Studies of parity and time reversal symmetries in neutron scattering from165Ho

We describe searches for parity and time reversal violations in the scattering of polarized neutrons from polarized and aligned¹⁶⁵Ho targets. We have completed a search with 7.1 and 11.0 MeV neutrons for P_oddT_odd terms in the elastic scattering forward amplitude of the form s. (I×K), wheres is the neutron spin,I is the target spin andk is the neutron momentum vector. The target was a single crystal of holmium, polarized horizontally along itsb axis by a 1 Tesla magnetic field. The neutrons were polarized vertically. Differences in the neutron transmission were measured for neutrons with spins parallel (antiparallel) toI×k. The P,T violating analyzing powers were found to be consistent with zero at the few 10⁻³ level: ρ_P,T(7.1 MeV)=−0.88 (±2.02) x 10⁻³, ρ_P,T(11.0 MeV)=−0.4 (±2.88) x 10⁻³. We have also attempted to find enhancements with MeV neutrons in P-violation due to the term s\k. We are preparing an aligned target cryostat for investigations of P_evenT_odd terms {bd(I\k)(I×k)\s} in neutron scattering. The target will be a single crystal cylinder of¹⁶⁵Ho cooled to 100 mK in a bath of liquid helium and rotated by a shaft from a room temperature stepping motor. The cylinder will be oriented vertically and the alignment (c) axis oriented horizontally. Warming or rotation of the sample allows one to separate effects that mimic the sought-after time reversal violating term.     

Energy levels and transitions in165Ho from neutron scattering

The¹⁶⁵Ho (n, ń) and¹⁶⁵Ho (n, ń γ) reactions were utilized to obtain information on the energy levels of¹⁶⁵Ho up to about 1400 keV excitation. A Ge (Li) detector was used in the time-gated mode to measure the de-excitation γ-rays. Neutrons were detected by a conventional time-of-flight spectrometer. Results from the two sets of measurements are combined to construct an energy level scheme for¹⁶⁵Ho. The level scheme is compared with results from other sources and some new levels are proposed.     

Dissipation coefficients and conductances in mesoscopic systems without time reversal invariance

It is shown that in the presence of a magnetic field a multi-probe generalization of the Landauer formula can be derived from linear response theory. The symmetric and antisymmetric parts of the current with respect to magnetic field reversal are discussed separately to show that the symmetrized conductances obtained by Stone and Szafer for zero magnetic field are the coefficients in the quadratic form which relates the asymptotic values of the potential to the power dissipated outside the mesoscopic sample. A derivation of the reciprocity theorem is given without using Büttiker's version of the Landauer formula.     

Magnetic moment of the 3/2 + state in 165Ho

The Larmor precession for the 362 keV state in ¹⁶⁵Ho(I ^π ?=?3/2^?+?, T _1/2?=?1.512 μs) in Dy₂O₃ with an external magnetic field of 0.3 T was determined to be ??32.3 ± 0.6 MHz by use of the perturbed angular correlation technique, intending to determine the magnetic moment and apply it to the measurement of the hyperfine field at Ho in Fe. The magnetic moment for this state was tentatively deduced under the assumption that the paramagnetic correction factor for a free Ho^3?+? ion is applicable to the present case. The independent A ₂₂ measurement for the 633???362 keV γ cascade for the sign assignment of the Larmor frequency is inconsistent with that from known multipolarities and mixing ratios for this cascade, implying that the mixing ratios may be different from the reported values.     

The significance of detailed balance tests of time reversal invariance in the fluctuation region

For detailed balance tests of time reversal invariance in the region of strongly over-lapping resonances the underlying theory which has throughout been employed is shown to exhibit a serious lack of empirical support. Certain conclusions that have been drawn from that theory are critically examined and quantitative criteria as to the significance of such tests are derived.     

Inelastic neutron scattering from H2 on vapour deposited CO2

Inelastic neutron scattering spectra at 17 meV and 68 meV incident energies of molecular hydrogen adsorbed on vapour deposited substrates of pure CO₂, 90:10 and 50:50 CO₂:Kr are reported. The ortho-para transition is shifted from 14.7 meV in the free H₂-molecule to 9.4 meV in a presumably commensurate ortho-H₂ monolayer on the CO₂ surface. The quadrupole-quadrupole interaction of ortho-H₂ molecules with the CO₂ substrate results in a strongly anisotropic potential. In addition to rotations the dynamics of this layer comprise a local Einstein mode and phonons in resonance with the substrate, giving rise to intense multiphonon transitions. Quasielastic scattering on warmer samples is assigned to a liquidlike adsorption layer, in which the H₂ rotations are strongly perturbed. Received: 15 October 1996 / Revised: 25 August 1997 / Accepted: 24 October 1997     

Spin-echo small-angle neutron scattering device: Test experiment using SiO2 colloidal particles

The results of the first experiments with a spin-echo small-angle neutron scattering (SESANS) device built at the VVR-M reactor at the St. Petersburg Institute of Nuclear Physics (Gatchina) are presented. SESANS utilizes the possibilities of the spin-echo method for determining the structural characteristics of materials in real space with on the 10–10⁴-nm length scale. Validation measurements are conducted using SiO₂ colloidal particles. Samples of SiO₂ spheres with a diameter determined through scanning electron microscopy and synchrotron-radiation ultra-small-angle scattering are used for calibration of the device. Approximation of the data obtained with the SESANS device was conducted using the autocorrelation function for dilute monodisperse spheres. The sizes of the spheres determined via SESANS are in agreement with those determined by other methods within the experimental error.     

