arXiv subjects

H. Nagata

Publications and source records attributed to H. Nagata.

5 recordsLinked to original sources

arXiv2024

Measurement of $γ$-ray production via the neutron-$^{16}$O reaction using a 77 MeV quasi-monoenergetic neutron beam

Understanding of $γ$-ray production via neutron interactions on oxygen is essential for the study of neutrino neutral-current quasielastic interactions in water Cherenkov detectors. A measurement of $γ$-ray production from such reactions was performed using a 77~MeV quasi-monoenergetic neutron beam. Several $γ$-ray peaks, which are expected to come from neutron-${\rm ^{16}O}$ reactions, are observed and production cross sections are measured for nine $γ$-ray components of energies between 2 and 8~MeV. These are the first measurements at this neutron energy using a nearly monoenergetic beam.

nucl-ex↗

arXiv2018

Separation of gamma-ray and neutron events with CsI(Tl) pulse shape analysis

Fast neutrons are a large background to measurements of gamma-rays emitted from excited nuclei, such that detectors which can efficiently distinguish between the two are essential. In this paper we describe the separation of gamma-rays from neutrons with the pulse shape information of the CsI(Tl) scintillator, using a fast neutron beam and several gamma-ray sources. We find that a figure of merit optimized for this separation takes on large and stable values (nearly 4) between 5 and 10 MeV of electron equivalent deposited energy, the region of most interest to the study of nuclear de-excitation gamma-rays. Accordingly this work demonstrates the ability of CsI(Tl) scintillators to reject neutron backgrounds to gamma-ray measurements at these energies.

physics.ins-det↗

arXiv2013

Monte Carlo simulation of the three-dimensional XY model with bilinear-biquadratic exchange interaction

The three-dimensional XY model with bilinear-biquadratic exchange interactions $J$ and $J'$, respectively, has been studied by Monte Carlo simulations. From the detailed analysis of the thermal variation of various physical quantities, as well as the order parameter and energy histogram analysis, the phase diagram including two different ordered phases has been determined. There is a single phase boundary from a paramagnetic to a dipole-quadrupole ordered phase, which is of second order in a high $J/J'$ ratio region, changing to a first-order one for $0.35 \leq J/J' \leq 0.5$. Below $J/J'=0.35$ there are two separate transitions: the first one to the quadrupole long-range order (QLRO) phase at higher temperatures, followed by another one to the dipole-quadrupole long-range order (DLRO) phase at lower temperatures. The finite-size scaling analysis yields values of the critical exponents for both the DLRO and QLRO transitions close to the values for the conventional XY model which includes no biquadratic exchange.

cond-mat.stat-mech↗

arXiv2009

Constraints on the Intracluster Dust Emission in the Coma Cluster of Galaxies

We have undertaken a search for the infrared emission from the intracluster dust in the Coma cluster of galaxies by the Multiband Imaging Photometer for Spitzer. Our observations yield the deepest mid and far-infrared images of a galaxy cluster ever achieved. In each of the three bands, we have not detected a signature of the central excess component in contrast to the previous report on the detection by Infrared Space Observatory (ISO). We still find that the brightness ratio between 70 and 160 microns shows a marginal sign of the central excess, in qualitative agreement with the ISO result. Our analysis suggests that the excess ratio is more likely due to faint infrared sources lying on fluctuating cirrus foreground. Our observations yield the 2 sigma upper limits on the excess emission within 100 kpc of the cluster center as 5 x 10^-3 MJy/sr, 6 x 10^-2 MJy/sr, and 7 x 10^-2 MJy/sr, at 24, 70, and 160 microns, respectively. These values are in agreement with those found in other galaxy clusters and suggest that dust is deficient near the cluster center by more than 3 orders of magnitude compared to the interstellar medium.

astro-ph.GA↗

arXiv2007

The Infrared Astronomical Mission AKARI

AKARI, the first Japanese satellite dedicated to infrared astronomy, was launched on 2006 February 21, and started observations in May of the same year. AKARI has a 68.5 cm cooled telescope, together with two focal-plane instruments, which survey the sky in six wavelength bands from the mid- to far-infrared. The instruments also have the capability for imaging and spectroscopy in the wavelength range 2 - 180 micron in the pointed observation mode, occasionally inserted into the continuous survey operation. The in-orbit cryogen lifetime is expected to be one and a half years. The All-Sky Survey will cover more than 90 percent of the whole sky with higher spatial resolution and wider wavelength coverage than that of the previous IRAS all-sky survey. Point source catalogues of the All-Sky Survey will be released to the astronomical community. The pointed observations will be used for deep surveys of selected sky areas and systematic observations of important astronomical targets. These will become an additional future heritage of this mission.

astro-ph↗