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Abstract: A femtosecond (fs) electron bunching was observed in a photoinjector with a magnetic compressor by rotating the bunch in longitudinal phase space. The bunch length was obtained by measuring Cherenkov radiation of the electron beam with a femtosecond streak camera technique. A single electron bunch with rms bunch length of 98fs was observed for a 32MeV electron beam at a charge of 0.17nC. The relative energy spread and the normalized transverse emittance of the electron beam were 0.2% and 3.8mm-mrad, respectively. The effect of space charge on the bunch compression was investigated experimentally for charges from 0.17 to 1.25nC. The dependences of the relative energy spread and the normalized beam transverse emittance on the bunch charge were measured. [Copyright &y& Elsevier]

The COMET Phase-I experiment plans to search for muon to electron conversion. In order to get a good signal-to-noise ratio and time resolution, all the front-end readout boards are installed near the detector region where the radiation level is high. The radiation effects, in particular from neutrons, onto FPGA hardware will be a severe problem. We developed high reliable firmware with auto-recovery schemes for three different series of FPGAs, and evaluated them with a neutron beam. In these tests, soft error rates were measured and good performances of the schemes were demonstrated. [ABSTRACT FROM AUTHOR]

Abstract: The process of neutron leaking from a 14MeV neutron source facility was analyzed by calculations and experiments. The experiments were performed at the Fusion Neutron Source (FNS) facility of the Japan Atomic Energy Institute, Tokai-mura, Japan, which has a port on the roof for skyshine experiments, and a 3He counter surrounded with a polyethylene moderator of different thicknesses was used to estimate the energy spectra and dose distributions. The 3He counter with a 3-cm-thick moderator was also used for dose measurements, and the doses evaluated by the counter counts and the calculated count-to-dose conversion factor agreed with the calculations to within ∼30%. The dose distribution was found to fit a simple analytical expression, and the parameters and are discussed. [Copyright &y& Elsevier]

Abstract: A phoswich detector composed of a thin plate CsI(Tl) scintillator and a plastic scintillator (BC-400) has been designed and evaluated in order to improve the sensitivity in the low-energy region of a large-area plastic scintillation detector. This newly designed phoswich detector can be applied to both gross gamma measurement and energy spectrometry for low-energy gamma-ray emitters. Judging by estimations of minimum detectable activity, the lower measurable energy of a large-area plastic scintillation detector can be expanded down to a few tens of keV by adding a thin plate CsI(Tl) scintillator. [Copyright &y& Elsevier]

Abstract: The moderator structure for a neutron spectrometer was optimized with the Monte Carlo code MCNP-4B. The spectrometer consists of a cylindrical moderator and a position-sensitive thermal neutron detector and obtains energy spectra from thermal neutron distribution along its cylindrical axis. The structure of the moderator was improved by using a low hydrogen density material on one end and a high hydrogen density on the other, and inserting a neutron absorber that eliminates thermal neutron diffusion. This design improves the energy resolution of the spectrometer, especially for low-energy neutrons from a few to 100keV. The designed spectrometer can be applied to the measurement of energy spectra over a neutron energy range from a few keV to 20MeV. [Copyright &y& Elsevier]

Abstract: A picosecond stroboscopic pulse radiolysis system which consists of a femtosecond laser and a picosecond L-band linear accelerator (linac) is demonstrated. A newly installed femtosecond laser system operated at 960Hz can cover a wide region of wavelength ranging from <300nm to 10μm, although the upper limit is 1.7μm to date because of the sensitivity of photodetectors. In order to achieve a high accuracy of synchronization between the laser and the linac, a new timing and synchronization circuit was developed. A double pulse detection method was applied for the new system, resulting in doubling of the improvement in signal-to-noise ratio. The time resolution and time jitter were estimated from the rise time of hydrated electrons at 600nm, and the transient absorption kinetics of electrons in n-dodecane was measured at 1300nm. [Copyright &y& Elsevier]

