We combine electromagnetic (EM) and gravitational-wave (GW) information on the binary neutron star (NS) merger GW170817 in order to constrain the radii and maximum mass of NSs. GW170817 was followed ...by a range of EM counterparts, including a weak gamma-ray burst (GRB), kilonova (KN) emission from the radioactive decay of the merger ejecta, and X-ray/radio emission consistent with being the synchrotron afterglow of a more powerful off-axis jet. The type of compact remnant produced in the immediate merger aftermath, and its predicted EM signal, depend sensitively on the high-density NS equation of state (EOS). For a soft EOS that supports a low , the merger undergoes a prompt collapse accompanied by a small quantity of shock-heated or disk-wind ejecta, inconsistent with the large quantity of lanthanide-free ejecta inferred from the KN. On the other hand, if is sufficiently large, then the merger product is a rapidly rotating supramassive NS (SMNS), which must spin down before collapsing into a black hole. A fraction of the enormous rotational energy necessarily released by the SMNS during this process is transferred to the ejecta, either into the GRB jet (energy ) or the KN ejecta (energy ), also inconsistent with observations. By combining the total binary mass of GW170817 inferred from the GW signal with conservative upper limits on and from EM observations, we constrain the likelihood probability of a wide range of previously allowed EOSs. These two constraints delineate an allowed region of the parameter space, which, once marginalized over NS radius, places an upper limit of (90%), which is tighter or arguably less model-dependent than other current constraints.
Elements heavier than zinc are synthesized through the rapid (r) and slow (s) neutron-capture processes. The main site of production of the r-process elements (such as europium) has been debated for ...nearly 60 years. Initial studies of trends in chemical abundances in old Milky Way halo stars suggested that these elements are produced continually, in sites such as core-collapse supernovae. But evidence from the local Universe favours the idea that r-process production occurs mainly during rare events, such as neutron star mergers. The appearance of a plateau of europium abundance in some dwarf spheroidal galaxies has been suggested as evidence for rare r-process enrichment in the early Universe, but only under the assumption that no gas accretes into those dwarf galaxies; gas accretion favours continual r-process enrichment in these systems. Furthermore, the universal r-process pattern has not been cleanly identified in dwarf spheroidals. The smaller, chemically simpler, and more ancient ultrafaint dwarf galaxies assembled shortly after the first stars formed, and are ideal systems with which to study nucleosynthesis events such as the r-process. Reticulum II is one such galaxy. The abundances of non-neutron-capture elements in this galaxy (and others like it) are similar to those in other old stars. Here, we report that seven of the nine brightest stars in Reticulum II, observed with high-resolution spectroscopy, show strong enhancements in heavy neutron-capture elements, with abundances that follow the universal r-process pattern beyond barium. The enhancement seen in this 'r-process galaxy' is two to three orders of magnitude higher than that detected in any other ultrafaint dwarf galaxy. This implies that a single, rare event produced the r-process material in Reticulum II. The r-process yield and event rate are incompatible with the source being ordinary core-collapse supernovae, but consistent with other possible sources, such as neutron star mergers.
A dilute ensemble of randomly oriented non‐interacting spherical nanomagnets is considered, and its magnetization structure and ensuing neutron scattering response are investigated by numerically ...solving the Landau–Lifshitz equation. Taking into account the isotropic exchange interaction, an external magnetic field, a uniaxial magnetic anisotropy for the particle core, and in particular the Néel surface anisotropy, the magnetic small‐angle neutron scattering cross section and pair‐distance distribution function are calculated from the obtained equilibrium spin structures. The numerical results are compared with the well known analytical expressions for uniformly magnetized particles and provide guidance to the experimentalist. In addition, the effect of a particle‐size distribution function is modelled.
Based on the Landau–Lifshitz equation, atomistic simulations of the magnetic neutron scattering from inhomogeneously magnetized spherical nanoparticles with a strong surface anisotropy are carried out.
