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We developed [Lu.sub.0.4][Gd.sub.1.6]Si[O.sub.5] (LGSO) crystal as a new scintillator for medical imaging applications. The size of the LGSO ingot obtained for this investigation was approximately 60 mm in diameter and 170 mm in length. The as-grown crystal was yellow in color. To eliminate the tint, the crystal was annealed in pure [N.sub.2] atmosphere after the growth. As a result, the LGSO became colorless with uniform and large light output which is about 2.0 times that of GSO. Index Terms--Annealing, LGSO, scintillation properties.

The emission spectra for X-ray and UV excitation, decay curve for emission above 460 nm under [gamma]-ray excitation, and energy spectrum by using avalanche photodiode (APD) for excitation with [sup.137] Cs [gamma]-rays have been measured for [Lu.sub.0.4] [Gd.sub.1.6] Si[O.sub.5] having 2.0 mol% Ce. The emission spectrum under X-ray excitation showed two peaks around 430 and 495 nm. The excitation-emission spectrum under UV excitation also had two peaks at 425 and 510 nm for excitation wavelength of 285 and 385 nm, respectively. There was no significant difference in decay constants of emission between the longer and shorter wavelength components. Energy resolution by using an APD was 8.0% for [sup.137] Cs [gamma]-ray excitation. Index Terms--Emission wavelength, radiation detector, scintillator.

Single crystal Ce-doped [Gd.sub.2]Si[O.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 x 20 x 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.

A Ce doped [Gd.sub.2]Si[O.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 [degrees] C. The process was also proved to be applicable to large size crystal such as 20x20x200 [mm.sup.3] preventing thermal shock crack. An improvement in the scintillator efficiency was confirmed using the chemical polishing process.

ACe doped [Gd.sub.2]Si[O.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 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.

We developed Lu0 .4 Gd1 .6 SiO5 (LGSO) crystal as a new scintillator for medical imaging applications. The size of the LGSO ingot obtained for this investigation was approximately 60 mm in diameter and 170 mm in length. The as-grown crystal was yellow in color. To eliminate the tint, the crystal was annealed in pure N2 atmosphere after the growth. As a result, the LGSO became colorless with uniform and large light output which is about 2.0 times that of GSO. [ABSTRACT FROM AUTHOR]

The emission spectra for X-ray and UV excitation, decay curve for emission above 460 nm under γ-ray excitation, and energy spectrum by using avalanche photodiode (APD) for excitation with 137Cs γ-rays have been measured for Lu0.4Gd1.6SiO5 having 2.0 mol% Ce. The emission spectrum under X-ray excitation showed two peaks around 430 and 495 nm. The excitation-emission spectrum under UV excitation also had two peaks at 425 and 510 nm for excitation wavelength of 285 and 385 nm, respectively. There was no significant difference in decay constants of emission between the longer and shorter wavelength components. Energy resolution by using an APD was 8.0% for 137Cs γ-ray excitation. [ABSTRACT FROM AUTHOR]

Analyzes the causes of cracks in single-crystal gadolinium-silicon oxide (GSO), and studies the growth conditions of GSO. Scintillation properties of GSO crystals; History of single-crystal cerium GSO; Observations made of the GSO crystal boule; Possible causes of the cracks; How the causes of the cracks were eliminated.