Nuclear spin relaxation of Xe in liquid Te

By the method of time differential perturbed angular distribution following a nuclear reaction, the relaxation rateT _r ^?1 of the 8 msI ^π=10⁺ isomer of¹³²Xe has been measured in liquid Te. Between 670 °K (supercooled liquid) and 1,000 °K the rate decreases from about 720/s by about a factor of two. From existing experimental material it is concluded thatT _r ^?1 is mainly due to quadrupolar interaction (T _r ^?1 ≈T _Q ^?1 ). Its magnitude is discussed considering the metallic and the noble gas limit as models for the Xe-Te-interactions. The temperature dependenceT _Q(T) apparently does not correlate with the diffusion constant of Te in contrast to a simplified theoretical treatment. — The nuclearg value of the isomer has been determined to be g=(?)0.195(5) thus confirming the configuration (vh_11/2)².     

The temperatures of protons andπ − mesons in central nucleus-nucleus interactions at a momentum of 4.5 GeV/c per incident nucleon

An estimate of the temperature of protons and ^– mesons in central He–Li, He–C, C–C, C–Ne, C–Cu, C–Pb, O–Pb, Mg–Mg interactions is presented. The results indicate an increase of the proton temperature with increasing mass numbers of projectile and target nuclei (A _p ,A _T ) fromT _p =(118±3) MeV for He–Li toT _p =(141±2) MeV for C–Pb. The temperature of ^– mesons does not depend onA _P ,A _T andT 95 MeV. A satisfactory fit for ^– mesons in C–Cu, C–Pb, O–Pb, Mg–Mg collisions can be achieved by using a form involving two temperatures,T ₁ andT ₂. The relative yield of the high temperature component (T ₂) is 24% for C–Cu, C–Pb, and Mg–Mg interactions. The observed results forT _P in C–Ne, C–Cu and C–Pb collisions are consistent with the prediction of the thermodynamic hagedorn model.     

General relativity in a (2+1)-dimensional space-time: An electrically charged solution

We have found a static electrically charged solution to the Einstein-Maxwell equations in a (2+1)-dimensional space-time. Studies of general relativity in lower dimensional space-times provide many new insights and a simplified arena for doing quantum mechanics. In (2+1)-dimensional space-time, solutions to the vacuum field equations are locally flat (point masses are conical sigularities), but when electromagnetic fields are presentT ^ab O and the solutions are curved. For a static chargeQ we find andds ²= –(kQ ² /2)In(r _c /r)dt ² + (2/kQ ²[ln(r _c /r)]^–1 dr ² +r ² d ² wherer _c is a constant. There is a horizon atr =r _c like the inner horizon of the Reisner-Nordström solution. We have produced a Kruskal extension of this metric which shows two static regions (I and III) withr <r _c and two dynamical regions (II and IV) withr>r _c . A spacelike slice across regions I and III shows a football-shaped universe with chargeQ at one end and –Q at the other. Slices in the dynamical regions (II and IV) show a cylindrical universe that is expanding in region II and contracting in region IV. Electromagnetic solutions to the Einstein-Maxwell field equations in lower dimensional space-times can be used to provide new insights into Kaluza-Klein theories. In terms of the Kaluza-Klein theory, for example, electromagnetic radiation in a (2+1)-dimensional space-time is really gravitational radiation in the associated (3+1)-dimensional Kaluza-Klein space-time. According to Kaluza Klein theory the absence of gravitational radiation in (2+1)-dimensional space-time implies (correctly) the absence of electromagnetic radiation in (1+1)-dimensional space-time.     

Half-lives andg-factors of some microsecond isomers in the lead region

The g-factors and half-lives of the (8^–) isomer in¹⁹⁸Pb, the 29/2^– isomer in¹⁹⁹Pb and the 19⁺ isomer in²¹⁰At have been remeasured by the time differential perturbed angular distribution technique. A new beam pulsing equipment was used in these experiments. The results are for¹⁹⁸Pb; g=–0.0471(8) and T_1/2=4.19(10)s, for¹⁹⁹Pb; g=–0.0742(9) and T_1/2=9.8(4) s and for²¹⁰At; g=0.698(7) and T_1/2=5.9(3)s.     

