The effect of low-temperature electron irradiation on the transition temperature of YBa2Cu3O7−δ superconductors

Measurements of the complex susceptibility =–i of electron-irradiated YBa₂Cu₃O_7– show a strong influence of the electron irradiation dose, ·t on the transition temperatureT _c . For irradiation doses of ·t=2.2·10¹⁹ e^–/cm² we find a damage rate of T _c /(·t)=–1.6·10^–19 K/(e^–/cm²). It is assumed that the decrease ofT _c is mainly a bulk effect due to the production of atomic defects like vacancies and interstitials in the Cu–O–Cu chains and in the basal planes of the unit cells.     

Decay of Hf172

The internal conversion spectrum of Hf¹⁷² was examined with an intermediate image magnetic spectrometer. The gamma-ray spectrum and gamma-gamma coincidence spectrum were studied by means of scintillation spectrometers. The half-life of the 65·9 keV excited level in Lu¹⁷² was found to beT _1/2 = (3·32±0·20) × 10^–7 sec. The proposed decay scheme is discussed.On the same apparatus the half-life of the 206·25 keV excited level in Re¹⁸⁷ was measured and the result isT _1/2 = (5·05±0·13) × 10^–7 sec.The authors wish to thank to Ing. Vobecký and Ing. Matalka for the separation of Hf and Z. Praáková for assistance in the numerical calculation.     

Inclusive production of φ-mesons in neutron-proton interaction at 30–70 GeV/c

A signal of the-K⁺K^– decays has been observed in neutron-hydrogen interactions at energies of 30–70 GeV in an experiment using the BIS-2 spectrometer. The longitudinal momentum spectrum in the forward region,x _F<0·1 atp _T<1 GeV/c, can be well described by a power law dependence (1–x _F)^N withN=4·28±0·42. Thep _T ² -spectrum has been parametrized by the exp(–Bp _T ² ) law with the exponentB=(3·02±0·55) (GeV/c)^–2. The extrapolation of the measured cross section to the full kinematic region yields a value of (220±85) b in agreement with measurements from the proton beams.     

Translational and rotational diffusion in supercooled orthoterphenyl close to the glass transition

Self diffusion coefficients in supercooled orthoterphenyl (OTP) have been determined down toD _t =3·10^–14 m²s^–1 using a¹H-NMR technique applying static field gradients up to 53T m^–1 In a range of more than two decades theD _t values agree with those of photochromic tracer molecules of the same size determined by forced Rayleigh scattering down to the glass transition temperatureT _g . A change of mechanism is found for translational diffusion atT _c 1.2T _g whereD _t is proportional to the inverse shear viscosity ^–1 atT>T _c butD _t with =0.75 atT<T _c . Rotational correlation times determined by²H-NMR stimulated echo techniques in deuterated OTP remain proportinal to ^–1 down toT _g . Our results are discussed in relation with mode coupling theory and with models of cooperative motion at the glass transition.     

Nuclear orientation study of the decay of204BiFe

The decay of²⁰⁴Bi nuclei (I =6⁺, T_1/2=11·22 h) oriented in an iron host was investigated on the JINR low-temperature nuclear orientation facility SPIN. The orientation parameterB ₂=1·17 (6) was obtained from the analysis of six prominent E1 gamma-transitions. From the measured normalized intensities of the gamma-rays observed some 70 values of multipole mixing ratios for the gamma-transitions in²⁰⁴Pb nucleus were determined for the first time. The spins 6, 6, 5 and 4 could be uniquely assigned to the²⁰⁴Pb negative parity levels at 3891·5 keV, 3768·4 keV, 3301·5 keV and 2338·2 keV, respectively. The spin-parity assignments of the levels at 4183·8 keV, 4094·2 keV, 3782·0 keV, 2506·9 keV and 2065·1 keV were confirmed as 6^–, 6^–, 5^–, 5^– and 5⁺, respectively. For the level at 3105·1 keV spin-parity 5^– was suggested and spinparity 7^– of the level at 2696·4 keV was called in question. The possible placements of the gammatransitions 3 1351·7 keV and 1353·4 keV in the decay scheme is discussed. The reorientation parameters for the long-living levels at 2264·2 keV (T _1/2=0·45 s) and 1273·9 keV (T _1/2= =265 ns) were determined asG ₂=0·41 (14) andG ₂=0·60 (17), respectively. For the isomeric level at 2185·7 keV (T _1/2=67·2 min) the value ofG ₂=0·88 (49) was proposed.The authors would like to express their thanks to T. I. Kracíková and M. Trhlík for the valuable discussions in the course of the evaluation of the experimental data.     

