1,499 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
Nucleosynthesis in Baryon-Rich Outflows Associated With Gamma-Ray Bursts
Robust generation of gamma-ray bursts (GRBs) implies the formation of
outflows with very low baryon loads and highly relativistic velocities, but
more baryon-rich, slower outflows are also likely to occur in most GRB central
engine scenarios, either as ``circum-jet winds'' or ``failed GRBs''. Here we
study the possibility of nucleosynthesis within such baryon-rich outflows by
conducting detailed reaction network calculations in the framework of the basic
fireball model. It is shown that high baryon load fireballs attaining mildly
relativistic velocities can synthesize appreciable quantities of heavy neutron
capture elements with masses up to the platinum peak and beyond. Small but
interesting amounts of light elements such as deuterium and boron can also be
produced. Depending on the neutron excess and baryon load, the combination of
high entropy, rapid initial expansion and gradual expansion at later times can
cause the reaction flow to reach the fission regime, and its path can be
intermediate between those of the - and -processes (``-process''). The
nucleosynthetic signature of these outflows may be observable in the companion
stars of black hole binary systems and in the most metal-poor stars,
potentially offering an important probe of the inner conditions of the GRB
source. Contribution to the solar abundances for some heavy elements may also
be possible. The prospects for further developments in various directions are
discussed.Comment: ApJ, in press; 11 pages, 3 figure
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
Measurement of Low-Energy Cosmic-Ray Antiprotons at Solar Minimum
The absolute fluxes of the cosmic-ray antiprotons at solar minimum are
measured in the energy range 0.18 to 1.4 GeV, based on 43 events unambiguously
detected in BESS '95 data. The resultant energy spectrum appears to be flat
below 1 GeV, compatible with a possible admixture of primary antiproton
component with a soft energy spectrum, while the possibility of secondary
antiprotons alone explaining the data cannot be excluded with the present
accuracy. Further improvement of statistical accuracy and extension of the
energy range are planned in future BESS flights.Comment: REVTeX, 4 pages including 4 eps figures. Submitted to PR
Development of HPD Clusters for MAGIC-II
MAGIC-II is the second imaging atmospheric Cherenkov telescope of the MAGIC
observatory, which has recently been inaugurated on Canary island of La Palma.
We are currently developing a new camera based on clusters of hybrid photon
detectors (HPD) for the upgrade of MAGIC-II. The photon detectors feature a
GaAsP photocathode and an avalanche diode as electron bombarded anodes with
internal gain, and were supplied by Hamamatsu Photonics K.K. (R9792U-40). The
HPD camera with high quantum efficiency will increase the MAGIC-II sensitivity
and lower the energy threshold. The basic performance of the HPDs has been
measured and a prototype of an HPD cluster has been developed to be mounted on
MAGIC-II. Here we report on the status of the HPD cluster and the project of
eventually using HPD clusters in the central area of the MAGIC-II camera.Comment: Contribution to the 31st ICRC, Lodz, Poland, July 200
Constraints on Resonant Particle Production during Inflation from the Matter and CMB Power Spectra
We analyze the limits on resonant particle production during inflation based
upon the power spectrum of fluctuations in matter and the cosmic microwave
background. We show that such a model is consistent with features observed in
the matter power spectrum deduced from galaxy surveys and damped Lyman-alpha
systems at high redshift. It also provides an alternative explanation for the
excess power observed in the power spectrum of the cosmic microwave background
fluctuations in the range of 1000 < l < 3500. For our best-fit models, epochs
of resonant particle creation reenter the horizon at wave numbers ~ 0.4 and/or
0.2 (h/Mpc). The amplitude and location of these features correspond to the
creation of fermion species of mass ~ 1-2 Mpl during inflation with a coupling
constant between the inflaton field and the created fermion species of near
unity. Although the evidence is marginal, if this interpretation is correct,
this could be one of the first observational hints of new physics at the Planck
scale.Comment: 9 pages, 6 figures, Phys. Rev. D15, in Press, Septermber 15 (2004)
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