ИжМЕРЕНИЕ пОльРИжАцИИ пРОтОНОВ с ЁНЕРгИЕИ 6,7 MeV пРИ РАссЕьНИИ НА УглЕРОДЕ

A carbon polarimeter for proton polarization measurements at energies higher than 4 MeV has been designed. Considerable transmission has been attained by using a thick polarimeter target and larger scattering solid angles. The effective polarization value at the region ofE _p from 4·6 to 6·0 MeV varies only slightly with energy and attains an average value ofP _eff–0·8. Solid state detectors were used for proton recording. The instrument calibration curve was determined by means of a triple experiment.The angular distribution of polarized protons scattered elastically has been measured at an energy of 6·7 MeV and in an angle range of _lab form 30 to 120. This distribution has two minima ofP(40_lab)=–056±0·03 andP(100_lab)=–088±0·06 and one maximum ofP(70_lab)=+1·03±0·04.     

Iterated networks and the spectra of renormalizable electromechanical systems

Beginning with anLRC network with impedance functionZ(), a sequence of iterated networksN _k with impedance functionsZ ^k(), k= 1, 2, 3,..., is introduced. The asymptotic comportment ofZ ^k() and the spectra ofN _k are analyzed in terms of the Julia set ofZ. An example is given of an iterated network associated with a cascade of period-doubling bifurcations.     

Pulse measurements of thermostimulated currents in AgCl crystals

The course of thermostimulated currents in AgCl crystals was measured in a temperature region between 200 and 300K. Maxima at 240, 275 and 290K were observed on the curves obtained.     

Influence of moisture on molecular motion in nylon 4 studied by NMR

A proton nuclear magnetic resonance (NMR) in solid poly-2-pyrrolidone (Nylon 4) was studied at temperatures between –165 C and 185 C. Wideline NMR spectra were measured on powdered samples of dry Nylon 4 and of moist Nylon 4. The second momentsM ₂ were calculated and likewise an analysis of the spectra according to K. Bergmann and K. Nawotki was performed for the purpose of the study of molecular motion in these samples. The second moment and the linewidth decrease with an increasing temperature. This fact testifies to an increasing intensity of molecular motion. It was found out that molecular motion is influenced by the presence of water and of low molecular fractions of the polymer. The presence of both factors is manifested by the decrease of theM ₂ values at temperatures higher than –60 C. It was found out from the analysis of the NMR spectra that processes in noncrystalline ( _a) and crystalline ( _c) regions of the dry sample start at 110 C. Crystallinity calculated by means of analysis of the spectra is 0·29. This value is in good agreement with the result obtained from the X-ray measurements.     

Growing of CdTe single crystals by static sublimation on a cool wall under the pressure of one of the components

The results obtained hitherto for equilibrium of the solid and gaseous phases of the CdTe semiconductor compound are summarized. The growth conditions of the static sublimation of CdTe on a cool wall were estimated from the relations at equilibrium. The single crystals grown had maximum dimensions 5×5×15 mm³, the concentration of the carriers (at 25C) wasp=4·8×10¹³ cm^–3, the mobility of the carriers (at 25C) was _p=66 cm²/Vsec.In conclusion the authors thank laboratory assistant J.Vlek for help in the work.     

Double N-N scattering on polarized proton target

The triple scattering depolarization transfer parameterD _t in elastic p-p scattering was measured at an energy of 660 MeV using a polarzied proton target. All measurements have been carried out with the help of an optical spark chamber.The following results have been obtained:D _t (90)=D(90)=0·54±0·10.D _t (130)=D(130)=0·72±0·11.Devoted to Professor V. Petrílka on his sixty-fifth birthday.On leave of absence from theInstitute for Computing Technique of the Czechoslovak Academy of Sciences, Prague.On leave of absence from theNuclear Research Institute of the Czechoslovak Academy of Sciences, e.On leave of absence from theFaculty of Nuclear Science and Physical Engineering of the Technical University, Prague.In conclusion the authors express their deep gratitude to S. M. Bilenky, G. Gozzika, M. Hansroul, L. Lapidus, M. Odehnal, M. Maly, B. S. Neganov, R. M. Ryndin and P. Winternitz for helpful discussions and J. Cechová, E. Dudová and H. Sternová for help in the work.     

Mössbauer study of the dynamics of iron ions in bipyramidal positions of strontium hexaferrite

The dynamics of Fe³⁺ ions in bipyramidal 2b positions of a type M hexaferrite are studied on single-crystal and polycrystalline SrFe₆Ga₆O₁₉ samples in the paramagnetic temperature range. We show that when the angle between the c axis of the crystal and the direction of -ray emission varies from 0 to 32 the area under the resonance lines corresponding to Fe³⁺ ions in 2b positions increases by a factor of roughly 1.5. The effect is more pronounced upon passing from a single-crystal sample (=0) to a polycrystalline sample. A comparison of the line intensities under different experimental conditions served as a basis for an evaluation of the difference between the mean-square displacements of the Fe³⁺ ions in 2b positions along the c axis in the perpendicular plane.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 5–8, January, 1991.     