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.     

Dielectric/piezoelectric properties and temperature dependence of domain structure evolution in lead free single crystal

(K_0.5Na_0.5)NbO₃ (KNN) single crystals were grown using a high temperature flux method. The dielectric permittivity was measured as a function of temperature for [001]-oriented KNN single crystals. The ferroelectric phase transition temperatures, including the rhombohedral–orthorhombic T_R−O, orthorhombic–tetragonal T_O−T and tetragonal–cubic T_C were found to be located at −149  C, 205 C and 393 C, respectively. The domain structure evolution with an increasing temperature in [001]-oriented KNN single crystal was observed using polarized light microscopy (PLM), where three distinguished changes of the domain structures were found to occur at −150  C, 213 C and 400 C, corresponding to the three phase transition temperatures.     

The Debye-Waller factor and the diffusion process for hydrogen in Nb,Ta, and V single crystals investigated by neutron spectroscopy

Quasielastic scattering of slow neutrons on hydrogen diffusing in the-phase of NbH_0.02, TaH_0.13 and VH_0.07 single crystals was investigated in a wide range of temperatures and scattering vectorsQ (0.5Q2.5 Å^–1). The incoherent scattering lawS _d (Q,) for four different diffusion models was consistently compared with the measured lineshapes. At elevated temperatures one had to introduce correlated jumps to describe the experimental data, whereas at room temperature a model with jumps between adjacent sites is sufficient. The integrated quasielastic intensityI(Q) obtained from the fit ofS _d (Q,) with the measured spectra follows an isotropic Debye-Waller factor with mean square amplitudes u ²=0.02–0.04 Ų for H in Ta (20°C–500°C), and u ²=0.03–0.04 Ų for H in Nb (20°C–300°C). For H in V,I(Q) obtained from the analysis of the quasielastic scattering deviates from a normal Debye-Waller factor behaviour. This effect is assumed to be due to the flight process between the interstitial sites. On the other hand, a normal Debye-Waller factor was obtained from theQ-dependence of the inelastic scattering of the band modes, with values of u ²=0.02–0.04 Ų (135°C–500°C). The observed values of u ² were compared with theoretical calculations.     

Critical thermodynamics of dysprosium ethyl sulphate, a pure dipolar Ising ferromagnet

Using a SQUID magnetometer the magnetization of the Ising ferromagnet dysprosium ethyl sulphate has been measured in the temperature range 0.015–3K and in external fields 0.004–30 Oe. The results atT0.4 K (precritical regime) confirm the pure dipolar nature of the magnetic interactions. Particular interest has been paid to the immediate neighbourhood of the critical pointT _c =118.17 mK andH=0 where the zero-field susceptibility(T) aboveT _c , the spontaneous magnetizationM _s (T), and the magnetization atT _c ,M _c (H), can be described by mean field laws modified by logarithmic singularities. The critical amplitudes, B, andD of, M _s andM _c , respectively, satisfy the relation (2/3B ²)^1/3=D. All these results agree with predictions of (i) the Larkin-Khmel'nitskii theory and (ii) exact solutions of the renormalization group equations for 3-dimensional dipolar Ising ferromagnets.     

Temperature dependence of the electric field gradient of Hg in Bi

The temperature dependence of the nuclear quadrupole interaction of the¹⁸⁸Hg(12⁺) isomer in a Bi host has been measured by the TDPAD technique. Assuming that the T^3/2 law is valid for this system a fit at the high temperature region yields _Q(T=0)=132(6) MHz and B=7.2(6)×10^–5K^–3/2. The EFG of HgBi and the temperature dependence strength follow the general trend of other probes in Bi.Supported in part by the MINERVA Foundation, Munich, Germany and the Israeli Academy of Science, Jerusalem, Israel.Incumbent of the Arye Dissentshik Career Development Chair.Incumbent of the Ruth Epstein Recu Career Development Chair.     

