[en] Scintillation performance of recent (2X) grown BGO is studied. Results indicate BGO to perform better than 8% ¹³⁷Cs FWHM NaI(Tl) at energies 2.6 MeV and higher. Even the low energy performance of BGO is suitable for considering it in lieu of NaI(Tl) for many spectroscopic applications

[en] The different geometrical effects that determine the light output of BGO crystals are investigated. Several bulk shapes, attenuation lengths and reflectors are compared. The highest light output is obtained from trapezoids with specular reflecting walls

[en] In this note we are reporting results of studies on single crystals of bismuth germanium oxide (BGO) by positron annihilation technique. (WL)

[en] We measured the radiation hardness of undoped BGO crystals from two different manufacturers. Such crystals are proposed to be used in a small-angle calorimeter of the BELLE detector of the KEK B-factory. Transparency and scintillation light output of the crystals were monitored to see the effect of radiation damage. The crystals show considerable radiation hardness up to 10.2 Mrad equivalent dose, which is much higher than the maximum expected dosage of 500 krad per year of running at BELLE. (orig.)

[en] In order to improve the scintillation performance of bismuth germanate scintillators, the influence of surface roughness and crystal shape upon the light output has been studied experimentally. Through this study, it was found that scintillator surfaces optimizing the light output have their own optimum values in the ratio of the longitudinal-direction length h to the shorter length a (h/a). In other words, if h/a is greater than 6 a higher scintillation performance can be obtained in rough surfaces; while in polished surfaces, it can be obtained when h/a is smaller than 6. Further, if scintillator surfaces are provided with reflective coating, the light output is markedly improved. Regarding the relationship between the light output and the surface state or crystal shape, it was discussed from the viewpoint of transmission loss inside the scintillator and reflection loss on the surface. 9 figures

[en] Transparency is studied at 480 nm with a laser beam. Longitudinal and transversal transmission, transparence variations with laser exposure time (showing a memory effect), absorption coefficient, excitation and fluorescence spectra are investigated. At 480 nm the resistivity of the crystal in an electric field of 2800 V/cm varies linearly with the intensity of a laser beam perpendicular to the electric field and is strongly temperature dependent. The fluorescence spectra show a maximum at 310 nm

[en] The formation of optical waveguides in bismuth germanate doped rare earth elements (Bi₃Ge₄O₁₂:RE) has been studied. The samples were implanted with 77 K. The energy and the dose of the He implanted samples are 2 Mev and 5x10¹⁶ ions/cm² respectively. The samples were annealed for one hour from 250 to 450 deg. C. The losses of the waveguides have been measured and found to be improved with increasing annealing temperature. The ion beam modified the surface of the bulk material so within the region of the waveguide there is an optical rotation, which was observed after 450 deg. C temperature annealing. A net optical rotary power was found to be around 4.1, and 57.5 degree/mm for 632.8, and 488 nm wavelengths respectively. The evidence suggests this is due to a phase change of the BGO, which has been modified from the cubic structure into an anisotropic guide layer. The modified structure in the waveguide has been investigated by monitoring the SHG signal from the waveguide and comparing it with the bulk. The SHG intensity improved with increasing annealing temperature, due to removal of defects caused by the implantation. The restructuring of the implanted guide results in a modified crystal lattice and a greatly improved SHG. The effect increases with the difference between the radius of the RE ions and the Bi ion. The latter effect could be explained by the mismatch of ion size of the RE ion, which distorts the cubic structure of BGO in the implanted region to become slightly anisotropic, which in turn improves the SHG of the BGO:RE waveguide layer. The photoluminescence of the BGO:RE has been studied after excitation with an argon laser. The study was performed at room temperature as well as at low temperature for the waveguide and the bulk regions. The defects caused by the implantation broaden the luminescence spectra of the RE ions within the waveguides. Increasing the annealing temperature narrows the lines, presumably by defect removal. The spectra resemble those of the bulk after anneals at 450 deg. C. There is a correlation between the broadening and the size of the RE ion dopants. The differences between bulk and waveguide luminescence are most clearly observed for the Nd and Er ions. Reasons for this are discussed. (author)

[en] Painting black the crystal close to the photomultiplier and significantly improves the uniformity. Use of a photomultiplier whose photocathode is slightly narrower than the cross section of the crystal also improves the uniformity. Both results may be interpreted in terms of the important role of the total internal reflection of light at the crystal surface. If the above two techniques are employed, the uniformity of the signal output in a typical BGO crystal of 10 x 10 x 200 mm³ is +-10% over 10 to 190 mm from the photomultiplier end and +-2.2% over 50 to 190 mm

[en] In this study, a gamma-gamma coincidence spectrometry was developed and examined for environmental low-level cosmogenic ²²Na monitoring purposes. The spectrometry consists of two bismuth germanate scintillators (BGO) and XIA LLC Digital Gamma Finder (DGF)/Pixie-4 software and card package. The developed spectrometry was optimized according to the considerations of output count rate and gamma peak energy resolution. This spectrometry provides a more sensitive and effective way to quantify even trace amounts of ²²Na with critical detection limit of 9 mBq. A sophisticated computer simulation was also created with the goal of obtaining a better understanding of the experimental results and gamma-gamma coincidence efficiencies at different sample geometries. (author)

[en] The silicon-avalanche photodiode was investigated as an alternative to available silicon photodiodes. The device is a solid-state photosensor fabricated on a thin wafer of silicon, which has internal gain. Avalanche photodiodes can have high internal gain which when coupled to a scintillator crystal, results in a sensitive and compact nuclear detector. The importance of the compactness for high-energy physics experimentation, especially in magnetic fields, is discussed. The solid-state nature of the photodetector renders it more stable, reducing the need for recalibration and adjustment. The program has demonstrated the suitability of the newly developed, large-area, blue-sensitive avalanche photodiode for use in high-energy physics experimentation