Search results for "waves"

Polarization in mott scattering of multi-MeV electrons from heavy nuclei

1999

To aid fundamental studies on the polarization of electrons in beta decay, measurements were made of the spin dependence in the scattering of 14 MeV electrons from Pb as a function of scattering angle and foil thickness. The experiment made use of a beam of polarized electrons from a strained GaAsP cathode. A simple theoretical model based on plural scattering explains the observed dependence of the analyzing power on foil thickness. The results extrapolated to infinitely thin targets are in excellent agreement with theory if the finite nuclear size is taken into account.

Realization of a broad-band neutron spin filter with compressed, polarized 3He gas

1997

The strongly spin-dependent absorption of neutrons in nuclear spin polarized 3He opens the possibility to polarize beams of thermal and epithermal neutrons. An effective 3He neutron spin filter (NSF) requires high 3He nuclear polarization as well as a filter thickness corresponding to amount of gas in the order of 1 bar 1. We realized such a filter using direct optical pumping of metastable 3He∗ atoms in a 3He plasma at 1 mb. Metastable exchange scattering transfers the angular momentum to the whole ensemble of 3He atoms. At present 3.6 × 1018 3He-atoms s−1 are polarized up to 68%. Subsequent polarization preserving compression by a two-stage compressor system enables to prepare NSF cells o…

Neutron optics P-violation effects near p-wave resonance

1999

Abstract The observations of large enhancement of parity-violation at p-wave compound resonance encourage prompt active discussion of TRI test in neutron optics. One of the most attractive objects for investigation is the p-wave resonance of 139 La at energy 0.734 eV for which the strongest P-odd effect of spin dichroism has been observed. A new technique of neutron spin analysis based on optically pumped 3 He spin filter has been applied successfully to measure the complementary effect of P-odd spin rotation near the same p-wave resonance of 139 La . The results obtained are consistent with theory predictions.

Dynamic N14 nuclear spin polarization in nitrogen-vacancy centers in diamond

2020

We studied the dynamic nuclear spin polarization of nitrogen in negatively charged nitrogen-vacancy (NV) centers in diamond both experimentally and theoretically over a wide range of magnetic fields from 0--1100 G covering both the excited-state level anticrossing and the ground-state level anticrossing magnetic field regions. Special attention was paid to the less studied ground-state level anticrossing region. The nuclear spin polarization was inferred from measurements of the optically detected magnetic resonance signal. These measurements show that a very large (up to $96\ifmmode\pm\else\textpm\fi{}2%$) nuclear spin polarization of nitrogen can be achieved over a very broad range of mag…

Spin pumping in noncollinear antiferromagnets

2021

The ac spin pumping of noncollinear antiferromagnets is theoretically investigated. Starting from an effective action description of the spin system, we derive the Onsager coefficients connecting the spin pumping and spin-transfer torque associated with the dynamics of the SO(3)-valued antiferromagnetic order parameter. Our theory is applied to a kagome antiferromagnet resonantly driven by a uniform external magnetic field. We demonstrate that the reactive (dissipative) spin-transfer torque parameter can be extracted from the pumped ac spin current in-phase (in quadrature) with the driving field. Furthermore, we find that the three spin-wave bands of the kagome AF generate spin currents wit…

Phase-sensitive measurement of trapped particle motions

2005

We have developed and applied a novel method for the precise determination of small frequency differences of particle motions inside a Penning trap. In the present case, the frequency differences on the order of 100 mHz at motional frequencies on the order of 1 MHz are used to determine the spin state of an electron bound in a hydrogen-like ion. This novel technique measures the integrated phase difference of the particles' motions relative to an excitation with a well-defined phase. Thereby, the Fourier-limit for frequency measurements based on Fourier-analyses of detection signals can be overcome.

Nuclear-spin comagnetometer based on a liquid of identical molecules

2018

Atomic comagnetometers are used in searches for anomalous spin-dependent interactions. Magnetic field gradients are one of the major sources of systematic errors in such experiments. Here we describe a comagnetometer based on the nuclear spins within an ensemble of identical molecules. The dependence of the measured spin-precession frequency ratio on the first-order magnetic field gradient is suppressed by over an order of magnitude compared to a comagnetometer based on overlapping ensembles of different molecules. Our single-species comagnetometer is shown to be capable of measuring the hypothetical spin-dependent gravitational energy of nuclei at the $10^{-17}$ eV level, comparable to the…

Accurate Period Determination of an Eclipsing Binary X-Ray Source in M33

1993

We have analyzed the time variability of one of the X-ray sources in M33 observed by both the ROSAT and Einstein Observatory telescopes. The light curve of M33 X-7 exhibits a variability pattern of high and low states, suggesting an eclipsing binary X-ray source. The data suggest a binary period P=1.78572 days (very close to that of Her X-1) and an eclipse duration of ∼0.4 days. The low phase lasts about one-fourth of the period as in Cen X-3

Novel prospects in hyperbolic metamaterials: Dyakonov-like surface waves

2014

A distorted radio shell in the young supernova SN1986J

2002

We report here on 5 GHz global very-long-baseline interferometry (VLBI) observations of SN 1986J, 16 yr after its explosion. We obtained a high-resolution image of the supernova, which shows a distorted shell of radio emission, indicative of a deformation of the shock front. The angular size of the shell is $\sim4.7 {\rm mas}$, corresponding to a linear size of $\sim6.8 \times 10^{17} {\rm cm}$ for a distance of 9.6 Mpc to NGC 891. The average speed of the shell has decreased from $\sim$7400 \kms in 1988.74 down to about $6300 {\rm km s^{-1}}$ in 1999.14, indicative of a mild deceleration in the expansion of SN 1986J. Assuming a standard density profile for the progenitor wind ($\rho_{\rm c…