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.     

Gyromagnetic ratios of first 2+ states in126, 128, 130, 132Xe

Gyromagnetic ratios of first 2⁺ states in^{126, 128, 130, 132}Xe were determined by implantation perturbed angular correlations (IMPAC). The effective hyperfine magnetic field together with the transient magnetic field at xenon nuclei in iron was utilized to obtain the precession of the angular correlation. The precession due to the transient field was taken from systematics to be /g=–36±6 mrad. The effective hyperfine magnetic field was determined in an experiment on¹²⁶Xe in iron to be 900±200 kG. The results for theg-factors areg(128)=0.41±0.07,g(130)=0.38±0.07 andg(132)=0.37±0.05. Theg-factor of the 2⁺ state in¹²⁶Xe was determined in a separate experiment using a radioactive source of¹²⁶I to beg(126)=0.37±0.07, and was used as calibration for the IMPAC-data.     

The electric field gradient for Gd in gadolinium metal

We have examined the temperture dependence of the efg for GdGd above the Curie point. Using anI =10⁺ isomer in¹⁴⁴Gd as a probe nucleus, we find a weakT ^3/2 dependence withB=(1.5±0.4) 10^–5 K^–3/2. The absolute value of the efg at 332 K was measured by Coulomb excitation of 2⁺ states in^{156, 158, 160}Gd, yielding |eq(332 K)|=(3.43±0.14) 10¹⁷ V/cm². A possible small deviation from theT ^3/2 temperature dependence of the efg for ferromagnetic Gd is discussed.     

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.     

Nuclear magnetic moment of 12 d 11/2− 131mXe

NMR-ON measurements were performed on^131mXe (I=11/2^–; T_1/2=12.0 d) in Fe, the sample being prepared by recoil implantation after the¹³⁰Te(,3n)^131mXe compound reaction at E=40 Mev. The hyperfine splitting _NB_HF/h¦, extrapolated to zero external magnetic field, was found to be 209.9(1) MHz. Taking B_HF=+1523(8) kG for the hyperfine field of XeFe, the magnetic moment of^131mXe is deduced to be (–)0.994(5) _N. As a byproduct, the zero-field hyperfine splitting of^129mXe (I=11/2^–; T_1/2=8.9d) in Fe was measured as 188.1(1) MHz, with which a magnetic moment of (–)0.891(5) _N is deduced for^129mXe.     

Muonium quantum diffusion and spin dynamics in solid xenon

We present measurements of the transverse (T ₂ ^–1 ) and longitudinal (T ₁ ^–1 ) spin relaxation rates of muonium (Mu) atoms in solid natural xenon (n-Xe) as well as pure¹³⁶Xe (which has no nuclear moments). The temperature dependences ofT ₂ ^–1 andT ₁ ^–1 in natural Xe belowT 115 K demonstrate the quantum character of Mu diffusion governed by one-phonon interactions. Taking into account both the polaron effect (PE) and the effect of fluctuational preparation of the barrier (FPB) makes it possible to consistently describe Mu diffusion in Xe. Mu spin relaxation in¹³⁶Xe at high temperatures is not due to nuclear hyperfine (NHF) interactions.     

Synthesis and Reactivity of Mg(II)–Fe(II)–Fe(III) Hydroxycarbonates

Green rust-like compounds (GRs) were discovered as natural minerals in various hydromorphic soils, where anoxic conditions allow their stability. They may control some redox processes in aquifers and participate to the transformation of various pollutants. Since Mg(II) cations are present in the fields where GRs were discovered, a partial substitution of Mg(II) to Fe(II) leading to intermediate compounds between GRs and usual Mg(II)–Fe(III) hydroxysalts is suspected. Mg(II)–Fe(II)–Fe(II) hydroxycarbonates can be obtained as intermediate oxidation products of (Mg, Fe)(OH)₂ in carbonate-containing aqueous media obeying to [Fe^II _4(1–x)Mg^II _4x Fe^III ₂(OH)₁₂]²⁺ [CO₃ ^2– nH₂O]^–2. TMS spectra at 12 K are similar to those of GRs, i.e., two quadrupole doublets, one due to Fe(II) with a large isomer shift =1.29 mms^–1 (with respect to -iron at room temperature) and quadrupole splitting E _Q=2.76 mms^–1, the other one due to Fe(III) with smaller hyperfine parameters =0.49 mms^–1 and E _Q=0.44 mms^–1. Fe(II) ions oxidise rapidly into Fe(III) with dissolved O₂. The reactivity is similar to that of Fe(II)–Fe(III) hydroxysalts GR, and thus the potential of Mg(II)–Fe(II)–Fe(III) compounds for reducing pollutants.     

