329 research outputs found
Development of an advanced Compton camera with gaseous TPC and scintillator
A prototype of the MeV gamma-ray imaging camera based on the full
reconstruction of the Compton process has been developed. This camera consists
of a micro-TPC that is a gaseous Time Projection Chamber (TPC) and
scintillation cameras. With the information of the recoil electrons and the
scattered gamma-rays, this camera detects the energy and incident direction of
each incident gamma-ray. We developed a prototype of the MeV gamma-ray camera
with a micro-TPC and a NaI(Tl) scintillator, and succeeded in reconstructing
the gamma-rays from 0.3 MeV to 1.3 MeV. Measured angular resolutions of ARM
(Angular Resolution Measure) and SPD (Scatter Plane Deviation) for 356 keV
gamma-rays were and , respectively.Comment: 4 pages, 5 figures. Proceedings of the 6th International Workshop On
Radiation Imaging Detector
Investigating the hard X-ray emission from the hottest Abell cluster A2163 with Suzaku
We present the results from Suzaku observations of the hottest Abell galaxy
cluster A2163 at . To study the physics of gas heating in cluster
mergers, we investigated hard X-ray emission from the merging cluster A2163,
which hosts the brightest synchrotron radio halo. We analyzed hard X-ray
spectra accumulated from two-pointed Suzaku observations. Non-thermal hard
X-ray emission should result from the inverse Compton (IC) scattering of
relativistic electrons by the CMB photons. To measure this emission, the
dominant thermal emission in the hard X-ray band must be modeled in detail. To
this end, we analyzed the combined broad-band X-ray data of A2163 collected by
Suzaku and XMM-Newton, assuming single- and multi-temperature models for
thermal emission and the power-law model for non-thermal emission. From the
Suzaku data, we detected significant hard X-ray emission from A2163 in the
12-60 keV band at the level (or at the level if a
systematic error is considered). The Suzaku HXD spectrum alone is consistent
with the single-T thermal model of gas temperature keV. From the XMM
data, we constructed a multi-T model including a very hot ( keV)
component in the NE region. Incorporating the multi-T and the power-law models
into a two-component model with a radio-band photon index, the 12-60 keV energy
flux of non-thermal emission is constrained within . The 90% upper limit of detected IC
emission is marginal ( in the
12-60 keV). The estimated magnetic field in A2163 is .
While the present results represent a three-fold increase in the accuracy of
the broad band spectral model of A2163, more sensitive hard X-ray observations
are needed to decisively test for the presence of hard X-ray emission due to IC
emission.Comment: 7 pages, 7 figures, A&A accepted. Minor correctio
Studies of the performance of different front-end systems for flat-panel multi-anode PMTs with CsI(Tl) scintillator arrays
We have studied the performance of two different types of front-end systems
for our gamma camera based on Hamamatsu H8500 (flat-panel 64 channels
multi-anode PSPMT) with a CsI(Tl) scintillator array. The array consists of 64
pixels of which corresponds to the anode pixels of
H8500. One of the system is based on commercial ASIC chips in order to readout
every anode. The others are based on resistive charge divider network between
anodes to reduce readout channels. In both systems, each pixel (6mm) was
clearly resolved by flood field irradiation of Cs. We also investigated
the energy resolution of these systems and showed the performance of the
cascade connection of resistive network between some PMTs for large area
detectors.Comment: 9 pages, 6 figures, proceedings of the 7th International Workshop on
Radiation Imaging Detectors (IWORID7), submitted to NIM
Development of Large area Gamma-ray Camera with GSO(Ce) Scintillator Arrays and PSPMTs
We have developed a position-sensitive scintillation camera with a large area
absorber for use as an advanced Compton gamma-ray camera. At first we tested
GSO(Ce) crystals. We compared light output from the GSO(Ce) crystals under
various conditions: the method of surface polishing, the concentration of Ce,
and co-doping Zr. As a result, we chose the GSO(Ce) crystals doped with only
0.5 mol% Ce, and its surface polished by chemical etching as the scintillator
of our camera. We also made a 1616 cm scintillation camera which
consisted of 9 position-sensitive PMTs (PSPMTs Hamamatsu flat-panel H8500), the
each of which had 88 anodes with a pitch of 6 mm and coupled to
88 arrays of pixelated 613 mm GSO(Ce) scintillators.
