More on the τ-μ-e problem: The process e+e−→l+l− in the region of the z-resonance

Theoretical and experimental aspects of the study of the e-- problem in effects of neutral weak currents in colliding e⁺e^– beams in the region of the Z resonance are discussed. Quantities that describe the degree of violation of e-- universality are analyzed. In particular, it is shown that by measuring the spin asymmetry for angles 160° it is possible to determine the degree of violation ofl-e universality =g _A ^e g _V ^l –g _V ^e g _A ^l to an accuracy of up to 0.01.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 5, pp. 88-91, May, 1989.     

Superconductivity and magnetic properties of Nb—Al phases: Nb2Al and NbAl3

Magnetic properties of tetragonal phases in Nb—Al system have been investigated down to 0.42°K. It has been found that the-phase (Nb₂Al) and the intermetallic compound NbAl₃ are superconductors with superconducting transition temperature 0.74°K and 0.64°K, respectively. Magnetic susceptibility of the investigated phases does not depend on temperature within the range 4.2°K–300°K, and is equal =(1.0±0.1) × 10^–6 emu)/g for Nb₂Al, and =(0.9±0.03) × 10^–6 emu/g for NbAl₃.On leave of absence from Institute for Solid State Physics of Bulgarian Academy of Sciences, Sofia, Bulgaria     

The electronic structure of Rhodium: Angle-resolved studies of photoelectron and secondary electron emission

We report electron spectroscopic studies of the Rh(111) surface, with the aim to obtain bulk band-structure information. We have measured normal photoemision using tunable synchrotron radiation in the range of photon energies between 11 eV and 55 eV, and angle-dependent photoemission along the LUX and LKL azimuths using the He resonance lines (=21.2 eV, 40.8 eV). To complement these data, we studied angleresolved secondary electron emission after excitation with electrons and photons. We derive parts of the one-electron energy dispersionE(k) along L, and determine the energies of several bulk critical points (in eV):E(> ₇₊/₈₊)=–2.75±0.10,E(> ₈₊=–0.85±0.10,E(> _7–=16.1±0.5,E(> _6–/> _8–)=20.5±0.5,E(X ₇₊)=–5.0±0.1,E(L ₆₊)=–5.6±0.5,E(L ₆₊/L ₄₊₊₅₊)=–2.65±0.10,E(L ₆₊)=9.0±0.5 eV. Our results are compared to several available band structure calculations.     

Beta-decay asymmetries in polarized12B and12N and theG-parity non-conservation

The decay asymmetries (A) in polarized¹²B and¹²N have been measured as a function of -ray energies (E). The coefficients _± inA = ±P(p/E) (1+_± E) have been determined to be _–(¹²B) =+(0.31±0.06)%/MeV and ₊(¹²N) = –(0.21±0.07)%/MeV. The experimental value, _––₊=(0.52±0.09)%/MeV, is larger than the prediction according to conservation of vector current which includes no second-class current, _––_{+ CVC}0.27%/MeV, and indicates the existence of the second-class induced-tensor current.This work has been done in collaboration with I. Tanihata and J. Göring.     

Analytic study of power spectra of the tent maps near band-splitting transitions

Successive band-splitting transitions occur in the one-dimensional map x_i+1=g(x_i),i=0, 1, 2,... withg(x)=x, (0 x 1/2) –x +, (1/2 <x 1) as the parameter is changed from 2 to 1. The transition point fromN (=2ⁿ) bands to 2Nbands is given by=(2)^1/N (n=0, 1,2,...). The time-correlation function _i=x_ix₀/(x₀)²,x_i x_i–x_i is studied in terms of the eigenvalues and eigenfunctions of the Frobenius-Perron operator of the map. It is shown that, near the transition point=2, _i–[(10–42)/17] _i,0-[(102-8)/51]_i,1 + [(7 + 42)/17](–1)ⁱe^–yi, where2(–2) is the damping constant and vanishes at=2, representing the critical slowing-down. This critical phenomenon is in strong contrast to the topologically invariant quantities, such as the Lyapunov exponent, which do not exhibit any anomaly at=2. The asymptotic expression for _i has been obtained by deriving an analytic form of _i for a sequence of which accumulates to 2 from the above. Near the transition point=(2)^1/N, the damping constant of _i fori N is given by _N=2(^N-2)/N. Numerical calculation is also carried out for arbitrary a and is shown to be consistent with the analytic results.     

