Hyperfine quantum beat of short-lived beta-emitter8Li polarized by the tilted foil technique

To disclose the basic mechanisms of nuclear polarization creation realized by the tilted foil technique, hyperfine quantum beats of the nuclear polarization of the short-lived beta-emitter⁸Li(I =2⁺,T _1/2=840 ms) were measured as a function of the distance between two tilted foils. From the observed beats of the⁸Li nuclear polarization, it was found that the Fermi-contact interaction of the⁸Li nucleus with the ground 1s-electron in LiIII plays a main role in the final stage of polarization transfer from polarized orbital electrons to the⁸Li nucleus.     

Giant quadrupole moment andproton halo discovered in8B

The nuclear quadrupole moment of⁸B(I =2⁺,T _1/2=769 ms) has been determined by use of a modified -NMR detection as |Q(⁸B)|=68.3±2.1 mb, which is twice the prediction of the Cohen-Kurath shell model calculation. The anomalous quadrupole moment which is carried mainly by the protons in the nucleus, has been accounted for by the proton halo effect.     

Precise measurement of the quadrupole moment of β-emitting12B

Hyperfine interactions of¹²B(I ,T _1/2=21 ms) implanted in the substitutional site of B atoms (stable) in a (single crystal like) BN (hexagonal) was studied by use of a -NMR detection. For efficient and simple measurements, the conventional -NMR has been modified as a new nuclear quadrupole resonance technique (NNQR). For the present case with the nuclear spinI=1 the detection efficiency is improved about 30 times compared with the one with the old method. The quadrupole moment of¹²B was determined precisely as ¦Q(¹²B; 1⁺)¦=13.21±0.26 mb.     

Precise measurement of quadrupole moment of8B by use of a modified β-NMR

The nuclear quadrupole moment of⁸B(I =2⁺,T _1/2=769 ms) has been determined by use of a modified -NMR detection as |Q(⁸B)|=68.3±2.1 mb. A field gradient was obtained in a single crystal Mg at room temperature.     

Hyperfine interactions of12B in BN (hexagonal)

Hyperfine interactions of¹²B(I =1⁺,T _1/2=21 ms) implanted in the substitutional site of B in BN (hexagonal) was studied by detecting -NMR. In order to measure the quadrupole coupling constant efficiently, we employed a newly developed quadrupole resonance technique (NNQR). The quadrupole moment of¹²B was determined to be |Q(¹²B)|=13.21±0.26 mb.     

Magnetic dipole moment of127Sb by NMR/ON

The technique of NMR on oriented nuclei has been applied to¹²⁷Sb to measure the magnetic dipole moment of the¹²⁷Sb ground state. Resonant destruction of gamma-ray anisotropy from¹²⁷Sb^g (I =7/2⁺) has been observed at 139.6(2) MHz forB _app=0.30(1) T andat 138.7(1) MHz forB _app=0.25(1) T. The deduced magnetic moment is ||=2.697(6) µ_N.     

Magnetic moment of23Mg

The magnetic moment of the²³Mg (I =3/2⁺, T_1/2=11.3 s), has been determined as |(²³Mg)|=0.5364±0.003 µ_N by use of -NMR detection with the recoil polarization obtained through a low energy nuclear reaction.     

Precise measurement of the magnetic moment of doubly closed shell + 1 nucleon nucleus17F(I π=5/2+,T 1/2=64.5 s)

Hyperfine interactions of -emitting¹⁷F implanted in single crystals of NaF and CaF₂ were studied. The nuclear magnetic moment of theI =5/2⁺ state was determined with improved precision to be |(¹⁷F;I =5/2⁺,T _1/2=64.5s)|=4.72130±0.00025 µ_N.     

Nuclear Spin Alignment of 12,13B Produced in Heavy Ion Collisions

The nuclear spin alignments of the β-emitting fragments ¹²B(I ^π=1⁺, T _1/2=20.2 ms) and ¹³B(I ^π=3/2⁻, T _1/2=17.4 ms) produced in the 100A-MeV ¹³C, ¹⁵N + ⁹Be collisions respectively have been observed for the first time detecting asymmetric β-ray emission from these nuclei. By means of the spin manipulation technique based on the hyperfine interaction of B isotopes in TiO₂, both the polarization P and the alignment A were determined reliably. The obtained P and A were significantly smaller than the expectation from the kinematical model. From the fact that the quenching factors for P and A are almost the same, there may be some depolarization mechanism in the collision process itself. This revised version was published online in September 2006 with corrections to the Cover Date.     