Abstract: In order to study the feasibility of a carbon nanotube-based electron gun for small and portable betatrons, the characteristics of electron emission from carbon nanotubes were measured at around ≉1×10-4Pa, a typical pressure in the vacuum chamber of such betatrons. The sample cathodes were made from powders of single-walled nanotube (SWNT) and multi-walled nanotube (MWNT) that were fixed on the stainless steel plate with gold paste. We found that the emission was weaker at the lower vacuum for both MWNT and SWNT. However, when the vacuum level was restored to ≉1×10-4 Pa after being kept at 4.0×10-4Pa for 15minutes, the emission-current recovered to some extent but did not fully come back to the original value. The observed current densities from SWNT and MWNT are 550 and 540μA/mm2, respectively, at the high-voltage we tried: 2kV for SWNT and 1.1kV for MWNT across a 300μm gap. It is likely that the carbon nanotube, under the pulsed operation, has advantages over the thermal cathode for the electron emitters of portable betatrons. [Copyright &y& Elsevier]

We have developed a new photomultiplier tube (PMT) with high sensitivity for a wavelength-shifter fiber readout of plastic scintillators. Improvements of the photoelectron yield were made on a 2-in. PMT (Hamamatsu R329) by adopting (1) a prism-shaped photocathode, (2) an extended-green photocathode material, and (3) an optical mirror surface of the electrodes. As a result, the number of photoelectrons obtained by the new PMT has increased to be 1.8-times that by R329. Other PMT characteristics, such as uniformity of sensitivity, time response and darkcurrent are not so much different from those of R329 for practical applications. [Copyright &y& Elsevier]

The lifetimes of our carbon stripper foils (10–25 μg/cm2) prepared by reactive nitrogen ion-beam sputtering were distributed in a wide range. Expressed in units of integrated beam current received, lifetimes of 750±400 mC/cm2 were usual for a 3.2 MeV Ne+ beam. This wide distribution of lifetimes have been improved by applying a binary gas mixture (N2+Ne) for sputtering of carbon. With high reproducibility, lifetimes of 475±80 mC/cm2, approximately 15 times those of the best standard commercially available foils, have been achieved. We have also investigated the influence light-element admixtures had on the lifetimes of carbon stripper foils. [Copyright &y& Elsevier]

Properties of Transition-Edge Sensor (TES) microcalorimeters operated with AC bias are studied utilizing the calorimeter Wheatstone bridge circuit called Calorimeter Bridge Biased by an AC Generator (CABBAGE). The CABBAGE eliminates the AC carrier significantly, thus enables us to study the AC responses of the TES with high sensitivity. We tested two kinds of TES devices operating at 110 and 440 mK, respectively. With the 110 mK device biased with 25 kHz, an energy resolution of 28 eV is obtained for Mn Kα line. On the other hand, we multiplexed the signals from two 440 mK device biased with 50 and 20 kHz, respectively, and obtained 167 and 271 eV energy resolutions. Even at the balance point of the bridge, AC signal did not disappear and odd-order harmonics were observed. They are considered to arise from the current dependence of the TES resistance, which is characterized by β≡d log R/d log I. Numerical solution for the CABBAGE response can reproduce the experimental results well if β=0.24±0.02. Since the harmonics may cause severe problem in the SQUID operation even after attenuated by a band-pass filter, especially at high bias frequency operation such as several hundred kHz, it is important to make β small. [Copyright &y& Elsevier]

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 a Ti/Au TES microcalorimeter array for future Japanese X-ray astronomy missions. The goal is an energy resolution of 2–5 eV at 6 keV, and an array of 100–1000 pixels to achieve a geometrical area of >1 cm2 and a moderate spatial resolution simultaneously. The energy resolution was improved to ∼6 eV at 6 keV with a very fast time constant (<100 μs). To achieve a high coverage fraction, it is necessary to fabricate mushroom-shaped X-ray microabsorbers. We are developing an electrodeposition fabrication technique that is suitable for our process. Sn was used as absorber material, but the energy resolution was not good due to the existence of long-lived quasiparticles. Bi is also used, and the process is under optimization now. The readout strategy is to multiplex signals in the frequency domain, using a bridge circuit. So far, we succeeded in multiplexing two pixels modulated with 50 and 20 kHz at 440 mK. The energy resolution obtained at 110 mK was 33 eV (25 kHz). [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]