Isotope shift and hyperfine structure measurements at the242f Am fission isomer

Istope shift and hyperfine structure measurements have been performed for the^242fAm fission isomer with target production rates of only a few per second. The method is based on resonance ionization spectroscopy (RIS) in a buffer gas cell with radioactive decay detection of the ionization process (RADRIS). A relative isotope shift ratioX _exp=IS^242f,241/ IS^243,241=41.7±0.9 has been measured for the 500.02 nm transition corresponding to a nuclear parameter ^242f,241=5.4±0.3 fm². The analysis of the quadrupole moment based on the deformed Fermi-model of the nuclear charge distribution including second order corrections results inQ ₂₀=38.2 ±1.4( _–0.8 ^+0.4 )_model eb. The measurement of the hyperfine structure splitting of the transition at 466.28 nm yields a negativeg-factor and a nuclear spin ofI=2 orI=3.Work supported by the Bundesministerium für Bildung und Forschung under contract 06 MZ 5661.     

Local quantum field theories involving the U(1) current algebra on the circle

The OPE algebra Q=Q(g ² ) generated by a pair of oppositely charged currents (z,±g)(|z|=1) of spin is specified by the leading terms in the small distance expansions of (z ₁,g)(z ₂, -g) and (z ₁,g)(z ₂,g). The current (z,g) splits into a product of a U(1)-Thirring field and a Zamolodchikov-Fattev parafermionic current. The quasilocal(i.e.single-or double-valued) representations of Q are classified. The level k states involve 2(k+1) (ks–k+1) lowest weights (dimensions). The results can be viewed as an extension of the (known) representation theory of the SU(2) current algebra in the bosonic case corresponding to even values of g ² and of the N=2 extended superconformal algebra in the fermionic case corresponding to odd g ².     

Time component of the mirror beta decays of12B and12N

Beta-ray angular distributions from aligned¹²B and¹²N have been observed in order to study the meson-exchange effect in a nucleus. Alignment-correlation coefficients for¹²B and¹²N were determined to be _–=–(0.0174±0.0059)%/MeV and ₊=–(0.2774±0.0086)%/MeV, respectively. These values are fairly consistent with the previous values, while the reliability was greatly improved. From these coefficients, the nuclear parametery, i.e. the ratio of the time component of the axial vector currents of the Gamow-Teller matrix element, was determined to bey=4.13±0.15. The value is enhanced by 33% from that calculated by use of the impulse approximation, which clearly shows a considerable effect due to meson-exchange currents.     

Forbidden lines in the hyperfine spectrum of the electron paramagnetic resonance of Mn++ in BaTiO3

The hyperfine spectrum of Mn⁺⁺ in powder BaTiO₃ was studied at 8740 MHz andT=80°K. The measured lines appearing as doublets between the hyperfine lines of Mn⁺⁺ are explained as forbidden transitions of the typeM=±1,m=±1. A theoretical expression for the position of these doublets is given and some of the constants of the spin Hamiltonian are determined:g=2.001±0.001, ¦A¦=86 Oe,D 40 Oe.     

Subthreshold kaon production in Au on Au collisions at 1 GeV/u

Subthreshold kaon production in¹⁹⁷ Au+¹⁹⁷ Au collisions at 1.0 GeV/u has been investigated with the Kaon Spectrometer at SIS. At _lab =44±4 we found aK ⁺/p ratio of>3 · 10^–4 for the momentum range 650 MeV/c to 1150 MeV/c.Dedicated to Prof. Dr. P. Kienle on the occasion of his 60th birthday     

ArF laser CVD of hydrogenated amorphous silicon: The role of buffer gases

ArF laser-induced CVD has been employed to generate hydrogenated amorphous silicon (a-Si:H) from Si₂H₆ gas dilute with He, Ar, or H₂. The formation of amorphous films or powder is found to depend critically on the kind of buffer gas, the stationary total and partial gas pressures, and the substrate temperature. These dependences have been investigated in the 1–5 Torr pressure and 100–400 °C temperature ranges. They are semiquantitatively discussed in terms of ArF laser photolysis of disilane, gas heating by heat flow from the substrate and laser irradiation, diffusion, and gas phase polymerization. Furthermore, photo ionization has been observed but found irrelevant for the a-Si:H layer properties. The photo and dark conductivities ( _ph, _d) of the semiconductor layers are determined by the substrate temperature. The _ph values range between 10^–7 and 10^{–4 –1} cm^–1 and the _d values between 10^–11 and 10^{–8 –1} cm^–1. The maximum ratio _ph/ _d amounts to 4×10⁴. The layers are further characterized by their optical band gap and activation energy. The layer properties are compared to literature values of amorphous films prepared by various photo, HOMO, and plasma CVD methods.     

