Teruko Sawamura

Response function measurement of layered type CVD single crystal diamond radiation detectors for 14 MeV neutrons

Response function measurement of layered-type chemical vapor deposition single crystal diamond radiation detectors for 14 MeV neutrons was carried out. The detector had a layered structure that was composed of a boron-doped diamond layer of 0.5 μm in thickness and a nondoped diamond layer of 20 μm on an inexpensive high pressure and high temperature-type Ib diamond substrate. The detector had energy resolution of 2.6% for 5.5 MeV α particles. This experiment was mainly carried out in order to understand the present status of the detector as a 14 MeV neutron spectrometer and an extent of charge trapping. As result, a peak caused by the 12C(n,α0)9Be reactions was clearly observed; the best energy resolution of 6% as for a synthetic diamond radiation detector was achieved. Detection efficiency was 3.2×10−7 counts/unit neutron fluence. However, taking the energy resolution for α particles, etc., into account, the energy resolution for 14 MeV neutrons was not so high. Further improvement based on better crysta...

Measurement of radiation skyshine with D-T neutron source

Abstract The D–T neutron skyshine experiments have been carried out at the Fusion Neutronics Source (FNS) of JAERI with the neutron yield of ∼1.7×1011 n/s. The concrete thickness of the roof and the wall of a FNS target room are 1.15 and 2 m, respectively. The FNS skyshine port with a size of 0.9×0.9 m2 was open during the experimental period. The radiation dose rate outside the target room was measured a maximum distance of 550 m from the D–T target point with a spherical rem-counter. Secondary gamma-rays were measured with high purity Ge detectors and NaI scintillation counters. The highest neutron dose was about 9×10−22 Sv/(source neutron) at a distance of 30 m from the D–T target point and the dose rate was attenuated to 4×10−24 Sv/(source neutron) at a distance of 550 m. The measured neutron dose distribution was analyzed with Monte Carlo code MCNP-4B and a simple line source model. The MCNP calculation overestimates the neutron dose in the distance range larger than 230 m. The line source model agrees well with the experimental results within the distance of 350 m.

Measurement of mass attenuation coefficients around the K absorption edge by parametric X-rays

When electrons at relativistic velocities pass through a crystal plate, such as silicon, photons are emitted around the Bragg angle for X-ray diffraction. This phenomenon is called parametric X-ray radiation (PXR). The monochromaticity and directivity of PXR are adequate and the energy can be changed continuously by rotating the crystal. This study measured the mass attenuation coefficient around the K-shell absorption edge of Nb, Zr and Mo as a PXR application of monochromatic hard X-ray radiation sources.

Fast-neutron-induced tracks in cellulose nitrate

The paper discusses the efficiency of formation of through-etched holes in LR-115 cellulose nitrate irradiated by fast neutrons from a 252Cf source and an Am-Be source. The relation between etch-through time and ranges of charged particles produced by neutrons is obtained. From the experimental results, the threshold energies of charged particles and neutrons for the formation of the holes are derived. It is shown that the efficiency is strongly dependent on etching conditions and detector thickness, as reported by other authors.

Effect of Twinning Caused by Thermal Annealing on Etched Tracks in Synthetic Quartz

Synthetic quartz crystal –x-, y- and z-cut plates– irradiated with fission fragments were heated to temperatures above 573°C and cooled to room temperature before etching in 65% NaOH. The crystals displayed twinning caused by the heating. The openings of etched tracks in twinned areas showed differences in shape in the x-cut plates and in orientation for the y- and z-cut plates (no differences in shape). The bulk etching rates of the twinned areas were also different for twins on the x-cut plates, but were the same for the y- and z-cut plates.

Fission fragment registration in synthetic quartz

Abstract Synthetic quartz crystals were irradiated with Cf-fission fragments to study track registration properties in the x-plane. It was found that the properties depend on the sense of the x-plane: the etched-track size is larger and the effective critical angle 〈θ〉 is higher on the + x x-plane than on the - x-plane and as a result the registration efficiency for fission fragments in 2Π-geometry is also higher. The development of an etched track and changes in the shape of the etched track opening with etching time are discussed. The application of this detector in neutron detection is considered.

Energy-Dependent Neutron Detection Sensitivity of Cellulose Nitrate Track Detector

A cellulose nitrate track detector, LR-115 (Type II), was studied experimentally to observe its neutron energy response when a radiator, such as fissionable material, is absent. The detector was exposed to monochromatic neutrons from the D (d, n) He reaction produced by a Van de Graaf accelerator. Through-etched and almost through-etched tracks in the detector were counted by two different methods: 1) optical microscope counting with an automatic image analyzing system and 2) spark counting. The detection sensitivity was obtained in the neutron energy region lower than 5 MeV and it was found that only α-particles from (n, α) reactions could be detected in both counting methods. We derived the counting probability of α-tracks induced in the detector and the threshold energies for neutron detection.

General formulation of the response of wireline-type beam monitors

The response of wireline-type beam monitors is formulated for waveform measurements of electron beam pulses in the high-frequency region. The response is generally derived for the electron energy, wireline shape and monitor-beam configuration, and the wireline termination condition. The monitor produces an output signal by electromagnetic interaction with the electron beam without interrupting the beam. The general response can, to some extent, be derived from just the wireline geometry, without calculating the beam-induced electromagnetic field, and this is discussed first. The limiting response for a short wireline and low frequency was obtained as the responses of a button-type monitor for the open wireline, and as the response of a loop-monitor subject to Faradays law for a shorted wireline. The output waveform of the monitor is calculated for a simplified field configuration induced by a typical electron-beam pulse emitted from an electron linear accelerator. The monitor sensitivity involving electron energy dependence was derived. The experimental confirmation for the derived response will be described in a separate paper.

Response of a wireline pickup for subnanosecond electron beam pulses

The response of a wireline-type beam monitor was measured for electron beams with energies of 28 MeV and pulsewidths of 20 ps from an electron linear accelerator. The output waveform from the wireline pickup was calculated according to the general formulation for responses of beam monitors based on electromagnetic interaction. In the calculations, a transfer function H(/spl omega/) and an effective length l/sub eff/ are introduced to express all the effects not included in the analysis. The function H(/spl omega/) is assumed to be Gaussian, and the FWHM of H(/spl omega/) and l/sub eff/ is experimentally determined. The effects of the termination, wireline length, height, and angle between the wireline and the beam direction are discussed. The test supported the analysis and, for the standard pickup, a charge sensitivity of 20 V/nC and an FWHM of H(/spl omega/) of 55 ps are obtained.

Measurement of the time profile of a single-bunch electron beam with wireline pickup by considering the wake-field effect

Abstract The effect of a wake-field generated by an electron beam passing through a linac beam exit window was studied experimentally, to establish the response of a beam monitor with a wireline pickup. To suppress the effect of the wake-field, a copper disk with a beam entrance-hole was placed in front of the pickup. A discussion of the frequency domain response for this monitor was also made, to corroborate the data of suppression of the effect. A considerable improvement in the time domain response was observed for a single-bunch electron beam from the linac at ISIR of Osaka University. A waveform with 50 ps rise time and 150 ps FWHM was obtained.