Sohan Kawamura

Floating zone growth and scintillation characteristics of cerium-doped gadolinium pyrosilicate single crystals

Growth of cerium-doped gadolinium pyrosilicate (Gd₂Si₂O₇:Ce) single crystals, which show 2.5 times greater light output for gamma-rays and five times greater light output for alpha particles than GSO single crystals, is accomplished using floating zone growth method (FZ method). Although growth of Gd₂Si₂O₇ (GPS) single crystal is considered to be difficult because it melts incongruently according to the phase diagram in a Gd₂O₃-SiO₂ system, we attempted crystal growth of Ce:GPS because the possibility exists that heavy Ce doping changes the phase diagram. Transparent single crystals were obtained, but cracks were observed in the crystals. The crystal structure was triclinic with space group P_/1 and density of 5.5 g/cm³. Two peaks were observed by photoluminescence spectrum measurement at 374 nm and 394 nm caused by 5d-4f transition in Ce³⁺ ion. Decay times of Ce:GPS were 46 ns for gamma-ray and 39 ns for alpha particles; its density was 5.5 g/cm³. We consider that the energy resolution of 23% will be improved by fabrication of large crystals and improvement of crystal perfectability.

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...

Scintillation Characteristics of

Cerium-doped gadolinium pyrosilicate single crystals Ce:Gd2Si2O7 (Ce:GPS) with various Ce concentrations of 2.5-30 mol% with respect to the total rare-earth sites were prepared by the floating zone method. Their scintillation performances were investigated under irradiation of gamma rays of 137Cs. The Ce concentration dependence of scintillation characteristics and high-performance scintillation characteristics were obtained: 3-6 times greater light output than that of BGO single crystals, rapid decay, and good energy resolutions of 5.1-8.4%. Furthermore, X-ray diffraction patterns of Ce:GPS revealed Ce concentration dependence of the crystal structure of Ce:GPS.

{\rm Ce}:{\rm Gd}_{2}{\rm Si}_{2}{\rm O}_{7}

Dependence of crystal structure and luminescence property of Gd2Si2O7(Ce:GPS) was investigated using poly-crystalline samples synthesized by a solid state reaction method. Three types of crystal structures and different luminescence spectra were observed according to concentration of cerium. The largest luminescence intensity was observed for orthorhombic structure whose cerium concentration was between 0.75 and 2.5 mol%.

(Ce 2.5–30 mol%) Single Crystals Prepared by the Floating Zone Method

Cerium-doped gadolinium pyrosilicate single crystals Ce : Gd₂Si₂O₇ with various Ce concentrations of 2.5-25 mol% were fabricated using floating zone method. Their scintillation performances were investigated under irradiation of gamma rays of ¹³⁷Cs. The Ce concentration dependence of scintillation characteristics and high- performance scintillation characteristics were obtained: 3-5 times greater light output than BGO single crystals, rapid decay, and good energy resolutions of 5.1-8.4%. X-ray diffraction patterns of Ce : Gd₂Si₂O₇ also showed Ce concentration dependence of the crystal structure of Ce : Gd₂Si₂O₇.

Dependence of crystal structure and luminescence property of Gd2Si2O7 on cerium concentration

Response function measurement of Gd2Si2O7 (GPS) scintillator for thermal neutrons was carried out. GPS single crystals exhibits light output twice higher than GSO single crystals for thermal neutrons. In addition, similar experiments with GPS scintillators of 50 mum in thickness were conducted to improve signal-to-noise ratio between neutrons and gamma-ray. GPS powder samples, size of each particle was 50 mum, showed lower light output than that of GPS single crystals, because absorption and scattering of scintillation light at the sample surface reduced the correction efficiency of scintillation light. Optimization of the particle size, reflectors and techniques to fix the GPS sample will improve the powder density and detection efficiency because powder samples were directly coated on a glass plate in this experiment.