Polarisation analysis for neutron scattering experiments is a powerful tool suitable for a wide variety of studies, including soft-matter samples which have no bulk magnetic behaviour and/or a ...significant hydrogen content. Here, we describe a method to leverage the versatility and spin-polarisation capabilities of a cold triple-axis spectrometer to perform a measurement to separate coherent and incoherent neutron scattering for a non-magnetic sample in the quasielastic neutron scattering (QENS) regime. Such measurements are complementary to unpolarised QENS measurements, which may typically be performed on a backscattering or time-of-flight spectrometer instrument where polarisation analysis can be significantly more difficult to achieve, and utilise the strengths of each type of instrument.
The contrast‐variation technique in neutron scattering experiments plays a pivotal role in distinguishing partial structures within multi‐component complexes, facilitating the elucidation of distinct ...sample constituents. This differentiation is achieved using different isotopes, namely hydrogen and deuterium, which possess varying neutron scattering characteristics. This study presents a novel vapor generator designed for neutron scattering experiments, enabling continuous control of the D2O/H2O ratio of the vapor. This feature is especially useful for contrast‐variation studies. The generator features two saturators and four mass flow controllers, allowing for the rapid and independent generation of D2O/H2O vapors. Additionally, the incorporation of the two‐temperature method ensures accurate dew point control within a margin of ±0.2°Cdp. This setup proves useful for conducting time‐resolved experiments and can accelerate research on functional polymers, such as polymer electrolyte membranes for fuel cells, where water potential assumes critical importance.
This work presents a novel water vapor generator designed for neutron scattering experiments that allows continuous control of the isotopic H/D ratio, which is particularly useful for contrast‐variation measurements.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
ABSTRACT We analyze archival data from the Parkes radio telescope, which was observing a location 35 6 away from SGR 1806−20 during its giant γ-ray flare of 2004 December 27. We show that no fast ...radio burst (FRB)-like burst counterpart was detected, and set a radio limit of 110 MJy at 1.4 GHz, including the estimated 70 dB suppression of the signal due to its location in the far sidelobe of Parkes and the predicted scattering from the interstellar medium. The upper limit for the ratio of magnetar giant flare radio to γ-ray fluence is SGR 107 Jy ms erg−1 cm2. Based on the nondetection of a short and prompt γ-ray counterpart of 15 FRBs in γ-ray transient monitors, we set a lower limit on the fluence ratios of FRBs to be FRB 107-9 Jy ms erg−1 cm2. The fluence ratio limit for SGR 1806−20 is inconsistent with all but one of the 15 FRBs. We discuss possible variations in the magnetar-FRB emission mechanism and observational caveats that may reconcile the theory with observations.
The relativistic Cowling approximation, where the metric perturbations are neglected during the fluid oscillations, is often adopted for considering the gravitational waves from the protoneutron ...stars (PNSs) provided via core-collapse supernova explosions. In this study, we evaluate how the Cowling approximation works well by comparing the frequencies with the Cowling approximation to those without the approximation. Then, we find that the behavior of the frequencies with the approximation is qualitatively the same way as that without the approximation, where the frequencies with the approximation can totally be determined within ∼ 20 % accuracy. In particular, the fundamental mode with the Cowling approximation is overestimated. In addition, we also discuss the damping time of various eigenmodes in gravitational waves from the PNSs, where the damping time for the PNSs before the avoided crossing between the f- and g1-modes, is quite different from that for cold neutron stars, but it is more or less similar to that for cold neutron stars in the later phase. The damping time is long enough compared to the typical time interval of short-Fourier transformation that often used in the analysis, and that ideally guarantees the validity of the transformation.
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CMK, CTK, FMFMET, IJS, NUK, PNG, UM
ABSTRACT X-ray bursts are thermonuclear flashes on the surface of accreting neutron stars, and reliable burst models are needed to interpret observations in terms of properties of the neutron star ...and the binary system. We investigate the dependence of X-ray burst models on uncertainties in (p, γ), ( , γ), and ( , p) nuclear reaction rates using fully self-consistent burst models that account for the feedbacks between changes in nuclear energy generation and changes in astrophysical conditions. A two-step approach first identified sensitive nuclear reaction rates in a single-zone model with ignition conditions chosen to match calculations with a state-of-the-art 1D multi-zone model based on the Kepler stellar evolution code. All relevant reaction rates on neutron-deficient isotopes up to mass 106 were individually varied by a factor of 100 up and down. Calculations of the 84 changes in reaction rate with the highest impact were then repeated in the 1D multi-zone model. We find a number of uncertain reaction rates that affect predictions of light curves and burst ashes significantly. The results provide insights into the nuclear processes that shape observables from X-ray bursts, and guidance for future nuclear physics work to reduce nuclear uncertainties in X-ray burst models.
A powder neutron scattering study of atom substitution in Nd2(Fe1-xCox)14B, Y2(Fe1-xCox)14B and Ce2(Fe1-xCox)14B compounds is presented. Compared to previous studies, this one benefits from the ...considerable progress made in neutron diffraction measurements and their analysis during the last 15 years. The normalization of the occupancy values to those expected for a random distribution permits to reveal small deviations from random distribution. On all crystallographic sites some preferential occupancy is evidenced, the extent of which depends on the Co versus Fe content. A statistical model quantitatively describing site occupancies is proposed, which allows us to study the extreme cases of very dilute substitutions. Steric considerations primarily determine atom substitution, more particularly Fe-substitution in Co-rich compounds. The enthalpy of mixing must also be considered to describe Co preferential occupancies more exactly.