Measurements of magnetic moments of Tc isotopes and the hyperfine field of Tc in Fe and Ni

We report measurements of nuclear magnetic resonance on oriented nuclei (NMR-ON) on⁹⁴Tc (I=7⁺,T _1/2=4.9 h),⁹⁵Tc (I =9/2⁺,T _1/2=20 h) and⁹⁶Tc (I =7⁺,T _1/2=4.3 d) in Fe and on⁹⁵Tc and⁹⁶Tc in Ni. In order to elucidate the discrepancies on the hyperfine field of TcFe in the literature, the resonances were measured with high precision as a function of the external magnetic field B_ext up to 2.0 T. In addition, TDPAC measurements were performed on⁹⁹TcFe at T=300 K and 13 K. TheT=0 K hyperfine fields of Tc in Fe and Ni were determined to be –314(3) kG and –51.8(5) kG, respectively. The g-factors of⁹³Tc,⁹⁴Tc,⁹⁵Tc,⁹⁶Tc and⁹⁹Tc(E=181 keV;I =5/2⁺) are redetermined as g(⁹³Tc)=1.405(14), g(⁹⁴Tc)=0.731(7),g(⁹⁵Tc)=1.321(13), g(⁹⁶Tc)=0.727(7), g(⁹⁹Tc)=1.390(17).We wish to thank E. Smolic and G. Seewald for experimental help. This work was funded by the German Federal Minister for Research and Technology (BMFT) under the contract number 06TM353/TP 4, by the Deutsche Forschungsgemeinschaft (DFG) under the contract numbers Ha 1282/3-1,2, and, partly, by the Kernforschungszentrum, Karlsruhe.     

Study of the centrally producer ππ andK \bar K systems at 85 and 300 GeV/c

We have studied the andK systems centrally produced in proton proton collisions at 300 GeV/c and ⁺/p proton collisions at 85 GeV/c using the CERN spectrometer. Clear evidence forS ^*/f _o(975) production is observed. An analysis performed on the ^{+ –} mass spectrum in the 1.0 GeV region, using a coupled channel formalism, shows that it is possible to describe theS ^*/f _o(975) effect with one single resonance once interference of theS ^*/f _o(975) with theS-wave background is introduced. The resultingS ^*/f _o(975) parameters arem _o =979±4MeV,g =0.28±0.04,g _K =0.56±0.18 corresponding to a pole position on sheet II at (1001±2)–i(36±4) MeV. Evidence is also found for a structure having a mass of 1472±12 MeV and a width of 195±33 MeV.     

Weak convergence of a random walk in a random environment

Let _i (x),i=1,...,d,xZ ^d , satisfy _i (x)>0, and ₁(x)+...+ _d (x)=1. Define a Markov chain onZ ^d by specifying that a particle atx takes a jump of +1 in thei ^th direction with probability 1/2 _i (x) and a jump of –1 in thei ^th direction with probability 1/2 _i (x). If the _i (x) are chosen from a stationary, ergodic distribution, then for almost all the corresponding chain converges weakly to a Brownian motion.     

Temporal optics of resonant transmission of gamma rays through57Fe

The development in time of the transmission through⁵⁷Fe of a broad Lorenztian radiation is calculated numerically. Examples are given for=0 and/2, for the magnetic hyperfine case, and for=/2 for pure quadrupole splitting.     

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.     

General tachyon absorption by Kerr-Newman black holes: Thermodynamic consequences

Following the analyses of B. Carter and J. V. Narlikar, the nature of the incomplete, spacelike trajectories about a charged, rotating black hole is described. The study concentrates on those paths which a charged tachyon would follow, incident from off the equatorial plane (on which=/2). The effect of the absorption upon the black hole is calculated and it is concluded that for _i /2 only certain charged tachyons will reduce its entropy. However, a sustained bombardment by such particles could cause the singularity to be exposed.     