Energy responses of three types of Japanese neutron dose-equivalent (DE) meters were evaluated by Monte Carlo simulations and measurements. The energy responses were evaluated for thermal neutrons, monoenergetic neutrons with energies up to 15.2 MeV, and also for neutrons from such radionuclide sources as 252Cf and 241Am–Be. The calculated results were corroborated with the measured ones. The angular dependence of the response and the DE response were also evaluated. As a result, reliable energy responses were obtained by careful simulations of the proportional counter, moderator and absorber of the DE meters. Furthermore, the relationship between pressure of counting gas and response of the DE meter was discussed. By using the obtained responses, relations between predicted readings of the DE meters and true DE values were studied for various workplace spectra. [Copyright &y& Elsevier]

The experimental apparatus used for the first direct observation of the tau neutrino (the DONUT experiment) is described. Its main features consisted of a target system composed of nuclear emulsion targets and scintillation fiber trackers, a magnetic charged-particle spectrometer and detectors for lepton identification. This paper will concentrate on the description of the electronic detectors and their performance in selecting neutrino interactions, making the vertex predictions necessary for locating events in the emulsion target and lepton identification. [Copyright &y& Elsevier]

In order to investigate the contamination due to the radioactive isotopes (RIs) in NaI(Tl) scintillator for dark matter search, a simple method of pulse shape discrimination (PSD) to extract α-rays energy spectrum was developed. Two linear signals of different timings were input into a single module charge-sensitive analog-to-digital converter. The α- and the γ-rays were discriminated by comparing the total charge integration of a pulse with the partial one. As a result, the α-rays energy spectrum with NaI(Tl) was successfully and clearly extracted. The present work showed that the PSD method was performed by the minimum electronic circuits. The sensitivity was high enough to measure RIs of a few μBq/kg in high pure NaI crystals for dark matter search. [Copyright &y& Elsevier]

We cleaned electrostatic accelerator tubes by applying a high-pressure water jet and examined their high-voltage performances at 1 and 3 MV. The cleaning was very effective in reducing discharge activities at their rated voltages. We did some experimental investigations with the tubes and their ceramic insulators. We found that removal of microparticles loosely bound on the vacuum-side ceramic surfaces had an important effect in eliminating the discharge activities. [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]

The effective analyzing power for a 3He polarimeter was calibrated at E3He=443MeV. For the calibration, the absolute magnitude of the polarization was determined by means of the double scattering method using the 3He scattering on 12C at 7° in the laboratory frame. The effective analyzing power of Ayeff=0.232±0.010−0.015+0.017 was obtained for the polarimeter with a plastic scintillator of 16mm thickness as analyzer. The energy dependence of Ayeff was measured. The first data of the induced polarization for 3He+12C elastic scattering at E3He=443MeV will be presented. [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]

An asymmetric-energy collider of 8 GeV electrons and 3.5 GeV positrons, KEKB, has been operating at KEK since 1998. On July 9, 2001 it achieved the highest record of luminosity, 4.5×1033 cm−2 s−1. This paper describes the interaction region (IR) extending about 8 m from the interaction point (IP) along each beam direction. The main machine components in the IR are focusing quadrupole magnets, compensation solenoids, and vacuum chambers, which are positioned on movable stages. They are designed to focus both beams into collisions with a finite angle crossing. [Copyright &y& Elsevier]

The transport lines of the KEKB for positrons and electrons convey the beams separately from the injector linac to the KEKB rings. The length is about 500 m for each line. In order to make the maximum use of the existing tunnels and also to avoid interference with the AR, the beam lines took a serpentine course, resulting in a rather large curvature in the arcs. The consequences were a large number of bends in the arcs with high fields and also a large dispersion function and, thus, a large R56 component. The latter issue is crucial for the KEKB rings, since it results in a longer bunch length at injection. We adopted a special optics that reduces the R56 coefficient sufficiently. We have developed novel water-cooled ceramic chambers for kickers, eddy-current-type septum magnets for injection, and a beam-abort system for the rings. The present paper describes the design and current status of the beam lines, the injection system, and the beam-abort system. [Copyright &y& Elsevier]

