Search

Abstract: Since diagnostic X-rays have been proven to be a cause of cancer, some precautions are essential to reduce the dose delivered to patients. In this paper, an idea to reduce the dose by a new type of X-ray computed tomography (CT) using silicon strip detectors is discussed. Thin tungsten plates placed between edge-on silicon strip detectors are the key element to reduce the background of scattered X-rays and improve the image contrast with low dose. The initial results of a feasibility study are also reported. [Copyright &y& Elsevier]

We report on the design and performance of a mixed-signal application specific integrated circuit (ASIC) dedicated to avalanche photodiodes (APDs) in order to detect hard X-ray emissions in a wide energy band onboard the International Space Station. To realize wide-band detection from 20 keV to 1 MeV, we use Ce:GAGG scintillators, each coupled to an APD, with low-noise front-end electronics capable of achieving a minimum energy detection threshold of 20 keV. The developed ASIC has the ability to read out 32-channel APD signals using 0.35 μ m CMOS technology, and an analog amplifier at the input stage is designed to suppress the capacitive noise primarily arising from the large detector capacitance of the APDs. The ASIC achieves a performance of 2099 e − + 1.5 e − /pF at root mean square (RMS) with a wide 300 fC dynamic range. Coupling a reverse-type APD with a Ce:GAGG scintillator, we obtain an energy resolution of 6.7% (FWHM) at 662 keV and a minimum detectable energy of 20 keV at room temperature (20 °C). Furthermore, we examine the radiation tolerance for space applications by using a 90 MeV proton beam, confirming that the ASIC is free of single-event effects and can operate properly without serious degradation in analog and digital processing. [ABSTRACT FROM AUTHOR]

We have developed multi-pixel TES microcalorimeters in order to realize high-energy resolution and X-ray imaging. A Sn absorber and a Bi absorber were formed on Si3N4 and SiO2 membrane using two-step exposure photolithography and electrodeposition. A FEM analysis was carried out to investigate the performance of the X-ray microabsorbers. In addition, a superconducting through-wafer interconnection was demonstrated considering the future X-ray imager using microcalorimeters. Detail of the fabrication techniques, characteristics and simulation results of two types of the microabsorbers, as well as those of the calorimeters are described. [Copyright &y& Elsevier]

We are developing transition edge sensor (TES) microcalorimeter arrays for future Japanese astronomy missions. Although 6.6 eV energy resolution for 5.9 keV and 74 μs decay time are achieved, our energy resolution was limited by the excess noise of unknown origin. The dominant noise showed 1/R dependence and it only appeared when the current through the TES, I, is larger than 10 μA. This is explained if we assume a constant voltage noise source with a level of ∼2(4kTCRn)1/2. We also investigated the influence of I on the TES performance and found the TES sensitivity α is reduced when the ratio of current to the critical current I/IC is large. It can explain the reduction of α observed when operated without a magnetic shield. We also found a strong correlation between IC and α or the baseline width. Thus, we conclude that IC is an essential parameter for the TES performance. [Copyright &y& Elsevier]

Effects of neutron irradiation on X-ray energy responses of silicon semiconductor detectors have been investigated. Neutron irradiation experiments were carried out for n-type photodiode arrays utilized in the Joint European Torus (JET) using deuterium (D) beam-injection into a tritium (T) target for a well-calibrated deuterium–tritium (D–T) fusion neutron production at the Fusion Neutronics Source (FNS) facility of Japan Atomic Energy Research Institute. X-ray energy responses of these detectors are characterized before and after irradiation by the use of synchrotron radiation from a 2.5 GeV positron storage ring at the Photon Factory of High Energy Accelerator Research Organization (KEK). A recovery of the degraded X-ray energy response after the neutron irradiation has been found at fluences beyond around 1013 neutrons/cm2. A further novel finding is followed as a “re-degradation” by a neutron irradiation level over about 1014 neutrons/cm2. This “non-linear response” may be physically interpreted in terms of a type inversion from n- to p-type silicon in the detectors. Long-term observations of X-ray energy responses of the detectors after neutron irradiation have also been made in order to clarify the “annealing effect”. [Copyright &y& Elsevier]

To develop the fourth generation light source, RIKEN has started research program on an X-ray FEL source based on SASE in 2002. For the first stage of the program, in order to develop key technology specially required for the X-ray FEL, and to study technique for handling of high-peak-power radiation, RIKEN is developing the SCSS-machine: SPring-8 Compact SASE Source, which aims to generate FEL radiation at VUV region using low-emittance electron beam at 0.5–1 GeV energy. SCSS uses three key technologies (1) low-emittance electron injector with 500 kV thermionic pulsed gun, (2) high-gradient C-band (5712 MHz) RF system and (3) in-vacuum type short period undulator. This paper reports the current R&D status of the SCSS project. [Copyright &y& Elsevier]

A new imaging system using the multi-color scintillator Gd2O2S:Eu has been developed for the X-ray radiography. In this method a color Charge Coupled Device detects the weak blue and green photons associated with the transitions from the terms like 5D1 and 5D2 in the Eu-ions as well as the dominant red photons. As these transitions become appreciable and saturate at quite different intensity levels of the X-ray, we can realize a big extension of the dynamic range of the imaging almost by hundred times in comparison with the conventional monochromatic method. As a result, the new system makes it possible to take a clear image of any complex object, which consists of various parts of the different X-ray penetrability, from plastic to heavy metal, at a single shot. [Copyright &y& Elsevier]

Abstract: A Compton scattering X-ray source consisting of an X-band (11.424GHz) electron linear accelerator (linac) and Q-switched Nd: YAG laser is currently under development at the University of Tokyo. Monochromatic X-rays are required for a variety of medical and biological applications. The X-ray source produces monochromatic X-rays via collision between a 35-MeV multi-bunch (104 bunches in a 1μs RF pulse) electron beam and 1.4J/10ns (532nm) Nd: YAG laser pulse. The linac uses an X-band 3.5-cell thermionic cathode RF gun and an alpha magnet as an injector. Until now, electron beam generation (2MeV, 1pC/bunch at the exit of the injector), beam acceleration, and X-ray generation have been verified. In order to increase X-ray energy and intensity, we have completed the design and construction of a new RF gun with relevant modifications in some structures. In this paper, we describe the details of the concepts of designing a new RF gun and discuss future works. [Copyright &y& Elsevier]

Abstract: We are currently developing a compact monochromatic X-ray source based on laser–electron Compton scattering for the purpose of medical applications at the University of Tokyo. To realize remarkably compact-, high-intensity- and highly stable system, we adopt an X-band (11.424GHz) multi-bunch linear accelerator (linac) and reliable Q-switch Nd:YAG laser. The injector of the system consists of a 3.5-cell X-band thermionic cathode RF-gun and an alpha magnet. So far, we have continued high-power experiment and beam generation on X-band thermionic cathode RF-gun. However, breakdown was frequently occurred at coaxial structure around the thermionic cathode. In order to resolve the breakdown, we adopt a choke structure around the thermionic cathode. In this paper, the details of Compton scattering X-ray source the University of Tokyo, the experimental results of the X-ray generation, and upgrade of the X-band thermionic cathode RF-gun will be presented. [Copyright &y& Elsevier]