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.     

Nonlocal theory of single pion photoproduction

A nonlocal interaction theory is formulated for photoproduction processes by introducing a form function. An effective nonlocal, Lorentz invariant and gauge invariant Lagrangian density for the four-field interaction that gives rise to a production amplitude is constructed. The general structure of the form function is investigated by using some restrictions of the form function. For low energy ⁰ photoproduction an explicit form of the Fourier component of the form function is obtained. The physical model of the present formalism is to assume, similar to the strong absorption model, that the system in intermediate states is confined in a finite domain of space. For ⁰ production the linear dimension of this domain is obtained to be ₀ = 3·88F. It is important to observe that the extent of electromagnetic distribution in a nucleon is also nearly the size of ₀. This is believed to be the reason that in low energy pion photoproduction the effects of electromagnetic structure of a nucleon are irrelevant. The unpolarized differential and total cross sections are calculated for ⁰ production in helicity representation and the predictions are found to be in good agreement with experiments.     

Collective structures of the <Superscript>131</Superscript>Cs nucleus

The collective structures of ¹³¹Cs have been investigated by in-beam -ray spectroscopic techniques following the ¹²⁴Sn (^11B , 4n) reaction at a beam energy E_lab = 57MeV. The previously established rotational bands, built on g_7/2, d_5/2 and the unique-parity h_11/2 orbitals, have been extended and evolve into new bands involving rotationally aligned (h_11/2)² and (h_11/2)² quasiparticles. In addition, a new multiquasiparticle band based on the g_7/2 g_7/2 h_11/2 configuration has also been observed. Theoretical interpretations for the assigned configurations are discussed in the framework of Total Routhian Surface (TRS) and Tilted Axis Cranking (TAC) model calculations. TAC model calculations predict a decrease in the B(M1) values with increasing rotational frequency for the g_7/2/d_5/2 (h_11/2)² and h_11/2 (h_11/2)² bands, thus indicating a magnetic rotation character for these bands.     

A Possible Nuclear Spin Dewar. Hyperfine Interactions of Short-Lived β Emitter 8Li and 12B in TiO2

It was confirmed by detecting the β-NMR of ¹²B (I ^π=1⁺, T _1/2=20.2 ms) in a TiO₂ (rutile) crystal that the nuclear spin polarization of ¹²B was totally maintained in the crystal as produced through a nuclear reaction before implantation. Two locations, site 1 and site 2, were found with the relative populations 9 and 1, respectively, and the electric field gradients (EFGs) at those sites were obtained to be q(site 1)=+(37.1±0.5)10¹⁵ V/cm², η(site 1)<0.03, q(site 2)=+(185±5)10¹⁵ V/cm² and η(site 2)=0.62±0.02. We also found that about 30% of the initial polarization of ⁸Li (I ^π=2⁺, T _1/2=838 ms) was maintained in the crystal. Since the polarizations of other β emitting nuclei, ^12,16N, ^13,19O, and ⁴¹Sc were also totally maintained in the crystal, the crystal can be a “Spin Dewar” in which many short-lived nuclides can be implanted with their polarizations totally maintained during their lifetimes for the studies not only on the electronic structure of impurities in it but also on the nuclear properties. This revised version was published online in September 2006 with corrections to the Cover Date.     

The random-phase-approximation in the weak coupling regime of the square lattice half-filled Hubbard model

We re-examine the random-phase approximation (RPA) in the antiferromagnetic spin-density-wave state of the half-filled square lattice repulsive Hubbard model. It is shown that forU/t1 the RPA yields a vanishing spinwave velocity, c(2t)^–1(U/t)^1/2, a diverging uniform transverse susceptibility, (2t)^–1(U/t ^–1/2, and a constant spin stiffness, _s 2t)^–2 t. The behavior of _s shows that the RPA cannot be correct in the weak coupling regime, because _s should vanish in the limitU/t0. We give a formally exact expression for _s and identify the term which is neglected within the RPA.