KEKB is a two-ring electron–positron collider with asymmetric energies of 8 and 3.5 GeV to study CP violation in B meson decay. In KEKB, there are 21 types of magnets; about 1600 in total. About 430 dipole and quadrupole magnets were recycled from TRISTAN, the preceding program. All quadrupole magnets are equipped with vertical and horizontal steering dipole magnets. The number of steering magnets is about 1700. There are 212 sextupole magnets, and all of them are fixed on remotely controlled movers to adjust their positions to the beam passage. All main dipole magnets have back-leg coils to steer beams precisely. All quadrupole and sextupole magnets are equipped with correction coils to have a capability for beam-based alignment. Also one-turn coils are installed as well to each magnetic pole of the main magnets to monitor the magnetic flux in the case of trouble. The magnetic field in all magnets was measured and its quality strictly checked. After field measurement, the magnets were installed and precisely aligned. A cooling water system and a power supply system for these magnets were constructed. Magnet design was started in 1994, and construction of the two rings was completed in November 1998. The parameters of the magnets and the construction of the KEKB magnet system are described. Some of the problems experienced during this construction work are also presented. [Copyright &y& Elsevier]

The concentration of Th-chain was precisely measured. Two alpha rays from 220Rn and 216Po were extracted by the time correlation analysis. The time correlation between two events was found to agree with the half-life of 216Po. The sensitivity of this method for Th-chain was discussed. [Copyright &y& Elsevier]

We have accurately determined U-chain concentration in a detector by means of the β–α delayed coincidence method. This method can measure the radioactivity of the order of 10−7 Bq/kg. It corresponds to the concentration of the order of 0.01 ppt under the assumption that the U-chain is in the secular radioactive equilibrium, by a signal-to-noise ratio of one to one. [Copyright &y& Elsevier]

Scintillating-fiber-block detectors have been constructed using 0.5 mm square fibers for the KEK-PS E373 experiment, which searches for double-strangeness nuclei. The main aim of the detector is to measure the energies of protons and pions produced from decay of double- or single-hypernuclei using their ranges. It is also used to detect Λ hyperons or the H-dibaryon, and to make event selection. The performance of the detectors was studied with low-energy proton and pion beams as well as minimum-ionizing particles. The energy resolution determined by the range measurements was 0.86 MeV for 37 MeV π−''s and 1.4 MeV for 47 MeV protons. The excellent capability of π/p separation has been also demonstrated. [Copyright &y& Elsevier]

A micro-gap wire chamber (MGWC), a new tracking detector has been developed for use in high-rate experiments. A prototype of the MGWC of a sensitive area of 30×10 cm2 is made with a printed circuit board and finely spaced round thin wires stretched with a narrow gap of 50 μm between anode wires and cathode strips. The result shows a rate capability of more than 1×104/mm2/s. [Copyright &y& Elsevier]

Nowadays uniform, low-cost and large-size compound semiconductor detectors are available up to several square centimeters. We are trying to combine this technology with conventional gas detectors to upgrade an anticoincidence type proportional counter, Oeschger-type thin wall counter of 2.2 l, used for a 14C dating facility at the University of Tokyo. In order to increase the ratio of the signal to the background for smaller quantity of samples less than 1 g, an effective approach is to minimize the detector volume at higher gas pressure. However, the anticoincidence function suffers from such a small volume. Therefore we designed a new active wall gas counter of 0.13 l counting volume using CdTe compound semiconductor detectors as the wall of the gas proportional counter to perform anticoincidence. Simulation study showed that at noise thresholds less than 70 keV, the wall counters can reject above 99.8% of events arising from outer gamma rays. Measured noise levels of CdTe detectors were smaller than 24 keV which is low enough for 99.8% anticoincidence efficiency. The experiment showed an anticoincidence efficiency for outer gamma rays from 70% to 80%, similar to that of the old 14C counter. The lost anticoincidence efficiency results from the area of 21.74% which was not covered with CdTe due to two holes for the path of the center anode wire and slots between every two sides of CdTe detectors. [Copyright &y& Elsevier]

