHAV Y.: 1-6 LANDAU J.: 1-6 LANG S.: 1-3 SACK N.: A-9 LAZARUS D.: G-l SALZMANN D.: K-2 LEIBOWITZ E.: A-5 SAPIR M.: K-3 LEVICH B.: SUNDAY PLENARY SCHULMAN L.: MONDAY PLENARY LEVIN L.A.: B-5 SCHNOB J.L. K-1O LEVY B.: D-6 SEGAL M.: C-1O LEVY U.: B-9 SEIDMAN D.N.: G-4 LICHTENSTADT I.: A-9 SENDERICHIN A.: C-l LIPKIN Z.: MONDAY PLENARY SHAFT S.: H-12 LOEBENSTEIN H.M.: B-6, K-4 SHAHAL 0.: J-9 LUBAN M.: 1-1 SHAKAM J.: A-6 SHARED H.: G-6, 1-2 SHALTIEL D.: G-4 MAOR D.: F-3 SHAPIR Y.: H-4 MARCUS P.: C-6 SHAPIRA Y.: E-4, E-6, E-7, E-8 MARIANER S.: D-7 SHINAR J.: G-S MELAMUD M.: 1-2 SHTRIKMAN S.: H-l, 1-2 MERON M.: F-3 SHVARTS D.: K-8, K-ll MIL'SHTEIN S.: C-l SINGER P.: J-6 MIRON E.: B-4 SINVANI M.: D-8 MORDECHAI S.: J-8 SMILANSKI I. B-7 MOREH R.: J-4, J-9 SPECTOR N.: K-12 MUKAMEL D.: H-1O STEINITZ R.: A-7 STRAUSS W.: B-5 NAVON E.: F-2 SUSS J.T.: G-3, G-4 NIR D.: F-2, F-4, F-5 TANNER A.C.: 1-9 OPHER R.: 1-9, K-9 TFR GROUP : K-10 OPPENHEIM U.P.: B-1O TRIEMAN B.: G-9 ORBACH R.: G-4 OREG J.: B-5 UZI G.: C-12 OREN M.: C-ll OMEN D.A.: J-7 VAGER Z..* K-l VOLTERRA V.: G-7 PELAH I.: K-4 PERETZ M.: G-5 PINTO H.: G-6, 1-2 WANKLYN B.M.: D-9, 1-2 POLITCH J.: C-1O, C-ll, K-9 WEGER M.: D-7, H-9 POLTURAK E.: 1-7 NEIL R.: G-l PRIVMAN V.: J-6 WEINBERG Z.: E-2 NEISER K.: D-ll NISER N.: D-3, 1-8 RAIZMAN A.: G-3, G-4 WOLF A.: J-3, J-4, J-5 RAV-NOY Z.: C-9 MORTIS M.: H-ll RONEN Y.: A-4 YAEGER I.: 0-9 YATSIV S.: B-l YEKUTIELI G.: C-2 ZAMIR D.: I)-l ZEVIN V.: G-4, H-9, 1-11 ZIGLERA.: B-6, K-4, K-12 ZIPH-SCHAT2BERG h.: E-IO ZNORA H.: 15-6, K-4, K-12 ZNEIGENBAUM S.: B-6, K-4