The coherent K L 0 C → K S 0 C regeneration at high energies

New experimental results on the coherentK _L ⁰ C K _S ⁰ C regeneration in the momentum range 10p30 GeV/c are presented. For the quantity (f ₀–¯f ₀/k (where f₀ and¯f ₀ are theKC and¯K ⁰C forward scattering amplitudes andk is the wave number) we have obtained: arg (f ₀–¯f ₀)/k=–126±14 and ¦(f ₀–¯f ₀/k¦ p ^{–0.62±0.14} These results are well described by a simple Regge pole model including only the (-trajectory exchange in thet-channel with the intercept (0) close to 0.4.Presented at the IV International Symposium on High Energy and Elementary Particle Physics, Warszaw, September 1975.     

Features of current carrier scattering in epitaxial films

The properties of epitaxial cadmium selenide films obtained by condensation in a vacuum on mica substrates under almost equilibrium conditions are investigated. The temperature dependences of the conductivity and current carrier mobility and concentration are studied. The electron concentration in the films depended on the gas phase composition (coevaporation of CdSe + Se or CdSe + In) and varied between 5·10¹⁰cm^–3 and 3.5·10¹⁸. It is shown that the current carrier scattering mechanism depends on their concentration and production conditions. For n₁ 10¹⁶ cm^–2 (T_S520C),n₂ < 10¹⁵ (T_S=630C), scattering on intercrystallite barriers predominated. For n₁ and n₂ greater than the quantities mentioned, scattering by ionized defects becomes dominant. It is established that the magnitude of the intercrystallite barrier in films with 10¹⁵ < n < 10¹⁶ cm^–3 is comparatively small and does not exceed 4·10^–3 eV, whereupon scattering at the barriers is not explicitly manifest. Concentrations of the ionized centers, magnitudes of the intercrystallite barriers, and ionization energies of the donor levels are determined for films obtained under different conditions.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 9, pp. 98–103, September, 1977.     

Mössbauer study of internally oxidized silver-tin alloys

A Mössbauer study of internally formed oxides as a function of oxidation temperatures between 200 C and 850 C was performed on previously annealed 1 at%AgSn alloys. The oxide formed at high temperatures (t 500 C) consists in agglomerates of tin dioxide = 0.00 ± 0.01 mm/s, Q=0.50 ± 0.03 mm/s). The low temperature oxide (t 300 C) is characterized by = 0.29 ± 0.02 mm/s and Q=0.32 ± 0.03 mm/s, and could be in the form of one-Sn-atom oxide complexes in the silver matrix. From the measured isomer shifts in the range 400 t 550 C, the maximum contribution of the silver matrix to the effective number of electrons per Sn atom in oxide agglomerates has been estimated have a value of about 0.06. The effect of the cold work on the hyperfine parameters of the oxidized tin has also been investigated. As rolled samples were found to attain the same values of isomer shifts and quadrupole splittings as annealed specimens, but at lower temperatures.     

Atomic volume dependence of the153Eu isomer shift in ScxY1−x

Mössbauer studies of dilute¹⁵³Eu in Sm_0.05Sc _x Y_0.95–x (0x0.95) reveal large changes in the isomer shift as a function ofx. The strong dependence of the isomer shift on alloy composition, is interpreted in terms of changes in the charge density at the Eu nucleus ((0)), which result from changes in atomic volume. The isomer shift was found to depend linearly on V/V (V/V changes between 0 and –0.3). A value of (–17.5±2.0)a ₀ ^–3 was obtained for d(0)/d lnV.This research was supported by a grant from the United States—Israel Binational Science Foundation (BSF), Jerusalem, Israel.     

Mössbauer effect study of the Β-FeOOH to α-Fe2O3 phase transformation

-FeOOH was precipitated from a chloride solution. Mössbauer spectra were taken at room temperature (RT) and at 4.2 K in zero field and in external magnetic fields. Samples aged for successively longer time periods were studied. They contain -FeOOH and -Fe₂O₃, the Mössbauer spectra of which show superparamagnetic behavior. The transformation into -Fe₂O₃ is already induced by aging in the mother solution at 100 C. A final heat treatment at 350 C leads to the complete transformation into -Fe₂O₃ and to an increase of the crystallite size.     

Thermomagnetic properties of ferrite Cu0.5Fe2.5O4

The temperature dependences of the saturation magnetization and the paramagnetic susceptibility of several samples of the ferrite Cu_0.5Fe_2.5O₄ were studied in the temperature range from 4·2 up to 1200 K. It was found that the transformation which occurred in these ferrities above 350 C brought about anomalies in the regular temperature course of the magnetization. Taking into account also the results of the paramagnetic susceptibility measurements, the changes of the ferrites on heating to higher temperatures were discussed.     