The effects of nuclear fusion produced neutrons on the X-ray energy responses of semiconductor detectors are characterized. The degradation of the response of position-sensitive X-ray tomography detectors in the Joint European Torus (JET) tokamak is found after neutron exposure produced by deuterium–deuterium and deuterium–tritium plasma fusion experiments. For the purpose of further detailed characterization of the neutron degradation effects, an azimuthally varying-field (AVF) cyclotron accelerator is employed using well-calibrated neutron fluence. These neutron effects on the detector responses are characterized using synchrotron radiation from a 2.5 GeV positron storage ring at the Photon Factory (KEK). The effects of neutrons on X-ray sensitive semiconductor depletion thicknesses are also investigated using an impedance analyser. Novel findings of (i) the dependence of the response degradation on X-ray energies as well as (ii) the recovery of the degraded detector response due to the detector bias application are found and interpreted by systematically combined methods using a synchrotron facility, a cyclotron facility, a fusion plasma device, material analysis methods along with our recent theory on semiconductor X-ray responses. [Copyright &y& Elsevier]

Elliptically shaped transition-region plasmas located between circularly shaped central cell and fish-tail shaped anchor-cell plasmas have been observed using X-ray tomography techniques for the first time in the world largest tandem mirror device, GAMMA 10. These three regions are connected through the lines of magnetic forces. Electrons are, therefore, anticipated to move easily through these regions along the magnetic field lines when neither appreciable electron losses into the transverse direction across the magnetic field lines nor the formation of electron transport barrier potentials in the parallel direction are expected. From this viewpoint, comparisons of electron temperature (Te) profiles in these regions, thus, give information on one of the most critical issues in tandem mirror plasma confinement. The first data on good agreement in Te profiles of the central cell and the transition region have supported this basic and essential concept of tandem mirror confinement. Development of position sensitive semiconductor-detector arrays and an upgraded X-ray tomography algorithm for analysing elliptically shaped transition-region plasmas are also reported. [Copyright &y& Elsevier]

A new method for a simultaneous observation of both plasma ion and electron temperatures is proposed using one semiconductor-detector array alone. This method will provide a new application of semiconductor-detector arrays for monitoring the key parameter set of nuclear-fusion triple product (i.e., ion temperatures, densities, and confinement time) as well as for clarifying physics mechanisms of energy transport between plasma ions and electrons under various plasma confining conditions. This method is developed on the basis of an alternative “positive” use of a semiconductor “dead layer”; that is, an SiO2 layer is employed as a reliable ultra-thin energy analysis filter for low-energy charge-exchanged neutral particles from plasmas ranging in ion temperatures from 0.1 to several tens of kilo-electron-volts. Using recent fabrication techniques for the thin and uniform SiO2 layers of the order of tens to hundreds of angstrom, our computer simulation and its experimental verification show the availability of such semiconductors for distinguishing neutral particles (for ion temperatures) from X-rays (for electron temperatures). These are simultaneously emitted from the plasmas into semiconductor detectors; however, we employ their quite different penetration lengths and the resultant different deposition depths and profiles in semiconductor materials. As a result, their output signals are distinguishable for these two different and fundamental species of plasmas. [Copyright &y& Elsevier]

At the Belle II experiment, Aerogel RICH is used as the particle identification device that covers the forward end-cap part of the Belle II detector. We develop the readout system of Hybrid Avalanche Photo Detectors that are used as the photon sensors of the Aerogel RICH. We present overview of the readout system, and report the status of the mass production toward the Belle II experiment. [ABSTRACT FROM AUTHOR]

A hybrid photo-detector (HAPD) has been developed for the aerogel RICH (ARICH) of the Belle II experiment. In the present contribution we report the performance tests in magnetic fields, results of the neutron and gamma irradiation studies, and of aging tests. We also review the production status and plans. [ABSTRACT FROM AUTHOR]