This paper presents the measurement of the neutron star (NS) radius using the thermal spectra from quiescent low-mass X-ray binaries (qLMXBs) inside globular clusters (GCs). Such EoSs predict that ...the radii of NSs, R sub(NS), are quasi-constant (within measurement errors, of ~10%) for astrophysically relevant masses (M sub(NS) > 0.5 (M sub(middot in circle)). The present work adopts this theoretical prediction as an assumption, and uses it to constrain a single R sub(NS) value from five qLMXB targets with available high signal-to-noise X-ray specttoscopic data. Employing a Markov chain Monte-Carlo approach, we produce the marginalized posterior distribution for R sub(NS), constrained to be the same value for all five NSs in the sample. An effort was made to include all quantifiable sources of uncertainty into the uncertainty of the quoted radius measurement. We compare this result with previous radius measurements of NSs from various analyses of different types of systems. In addition, we compare the spectral analyses of individual qLMXBs to previous works.
Development of techniques for gantryless associated-particle imaging Heath, M.R.; Daughhetee, J.; Hausladen, P. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
20/May , Volume:
1062, Issue:
C
Journal Article
Peer reviewed
To move fast-neutron radiography using the associated-particle imaging technique from the laboratory to the field, the development of new analysis techniques is required. In particular, the relative ...positions of the source and detectors need to be determined when they have been placed by hand, the normalization for a particular source–detector geometry needs to be determined without a measurement in the same geometry with no object present, and accurate image stitching is required when multiple detector positions are necessary to image an object. The present work describes methods that employ transmission neutron data to localize a fast-neutron imaging panel with respect to the neutron source, calculate a normalization for a given source–detector geometry, stitch images together, and describes the required system calibrations. The reported techniques enable in-field neutron radiography for cases in which the source–detector geometry is not well known a priori and where operational constraints preclude a normalization measurement.
The robustness of the linear combination method to neutron source is demonstrated in the pulsed neutron source (PNS) experiment. The linear combination method reduces the spatial higher-mode (HM) ...components in neutron flux distribution by integrating the neutron counts obtained in the PNS experiment with the linear combination. In the previous study, we have confirmed the applicability of the linear combination method based on the PNS method conducted at Kyoto University Critical Assembly (KUCA) with a deuteron-tritium (D-T) neutron source. In this study, the PNS experiment is conducted at KUCA with 100 MeV proton accelerator and Pb-Bi target. The experiment is aimed at showing that the masking time dependence of the estimated prompt neutron decay constant is dramatically reduced by the linear combination method compared to the conventional method: these results demonstrate the linear combination method is applicable to spallation neutron source as well as D-T neutron source.
•For monoenergetic and continuous spectrum neutron sources.•Flat response up to 1 MeV neutron energy.•High efficiency and directional sensitivity.•For pulsed neutron detection.
The innovative single ...and array models of silver Geiger Muller (GM) activation counters were designed to measure the fast neutron fluence. These counters were made of inner and outer neutron moderators (PE) sections with special designs of silver foil and thin wall GM counter. The Monte Carlo N-Particles MCNPX2.6 code was used to simulate the optimum dimension and energy responses of these counters. The two counters were calibrated by means of 241Am-Be radioisotopic neutron source with 16Ci activity. The detection efficiencies of single and array counters were 0.07 ± 0.005 and 0.785 ± 0.05, respectively. The energy responses of these two counters were determined to be flat for low energy neutrons of 2 keV to 1 MeV which were rarely observed in other neutron detectors. The directional sensitivities were also improved after rejecting scattered neutrons by surrounding materials which will be of high importance for intense pulsed neutron sources.
Exotic particles carrying baryon number and with a mass of the order of the nucleon mass have been proposed for various reasons including baryogenesis, dark matter, mirror worlds, and the neutron ...lifetime puzzle. We show that the existence of neutron stars with a mass greater than 0.7 M_{⊙} places severe constraints on such particles, requiring them to be heavier than 1.2 GeV or to have strongly repulsive self-interactions.
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