Heterodiffusion of Cr in molten Fe in the temperature range 1800 to 1970 K

Heterodiffusion of Cr has been studied using the method of thin layer and the radionuclide⁵¹Cr. The diffusion characteristics determined from the experimental results in the temperature range 1800 KT1970 K areD _o=1·59×10^–2 cm²/s andE=22·3±1·6 kcal/mol. The experimental method is discussed in detail and the results are compared with those of other authors.     

Transient creep during transformation in Cd-Zn alloys

Transient creep of Cd-2 wt. % Zn and Cd-17·4 wt. % Zn alloys has been studied under different constant stresses ranging from 6·4 MPa to 12·7 MPa near the transformation temperature. The results of both compositions showed two transient deformation regions, the low temperature region (below 483 K) and the high temperature region (above 483 K). From the transient creep described by the equation _tr=Bt ⁿ, where _tr andt are the transient creep strain and time. The parametersB andn were calculated. The parameterB was found to change with the applied stress from 0·3×10^–4 to 3×10^–4 and from 0·6×10^–4 to 18×10^–4 for Cd-2 wt. % Zn and Cd-17·4 wt. % Zn, respectively. The exponentn was found to change from 0·8 to 0·95 for both alloys. The parameterB was related to the steady state creep rate through the equation , the exponent was found to be 0·5 for Cd-2 wt. % Zn and 0·6 for the eutectic composition. The activation energies of transient creep in the vicinity of the transformation regions (above 483 K) were found to be 50·2 kJ/mole for Cd-2 wt. % Zn and 104·7 kJ/mole for the eutectic composition characterizing the mechanisms of grain boundary diffusion and volume diffusion in Cd, respectively.     

Investigations of the excitation energy transport mechanism in donor-acceptor systems

Measurements of fluorescence quantum yield _D/_oD of Na-fluorescein (donor; D) versus concentration of rhodamine B (acceptor; A) in viscous solutions have been carried out. The donor concentration in these solutions was as follows:C _D=2·10^–2 M (system I), 1.5·10^–2 M (II), 10^–2 M (III), 3·10^–3 M (IV), and 5·10^–5 M (V). The experimental results have been compared with current theories of nonradiative electronic energy transfer (NEET). In the case of very strong migration (systems I, II, and III), a significant influence of correlations (between configurations of D and A molecules in the surroundings of successively excited donors) on quantum yield _D/_oD has been determined. Experimental values have been found to be clearly higher in comparison with those predicted theoretically. The influence of possible factors on the decrease in the effectiveness of excitation energy transport to traps-acceptors in systems of very strong migration has been discussed.Dedicated to Professor A. Kawski on the occasion of his 65th birthday.     

On the mechanism of the induced anisotropy of magnesium ferrites in the range of higher temperatures

A simple mechanism explaining not only the magnitude but also the type of induced anisotropy on the magnesium ferrite Mg_0·78 Fe_2·22 O_4·026 in the temperature range from 400 to 500°K has been designed. The experimentally estimated values of the microscopic bond energyl _p 7×10^–16 erg of the configuration contributing to theF-type anisotropy and the activation energy _exp = 1·1 eV are in good correspondence with the valuesl _d1·6×10^–16erg and _cal = 1·1₅ eV which have been calculated theoretically.Dedicated to Professor Dr. Jaromír Bro on his sixtieth birthday.The author would like to express his thanks to Dr. S. Krupika for valuable discussions and his interest in this paper.     

Influence of Vibrational Excitation of Triplet Molecules of Anthraquinone on the Photochemical Processes in Gas Mixtures with Amines

By the quenching of the delayed fluorescence (DF) of anthraquinone vapors by aliphatic amines (diethylamine, dibutylamine, cyclohexylamine) and pyridine the photoinduced processes proceeding with the participation of vibrationally excited triplet molecules of anthraquinone have been investigated. The DF quenchingrate constants K _q varying from 1·10⁶ sec^–1·torr^–1 in mixtures with diethylamine to 7·10³ sec^–1·torr^–1 in mixtures with pyridine have been estimated. A correlation between the values of K _q and the ionization potentials of foreign gases confirming the important role of interactions with charge transfer in the quenching of triplet molecules in the gas phase has been established. The influence of other relaxation processes on the DF quenching is considered. It is shown that the intermolecular vibrational relaxation in the T ₁ triplet state leading to the establishment of relaxation equilibrium at a vibrational temperature T _vib considerably increasing the medium temperature is the fastest process among the biomolecular processes (rate constants K _col ^V > 10⁶ sec^–1·torr^–1 > K _q). The values of T _vib and the vibrational energies E _vib of the triplet molecules after the energy exchange in the collisional complex have been estimated. It has been concluded that the photochemical reaction yield is determined by the intermolecular processes proceeding in the T ₁ state at a vibrational equilibrium characterized by high values of T _vib. The influence of E _vib of triplet molecules on the DF quenching rates at a photoinduced electron transfer is considered.     