CsI(Tl) scintillation detectors based on a silicon photomultiplier (SiPM) were tested for low-energy proton detection. Pulse shape analysis of the SiPM signals with a transimpedance amplifier was conducted to investigate the saturation effect due to the recovery time of a pixel and to evaluate particle identification capability. To recover energy linearity, a saturation correction method based on a non-paralyzable dead time model was proposed. The setup using the SiPM with a 25 μ m pixel pitch well separated protons and deuterons at energies from 3 to 12 MeV. Additionally, a readout circuit without an amplifier was tested to investigate another type of saturation due to the voltage drop effect. [ABSTRACT FROM AUTHOR]

A method for controlling the energy of slowed-down RI beams with the goal energy of 20 MeV/u was developed at the RIKEN RI Beam Factory. The 93Zr beam energy was successfully tuned to 20.2 MeV/u in a single step by adjusting its momentum selected by the first dipole magnet after a primary target. A method for particle identification was developed for the secondary reaction fragments at 50 MeV/u. The dispersive mode was applied to the ZeroDegree spectrometer to measure the momentum at the final focus F11. The reaction fragments were stopped in the multi-sampling ionization chamber (MUSIC) placed at F11, which measured the Δ E − E of the beam particles. In addition, the range R in MUSIC was determined with a resolution of 1.4 mm (σ) by using the energy ratio obtained from multi-sampled energy deposits. The atomic number was determined from the E − R correlation with a resolution of 0.15 (σ). To distinguish the charge state of the RI beam after the secondary reaction target, the range with the correction for the β dependence was combined with the mass-to-charge ratio determined from the time-of-flight and magnetic-rigidity measurements. A 5.6 σ separation was obtained between 92Zr 40 + and 90Zr 39 + using these two values. [ABSTRACT FROM AUTHOR]

Abstract: Bunch length measurement in the 100fs range is proposed for electron accelerators, based on the spectral width of monochromatic synchrotron radiation. The parameters of an undulator that produce the required radiation are described. [Copyright &y& Elsevier]

Nuclear emulsion is a film-type charged particle track detector that uses the technology of silver halide photosensitive material. Because nuclear emulsion is compact and does not require an electric power source, it is suitable as a detector for cosmic-ray imaging (also called cosmic-ray muon radiography or muography) that requires outdoor observation. However, problems with the long-term stability and temperature tolerance of nuclear emulsion limit the observation periods, seasons and locations where it might be used. To enable long-term observation and outdoor use throughout the year, we investigated factors that affect the long-term characteristics of nuclear emulsion. The results of our experiments clearly showed that gelatin, additive chemicals, and packing material affect the long-term stability. Based on these results, we have developed a nuclear emulsion with excellent long-term stability. To confirm the properties of this newly developed nuclear emulsion, we examined the temperature dependence, and created an Arrhenius plot of the reaction rate. The prediction based on Arrhenius law showed that the Grain Density stayed at 25/ 100 μ m or more for more than one year at 10 °C and 20 °C, and for 260 days at 30 °C; and the Fog Density stayed at 5/ 1000 μ m 3 or less for more than one year at 10 °C and 20 °C, and for 270 days at 30 °C. This represents a new nuclear emulsion that is not limited by the observation period, season, and location. In fact, the developed stable nuclear emulsion is being used for cosmic-ray imaging observations in the pyramid of Khufu and is expected to be used for future cosmic-ray imaging observations and other elementary particle research. [ABSTRACT FROM AUTHOR]

AXEL is a high-pressure xenon gas time projection chamber for neutrinoless double-beta decay (0 ν 2 β) search. The AXEL has a unique readout system called ELCC which has a cellular structure and photosensors to detect electroluminescence light produced by ionization electrons. We demonstrated the performance of the ELCC with a small prototype detector (AXEL-HP10L). The obtained energy resolution corresponds to 0. 82 − 1. 74 % (FWHM) at the 0 ν 2 β Q-value. We are constructing a new prototype (AXEL-HP180L) in order to study the energy resolution at the Q-value of 0 ν 2 β with a new design of ELCC with unit structure, newly developed electronics board, field-shaping electrodes, and Cockcroft–Walton-type high voltage power supply. For a future 1-ton scale large AXEL detector, we are developing new background-reduction techniques; topology identification with machine learning, positive-ion detection, and active-shield options. [ABSTRACT FROM AUTHOR]

