Shigehiro Owaki

Scintillation Pulse Shapes of Anthracene Single Crystals in Nanosecond Region. I. Initial Spikes in α-Scintillation Pulse

The accurate measurement of scintillation pulse shapes of anthracene single crystals has been performed by a newly constructed device with the time resolution of nanosecond by means of the sampling method under the pulse height selection and the accumulation of pulse shapes. The distinctive differences between the pulse shapes of luminescence excited by α-, β-particles, γ-ray and UV light pulse were observed. In case of excitation of α-particle, there appeared a characteristic peak which seemed to be superposed on a scintillation peak excited by β- or γ-ray. The dependence of this faster component, that is, the initial spike on the values of d E /d x of α-particle in anthracene crystal has been studied.

Acoustic emission of composite materials in tensile tests at cryogenic temperatures

Abstract Tensile tests of fibre reinforced plastics are performed at cryogenic temperatures and simultaneously acoustic emission (AE) is observed to examine the microscopic deformation and fracture processes of these materials. AE behaviours at liquid helium temperature are different from those at liquid nitrogen temperature, although the mechanical behaviours are similar. From these results, correlations of the AE sources with the microscopic deformation and fracture processes are discussed.

A Light Pulse Source of a Few Tens of a Picosecond to Nanosecond Width with Cherenkov Radiation

It was experimentally proven that Cherenkov radiation arising from intense electron pulses passing through a dielectric material could be utilized for a light source of short pulse width. A linear accelerator at ISIR, Osaka University, which can produce intense single-bunch electron pulses, was used for a Cherenkov radiation exciter. The spectral distribution and pulse shape of the Cherenkov radiation from an air radiator with these electron pulses were investigated with a fast detection system for this purpose. The spectrum showed a peak at 200 nm and a continuous band of which intensity decreased towards the longer wavelength. The minimum pulse width of the Cherenkov radiation with the single-bunch electrons was about 40 ps, and the light peak power was about 10 kW in the spectral region of 200 to 600 nm.

Tunable Near-Infrared and Visible All-Solid-State Optical Parametric Oscillator Amplifier System Based on Potassium Titanyl Phosphate Crystal

We present the design details and performance characteristics of a low-energy all-solid-state near-infrared optical parametric oscillator amplifier (OPOA). The pump source is a laser diode (LD) pumped frequency-doubled Nd:YAG laser with a single mode energy of 4 mJ in 8 ns, 50 Hz pulses. The OPOA system, based on potassium titanyl phosphate (KTP) crystal, features a low pump energy threshold at 532 nm of less than 0.4 mJ, broad tunability from 750 to 1040 nm for the signal and a conversion efficiency of 27% at 920 nm. External cavity second harmonic conversion of the idler to visible green-red light in a type II KTP crystal and of the signal to visible blue-green light in a type I BBO crystal was performed with efficiencies up to 10%. We have used the near-infrared output for wavelength-dependent fluorescence lifetime studies in ytterbium-doped laser materials. We have also used the second harmonic wavelengths between 565–600 nm to measure the transmission of Nd:YAG in a preliminary experiment to demonstrate the utility of the system.

Photoacoustic Spectroscopy on the Metallic Colloids in Ionic Crystal after Pulsed Electron Irradiation

Thin single crystals of NaCl were deeply colored by intense electron irradiation. The PAS peak due to small Na colloids formed in the crystal is shown to agree well with the optical absorption peak in a spectrum of transmission method. Dependence of the PA signal on modulation frequency of the exciting light reveals thermal diffusion of Na colloids out of the crystal during the heat treatment at 463 K.

Measurements of Photostimulated Electron Emission from Superconducting Metals at 9–300 K

PSEE measurements for superconducting and other type metals were carried out between about 9 and 300 K. Electron emission decreased upon lowering the sample temperature to that of liquid N2 and showed two peaks in the course of the temperature change. One was attributed to residual gas adsorption and the other to sample deformation. PSEE yield did not change at the transition between the normal and the superconducting states.

Metallic Na formation in NaCl crystals by electron and VUV photon irradiation

Abstract Metallic Na was formed on crystal surfaces of NaCl with irradiation by electron beams of low energy (10–30 KeV) or photon fluxes in the VUV region and was evaluated with AES and UPS. The states of Na formed in or on NaCl crystals with irradiation of high (21 MeV) and low energy electrons and VUV photons are discussed comparing the results from different analysis methods.

Fracto-Emission from Crystalline and Non-Crystalline Materials at Cryogenic Temperatures

Electron emissions from metals, FRP and ceramics during the fracture process (fracto-emission) at cryogenic temperatures have been reported in previous conferences. In this paper, the FEs from some crystalline (single and poly-crystal) and non-crystalline (glassy state) insulating materials are compared and discussed. The FEs from sodium silicate glass and pure fused silica are very similar to those from poly-crystalline ceramics, but are different from those from synthetic quartz (single crystal) especially for fracture at room temperature. From experimental results, the fracture modes, generation of free electrons and its compensation in these materials are discussed.

Fracto-Emission from Ceramics at Cryogenic Temperatures

Electron emissions from fine ceramics of alumina during the fracture process (fracto-emission, FE) at cryogenic temperatures were observed and compared with those from brittle metals, glass and single crystals of SiO2 etc. The features of FEs are intended to be classified in metals and insulators, and moreover, the latter are into single and poly-crystals, and non-crystalline (glassy state). However, the FEs from alumina ceramics of polycrystalline are very similar to those from sodium silicate glass and pure fused silica, but are different from those from synthetic quartz (single crystal) especially for fracture at room temperature. From experimental results, it is supposed that they depend on the fracture modes, fracture strength and electronic properties for generation of free electrons and its compensation on fracture surfaces of these materials. These problems are discussed here.

Piled ionization chamber for selective measurement of radioactive gas with three .BETA.-ray energy groups.

This paper describes the development of a piled ionization chamber system consisting of 3 stacked thin box-type ionization chambers, which is used for measuring the radioactive concentration of three energetically grouped β-emitters.This system consists of a central ionization chamber in which the sample gas flows and two outer ionization chambers which detect medium and high energy β-rays penetrating through the walls of the central chamber.This radioactive concentration ofβ-emitters of each energy group is determined by the ionization current from the chambers. Performance tests were carried out for the central chamber filled with tritium and 133Xe. It was experimentally found that the radioactive concentration can be measured for each energetically grouped β-emitter and the minimum detectable tritium concentration for this system is about 3.8×10-3 Bq/cm3 in He.