119Sn-mössbauer,IR, and DSC study of tin oxyfluoride glasses

The¹¹⁹Sn-Mössbauer spectra ofxSnO·(70–x)SnF₂·30P₂O₅ glasses (0 x70) measured at 78 K comprised a doublet due to Sn²⁺ (=3.30–3.36 mm s^–1, = 1.70–1.72 mm s^–1) and a weak singlet due to Sn⁴⁺ located at –0.23 mm s^–1 with respect to BaSnO₃. The and of Sn²⁺ were comparable to those of Sn₂P₂O₇. Small Debye temperatures (146 and 155 K) were obtained from the low-temperature measurements. These results indicate that Sn²⁺ and Sn₄₊ occupied interstitial sites, being loosely and ionically bonded to distorted PO_4–x F _x tetrahedra.     

On determination of the 2p-energy level shift and width for π−-4He atom

The strong interaction shift and width in the 2p-level of the pionic helium have been deduced from the analysis of the low-energy -⁴He scattering data. The obtained values are: _2p=4·0 × × 10^–3 eV and _2p=1·6 × 10^–3 eV. The analysis has been performed within the framework of the UST approach.Presented at the IV International Symposium Mesons and Light Nucler, Bechyn, Czechoslovakia, September 5–10, 1988.     

Comparison of (π− d→nn withdσ(π+ d→pp) to test charge symmetry in the Δ-region

First results on ^– d are reported. The measurements were made using 8 specially designed neutron counters, which were carefully calibratedin situ. The differential cross sections atT =142, 180, 217, and 254 MeV were obtained at four angles between 0° and 90°, they are compared to ⁺ d pp data measured at the same energies and angles with the same setup. At every beam energy, the shape of the angular distributions of ^– d nn and ⁺ d pp is the same to ±2%. The absolute cross sections differ by 1 to 10%. The error in this comparison is ±4% implying a small violation of charge symmetry.Dedicated to Prof. I. laus on the occasion of his 60th birthdayDeceased     

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).     

Mössbauer and EPR study of nitrosyl hemoglobin

Nitrosyl hemoglobin was prepared by bubbling fresh⁵⁷Fe-enriched rat hemoglobin with NO. S- and X-band EPR spectra at 77 K are typical for anS=1/2 system with an anisotropicg-tensor and exhibit hyperfine interactions of¹⁴N with the electronic spin. Mössbauer spectra at 4.2 and 100 K consist of a superposition of spectra from high- and low-spin Fe(III), deoxygenated hemoglobin and a component corresponding toS=1/2,g=2, hyperfine constantsA _xx /g _{n n} =A _yy /g _{n n} =–19.6 T,A _zz /g _{n n} =6.8 T, quadrupole splitting E _Q=1.5 mm s^–1, isomer shiftI _s=0.42 mm s^–1 and linewidth 0.4 mm s^–1. The spin-lattice relaxation rate at 100 K is <2×10⁶ s^–1.     

The d + d reactions at low energies I. The structure of4He in the vicinity of the d-d threshold

Polarization data concerning the polarization of the outgoing nucleons from the²H(d, n)³He and²H(d, p)³H reactions have been analysed in order to search for a resonanceJ =1^– near the d-d threshold in⁴He. The data were analysed in the theoretical framework of theR-matrix approach. The non-resonant behaviour of these polarization observables showed no evidence for aJ =1^– level of the⁴He at 24.1 MeV.     

Local observables and particle statistics I

We consider the family of those states which become asymptotically indistinguishable from the vacuum for observations in far away regions of space. The pure states of this family may be subdivided into superselection sectors labelled by generalized charge quantum numbers. The principle of locality implies that within this family one may define a natural product composition (leading for instance from single particle states ton-particle states). Intrinsically associated with then-fold product of states of one sector there is a unitary representation ofP ⁽ⁿ⁾, the permutation group ofn elements, analogous in its role to that arising in wave mechanics from the permutations of the arguments of ann-particle wave function. We show that each sector possesses a statistics parameter which determines the nature of the representation ofP ⁽ⁿ⁾ for alln and whose possible values are 0, ±d ^–1 (d a positive integer). A sector with 0 has a unique charge conjugate (antiparticle states); if =d ^–1 the states of the sector obey para-Bose statistics of orderd, if =–d ^–1 they obey para-Fermi statistics of orderd. Some conditions which restrict to ± 1 (ordinary Bose or Fermi statistics) are given.