Experimental determination of the rates of the excited muonic hydrogen charge exchange on helium

The data of the experiment with the H₂+⁴He mixture are analyzed in order to estimate muon transfer rates from the excited states of p atoms to helium. Experimental data turned out to be insensible to the transfer rates from the metastable 2s state. The rates forn=3, 4, 5 were found to be: ⁽³⁾=(2±7)×10¹⁰ s^–1, ⁽⁴⁾=(16±13)×10¹¹ s^–1, ⁽⁵⁾=(75±60) ×10¹¹ s^–1, respectively.     

Self-avoiding random walks on the hexagonal lattice

We use the algorithm recently introduce by A. Berretti and A. D. Sokal to compute numerically the critical exponents for the self-avoiding random walk on the hexagonal lattice. We find=1.3509±0.0057±0.0023v=0.7580±0.0049±0.0046=0.519±0.082±0.077 where the first error is the systematic one due to corrections to scaling and the second is the statistical error. For the effective coordination number we find=1.84779±0.00006±0.0017 The results support the Nienhuis conjecture=43/32 and provide a rough numerical check of the hyperscaling relationdv=2–. An additional analysis, taking the Nienhuis value of=(2+2^1/2)^1/2 for granted, gives=1.3459±0.0040±0.0008     

F.c.c. type-III antiferromagnetism in YbN

Neutron diffraction experiments performed for YbN in the temperature range from 7 mK to room temperature prove the existence of long-range f.c.c. antiferromagnetic ordering of type III belowT _N =(0.790±0.005) K. The low ordered magnetic moment of Yb at saturation, =(0.39±0.05)> _B , is presumably caused by Kondo hybridization. By means of inelastic neutron scattering the crystalfield level scheme was established to be ₆ – ₈(33 meV)– ₇(81 meV). The ₆ – ₈ transition was found to be split into two lines which may be due to a bound state between the crystal-field excitation and phonons.     

The hydrodynamic limit of a one-dimensional nearest neighbor gradient system

We study the hydrodynamic behavior of a one-dimensional nearest neighbor gradient system with respect to a positive convex potential . In the hydrodynamic limit the density distribution is shown to evolve according to the nonlinear diffusion equation ,(q)/t= (²/dq²){F([1/₁(q)]), with F= –.     

Magnetic moments of proton drip-line nuclei13O and9C

The magnetic moments of the proton drip-line nuclei¹³O(I = 3/2^–,T _1/2 = 8.6 ms) and 9C(I = 3/2^–,T _1/2 = 126 ms) have been determined for the first time through the combined techniques of polarized radioactive nuclear beams and-NMR detection. The observed magnetic moments are ¦(¹³O)¦ = 1.3891 ±0.0003 _N and ¦(⁹C)¦ = 1.3914 ±0.0005 _N. Spin expectation values are deduced to be 0.76 and 1.44 for¹³O and⁹C, respectively. While the of¹³O is consistent with the systematics from isospinT= 1/2 mirror pairs, the of⁹C is unusually large, even far larger than the single particle value, = 1.     

The PSI experiments on muon-catalyzed pt fusion

The experiments on pt fusion performed at Paul Scherrer Institut, Villigen, Switzerland, are described. Liquid triple mixtures of protium, deuterium and tritium with low concentrations on deuterium and tritium were used. Gamma rays, X-rays, neutrons and, for the first time, conversion muons, were measured. Preliminary results are: Rate for spin flip from the triplet to the singlet state of t(1s), ₁₀=(1.0±0.2) × 10³s^–1; rate for muon-catalyzed pt fusion from the (I=1) nuclear-spin state, _pt ^f (I=1)=0.07±0.01s^–1; and the molecular formation rate, _pt ^m =(7.5±1.3)s^–1 (all normalized to liquid hydrogen density).     

