Low-frequency Neutron Research Articles

Properties of rotating neutron star in density-dependent relativistic mean-field models

Equilibrium sequences were developed for rotating neutron stars in the relativistic mean-field interaction framework using four density-dependent equations of state (EOSs) for the neutron star matter. These sequences were constructed for the observed rotation frequencies of 25, 317, 346, 716 and 1122[Formula: see text]Hz. The bounds of sequences, the secular axisymmetric instability, static and Keplerian sequences were calculated in each model to determine the stability region. The gravitational mass, quadrupole moment, polar, forward and backward redshifts, and Kerr parameter were calculated according to this stability region, and the allowable range of these quantities was then determined for each model. According to the results, DDF and DD-ME[Formula: see text] were unable to properly describe the low-frequency neutron stars, PSR J0348+432, PSR J1614-2230 and PSR J0740+6620 rotate at a frequency of 25, 317 and 346[Formula: see text]Hz, respectively. On the other hand, all the selected EOSs properly described the rotation of PSR J1748-244ad and PSR J1739-285 at a frequency of 716 and 1122[Formula: see text]Hz, respectively. The mass of these stars was, therefore, in the range of [Formula: see text] and [Formula: see text], respectively. The polar, forward and backward redshifts, and the quadrupole moment were calculated in all the selected rotating frequencies and the Keplerian sequence. The results were consistent with observations. Confirming the mass of [Formula: see text] for EXO 0748-676, our result, [Formula: see text], will be close to the observed value, and the EOSs used in this study properly describe this star. Interestingly, the extremum of Kerr parameter, polar, forward and backward redshifts in all models reached constant values of, [Formula: see text], [Formula: see text], [Formula: see text] and [Formula: see text], respectively. These behaviors of redshifts and Kerr parameter are approximately independent of EOS. The observed behaviors must evaluate by other EOSs to find universal relations for these quantities. Also, a limit value was found for each of these parameters. In this case where these parameters are greater than the limit value, the star can rotate at a frequency equal to or greater than [Formula: see text][Formula: see text]Hz.

Study of L-ascorbic acid (vitamin C)/H 2O mixture across glass transition

In this paper, we report quasi elastic neutron scattering (QENS) spectra of vitamin C aqueous solutions, obtained using MIBEMOL spectrometer (LLB). The main purpose of this work is to characterize the relaxational and vibrational properties of the Vitamin C/H 2O system below and above the glass transition temperature by analysing the low-frequency neutron scattering spectra. The determination of the relative weight of vibrational over relaxational contributions allows to get information on the fragility degree of this peculiar hydrogen-bond system.

Influence of quenching on low-frequency neutron and Raman spectra of glasses

Quenched and annealed samples of g-As 2S 3 are investigated by the low-energy Raman and inelastic neutron scattering and by diffraction of neutrons. The structure modifications caused by quenching lead to significant changes only of the low-frequency part of the vibrational spectrum: the density of vibrational states g( E) and the light to vibrations coupling constant C( E) increase uniformly along the spectrum in the energy interval 2< E<12 meV. The relative changes are the same both for g( E) and C( E) and are equal to 8%. Similarly the structure factor S( q) demonstrates a sufficient (15%) increase of the amplitude of the first sharp diffraction peak (FSDP) after quenching and negligible small changes of the main peaks. Uniformity of the relative changes of g( E) and C( E) along the acoustical spectrum probably means that these changes are caused by the changes of sound velocity and density as a result of quenching.

Investigation of low-frequency neutron and temperature noise signals induced by local coolant boiling in a PWR

In special experiments performed in a PWR-NPP low-frequency neutron noise effects were found to be induced by local coolant boiling. A model for describing this phenomenon is developed. It is based on the assumption that integral void fluctuations are the neutron physical perturbation source. The void fluctuations themselves depend on primary noise sources (fluctuations of inlet temperature, coolant flow rate, reactor power) which are estimated with a thermohydraulic model from the axial dependence of temperature noise signals. The theoretical results are compared with measured values. It is shown that the low-frequency neutron noise can be used for boiling monitoring in PWRs.

Exact Statistical Analysis of Nonlinear Dynamic Power Reactor Models by the Fokker-Planck Method. Part II: Reactor with On-Off Control

The paper deals with the exact stochastic analysis of the low-frequency neutron density fluctuations in an on-off controlled nuclear power reactor without delayed neutrons and perturbed by Gaussian white reactivity noise. The stochastic process, being Markovian, is completely characterized by its first-order probability density function (pdf) and the transition pdf. The first-order pdf is the normalized solution to the time-independent Fokker--Planck equation (FPE). Using this pdf, a general expression for the moments is obtained. The conditions for stochastic stability in probability, in the mean, and in the mean-square are derived. The time-dependent FPE is solved using the Laplace transform technique, which results in four distinct expressions for the transition pdf, according to the relative magnitude of initial and final reactor power with respect to the regulator level. After Laplace inversion, a physical interpretation of the controller's effect on the stochastic process becomes possible. Finally, making use of the obtained pdf's, the spectral density of the reactor power fluctuations is calculated.