Takahisa Koike

Development of GEM-based detector for thermal neutron

We have developed a two-dimensional imaging detector with a gas electron multiplier (GEM) for thermal neutron detection. The basic characteristics of the GEM-based detector have already been measured. In order to improve the detector performance such as the nγ discrimination capability and the position resolution, a neutron irradiation test was performed at BL21 in the Materials and Life Science Experimental Facility (MLF). This paper describes the potential for improving the detector performance on the basis of the results of the neutron irradiation test.

Compact imaging system for GEM detectors

We have developed a compact imaging system for GEM detectors, which is applied to thermal neutron imaging. A GEM chamber and a readout board are integrated into one device. The detector is connected to a readout PC with Gigabit Ethernet. This system generates image data of 14.4K pixel from 240 signals employing strip readout method. We have measured performance of the developed system with a pulsed neutron source. A position resolution of 0.6 mm, a detection efficiency of about 30%, and the maximum detection rate of 11.9M event/sec have been obtained.

Development of new type gaseous gamma camera with GEM

We are developing a new gaseous detector with Gas Electron Multiplier (GEM) as a gamma camera for biomolecular analysis and medical applications. Our system consists of the gamma conversion layers (gold) and the amplification layers. In order to know the performance of the prototype gamma camera, gamma-ray irradiation test was performed with radioactive source of 99mTc (141keV). 2D images were obtained using a pinhole collimator.

A new gamma camera with a Gas Electron Multiplier

We have developed a prototype gaseous gamma camera with a Gas Electron Multiplier (GEM) for biomolecular analysis and medical applications. The system consists of three devices: a detector, an Ethernet hub, and a PC. The detector consists of a GEM-chamber and integrated readout electronics. The GEM-chamber consists of three parts: the gamma-ray conversion and amplification layers consisting of GEM foils, and a readout component. To increase gamma-ray-detection efficiency, we constructed a new type of GEM foil. The gamma-ray conversion layers are plated with gold 3 µm thick on both surfaces. In order to test the performance of the prototype camera, several measurements were performed with a phantom filled with 99mTc(141 keV) as the radioactive source, and two-dimensional (2D) images were obtained using a pinhole collimator. The camera showed good capability to resolve objects of a few mm2.

Performance of a neutron beam monitor with a GEM for the high-intensity total diffractometer at J-PARC

We are developing a neutron beam monitor with a gas electron multiplier (GEM) for the high-intensity total diffractometer at J-PARC. In order to analyze the basic characteristics of the GEM-based detector, a neutron irradiation test was carried out at J-PARC. The wavelength-spectrum distribution obtained from the test is consistent with the calculations, and the beam profiles agree with the simple Monte Carlo (MC) simulation. Therefore we found that as a neutron beam monitor, the GEM-based detector has good two-dimensional imaging ability.

Calculations of Intense Laser Pulse Propagation and Soft X‐Ray Lasing in Capillary Plasma Channels

When intense and short laser pulses pass through a preformed Z‐pinch discharge plasmas, the wave guiding of the laser lights is created in performing the high density and high temperature plasma phase. The dynamics of the laser propagation is analyzed by the wave equation of the laser electric field coupled with the plasma hydrodynamic equations and the rate equations describing the plasma ion states. The optimum soft x‐ray repetition lasing occurs in the 3s‐3p transition in Ar IX, Ne‐like plasmas, in the irradiated plasma channel. A gain coefficient 4.55 cm−1 without opacity was obtained by numerical computations.

Soft X-ray laser amplification and plasma dynamics in capillary discharge

The optimum conditions for soft x-ray laser amplification through the dynamics of Ar plasma, created by the capillary discharge Z-pinch, have been investigated. The numerical simulation of plasma dynamics was based on magnetohydrodynamic one-dimensional radiation model. The plasma behavior of the implosion-pinch phase was analyzed, taking plasma atomic processes into account. The optimum soft x-ray lasing occurs in the 3 s -3 p transition in Ne-like Ar plasma. Radiation emission and absorption processes of the resonance line on this plasma were calculated by means of escape probabilities. The temporal and spatial distribution of the density and temperature in plasmas, and the gain of lasing were evaluated at different initial discharge pressures ranging from 300 to 3000 mTorr.