Resonant shielding of an inhomogeneous gyrotropic plasma slab

Conclusions The problem of the incidence of a plane TM electromagnetic wave on an isotropic, symmetric, resonance plasma slab (n=2, 4, 6, ...), discussed in [1], was solved by an iteration method in a recent paper [6]. The physical results found there are the same as those of [1]. Zhivulin and Makarov [6] then applied the iteration method to the analogous problem of a gyrotropic resonance plasma slab [7]. The analysis in these papers furnishes a clearer mathematical justification of the results of [1] and the present paper and thus of the method used there. The present method, which satisfies only a physical condition of rigor, is preferable to the mathematically more rigorous methods (in particular, the iteration method) because of its simplicity, its graphic nature, and its clear physical meaning. It also answers many questions which cannot be answered in the more rigorous approach because of the serious difficulties which arise (and which have not yet been overcome).N. G. Denisov has called our attention to the fact that complete shielding was actually found previously by Rytov and Yudkevich [8], who treated the problem of the incidence of a plane TE electromagnetic wave on a slab with a dielectric constant (x)=₁ – A₁/(a – x)² for x<0. (x)=₂ – A₂/(b + x)² for x>0, and ₁ – A₁/(a² = ₂ – A₂/b² in the plane x=0. In the limita0, b0, they found results corresponding to a slab with a dielectric constant having a first-order pole; it is in this case that complete shielding is achieved. This method for obtaining the corresponding results is analogous to the method used in [1] and the present paper. We also note that the distribution of the effective dielectric constant (6) in the immediate vicinity of the pole—where the contribution of the last term. (1–u)x², can be neglected—is the same as the distribution adopted in [8] if we seta-b-0, ₁ = ₂, A₁=A₂=u.Scientific-Research Institute of Radiophysics. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 19, No. 8, pp. 1130–1141, August, 1976.     

The metal-semiconductor transition in amorphous Si1−x Cr x films:T 0.19-contribution to the metallic conductivity

A detailed phenomenological re-analysis of previously published conductivity data, (T, x), is presented. It is based on the investigation of differences, (T, x ₁)–(T, x ₂). In this way, the cusp-like low-temperature term is amplified against the other temperature dependent contributions. This term can be described by wherep=0.19±0.03. It is present, if (4.2 K,x) exceeds 260 ^–1 cm^–1, at least up to (4.2 K,x)1350 ^–1 cm^–1 and forT60 K. But it is absent, if (4.2 K,x)180 ^–1 cm^–1. The disappearance of this contribution should be related to the metal-semiconductor transition, taking place atx _c 0.14. On the other hand, the presence of a term proportional toT ^1/2, as predicted by Altshuler and Aronov, seems unlikely.It is argued that the term should be related to the interplay of electron-electron interaction and disorder. The comparison with data from the literature shows that this contribution might also be present in heavily doped crystalline semiconductors.     

Positron mobility in anthracene

We have measured the positron mobility in a sample of scintillation grade anthracene at two temperatures. We obtain at 300 K: =(26.0±0.9±2.6) cm²V^–1s^–1 and at 77 K: =(33.4±1.1±3.3) cm²V^–1s^–1, where the first error estimate is statistical and the second is systematic. We have also made preliminary measurements on a highly purified sample that yields =(130±3±20) cm² V^–1 s^–1 at 300 K. The data are consistent with the hypothesis that the positron is scattered from both impurities and acoustic phonons in the first sample, and predominantly from photons in the second. It appears that positrons in pure anthracene crystals are delocalized and have a mean free path of about 85 Å at room temperature.     

Measurement of the magnetic dipole moment of the 57 keV state of143Pr by time-differential perturbed angular correlation technique

The magnetic dipole interaction of the 57 keV state of¹⁴³Pr in an environment of metallic cerium and in an aqueous solution of Ce(NO₃)₃ has been investigated by time-differential perturbed angular correlation experiments. The measurements were performed in external magnetic fields between 0.94 T and 2.24 T and at temperatures between 77 K and 1200 K. From the temperature dependence of the observed spin rotation the ionicity of the Pr ion is determined as Pr⁴⁺ in the Ce(NO₃)₃ and as Pr³⁺ in Ce metal in the intermediate nuclear state. The magnetic dipole moment of the 57 keV state is derived as = +(3.4±0.1)_K. From the room temperature relaxation constants ₂ = (0.19±0.03)10⁹s^–1 for Ce(NO₃)₃ and ₂= (0.07±0.02)10⁹s^–1 for Ce metal the correlation times _J = (3.8±0.7)10^–13s and _J = (1.4±0.4)10^–13s respectively are deduced. The angular correlation coefficientA ₂=+0.17±0.02 is in good agreement with the result of a decoupling experiment.     