Hyperfine structure measurements in metastable states of165Ho

The hyperfine structure constants and the electronic g _J factor of the state 4f ¹¹ 6s ^{2 4} I _11/2 belonging to the holmium ground multiplet have been measured using the atomic beam magnetic resonance technique combined with a state-selective laser-induced detection of the resonant atoms. By the same method the g _J factor of the level 4f ¹¹6s ²⁴ I _9/2 was determined, while the hyperfine structures of this metastable state and of two high-lying even parity states have been investigated by high resolution laser spectroscopy. The results for the experimentalA andB factors of all four members of the ground multiplet allow a least-squares evaluation of the three magnetic dipole and the three electric quadrupole effective radial parameters for the configuration 4f ¹¹ 6s ² of holmium, yielding an accurate value for the spectroscopic nuclear electric quadrupole moment:Q _hfs(¹⁶⁵Ho)=2.716(9)b (uncorrected for quadrupole shielding). From a comparison to the quadrupole moments measured in mesic holmium atoms the shielding factor could be estimated.     

用于实现散射介质中时间反演的数字相位共轭的相干性

抑制散射介质对光的散射,调控光在散射介质中的传输,是光通信、生物光子学、光镊等领域的重要课题.设计并实现了基于宽谱光源和数字相位共轭的可调控光在散射介质中传输的时间反演实验系统.实验获取了不同相干长度下物光和参考光束之间的光程差与干涉图样、相位图及时间反演信号之间的关系,分析了光源相干性对调控光在散射介质中传输的影响.实验结果表明,基于宽谱光源的相干特性和数字相位共轭技术,通过调节光程差能选择性获取同一散射角度及相同传输路径的光束的相对相位,再利用空间光调制器对参考光束进行调控,实现光束的反向传播,从而选择性实现对同一散射角度及相同传输路径的光的时间反演.     

Hexadecapole interaction in the atomic ground state of165Ho

Using the atomic beam magnetic resonance method several hyperfine transitions in the ground state of¹⁶⁵Ho were measured at magnetic fields near zero Oe. Including a hexadecapole interaction constantD a perfect fit of the seven hyperfine separations was possible giving the following results:A′=800.583645 (6)MHz,C′=?1.504 (37)kHzB′=?1668.00527 (33)MHz,D′=?0.137 (14)kHz. These interaction constants have been corrected for second order hyperfine interaction within the⁴I ground multiplet. The corrected constants are the following:A=800.583173 (36)MHz,C=?0.249 (140)kHzB=?1668.078 70 (330) MHz,D=?0.148 (16) kHz. Using a value for 〈r _4f ^/?5 〉_Ho of Fraga a nuclear hexadecapole moment can be calculated:Π(¹⁶⁵Ho)=0.89·10^?48cm⁴. Because of severe uncertainties still present in the theory for calculating the electronic matrix elements this value can be only regarded as highly speculative.     

Statistics of quantum beats in the time dependence of the neutron scattering

The numerical calculations of the delay time distributions for the neutron scattering have been carried out. The scattering of the short wave packet of neutrons with the broad energy interval 500–800 keV by ⁵⁸Ni nuclei has been studied. The decay curves and average times of the compound scattering were found as for the forward scattering as for the specific spin-parity states. The time oscillations of the decay curves were identified as quantum beats that were caused by the interference of the excited resonance set. The statistical analysis of the frequency spectra of the decay curves oscillations has been carried out. The behavior of the examined statistical observables turns out to be close to the Poisson law.     

Incoherent quasielastic neutron scattering from H2O and aqueous ZnCl2 solutions

A study of the diffusive motions of the protons in pure water and ZnCl₂ aqueous solutions has been performed, using incoherent quasielastic neutron scattering. It is shown that it is essential to take into account the rotational motion of the water molecules. The translational linewidth is conveniently fitted over the whole Q-range, using the Random Jump Diffusion model for which the jump length turns out to be roughly the same for pure H₂O and the saturated solution, fairly close to the distance between protons in the water molecule.     

On a symmetry topological classification of edge states in crystalline spin-Hall insulators with the time reversal invariance

Symmetry analysis reveals all types of singularities of the edge states in two-dimensional systems with a boundary (2D → 1D systems), which are invariant under time reversal. Symmetry reasons also provide the matching condition for material functions parameterizing the Hamiltonian at various points of the Brillouin zone. The unified parameterization of the Hamiltonian makes it possible to construct the mapping of trajectories closed in the quasimomentum k in the Brillouin zone into the SU(2) topological group. There are only two equivalence classes of Hamiltonians, which are given by the elements of the first fundamental group . The first type of surface states corresponds to a normal insulator and the second type corresponds to a topological spin-Hall insulator. Comparison with the classification based on the Pfaffian method is performed.     

Low temperature relaxation behavior of 165Ho2+, a coupled nuclear-electronic spin system

The low field relaxation time for various states of the ¹⁶⁵Ho²⁺, a coupled nuclear-electronic system, is observed to depend exponentially on temperature down to 0.15°K.