Xenon plasma with caesium as additive

The concentration dependence of xenon plasma with caesium as additive in the temperature region of 2 000 K to 20 000 K has been analysed. Plasma has been considered as weakly nonideal in the complete local thermodynamic equilibrium and the interaction between plasma and vessel walls was not taken into account. The values of some of the parameters for nonideality of plasma with 1% of caesium (=0·01010) and 10% of caesium (=0·11111) are computed, for initial pressure in plasma ofp ₀=13 000 Pa and initial temperatureT ₀=1 000 K. Also the ratio of electrical conductivity of plasma computed by Lorentz's formula and electrical conductivity computed by Spitzer's formula in the same temperature interval has been analysed.     

The dependence of the neutron temperature on the geometric parameter for water and loose diphenyl

The dependence of the neutron temperatureT _n on the geometric parameterB ² was measured by the pulse method in water and loose diphenyl. The measurements were made on a moderator poisoned by cadmium sulphate, a substance whose absorption cross-section is non 1/v.The following results were obtained: For waterT _n [eV]=–(0·00391±0·00045)B ² [cm^–2]+(0·02537±0·00035) for loose diphenyl:T _n [eV]=–(0·01014±0·00152)B ² [cm^–2]+(0·02518±0·00054).We are indebted to J. Jirou and J. Jadavan for their assistance in the measurements, the accelerator operation and electronic apparatus maintenance.     

Free energy of the chiral Potts model in the scaling region

We explicitly calculate the free energy of the general solvableN-state chiral Potts model in the scaling region, forT<T _c . We do this from both of the two available results for the free energy, and verify that they are mutually consistent. Ift=T _c –T, then we find that - _c /t has a Taylor expansion in powers oft ^2/N (together with higher-order non-scaling terms of ordert, ort logt).     

Magnetic relaxation in a three-dimensional ferromagnet with weak quenched random-exchange disorder

Isothermal remanent magnetization decay,M _r(t), and ‘in-field’ growth of zero-field-cooled magnetization,M _ZFC(t), with time have been measured over four decades in time at temperatures ranging from 0.25T _c to 1.25T _c (whereT _c is the Curie temperature, determined previously for the same sample from static critical phenomena measurements) for a nearly ordered intermetallic compound Ni₃Al, which is an experimental realization of a three-dimensional (d = 3) ferromagnet with weak quenched random-exchange disorder. None of the functional forms ofM _r(t) predicted by the existing phenomenological models of relaxation dynamics in spin systems with quenched randomness, but only the expressions and closely reproduce such data in the present case. The most striking features of magnetic relaxation in the system in question are as follows: Aging effects are absent in bothM _r t andM _ZFC(t) at all temperatures in the temperature range covered in the present experiments. A cross-over in equilibrium dynamics from the one, characteristic of a pured = 3 ferromagnet with complete atomic ordering and prevalent at temperatures away from T_c, to that, typical of ad = 3 random-exchange ferromagnet, occurs asT → T_c. The relaxation times τ₁(T)(τ₁ ^′(T)) and τ₂(T)(τ₂ ^′(T)) exhibit logarithmic divergence at critical temperatures and ; and both increase with the external magnetic field strength,H, such that at any given field value, . The exponent characterizing the logarithmic divergence in τ ₁ ^′ (T) and τ ₂ ^′ T possesses a field-independent value of ≃16 for both relaxation times. Of all the available theoretical models, the droplet fluctuation model alone provides a qualitative explanation for some aspects of the present magnetic relaxation data     

Electrophysical properties of ionic alloys of GaAs obtained by implanting Zn+ (150 keV) with subsequent annealing at 500–1000°C

A study is made of the electrophysical properties (N_s, _eff) of ionic alloys of GaAs obtained by implanting 150-keV Zn ions at 20 and 300°C. The ion dose D=5·10¹³–10¹⁶ ions/cm²; the alloys were subsequently annealed for 10 min in an H₂ atmosphere with temperatures in the range 500–1000°C. The optimal parameters of the ionic alloys are obtained for T_i=300°C and T_a=700°C. Thermal acceptance of the GaAs under a SiO₂ film (d0.2–0.3 m) is observed for T_a>700°C. The limiting concentration of thermal acceptors N_s(TA)3·10¹³ cm^–2) for T=1000°C and t=10 min.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 3, pp. 22–26, March, 1979.     