Asymptotic behaviour of spin-momentum distribution observables for fermion fields with cut-off self-coupling

In a previous paper asymptotic creation and annhilation operatorsa _± ^# have been constructed by the Kato-Mugibayashi method from the creation and annihilation operatorsa ^# for spin 1/2 fields with an interaction Hamiltonian density which is an evendegree polynomial in the field with ultra-violet cut-off and its derivatives. For any eigenvector of the total HamiltonianH=H ₀+H _I partial isometries _± have been defined so thata _± ^# equal _± a ^# *_± on the ranges _± of _±. Since the existence of a groundstate ofH has been proved, the existence of at least one pair _± follows. The purpose of this paper is to show that for any _± orthogonal to the distribution of spins and momenta of the interacting Schrödinger states exp[–itH]_± approaches fort the distributions of spins and momenta of the free state exp[–itH ₀] if a wave-amplitude renormalization is carried out in _±. This is achieved by studying the expectation values of the operators in themaximally abelian W*-algebra generated by operators of the form a*a, in terms of whichany information about spins and momenta can be expressed.Supported in part by the National Research Council of Canada.     

Determination of the nuclear parameters of155Gd excited states using the Mössbauer effect

From Mössbauer spectra of GdAlO₃ and GdVO₄ above and below the Néel temperature and fitted using a transmission integral, we have determined the following parameters of the 86.5 keV and 105 keV levels:g(86)/g(0)=+1.217±0.005,Q(86)/Q(0)= +0.10±0.02,g(105)/g(0)=–0.55±0.02,Q(105)/Q(0)=+0.74±0.02, r ²₁₀₅/ r ²₈₆=+1.30±0.05. The linewidth observed for the 105 keV transition is less than the calculated natural linewidth.     

Nuclear structure effect in internal conversion of the 166 kev hinderedM1 transition in139La

The internal conversion coefficients were calculated for the 165.853 keV 5/2⁺7/2⁺ hindered transition in ₅₇ ¹³⁹ La using the new computer program NICC for conversion coefficients of all atomic shells. The algorithm employed in this code is described. The analysis of precise experimental data yielded the nuclear penetration parameter=4.2±0.8. This value was found to be in accord with theoretical estimates and to correspond to the Nilsson deformation parameter=–0.056±0004 of the¹³⁹La nucleus. Using the Nilsson wave functions for above the mixing ratio ² = N(E2)/N(M1) was determined to be less than 8.10^–5, which supports the assumption of a pureM1 multipolarity of this transition.Presented at the 26th All-Union Conference on Nuclear Spectroscopy and Nuclear Structure (February 1976, Baku, USSR).We are obliged to Dr. B. N.Subba Rao for the communication of his value for the investigated transition.     

Optical absorption and electronic transport in ion-implantation-doped polycrystalline SiC films

Fine-grained (d0.1 m), polycrytalline SiC films were prepared on top of insulating and optically transparent sapphire substrates by means of a thermal crystallization technique. Optical absorption measurements indicate that the individual SiC grains consist of relatively defect-free -SiC surrounded by high-defect density grain-boundary material. Nominally undoped material exhibits a low de conductivity (10^{–8 –1} cm^–1) in the dark and an efficient photoconductivity apon illumination with short-wavelength UV light. The temperature dependence of the de transport exhibits a quasi-Arrhenius-type behaviour with average activation energies of the order to 0.6 eV. A characteristic feature of this kind of transport is a continuous increase in activation energy with increasing film temperature. Upon doping with N, P and Al ions, the average activation energy is decreased and room temperature conductivities of the order of 0.1 ^–1 cm^–1 are reached. Doping with B ions, on the other hand, only leads to high-resistivity material. It is shown that the electronic transport in doped SiC-On-Sapphire (SiCOS) films can be successfully modelled in terms of a grain-boundary-dominated conduction process. In this process thermal activation across potential barriers at the grain-boundary surfaces competes with funneling through these same barriers.     

Parity violation in the 17/2−–17/2+ doublet in93Tc

The parity-violating mixing of the 17/2^– and 17/2⁺ levels in⁹³Tc nuclei, polarized by the tilted multifoil interaction, was measured by the observation of the forward-backward-ray asymmetry. The nuclear polarization, induced by the tilted multifoils, was measured directly for the neighboring^88,90Zr isomers. The forward to backward asymmetry was determined to be A=(2.5±2.1) 10^–3 which implies a parity violating matrix element ¦H _PV )¦=(4.0±3.7)meV.