NMR enhancement and NMR relaxation in a <110> FeSi Néel-type single crystal

⁵⁷Fe NMR measurements with a Néel-type single crystal are described. The behaviour of the magnetic structure was calculated as function of the internal fieldH _i. A clear distinction between wall and domain signals could be made. The corresponding relative enhancement factors _w ^r (H _i) and _D ^r (H _i) have been calculated and are in agreement with the measurements. The relaxation in the 90° Bloch walls is pure exponential. Both ratesT ₁ ^–1 andT ₂ ^–1 are proportional to _w ² (H _i). The measurements make proof, that the 90° walls are folded inside the crystal.K.-H. König and H. Brömer, Verhandl. DPG(VI)22, I, AM-14.11 (1987)     

Tau decays into K* mesons

Using the ARGUS detector at the storage ring DORIS II we have measured decays into three charged mesons containingK ^* mesons. Exploiting the good particle identification capabilities of the detector we have determined the following branching ratios: ,B _r (^–K ^*0 K ^– v )= (0.20±0.05±0.04)%, andB _r (^–K ^*– X ⁰ v ) =(1.15±0.15_–0.18 ^+0.13)%.Supported by the German Bundesministerium für Forschung und Technologie, under contract number 054DO51P.     

Energieverlust und Lichtausbeute bei axialem Channeling von α-Teilchen in Anthrazen

In an atomic beam experiment we measured the hyperfine structure (hfs) of the metastable states 3d ² 4s ⁴ F _3/2,9/2 of Scandium, which were populated by electron impact. A single mode cw dye laser was used to create a population difference between neighbouring hfs states by optical pumping. Rf transitions between these states, equalizing the population numbers, could then be detected by repeating the optical pumping experiment and looking for the laser induced fluorescent light. The following constants of the magnetic dipole and electric quadrupole interactions have been obtained by this method:A _3/2=–158.513(3)MHzB _3/2=–5.19(2)MHzA _9/2=285.967(9)MHzB _9/2=–15.46(70)MHzFrom these constants and the corresponding values forJ=5/2, 7/2, as measured by [1], the following parameters can be calculated: r ^–3 _d ⁰¹ =0.911(4)a ₀ ^–3 r ^–3 _d ¹² =2.395 (62)a ₀ ^–3 and:=r ^–3 _d ⁰¹ /r ^–3 _d ¹² =0.38(1).     

Structural phase transition and internal fields in rubidium thiocyanate probed through vibrational spectroscopy

A comprehensive vibrational study of Rubidium thiocyanate (RbNCS), in the 298–448°K range reveals that the orthorhombic to tetragonal transition atT _c440°K is of order-disorder type exhibiting purely second order characteristics. A consistent order-parameter exponent 0.45±0.04 has been obtained from both Raman and IR measurements. In the Raman spectra, the appearance of sidebands in both the C–N&C–S stretching modes and their temperature dependence indicate the existence and a gradual diminution of internal electric field asT approachesT _c. These results have been discussed in the context of an anharmonic oscillator model. An activation energy (U) for the reorientational motion of NCS^– ions,U0.29±0.02 eV, has been calculated from large changes in the bandwidth (_C-N) nearT _c.     

Observation of the decaya 2 − (1320)→π − η′

The reaction ^– C ^– C has been studied at 36 GeV/c. A clear signal for the decaya ₂ ^– (1320) ^– · is observed in the ^– mass spectrum. The measured ratio of branchings is BR (a ₂ ^{– –} )/BR(a ₂ ^{– –} );(3.4±0.8±0.5)·10^–2.     

Magnetic and electric hyperfine interactions in the system EuSm

Magnetic and electric hyperfine interactions in the system EuSm were investigated with the isomeric 11/2^– state in¹⁴⁵Eu by applying the time-differential perturbed angular distribution (TDPAD) method. The temperature dependence of paramagnetism was studied between 90 K and 1000 K by measuring the magnetic hyperfine interaction frequency _L=g_NN¹ (T)B_ext. The paramagnetic correction factor strictly follows the Curie-Weiss relation =1+C/(T-), withC=–50(2) K and =–29(5) K. This is compatible with a hyperfine field ofB _int(0)=–25(1) T, a valence of two for Eu in Sm, and antiferromagnetic order at low temperatures.The temperature dependence of the electric quandrupole coupling constant v_Q, investigated between 100 K and 400 K, can be reproduced by a linear temperature variation v_Q(T)=v_Q(0) (1-AT), with v_Q(0)=16.2(4) MHz andA=7.2(8)·10^–4 K^–1.The paramagnetic relaxation time _rel of the nuclear alignment is proportional to the temperature of the sample, with _rel T^–1=3.7(2) ·10^–9s K^–1.This leads to the Korringa relation _J T=const=5.1(5)·10^–11s K for the relaxation time of the 4f electronic spinJ. Assuming that the relaxation ofJ is mainly caused by exchange interaction between conduction electrons and localized 4f electrons at the Eu site, an exchange integral of |J _eff|=0.10(2) eV can be deduced.     