The current status of laboratory for Dark Matter search at the Kamioka mine and specialized facility for production of NaI(Tl) detectors is described. Techniques developed for purification and growth of ultra-low background NaI(Tl) crystals are reported. Achieved activity levels of the 210Pb, 40K, 238U, 232Th isotopes in the latest NaI(Tl) Dark Matter detector prototypes and the DAMA/LIBRA detectors are compared. [ABSTRACT FROM AUTHOR]

Radiation damage on front-end readout and trigger electronics is an important issue in the COMET Phase-I experiment at J-PARC, which plans to search for the neutrinoless transition of a muon to an electron. To produce an intense muon beam, a high-power proton beam impinges on a graphite target, resulting in a high-radiation environment. We require radiation tolerance to a total dose of 1. 0 kGy and 1 MeV equivalent neutron fluence of 1. 0 × 10 12 n eq cm − 2 including a safety factor of 5 over the duration of the physics measurement. The use of commercially-available electronics components which have high radiation tolerance, if such components can be secured, is desirable in such an environment. The radiation hardness of commercial electronic components has been evaluated in gamma-ray and neutron irradiation tests. As results of these tests, voltage regulators, ADCs, DACs, and several other components were found to have enough tolerance to both gamma-ray and neutron irradiation at the level we require. [ABSTRACT FROM AUTHOR]

Research on the distribution and dynamics of photoassimilates in plants, especially those in fruits, is important for increasing food production. Positron emission tomography (PET) and carbon-11 (11C) can be used for obtaining 3-D images of photoassimilates. For plant experiments, however, it is important to adjust the system to the plant's growth environment. A small OpenPET prototype can visualize an open space between two detector rings, and thus facilitate adjustment of the environment around a target plant during fruit PET imaging. In this work, we improve the OpenPET for plant studies and discuss its applications in the analysis of the dynamics and distributions of photoassimilates in plants with fruits. 11C-labeled photoassimilate translocation into the fruit of a strawberry plant is imaged using 11C-labeled CO 2 and the OpenPET. The OpenPET has been found to be promising for researching the physiological functions of the photoassimilates in plants with fruits. [ABSTRACT FROM AUTHOR]

Abstract: We succeeded in fabricating 256-pixel arrays of Ti/Au transition edge sensor (TES) microcalorimeters with electrodeposited microabsorbers made of Bi, and report on their test results. We confirmed all pixels tested so far were alive, however most of the microabsorbers were stripped off during cooling cycles. We investigated some pixels by irradiating with 5.9keV X-rays, and confirmed that they actually worked as microcalorimeters. The X-ray pulses are represented by a sum of two components with different decay times. The ratio of the two components fluctuates from pulse to pulse, which limits the energy resolution to . We discuss the pulse shape of two decay-time components considering thermal conductivities, i.e., inside microabsorbers, between microabsorbers and TES. [Copyright &y& Elsevier]

We have developed a new laser-based time calibration system for highly segmented scintillator counters like the MEG II pixelated Timing Counter (pTC), consisting of 512 centimetre-scale scintillator counters read out by silicon photomultipliers (SiPMs). It is difficult to apply previous laser-based calibration methods for conventional metre-scale Time-Of-Flight detectors to the MEG II pTC from the implementation and the accuracy points of view. This paper presents a new laser-based time calibration system which can overcome such difficulties. A laser pulse is split into each scintillator counter via several optical components so that we can directly measure the time offset of each counter relative to the laser-emitted time. We carefully tested all the components and procedures prior to the actual operation. The laser system was installed into the pTC and thoroughly tested under the real experimental condition. The system showed good stability and being sensitive to any change of timing larger than ∼ 10 ps. Moreover, it showed an uncertainty of 48 ps in the determination of the time offsets, which meets our requirements. The new method provides an example of the implementation of a precise timing alignment for the new type of detectors enabled by the advance of SiPM technology. [ABSTRACT FROM AUTHOR]

