Kazuhisa Kurashige

Energy Resolution of LGSO Scintillators

Several LGSO samples with different Ce doping were studied in comparison to GSO crystal. The light output, non-proportionality of the light response, energy resolution and intrinsic resolution were measured and compared to the intensity of the afterglow recorded in the second range of time. A high light output of 17000plusmn1700 ph/MeV and a good energy resolution of 6.5plusmn0.2% for 662 keV gamma rays from a Cs source were obtained for the best sample, doped with 1 mol% of Ce. The energy resolution and, in particularly the intrinsic resolution varied with the concentration of Ce in the tested crystals and were not correlated with their common non-proportionality characteristics. In contrast, the observed correlation of the intrinsic energy resolution of the LGSO crystals and the intensity of their afterglow indicates that the energy resolution of scintillation detectors may be affected by a strong afterglow of the crystals. Thus, it suggests to the manufacturers to make more efforts to reduce afterglow in the crystals.

Scintillation performance of large Ce-doped Gd/sub 2/SiO/sub 5/ (GSO) single crystal

Single crystal Ce-doped Gd/sub 2/SiO/sub 5/ (GSO) has a good balance of scintillation properties such as high density, intense light output, and short decay time, and also has an excellent temperature response and excellent radiation hardness. We studied causes for cracks in single-crystal GSO which have been a major problem in GSO growth, and tried to optimize the growth conditions by using a two-zone furnace which reduced thermal gradient. We were thus able to grow a crack-free single-crystal of GSO that was 80 mm in diameter and 280 mm long. Specimens with 20/spl times/20/spl times/200 mm/sup 3/ sampled from the large GSO boules with 0.5 and 1.5 mol% Ce have been evaluated for high energy physics application.

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.

Surface polishing of GSO scintillator using chemical process

A Ce doped Gd/sub 2/SiO/sub 5/, (GSO) single crystal is an excellent scintillator featuring a large light output, a short decay constant and a high absorption coefficient. It was shown in our previous studies that the surfaces of the scintillator should be polished to get scintillation light output efficiently especially for long and narrow scintillators. Therefore, we newly developed a chemical process to polish the GSO crystal. The surface of the GSO crystal was found to become smooth when it was etched using anhydrous orthophosphoric acid at 150-300/spl deg/C. The process was also proved to be applicable to large size crystal such as 20/spl times/20/spl times/200 mm/sup 3/ preventing thermal shock crack. An improvement in the scintillator efficiency was confirmed using the chemical polishing process.

Scintillation characteristics of GSO single crystal grown under O/sub 2/-containing atmosphere

A Ce doped Gd/sub 2/SiO/sub 5/ (GSO) single crystal is an excellent scintillator featuring a large light output, a short decay constant and a high absorption coefficient. We have investigated dependence of the scintillation characteristics on the growth atmosphere. GSO crystal is usually grown in pure N/sub 2/, which due to thermal etching during the growth always roughens the boule surface, inducing some micro-cracks on the surface which often triggers the large crack in the boule. To eliminate this, we first introduced 1 vol% O/sub 2/-containing N/sub 2/ gas for the growth atmosphere. The resultant boule turned to be very smooth in surface, but pale yellow in color and degraded in the scintillation characteristics. To retain these properties, we then introduced an annealing process and found the annealing under pure N/sub 2/ atmosphere quite effective on the recovery both in color and scintillation properties. >

Scintillation Properties of Lu

We have developed Lu

_0.4

_0.4

Gd

Gd

_1.6

_1.6

SiO

SiO