Fumio Shiraishi

Variation of luminescence decay in BaF2 crystal excited by electrons, alpha particles and fission fragments

Abstract The time dependence of the luminescence from BaF 2 crystal excited by electrons, alpha particles and fission fragments has been studied for wavelengths of 180–400 nm by a single-photon counting technique. A (220 ± 10) nm component with a lifetime of 0.88 ns is observed for electron and fission fragment excitation. No 220 nm component is observed for alpha particle excitation. The (300+50(−40)) nm component has lifetimes of 600 and 100 ns for electron excitation, 550 and 50 ns for alpha particle excitation, and 580 and 9 ns for fission fragment excitation. The variation in time dependence is attributed to the difference in track structure produced by ionizing charged particles for different LET.

Decay curves of NaI(Tl) scintillators with different Tl+ concentrations under excitation of electrons, alpha particles and fission fragments

Decay curves of NaI(Tl) crystals with Tl + concentrations of 0.01, 0.07, 0.1 and 0.22 mole% have been measured under excitation by photo-electrons from a 137 Cs source, alpha particles from an 241 Am source and fission fragments from a 252 Cf source. A striking difference between the decay curve for electron excitation and those for excitation by alpha particles and fission fragments is observed. A flat top of the decay curve which is observed under electron excitation is analyzed on the bases of energy transfer processes of electrons and V k centers to Tl + ions reported by Dietrich et al. [Phys. Rev. B 8 (1973) 589]. A flat top of the decay curve from NaI(Tl) with a Tl concentration of 0.01 mole% under alpha particle excitation is also observed. Faster decay components of 34±5 ns (in addition to the main scintillation component of 150±10 ns) and 15±5 ns (in addition to the main component of 100±10 ns) are observed under alpha particle excitation and fission fragment excitation, respectively. This findin...

Investigation of single event upset subject to protons of intermediate energy range (RAM)

Nuclear reaction models to reproduce p+Si nuclear reactions precisely in the incident proton energy region of below 50 MeV are investigated, and a computer code based on exciton models is developed. Si irradiation experiments in the intermediate energy region were performed to measure energy deposited by p+Si nuclear reactions with two totally depleted Si detectors in face-to-face arrangement. Coincident signals were analyzed by a two-dimensional pulse height analyzer. This method is shown to be effective in discriminating signals of contaminating particles. The experimental observations are in good agreement with the computed predictions. The single-event upset (SEU) cross section of the 93L422 (RAM) is also compared with the calculated values. >

A new type personnel neutron dosimeter with thin Si detectors

A recently developed Si detector system that is capable of distinguishing recoil protons from a hydrogen-rich radiator, depending on charged particles generated by /sup 6/Li(n, alpha)T nuclear reaction, is investigated, taking essential requirements for personnel dosimeters into account. This dosimeter is a REM counter based on a new principle. It possesses two different target materials and distinguishes low-energy neutrons from fast neutrons. Results of response measurements for both types of neutrons are presented, and the results are evaluated. It is concluded that this method can be used to make a compact personnel neutron dosimeter with sufficient detection efficiency. >

Time delay of recombination luminescence in xenon gas excited by 252Cf fission fragments

Abstract The time dependence of recombination luminescence of 1–3 atm xenon excited by 252 Cf fission fragments has been measured and a delay has been clearly observed. The measured delay time T d is inversely proportional to pressure and is 2.2 μs for 1 atm, which is in agreement with the calculated thermalization time (2 μs) for electrons by Mozumder. For t > T d , the decay is well represented by the formula (1 + T r −1 t ) −2 , where T r = 1.8 μ s for 1 atm.

Radiation Damage of NaI(Tl) by Fast Neutron Irradiation: Blocking of the Energy Transfer Processes from Vk Centers and Electrons to the Activator of Tl.

The scintillation pulse heights and decay curves from fast-neutron irradiated NaI(Tl) crystals up to the integrated fast neutron flux of 2.4×10 15 cm -2 were measured under excitation by electrons, alpha particles and fission fragments. For Tl concentrations of 0.01, 0.07 and 0.22 mole%, decreases by 20∼40% in scintillation pulse heights are observed for the irradiated crystals compared with those of non-irradiated crystals. The decreases are enhanced for electron excitation compared with those for alpha particle and fission fragment excitation. The decrease in scintillation pulse height is attributed to blocking of the energy transfer processes of V k centers and electrons by the traps and lattice disorders which were produced by fast neutrons. The effect of this blocking of the energy transfer processes is clearly observed as a difference in decay curves for the crystals before and after fast neutron irradiation; a flat top which appeared before the irradiation is not present after irradiation.

A large area solid state detector made of ultra high purity p-type Si

Abstract A Surface Barrier Detector for environmental monitoring was fabricated with an ultrahigh purity p-type Si crystal. The crystal had a nominal resistivity of 50 kΩ cm, and Al was evaporated on the outer surface to form a positive electrode of 50 mm o. The excellent light-tightness and adhesivity of the Al layer enables direct mounting of samples on the detector and decontamination of the surface with wetted soft tissues. The energy resolution for α and β particles is 36 and 33 keV fwhm respectively and simultaneous measurement of both α and β particles can be carried out. The detector fabrication procedure, its characteristics and application are reported in this paper.

Surface barrier detectors made of ultra-high purity p-type silicon crystals

Abstract Surface barrier detectors have been fabricated with new high purity p-type silicon crystals whose resistivity is greater than 80 kωcm, and their charge collection behavior has been extensively investigated. The thickness of the detectors ranges from 3.1 to 13.8 mm. It was found that the depletion layers extend from both faces, front and rear, at room temperature, but that they extend from the front aluminum face only at liquid nitrogen temperature. Totally depleted thick detectors of excellent characteristics can easily be fabricated with these silicon crystals. The fabrication procedure and charge trapping effect will also be discussed in the paper.

Scintillation process in NaI(Tl): Comparison with scintillation models

The scintillation efficiency of NaI(Tl) crystals, containing Tl concentration of 0.01, 0.07 and 0.22 mole%, has been measured under electron, alpha particle and fission fragment excitations. The pu...

Direct-Coupled High Tc DC Superconducting Quantum Interference Device Magnetometers on SrTiO3 Substrate: Theoretical Description and Comparison with Experiment

A comprehensive quantitative comparison between the measured performance of direct-coupled high Tc superconducting quantum interference device (SQUID) magnetometers with 30° bicrystal junctions and a numerical simulation is presented. It is shown that the characteristics of the SQUID magnetometer are considerably affected by resonances due to the large dielectric constant of the SrTiO3 substrate. In the realized magnetometer layout, the strip line resonance occurring in the SQUID inductance increases the voltage modulation depth and the output voltage noise of the SQUID, while the flux noise of the SQUID is nearly unchanged. It is also shown that the distortion of the voltage versus flux characteristic is caused by the LC resonance in the pickup loop of the magnetometer in combination with a capacitive feedback. Good agreement between experiment and simulation has been obtained.