Yuki Mitsuya

Development of a scintillating G-GEM detector for a 6-MeV X-band Linac for medical applications

The temporal signals from a large gas detector may show dynamical scaling due to many correlated space points created by the charged particles while passing through the tracking medium. This has been demonstrated through simulation using realistic parameters of a Time Projection Chamber (TPC) being fabricated to be used in ALICE collider experiment at CERN. An interesting aspect of this dynamical behavior is the existence of an universal scaling which does not depend on the multiplicity of the collision. This aspect can be utilised further to study physics at the device level and also for the online monitoring of certain physical observables including electronics noise which are a few crucial parameters for the optimal TPC performance.We recently developed glass gas electron multipliers (G-GEMs) with an entirely new process using photo-etchable glass. The photo-etchable glass used for the substrate is called PEG3 (Hoya Corporation). Taking advantage of low outgassing material, we have envisioned a medical application of G-GEMs. A two-dimensional position-sensitive dosimetry system based on a scintillating gas detector is being developed for real-time dose distribution monitoring in X-ray radiation therapy. The dosimetry system consists of a chamber filled with an Ar/CF4 scintillating gas mixture, inside of which G-GEM structures are mounted. Photons produced by the excited Ar/CF4 gas molecules during the gas multiplication in the GEM holes are detected by a mirror-lens-CCD-camera system. We found that the intensity distribution of the measured light spot is proportional to the 2D dose distribution. In this work, we report on the first results from a scintillating G-GEM detector for a position-sensitive X-ray beam dosimeter.

High-photon-yield scintillation detector with Ar/CF4 and glass gas electron multiplier

The glass made gas electron multiplier (GEM) and Ar/CF4-gas-based gaseous detector is developed as a scintillation detector and ultra high photon yield is demonstrated. The light yield of a glass GEM (G-GEM)-based gaseous detector is estimated to be 85,000 photons/keV, which is three orders of magnitude brighter than inorganic scintillators. The radioluminescence spectrum peak appeared at around 620 nm, which matches the spectral response of commonly used photosensors such as photomultiplier tubes, photodiodes, CMOSs, CCDs, and other photo-sensors. In X-ray spectroscopy, the light yield showed excellent proportionality and the device was successfully operated as a gas proportional scintillation counter. With this design, we obtained a high photon yield of the G-GEM, which has the further advantage of being much more sensitive to low-energy radiation than solid-scintillator-based detectors.

Fine-pitch glass GEM for high-resolution X-ray imaging

We have developed a fine-pitch glass gas electron multiplier (G-GEM) for high-resolution X-ray imaging. The fine-pitch G-GEM is made of a 400 μm thick photo-etchable glass substrate with 150 μm pitch holes. It is fabricated using the same wet etching technique as that for the standard G-GEM. In this work, we present the experimental results obtained with a single fine-pitch G-GEM with a 50 × 50 mm2 effective area. We recorded an energy resolution of 16.2% and gas gain up to 5,500 when the detector was irradiated with 5.9 keV X-rays. We present a 50 × 50 mm2 X-ray radiograph image acquired with a scintillation gas and optical readout system.

A new glass GEM with a single-sided guard-ring structure

The gas electron multiplier (GEM) is a gaseous detector that is widely used in many applications. Our glass GEM (G-GEM) comprises a photo-etchable glass (PEG3, HOYA Corporation, Japan). Our research indicated that it shows superior performance compared with other gas detectors. In this article, a new type of G-GEM is introduced. It has a guard-ring structure around the holes in order to improve the spark tolerance by reducing the total capacitance of each hole structure. A measured gas gain of approximately 7500 is attained for this new G-GEM with a single-sided guard-ring structure using a gas mixture of Ar (90%) and CH4 (10%) in the gas flow mode. An energy resolution of 17.3% (FWHM) is also achieved with a collimated 6 keV X-ray beam. The results of a 10 to 12 hour gas gain stability measurements are also shown.

Characteristics of a glass gem with a guard-ring structure

We recently developed a Glass GEM (G-GEM), and it exhibited a superior performance compared with other gaseous detectors. We are currently developing a G-GEM with a single-sided guard ring structure, in order to improve its spark tolerance. In this research, we compared its performance with that of a conventional hole structure. The single-sided guard-ring structure has shown strong polarity when it was operated upside down, however, the similar output pulse shapes were observed for both cases. The gain curves were consistent with simulation results. The energy resolutions were also compared.

Development of a transparent single-grid-type micro-strip gas chamber based on LCD technology

ABSTRACT The liquid crystal display (LCD) technology allows several simple circuits to be built using thin film transistors, thus making fabrication of compact, integrated, large-area, and low-cost micro-pattern gaseous detectors possible. In this work, a single-grid-type micro-strip gas chamber (S-MSGC) using transparent electrodes based on the LCD technology was fabricated and successfully operated in several gas mixtures. The detector was coupled with a multi-pixel photon counter to detect an optical signal through the transparent substrate in Ar/CF4 gas. Both electrical and optical signals were measured and the light yield of the detector was acquired. Successful operation of the S-MSGC can be considered the very important first step for development of the next target of integrated devices.

Development of 3.95 MeV X-band linac-driven x-ray combined neutron source

The existing non-destructive inspection method employed for concrete structures uses high energy X-rays to detect internal flaws in concrete structures and iron reinforcing rods. In addition to this conventional method, the authors are developing an innovative inspection system that uses a mobile compact linac-driven neutron source that utilizes neutron backscattering, to measure the moisture distribution in concrete structures and estimate the corrosion probability distribution of iron reinforcing rods.

Structural Analysis and Evaluation of Actual PC Bridge Using 950 keV/3.95 MeV X-Band Linacs

In Japan, bridges constructed during the strong economic growth era are facing an aging problem and advanced maintenance methods have become strongly required recently. To meet this demand, we develop the on-site inspection system using 950 keV/3.95 MeV X-band (9.3 GHz) linac X-ray sources. These systems can visualize in seconds the inner states of bridges, including cracks of concrete, location and state of tendons (wires) and other imperfections. At the on-site inspections, 950 keV linac exhibited sufficient performance. But, for thicker concrete, it is difficult to visualize the internal state by 950 keV linac. Therefore, we proceeded the installation of 3.95 MeV linac for on-site bridge inspection. In addition, for accurate evaluation, verification on the parallel motion CT technique and FEM analysis are in progress.

Further study of Glass GEM

We recently developed a Glass GEM (G-GEM), and it exhibited a superior performance. We also developed a G-GEM with a single-sided guard ring structure, in order to improve its spark tolerance. The guard ring G-GEM also showed good performance. The gas gain reached 7,500 with a single G-GEM setup. Energy resolution was 17.3% at maximum, with the collimated 6 keV X-ray source. Nowadays, large-area micro pattern gaseous detectors are required not only in physics field, but also in medical application or neutron detection application. Therefore, we are currently developing a large-area G-GEM. In this research, we will show the results of the preliminary experiments with it. Gas gain reached up to around 1000. The energy resolution was 33.6% at gain ~1,000.

Neutron response result of hybrid scintillator; Ce:LiCaAlF 6 covered with plastic scintillator coupled to APD

We report first read out result of inorganic-organic hybrid scintillator; Ce:LiCaAlF6 single crystal covered with plastic scintillator for neutron detection. The Ce:LiCaAlF6 sample coated with POPOP containing PPO showed great light output and energy resolution than the Ce:LiCaAlF6 itself when it was coupled to PMT. Light output was increased up to 203% and energy resolution was improved to 9%, which originally it was 16%. Moreover, we succeed in clear neutron peak this new hybrid scintillator APD (Hamamats S8664-1010).