Positive muon spin depolarization in quenched aluminium dilute alloys

Aluminum dilute alloys (Al-0.047 at% Mg, Al-0.052 at% Cu and Al-0.051 at% Si) were quenched from 600 and 450C. The positive muon behavior in the quenched alloys has been studied. Three peaks (Peak I, II and III) are found. Peak I is due to the trapping and detrapping of positive muons at single impurity atoms. The muon spin depolarization rate at the trap in Peak I was found to be 0.36sec^–1. Peak II is connected to impurity clusters. Peak III is the trapping of muons at quenched-in vacancies. The depolarization rate at the trapping site was found to be 0.2sec^–1. The activation energy of the trapping rate was found to be 25 meV. As the quenched-in vacancies annealed out, the trapping rates decreased to near zero.     

Perturbed angular correlation study of surface magnetization in iron single crystals

The behaviour of closure domains at the surface of iron single crystals in an external magnetic field was studied by DPAC on samples implanted with¹¹¹In. It is observed that the surface magnetization does not follow that of the bulk. The movement of both the 90 and 180 walls of the closure domains is blocked up to a certain starting value H_s of the external field that is related to the demagnetization factor D of the sample and also depends on the precise orientation of the crystal axes and on the implanted indium dose.On leave from the Institue of Nuclear Physics, Cracow, PolandOn leave from the Institue of Physics, Jagiellonian University, Cracow, PolandThis work forms part of the research program of the Foundation for Fundamental Research of Matter (FOM) subsidized through the Netherlands Organization for Pure Research (ZWO).     

Thermostimulated currents in p-type cadmium telluride single crystals

Ssveral samples of CdTe were measured in a temperature range of –190C to 100C. The activation energies of the levels and their cross-section were determined. With some samples it was found that for more rapid heating the maxima of the curves of thermostimulated currents are shifted towards lower temperatures. Altogether three trap levels were found.     

Softening during and after the hot deformation of the AISI 321 steel with respect to practical applications

The softening processes during and after the hot deformation (850–1180 C) in AISI 321 stainless steel were studied with respect to true strains _D and true strain rates . The analysis of deformation curves indicates the occurrence of dynamic recrystallization for values of Zener-Hollomon parameterZ10¹⁵ s^–1. The retardation of static recrystallization by fine Ti(N, C) precipitates is documented by microstructure studies and by variations of annealing conditions.     

The luminescence properties of SmD and EuTTA

The results of measuring the absorption and emission spectra, decay time and quantum yield of the luminescence of SmD and EuTTA as a function of temperature (in a 77K–300K interval) and concentration are discussed. The energy transfer from the molecule organic part to the rare earth ion and the influence of nonradiative transitions are studied.The authors express their appreciation of the careful assistance in preparing the chelates given by Miss. H. Voka'lová and Mr. J. Voráek.     

Interphase interactions in a Pd-GaAs system and their effect on electrical properties of schottky-barrier structures I. effect of heat treatment on characteristics of GaAs-Pd/Ni contacts

The electrical characteristics of surface-barrier GaAs-Pd/Ni structures and the physicochemical interaction processes at the metal-semiconductor boundary were comprehensively investigated in relation to heat treatment in various atmospheres. X-Ray structural analysis showed that in the investigated system metallurgical reactions begin at 300–350C: Unstable intermediate phases (presumably Pd₂Ga) are formed. At 400–550C all the palladium is converted to the bound state and the intermetallic compound PdGa is formed. The phase changes have no significant effect on the properties of diode structures fired in a hydrogen atmosphere. Heating in vacuum leads to degradation of the contact parameters at 300C or more. This effect is attributed to penetration of oxygen to the interface during formation of the intermediate phases.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 3–7, April, 1981     

Perturbed angular correlation measurements on the 40.9 keV level of62Cu. A preliminary study of 2Zn-insulin

Time-differential PAC measurements have been made using⁶²Zn, both in aqueous solution at pH 6.0 and also incorporated into crystalline 2Zn-insulin. Three Nal(Tl) detectors were used — a 2.54 cm thick scintillator detecting the stop 41 keV gamma ray and two 5.0 cm thick scintillators at 90 and 135 detecting the start 597 keV gamma rays. The need to separate the 597 keV line from the 511 keV background was found to require very careful setting-up conditions in the case of a fixed-detector spectrometer. The solution data produced a fast relaxation time of (75±25) ns, while the three 2Zn-insulin batches gave data which were analyzed using a static interaction with an assumed axial symmetry to give an electric quadrupole frequency of (77±8) MHz.