For the readout system of the 576 anodes of the PMTs, we used chained resistors
to reduce the number of readout channels down to 48 to reduce power
consumption. The camera has a position resolution of less than 6mm and a
typical energy resolution of 10.5% (FWHM) at 662 keV at each pixel in a large
area of 1616 cm. %to choose the best scintillator for our project.
Furthermore we constructed a 1616 array of 313 mm
pixelated GSO(Ce) scintillators, and glued it to a PMT H8500. This camera had
the position resolution of less than 3mm, over an area of 55 cm,
except for some of the edge pixels; the energy resolution was typically 13%
(FWHM) at 662 keV.Comment: Proceedings of PSD7 appear in NIM
Flood Risk Management: An Illustrative Approach
Widespread flooding with significant damage in many countries, such as the Philippines in 2013, highlights the ongoing need for effective flood risk management (FRM). This hinges on comprehensive access to and dissemination of information about the elements and the people at risk. Simulations, real-time graphs, and maps illustrate the spatial distribution of flood risks, spatial allocation and dissemination of flood effects, if flood risk reduction measures are not implemented, as well as the benefits to be derived from the effective implementation and maintenance of flood risk management measures not realized. Using precipitation, river water, and tide levels, a real-time monitoring site was set up for the Shirakawa River, Kumamoto, Japan. The data gathered from the July 2012 flood event is used as a demonstrator, illustrating a flood event as well as how to utilize the information provided on this site to determine the future time and possibility of flooding. Additionally, an electronically generated flood hazard map making process is being developed for distribution across Japan. These illustrative approaches can be utilized in cities and communities around the globe
An evolved disk surrounding the massive main sequence star MWC 297?
We present the results of the interferometric observations of the
circumstellar disk surrounding MWC 297 in the continuum at 230 GHz (1.3 mm) and
in the (J=2-1) rotational transitions of CO,CO and CO
using the Submillimeter Array. At a distance of 250 pc, MWC 297 is one of the
closest, young massive stars (M 10 M) to us. Compact
continuum emission is detected towards MWC 297 from which we estimate a disk
mass (gas+dust) of 0.07 M and a disk radius of 80 AU. Our
result demonstrates that circumstellar disks can survive around massive stars
well into their main sequence phase even after they have become optically
visible. Complementing our observations with the data compiled from the
literature, we find the submm dust opacity index to be between 0.1 and
0.3. If the emission is optically thin, the low value of indicates the
presence of relatively large grains in the disk, possibly because of grain
growth. We do not detect any CO emission associated with the continuum source.
We argue that the CO emission from the disk is likely optically thin, in
which case, we derive an upper limit to the gas mass which implies significant
depletion of molecular gas in the disk. The mass of this disk and the
evolutionary trends observed are similar to those found for intermediate mass
Herbig Ae stars and low mass T Tauri stars.Comment: 4 pages, 3 Figures, accepted for publication in ApJ
Molecular Evolution in Collapsing Prestellar Cores
We have investigated the evolution and distribution of molecules in
collapsing prestellar cores via numerical chemical models, adopting the
Larson-Penston solution and its delayed analogues to study collapse. Molecular
abundances and distributions in a collapsing core are determined by the balance
among the dynamical, chemical and adsorption time scales. When the central
density n_H of a prestellar core with the Larson-Penston flow rises to 3 10^6
cm^{-3}, the CCS and CO column densities are calculated to show central holes
of radius 7000 AU and 4000 AU, respectively, while the column density of N2H+
is centrally peaked. These predictions are consistent with observations of
L1544. If the dynamical time scale of the core is larger than that of the
Larson-Penston solution owing to magnetic fields, rotation, or turbulence, the
column densities of CO and CCS are smaller, and their holes are larger than in
the Larson-Penston core with the same central gas density. On the other hand,
N2H+ and NH3 are more abundant in the more slowly collapsing core. Therefore,
molecular distributions can probe the collapse time scale of prestellar cores.
Deuterium fractionation has also been studied via numerical calculations. The
deuterium fraction in molecules increases as a core evolves and molecular
depletion onto grains proceeds. When the central density of the core is n_H=3
10^6 cm^{-3}, the ratio DCO+/HCO+ at the center is in the range 0.06-0.27,
depending on the collapse time scale and adsorption energy; this range is in
reasonable agreement with the observed value in L1544.Comment: 21 pages, 17 figure
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