Search results for " NEUTRON"

Magnetic field and temperature dependent correlations in the singlet ground state system CsFeBr3

1992

Abstract In the singlet ground state system CsFeBr 3 the temperature and magnetic field dependence of the magnetic dispersion curves have been measured by inelastic neutron scattering. At a field of 4.1 T magnetic Bragg peaks appear at (⅓ ⅓ 1) and (⅔ ⅔ 1). The correlation lengths were derived from the experimental data by integrating the constant Q -scans over the energy transfer. The Q -dependence was fitted to Lorentzians and correlations lengths were extracted for different directions in the lattice. These correlation lengths decrease with increasing temperature and increase with increasing field. Above the phase transition the correlation lengths decrease again.

Magnetic excitations and phase transition of CsFeBr3 in an external magnetic field

1990

In CSFeBr3 the Fe2+ ion with effective spin one has locally a singlet ground state (m=0). The antiferromagnetic interactions between neighbouring Fe-ions are too weak as compared with the anisotropy constant to introduce long range order in the absence of an external field. By inelastic neutron scattering we studied the magnetic excitations in an external magnetic field up to 5 Tesla applied along thec-axis. A linear Zeeman splitting was observed with a Lande factorg=2.4. The field renormalizes the dispersion curves in such a way that the exchange interaction has decreasing influence with increasing field. Theoretical calculations according to the excitonic model of Lindgard describe the ex…

BeppoSAX observation of 4U 1705-44: detection of hard X-ray emission in the soft state

2007

4U 1705-44 is one of the best studied type I X-ray burster and atoll sources. Since it covers a wide range in luminosity (from a few to 50 x 10^{36} erg s^{-1}) and shows clear spectral state transitions, it represents a good laboratory to test the accretion models proposed for atoll sources. We analysed the energy spectrum accumulated with BeppoSAX observations (43.5 ksec) in August 2000 when the source was in a soft spectral state. The continuum of the wide band energy spectrum is well described by the sum of a blackbody (kT_{bb}~0.56 keV) and a Comptonized component (seed-photon temperature kT_W~1 keV, electron temperature kT_e~2.7 keV, and optical depth ~11). A hard tail was detected at…

nEDM experiment at PSI : data-taking strategy and sensitivity of the dataset

2018

We report on the strategy used to optimize the sensitivity of our search for a neutron electric dipole moment at the Paul Scherrer Institute. Measurements were made upon ultracold neutrons stored within a single chamber at the heart of our apparatus. A mercury cohabiting magnetometer together with an array of cesium magnetometers were used to monitor the magnetic field, which was controlled and shaped by a series of precision field coils. In addition to details of the setup itself, we describe the chosen path to realize an appropriate balance between achieving the highest statistical sensitivity alongside the necessary control on systematic effects. The resulting irreducible sensitivity is …

Helicity-dependent cross sections for the photoproduction of π0 pairs from nucleons

2020

The double-polarization observable $E$ and helicity-dependent cross sections $\sigma_{1/2}$, $\sigma_{3/2}$ have been measured for the photoproduction of $\pi^0$ pairs off quasi-free protons and neutrons at the Mainz MAMI accelerator with the Crystal Ball/TAPS setup. A circularly polarized photon beam was produced by bremsstrahlung from longitudinally polarized electrons and impinged on a longitudinally polarized deuterated butanol target. The reaction products were detected with an almost $4\pi$ covering calorimeter. The results reveal for the first time the helicity- and isospin-dependent structure of the $\gamma N\rightarrow N\pi^0\pi^0$ reaction. They are compared to predictions from re…

Binary evolution of PSR J1713+0747

2007

PSR J1713+0747 is a binary millisecond radio pulsar with a long orbital period (Porb ∼ 68 d) and a very low neutron star mass (M NS = 1.3 ± 0.2 M⊙). We simulate the evolution of this binary system with an accurate numerical code, which keeps into account both the evolution of the primary and of the whole binary system. We show that strong ejection of matter from the system is fundamental to obtain a mass at the end of the evolution that is within 1 - σ from the observed one, but propeller effects are almost negligible in such a system, where the accretion rate is always near to the Eddington limit. We show that there are indeed two mechanisms can account for the amount of mass loss from the…

Quantum Coherence Effects in One-Dimensional Chains with Inelastic Scattering

1991

To describe the ballistic transport in a 1 D chain Landauer [1] has calculated the resistance R of a series of elastic scatterers from their transmission coefficient T $$R = \frac{h}{{{e^2}}}\frac{{1 - T}}{T}$$ (1) This relation implies complete quantum coherence between incident and all backscattered waves. Dephasing due to irreversible processes has been introduced into this model by Buttiker [2] who added inelastic scatterers coupled to an external heat bath to the chain. In this way it is possible to describe also certain dissipative aspects of electron transport. However, his approach does not allow to study the gradual transition from coherent to incoherent transport with increasing s…

Inelastic neutron scattering by coupled rotational and translational modes in KCN

1980

The TA [100] phonon branch of the molecular crystal KCN was studied by inelastic neutron scattering in the cubic phase. In addition the distribution of the quasielastic scattered neutrons was investigated. The results are analysed by assuming a coupling of the phonon modes to the rotational degrees of freedom of the CN-dumb-bells which are regarded as a system of interacting quadrupoles. A good description of the present results and also of the existing ultrasonic and Brillouin data is achieved by a simple model which uses a single collective rotational mode of finite excitation energy and line width.

The neutron electric form factor and quasi-elastic electron-deuteron scattering

2008

BeppoSAX serendipitous discovery of the X-ray pulsar SAX J1802.7-2017

2003

We report on the serendipitous discovery of a new X-ray source, SAX J1802.7-2017, ~22' away from the bright X-ray source GX 9+1, during a BeppoSAX observation of the latter source on 2001 September 16-20. SAX J1802.7-2017 remained undetected in the first 50 ks of observation; the source count rate in the following ~300 ks ranged between 0.04 c/s and 0.28 c/s, corresponding to an averaged 0.1-10 keV flux of 3.6 10^{-11} ergs cm^{-2} s^{-1}. We performed a timing analysis and found that SAX J1802.7-2017 has a pulse period of 139.612 s, a projected semimajor axis of a_x sin i ~ 70 lt-s, an orbital period of ~4.6 days, and a mass function f(M) ~ 17 Msun. The new source is thus an accreting X-ra…