The characteristics of deuterated diamond-like carbon (D-DLC) as a neutron mirror was evaluated by ERDA, RBS and neutron reflectivity measurements. The number density of hydrogen in unit area is 1.4–3.2×1016 H/cm2 in D-DLC. This is same with the typical numbers of normal neutron mirrors. It has a good neutron reflectivity with high quality mirror surface and high optical potential. [Copyright &y& Elsevier]

Abstract: To evaluate the deposited dose distribution in a target, we have proposed to utilize the annihilation gamma-rays emitted from the positron emitters distributed in the target irradiated with stable heavy-ion beams. Verification of the one dimensional (1-D) dose distributions along and perpendicular to a beam axis was achieved through our previous works. The purpose of this work is to verify 3-D dose distributions. As the first attempt uniform PMMA targets were irradiated in simple rectangular parallelepiped shapes, and the annihilation gamma-rays were detected with a PET scanner. By comparing the detected annihilation gamma-ray distributions with the calculated ones the dose distributions were estimated. As a result the estimated positions of the distal edges of the dose distributions were in agreement with the measured ones within 1mm. However, the estimated positions of the proximal edges were different from the measured ones by 5–9mm depending on the thickness of the irradiation filed. [Copyright &y& Elsevier]

Abstract: We are constructing a three-dimensional imaging system for medical and biological applications. The system will allow simultaneous imaging at high spatial and energy resolutions across a wide energy range, from several tens of keV to a few MeV. The system relies on a Si/CdTe semiconductor Compton camera, incorporating state-of-the-art space-observation technology developed by ISAS/JAXA. The Si/CdTe Compton camera was developed for use at moderate temperatures. Moreover, the solid, thin scattering layer allows the target to be placed close to the camera, a good angular resolution corresponds directly to a good spatial resolution. These aspects allow the construction of a compact medical system. In this work, we have developed a prototype head module for a multi-head system. The performance of the prototype was evaluated with a sealed Ba-133 radiation source. The experiments confirmed that the imaging results were consistent with source positioning. The experimental results were also compared with those of a Monte Carlo simulation. [Copyright &y& Elsevier]

Abstract: In this study, we have analytically shown that if the electron bunch length is in the 100-as range, the energy loss of the bunch is proportional to the square of the number of electrons in the bunch. If the number of electrons is large, the collective loss introduces a high-energy-density state in the target. The results were verified by carrying out 2D PIC simulations. [Copyright &y& Elsevier]

Abstract: A femtosecond pulse radiolysis with a time resolution of 210fs has been developed by using a femtosecond electron beam and a femtosecond laser light. It has successfully opened the study of ultra-fast reactions or phenomena in materials—the first observation of the femtosecond formation process of the hydrated electron in water pulse radiolysis. The use of a photocathode femtosecond electron gun, which produces a near-relativistic 100fs electron beam, has been approached to construct femtosecond megavolt electron diffraction. The dependencies of the emittance, bunch length, and energy spread on the radio-frequency (rf) and space-charge effects in the rf gun have been investigated. [Copyright &y& Elsevier]

Abstract: At the Kansai Photon Science Institute of the Japan Atomic Energy Agency, we have developed a Compton backscattered X-ray source in the energy region of a few hundred keV. The X-ray source consists of a 150-MeV electron beam, with a pulse duration of 10ps (rms), accelerated by a Microtron accelerator and an Nd:YAG laser, with a pulse duration of 10ns (FWHM). In the first trial experiment, the X-ray flux is estimated to be (2.2±1.0)×102 photons/pulse. For the actual application of an X-ray source, it is important to increase the generated X-ray flux as much as possible. Thus, for the purpose of increasing the X-ray flux, we have developed the pulse compression system for the Nd:YAG laser via stimulated Brillouin scattering (SBS). The SBS pulse compression has the great advantages of a high conversion efficiency and a simple structure. In this article, we review the present status of the Compton backscattered X-ray source and describe the SBS pulse compression system. [Copyright &y& Elsevier]