Hiroki Kusano

Xenon Time Projection Chamber for Next-Generation Planetary Missions

Imaging of γ rays with 1–5 MeV with a xenon time projection chamber (Xe-TPC) has been simulated with the GEANT4 code. The clear image of a γ-ray source was obtained using the Xe-TPC. The dependence of angular resolution and imaging efficiency on xenon density were also investigated over the density range from 0.06 to 0.18 g/cm 3 . It was found that a Xe-TPC is promising for imaging of high-energy γ-rays (∼5 MeV) on planetary surface.

Development of an x-ray generator using a pyroelectric crystal for x-ray fluorescence analysis on planetary landing missions

The chemical element abundance on planetary surface is essential for planetary science. We have been developing an active X-ray spectrometer (AXS), which is an in-situ chemical element analyzer based on the X-ray florescence analysis for future planetary landing missions. The AXS consists of an X-ray detector and multiple X-ray sources. Although a pyroelectric X-ray generator is promising for the AXS as an X-ray source, the raise of emission X-ray intensity is necessary for short-time and precise determination of elemental composition. Also, in order to enhance the detection efficiency of light major elements such as Mg, Al, and Si, we have tested the low energy X-ray emission by changing the target material. In this study, the X-ray emission calculation at the target by Monte Carlo simulation and the X-ray emission experiments were carried out. More than 106 cps of the time-averaged X-ray emission rate was achieved in maximum using a LiTaO3 crystal with 4 mm thickness and Cu target with 10 um thickness. The performance of pyroelectric X-ray generator is presented in this paper.

Electron mobility and longitudinal diffusion coefficient in high-density gaseous xenon

Measurements of the mobility and longitudinal diffusion coefficient of electrons under external electric fields were performed in high-density gaseous xenon at room temperature. The xenon density and reduced electric field ranges were from 2.55 ×1020 to 1.73 ×1021 cm-3 and from 0.027 to 0.19 Td, respectively. The electron transport parameters of the density-normalized mobility, density-normalized longitudinal diffusion coefficient, and the ratio of the longitudinal diffusion coefficient to the mobility were found to increase with increasing density for reduced electric fields at around 0.04 Td. This result indicates the density-dependent variation of the effective momentum-transfer cross section for electron–atom scattering. It was also found that the density-dependent variations are different depending on the electron transport parameters, which can be attributed to the difference in parameter sensitivity to the momentum-transfer cross section.

Density Dependence of the Longitudinal Diffusion Coefficient of Electrons in Xenon

The longitudinal diffusion coefficient of electrons and the ratio of the longitudinal diffusion coefficient to the mobility of electrons were measured for the first time in high-density gaseous xenon in the extensive density range of 4.19×1019–4.82×1020 cm-3. The density dependence of the longitudinal diffusion coefficient was observed in the reduced electric field range of 0.025–0.055 Td.

Multi-purpose wide-angle vision system for remote control of planetary exploring rover

Wide-Angle Fovea Vision Sensor (WAFVS) system was designed and developed being inspired from advantages of the human eyes functions. This system is characterized by its space-variant data acquisition property, i.e., the WAFVS captures a 120-degree wide-angle input image in which its resolution (or magnification) changes like the human visual acuity. As well-known, the human visual acuity is the highest at its central field of view (FOV) and decreases rapidly towards its peripheral FOV. Thus, using the WAFVS, we can observe a target in detail by its central field of view while observing the whole of environment by its wide field of view. In addition, by controlling a view direction of the WAFVS, this WAFVS system gets visual information from the environment more in detail by smaller data amount. Hence, the WAFVS achieves a better performance of data transmission and data storage. One of severe problems in remote control of rovers, UAVs, and satellites is of a pay-load. In this point of view, the authors think that the WAFVS is suitable for the planetary exploring rover because it was originally developed for multi-purpose use of a single vision sensor. This paper describes the multi-purpose use of the WAFVS system, i.e., the following tasks: (1) observing the environment displayed to the operator for the remote navigation of the rover, (2) recording images of important scenes by changing a view direction of the WAFVS, and (3) monitoring if the instruments on the rover work well or not. Moreover, this paper experiments and discusses on how to display images to the operator when an eye-tracking device is applied as a target coordinate input device. Accuracy index, i.e., a measurement error of a target, is defined in order to evaluate performance of a combination among the vision sensor, the coordinate input device and the image display method.