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•Strong preference of Fe to occupy 8j1 sites is confirmed.•Occupancies normalized to random reveal small preferential occupancy in sites other than 8j1.•A diffusion model explains the affinity of Co/Fe for certain sites.•Correlation between preferential occupancy and site volume is proved.•Additional effects, namely enthalpy of mixing, explain the observed anomalous preferential occupancy of 4c and 8j1.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Abstract
Energy resolved neutron imaging has developed rapidly due to
its advantage on testing the inner structure of crystal
samples. Neutron detector is one of the key components to determine
the ...imaging results quality. The neutron sensitive microchannel
plate (nMCP) has been widely used in energy resolved neutron imaging
experiments because of the high spatial and timing
resolution. However, the ability to adjust field-of-view (FOV) and
spatial resolution has not been realized in the nMCP detector, which
is an attractive capability in energy resolved neutron imaging
experiments. In this paper, an energy resolved neutron imaging
detector was developed by coupling nMCP with a time stamping
camera. The neutrons were absorbed by nMCP and converted into light
through a phosphor screen. Then the light was focused on the camera
by optical lens. A data algorithm was designed to improve the data
quality. By changing the magnification of the optical lens, large
FOV (46mm diameter) and high spatial resolution (26 μm) were
realized in the experiments at CSNS beamline 20. The energy resolved
ability was demonstrated by a Bragg-edge transmission imaging
experiment for aluminum and stainless-steel samples. The performance
of this detector makes it a promising candidate used in energy
resolved neutron imaging.
The high resolution neutron diffractometer HRND is located at the 20 MW China Mianyang Research Reactor (CMRR), which is a neutron powder diffractometer especially dedicated to crystal and magnetic ...structure studies for polycrystalline powder samples. A vertical focusing Ge (511) monochromator produce a monochromatic neutron beam with a wavelength of 1.885 Å at a fixed take-off angle of 120ˆ. An array of 64 equidistant 3He filled proportional counters can acquire diffraction patterns with a large-scale diffraction angle range over 160ˆ. As all the Soller slit collimators of HRND have a collimation angle of 10′ and the monochromator has an average mosaicity of 0.359ˆ, HRND obtains a best resolution of about 1.6\textperthousand based on experiments, which makes the resolution of HRND can compete with the mainstream-level high resolution neutron powder diffractometers in the world. Equipped with a cryostat and a furnace, HRND allows structural characterization in an extremely broad temperature range. The details of the configuration and performance of the instrument are reported along with its specifications and performance assessments in the present paper.
Abstract
We present the fourth Open Gravitational-wave Catalog (4-OGC) of binary neutron star (BNS), binary black hole (BBH), and neutron star–black hole (NSBH) mergers. The catalog includes ...observations from 2015 to 2020 covering the first through third observing runs (O1, O2, O3a, and O3b) of Advanced LIGO and Advanced Virgo. The updated catalog includes seven BBH mergers that were not previously reported with high significance during O3b for a total of 94 observations: 90 BBHs, 2 NSBHs, and 2 BNSs. The most confident new detection, GW200318_191337, has component masses
49.1
−
12.0
+
16.4
M
⊙
and
31.6
−
11.6
+
12.0
M
⊙
;
its redshift of
0.84
−
0.35
+
0.4
(90% credible interval) may make it the most distant merger so far. We estimate the merger rate of BBH sources, assuming a power-law mass distribution containing an additive Gaussian peak, to be
16.5
−
6.2
+
10.4
(
25.0
−
8.0
+
12.6
)
Gpc
−3
yr
−1
at a redshift of
z
= 0 (0.2). For BNS and NSBH sources, we estimate a merger rate of
200
−
148
+
309
Gpc
−3
yr
−1
and
19
−
14
+
30
Gpc
−3
yr
−1
, respectively, assuming the known sources are representative of the total population. We provide reference parameter estimates for each of these sources using an up-to-date model accounting for instrumental calibration uncertainty. The corresponding data release also includes our full set of subthreshold candidates.
ABSTRACT
The gravitational-wave events GW170817 and GW190425 have led to a number of important insights on the equation of state of dense matter and the properties of neutron stars, such as their ...radii and the maximum mass. Some of these conclusions have been drawn on the basis of numerical-relativity simulations of binary neutron-star mergers with vanishing initial spins. While this may be a reasonable assumption in equal-mass systems, it may be violated in the presence of large mass asymmetries accompanied by the presence of high spins. To quantify the impact of high spins on multimessenger gravitational-wave events, we have carried out a series of high-mass binary neutron-star mergers with a highly spinning primary star and large mass asymmetries that have been modelled self-consistently using two temperature-dependent equations of state. We show that, when compared with equal-mass, irrotational binaries, these systems can lead to significant differences in the remnant lifetime, in the dynamical ejecta, in the remnant disc masses, in the secular ejecta, and on the bulk kilonova properties. These differences could be exploited to remove the degeneracy between low- and high-spin priors in the detection of gravitational waves from binary neutron-star mergers.
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