We have developed an Electron-Tracking Compton Camera (ETCC) as a next-generation MeV gamma-ray telescope. Our detector consists of a gaseous electron tracker as a Compton-scattering target and a ...position sensitive scintillation camera as a scattered gamma ray absorber. We launched a small size (10 cm cubic) ETCC loaded on a balloon in 2006, and obtained the fluxes of diffuse cosmic and atmospheric gamma rays in the energy range between 125 keV and 1:25 MeV. However, for MeV gamma-ray astronomy, we need to detect the photons at higher energy, thus we must improve the sensitivity of the ETCC in the higher energy range above 1 MeV. For this purpose, we investigate an electron absorber, which is placed between the electron tracker and the photo-absorber. Using Geant4 simulation, we confirmed that the detection energy range is shifted to the range of 0:35-5:0 MeV for the new configuration of the ETCC.
Staphylococcus aureus is one of the major causes of community-acquired and hospital-acquired infections. It produces numerous toxins including superantigens that cause unique disease entities such as ...toxic-shock syndrome and staphylococcal scarlet fever, and has acquired resistance to practically all antibiotics. Whole genome analysis is a necessary step towards future development of countermeasures against this organism.
Whole genome sequences of two related
S aureus strains (N315 and Mu50) were determined by shot-gun random sequencing. N315 is a meticillin-resistant
S aureus (MRSA) strain isolated in 1982, and Mu50 is an MRSA strain with vancomycin resistance isolated in 1997. The open reading frames were identified by use of GAMBLER and GLIMMER programs, and annotation of each was done with a BLAST homology search, motif analysis, and protein localisation prediction.
The
Staphylococcus genome was composed of a complex mixture of genes, many of which seem to have been acquired by lateral gene transfer. Most of the antibiotic resistance genes were carried either by plasmids or by mobile genetic elements including a unique resistance island. Three classes of new pathogenicity islands were identified in the genome: a toxic-shock-syndrome toxin island family, exotoxin islands, and enterotoxin islands. In the latter two pathogenicity islands, clusters of exotoxin and enterotoxin genes were found closely linked with other gene clusters encoding putative pathogenic factors. The analysis also identified 70 candidates for new virulence factors.
The remarkable ability of
S aureus to acquire useful genes from various organisms was revealed through the observation of genome complexity and evidence of lateral gene transfer. Repeated duplication of genes encoding superantigens explains why
S aureus is capable of infecting humans of diverse genetic backgrounds, eliciting severe immune reactions. Investigation of many newly identified gene products, including the 70 putative virulence factors, will greatly improve our understanding of the biology of staphylococci and the processes of infectious diseases caused by
S aureus.
Spatial resolution of a μPIC-based neutron imaging detector Parker, J.D.; Harada, M.; Hattori, K. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
10/2013, Letnik:
726
Journal Article
Recenzirano
We present a detailed study of the spatial resolution of our time-resolved neutron imaging detector utilizing a new neutron position reconstruction method that improves both spatial resolution and ...event reconstruction efficiency. Our prototype detector system, employing a micro-pattern gaseous detector known as the micro-pixel chamber (μPIC) coupled with a field-programmable-gate-array-based data acquisition system, combines 100μm-level spatial and sub-μs time resolutions with excellent gamma rejection and high data rates, making it well suited for applications in neutron radiography at high-intensity, pulsed neutron sources. From data taken at the Materials and Life Science Experimental Facility within the Japan Proton Accelerator Research Complex (J-PARC), the spatial resolution was found to be approximately Gaussian with a sigma of 103.48±0.77μm (after correcting for beam divergence). This is a significant improvement over that achievable with our previous reconstruction method (334±13μm), and compares well with conventional neutron imaging detectors and with other high-rate detectors currently under development. Further, a detector simulation indicates that a spatial resolution of less than 60μm may be possible with optimization of the gas characteristics and μPIC structure. We also present an example of imaging combined with neutron resonance absorption spectroscopy.
•Neutron imaging detector with micro-pattern gaseous detector and 3He was developed.•Detector combines imaging with energy by time-of-flight and high-rate capability.•Detector features 18% efficiency, 0.6μs time resolution, and γ sensitivity <10−12.•New analysis method with template fit achieves spatial resolution of nearly 100μm.•Simulation study indicates improvement to ∼60μm after optimization.
NEWAGE is a direction-sensitive dark matter search experiment using a micro-time-projection chamber filled with
$\rm CF_4$
gas. Following our first underground measurement at Kamioka in 2008, we ...developed a new detector with improved sensitivity, NEWAGE-0.3b’. NEWAGE-0.3b’ has twice the target volume of the previous detector, a lower energy threshold, and an improved data acquisition system. In 2013, a dark matter search was undertaken by NEWAGE-0.3b’ in Kamioka underground laboratory. The exposure of
$0.327\,{\rm kg}\cdot {\rm days}$
achieved a new
$90{\%}$
confidence level direction-sensitive spin-dependent cross-section limit of
$557\,{\rm pb}$
for a
$200\,{\rm GeV}/c^2$
weakly interacting massive particle. Relative to our first underground measurements, the new direction-sensitive limits are improved by a factor of
${\sim }10$
, and are the best achieved to date.
Gamma-ray bursts (GRBs) are the most energetic phenomena in the universe. To elucidate the radiation mechanism of GRBs, we are developing a Compton-scattering-type polarimeter using a plastic ...scintillator and CsI(Tl) scintillator attached to a silicon photomultiplier (SiPM). We constructed a small test model and investigated the basic performance. Moreover, irradiating the SiPM with protons, the radiation hardness has been also investigated. From these experiments, we have recognized that the Compton-scattering-type polarimeter will obtain the sensitivity to the energy above approximately 30 keV if the radiation damage to the SiPM is not serious. On the other hand, the dark current of the SiPM becomes several thousand times higher for a few krad of irradiation and can be accumulated in the space environment in a few years. This means that the polarimeter will work well in balloon-borne experiments for a few weeks.
Neutron imaging detector based on the μPIC micro-pixel chamber Parker, J.D.; Hattori, K.; Fujioka, H. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
01/2013, Letnik:
697
Journal Article
Recenzirano
We have developed a prototype time-resolved neutron imaging detector employing the micro-pixel chamber (μPIC), a micro-pattern gaseous detector, coupled with a field programmable gate array-based ...data acquisition system for applications in neutron radiography at high-intensity neutron sources. The prototype system, with an active area of 10×10cm2 and operated at a gas pressure of 2atm, measures both the energy deposition (via time-over-threshold) and three-dimensional track of each neutron-induced event, allowing the reconstruction of the neutron interaction point with improved accuracy. Using a simple position reconstruction algorithm, a spatial resolution of 349±36μm was achieved, with further improvement expected. The detailed tracking allows strong rejection of background gamma-rays, resulting in an effective gamma sensitivity of 10−12 or less, coupled with stable, robust neutron identification. The detector also features a time resolution of 0.6μs.
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