Basic studies on x-ray fluorescence analysis for active x-ray spectrometer on SELENE-2

An active X-ray spectrometer (AXS) is now being developed as a payload candidate for the rover on SELENE-2, the next Japanese lunar exploration mission. The AXS will determine the chemical compositions of lunar rocks and regolith around the landing site. The surface of lunar rock samples will be ground using a rock abrasion tool. Thus, fundamental studies on the X-ray fluorescence analysis for lunar rocks and regolith are required to design and develop the AXS. In this study, we have investigated the X-ray fluorescence analysis in order to evaluate the effects of surface roughness of samples and the angle of incident and emergent X-rays. It was found that the fluorescent X-ray yield for low energy X-rays, i.e. the light elements, decreases at rough surface samples. This effect of surface roughness becomes small for smooth surface samples. It was also found that the fluorescent X-ray yield depends on the incident angle, which is attributed to the fact that the X-ray fluorescence occurs closer to the sample surface at larger incident angles. Since the emergent X-rays are affected by the detection geometry and surface roughness, the incident angle effect also depends on the above conditions.

Longitudinal and transverse diffusion of electrons in high-pressure xenon

High-pressure xenon is an attractive medium for radiation detection in that the time projection chambers can be constructed by combined measurements of charge and light signals. The electron transport properties are essential information for developing and operating high-pressure xenon detectors. In this paper, our recent experimental results of electron diffusion coefficients in high-pressure xenon are presented. We measured the longitudinal diffusion coefficient of electrons under external applied electric fields in high-pressure xenon, ranging from 0.17 to 5.0 MPa in pressure at room temperature. A significant pressure dependence was found in the density-normalized longitudinal diffusion coefficient for low electric field region. We compared the longitudinal diffusion coefficient with the transverse one at a pressure of 1.0 MPa, and obtained the difference between both the diffusion coefficients. The longitudinal diffusion was found to become smaller than the transverse one when increasing the external electric field.

Measurements of Electron Drift Velocity in 3He Gas

Electron drift velocities in 3He and 4He gases were measured at 0.1 MPa and we compared the results in 3He and 4He under the electric field strength normalized by the number density of helium gas, E/N, from 0.04 to 1.0 Td. This is the first experimental confirmation of the fact that the electron drift velocity in 3He gas is larger than in 4He gas. The difference in the electron drift velocities is attributed to the difference in the atomic masses of 3He and 4He.

A study on color information corrected in human brain — Measurement and evaluation of color propagation

There exists a well-known visual illusion with respect to color propagation. That is, a human subject confuses a color in the subjects peripheral field of view (FOV) as another color in the central FOV (with a shape of circular disk) spreads into the peripheral FOV or as a color in the peripheral FOV erodes another color in the central FOV (also with a shape of circular disk) when he/she keeps gazing at a specific color visual stimulus in his/her central FOV for more than several seconds. In this paper, the authors experiment this illusion using multiple naive subjects in conditions of the visual stimuli as the central or peripheral colors and the disk size change. This paper has proposed a rate of propagation as a criterion and has analyzed and discussed the illusion using it.

Mona Lisa might be displeased

This paper presents a developed experimental system using an eye-tracking device, by which we can control displayed visual stimuli flexibly like visual trick. Using this system, comparisons between two faces with different expressions are experimented in a specific condition as one face is always forced to display as in the subjects central field of view, while another face is always displayed in his/her peripheral field of view. The results have proved that ability of discriminate faces in the peripheral field of view is quite poor. In addition, the experimental results indicate how we could live our daily lives more peacefully.