Spontaneous magnetization from NMR measurements and critical exponents in nickel

Nuclear magnetic resonance of Ni⁶¹ has been studied in pure nickel metal (of natural isotope composition) in the vicinity of the Curie point. The temperature dependence of NMR frequency has been measured up to 0·96T _c. Determination ofT _c was aided by initial susceptibility measurements. The analysis of these results yields =0·336±0·002 for the critical exponent describing the decrease of spontaneous magnetization to zero atT _c. This value of is in excellent agreement with the corresponding values obtained from NMR experiments in ferromagnetic EuS and antiferromagnetic MnF₂, it differs, however, from the values obtained for nickel by other methods. In a general discussion of this problem which uses the theoretical relations between various critical exponents the earlier data, in particular those of Weiss and Forrer, are reexamined.It is a pleasure for the authors to acknowledge the valuable advice and helpful comments of Professor J. Bro and Dr. J. ternberk. They are indebted also to Dr. V. Houdek for help with the susceptibility measurements, which were performed on his apparatus.     

Dynamics of the formation of two-dimensional ordered structures

The growth of ordered domains in lattice gas models, which occurs after the system is quenched from infinite temperature to a state below the critical temperatureT _c, is studied by Monte Carlo simulation. For a square lattice with repulsion between nearest and next-nearest neighbors, which in equilibrium exhibits fourfold degenerate (2×1) superstructures, the time-dependent energy E(t), domain size L(t), and structure functionS(q, t) are obtained, both for Glauber dynamics (no conservation law) and the case with conserved density (Kawasaki dynamics). At late times the energy excess and halfwidth of the structure factor decrease proportional tot ^–x, whileL(t) t ^x, where the exponent x=1/2 for Glauber dynamics and x1/3 for Kawasaki dynamics. In addition, the structure factor satisfies a scaling lawS(k,t)=t ^2xS(kt^x). The smaller exponent for the conserved density case is traced back to the excess density contained in the walls between ordered domains which must be redistributed during growth. Quenches toT>T _c, T=T_c (where we estimate dynamic critical exponents) andT=0 are also considered. In the latter case, the system becomes frozen in a glasslike domain pattern far from equilibrium when using Kawasaki dynamics. The generalization of our results to other lattices and structures also is briefly discussed.     

Interaction of Alkali Blue 6B with Cetyltrimethylammonium Bromide

The microsurface adsorption–spectral correction (MSASC) technique has been applied to investigate the interaction of alkali blue 6B (AB6B) with cetyltrimethylammonium bromide (CTAB). The aggregation of AB6B on CTAB obeys the Langmuir isothermal adsorption. The aggregate was characterized by MSASC. For the monomer aggregate AB6B₂CTAB formed, its binding constant is calculated to be K = 3.01·10⁵ and its molar absorptivity to be 2.45·10⁶ liters·cm^–1 at = 690 nm. The adsorption has been used to carry out quantitative detection of cationic surfactant in samples.     

Solubility of Na2Co3 in NaCl:CaCl2 crystals

Measurements of electrical conductivity of NaCl 10^–5 molar fr. CaCl2 (1–80)×10^–5 molar fr. Na₂CO₃ crystals have been used to determine the temperature dependence of the solubility of CO₃-ions over the temperature range from 75 to 530 °C. The total solubility of CO₃-ions and that of [CO ₃ ^2– -vacancy] complexes may be expressed by simple relationships andc _ka=3·19× 10^–2 exp (–0·25 eV/kT), resp. The heat of solution of complexes is equal to 0·25 eV and that of free CO ₃ ^2– ions is higher than 1·2 eV. Under conditions of the thermal equilibrium between the solid solution and precipitate, the ratio of Na₂CO₃ and CaCO₃ components in the precipitate has been calculated at various temperatures and CO₃ concentrations.     

Electrical properties of p-type ZnGeP2 irradiated by H+ ions

The properties of p-type ZnGeP₂ [p₀=(5–10)·10¹⁰ cm^–3, ₀=(2–5)·10^–7 (·cm)^–1], irradiated with H⁺ ions [E=5 MeV, T_irr=300 K, D=(1·10¹²–1.7·10¹⁶) cm^–2] are studied. An increase in the resistivity (to gr_max - 5·10¹¹ ·cm) and subsequent reduction in for large currents of H⁺ ions ( - 9·10⁸ ·cm for D - 1.7·10¹⁶ cm^–2), is observed in irradiated crystals. The resistivity of irradiated p-type ZnGeP₂ is found to be very sensitive to hydrostatic pressure [(4–5)·10^–5 bar^–1]. The annealing of radiation defects in the temperature interval (20–600) °C is examined.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 10, pp. 91–93, October, 1991.