Normal state resistivity of YBa2Cu3O7−x

A systematic study has been carried out on the normal state resistivity of YBa₂Cu₃O_7–x . Samples were cut from the same well-annealed material and were quenched from different temperatures (T _Q ). The resistivity is metallic whenT _Q 500 °C and becomes semiconductor-like whenT _Q 600 °C. The data on the latter was interpreted in terms of the three-dimensional localization model proposed by Mott.The work at USCD was supported by the California MICRO program     

Wetting transition on grain boundaries in Al contacting with a Sn-rich melt

The contact angle at the intersection of a grain boundary in Al bicrystals with the solid Al/liquid Al–Sn interphase boundary has been measured for two symmetric tilt <011> {001} grain boundaries with tilt angles of 32° and 38.5°. The temperature dependencies (T) present the evidence of the grain boundary wetting phase transition at T_w. The observed hysteresis is consistent with the assumption that the wetting transition is of first order. The determined discontinuity in the temperature derivative of the grain boundary energy is–5.6 J/m²K (T w1=617°C) for the boundary with a low energy (=38.5°) and –17 J/m²K (T w2=604°C) for the grain boundary with a high energy (=32°).     

The structure of28Si above 10 MeV excitation energy II: Assignments of quantum numbers

New assignments of quantum numbers have been obtained for more than 50 levels in²⁸Si between 8953 and 15915 keV excitation energy. They are based on the measurement of -ray angular distributions or anisotropies on 29 resonances of the²⁷Al(p, ) reaction and on the²⁴Mg(a, ) resonance atE =3355 keV. A total of 15 high-spin states withI=5–7 has been obtained and the spectrum ofT=1 states has been identified up to 15915 keV excitation energy and a maximum spinI=6.     

Relativistic dynamics of interacting point particles: Central position of the Wheeler-Feynman scheme

The Wheeler-Feynman (WF) relativistic theory of interacting point particles, generalized by acceptance of an arbitrary spacelike interaction, is shown to possess a privileged status, reminiscent of the central force interactions occurring in Newtonian mechanics. This scheme is shown to be isomorphic to the classical one of the statics of interacting flexible current-carrying wires obeying the Ampère-Laplace (AL) formulas: to the tensionT (T ² =const) of the wire corresponds the momentum-energy pⁱ (p_ipⁱ=–c²m²) of the particle; to the Laplace linear force density –iH×dr corresponds the Lorentz force QH^ij dr_j; to the Laplace potential ir^–1 dr corresponds the WF potential Q(r²) drⁱ, etc. Among the differences, there is self-action in the AL scheme and no self-action in the WF scheme. A stationary energy principle in the AL scheme is isomorphic to Fokker's stationary action principle in the WF scheme.     

Low temperature acoustic properties in YBa2Cu3O7−δ

Temperature dependencies of acoustic lossesQ ^–1 and of relative sound velocity change v/v in YBa₂Cu₃O_7– up to 60 K are calculated by the tunneling model theory. The tunneling systems are related to the off-centered positions of the apical oxygen atoms O(A) and are described through the pseudo-Jahn-Teller effect. Tunneling systems' parameters are distributed in narrow range of values and are in correspondence with the experimentally observed infrared phonon spectra and thermal ellipsoids of O(A). Respective relaxation times are calculated by the adapted reaction rate method. The calculatedQ ^–1(T) and v(T)/v dependencies are in good agreement with the experimental data, which is an additional support to the conclusion about the existence of tunneling systems in YBa₂Cu₃O_7– due to the pseudo Jahn-Teller effect.