GaN layers grown on ceramics, sapphire or SiC substrates using reactive ion płating method are presented. In reactive ion plating method gallium from a hot source reacts on a heated substrate with nitrogen partially ionized. Rutherford backscattering technique was applied to check the composition of the samples and gallium to nitrogen ratio was found to be close to one. However, Rutherford backscattering studies showed also a remarkable amount of unintentional impurities present in the layers. The structure of GaN was determined using reflection high-energy electron diffraction. It appeared that polycrystal and monocrystal can be grown, depending on growth conditions. Absorption spectra taken on the layers grown on sapphire showed a tail of band to band absorption starting at about 370 nm. Carrier concentration was of the order of 10 19 -1020 cm-3 at room temperature and did not change much with temperature decrease. No luminescence from the layers was detected, most probably due to high concentratioii of impurities.PACS numbers: 68.55. Gi, 81.15.J]
Plastic organic scintillators such as the blue-emitting BCF-12 are versatile and inexpensive tools. Recently, BCF-12 scintillators have been foreseen for investigation of the spatial distribution of neutrons emitted from dense magnetized plasma. For this purpose, small-area (5 mm × 5 mm) detectors based on BCF-12 scintillation rods and Hamamatsu photomultiplier tubes were designed and constructed at the Institute of Nuclear Physics. They will be located inside the neutron pinhole camera of the PF-24 plasma focus device. Two different geometrical layouts and approaches to the construction of the scintillation element were tested. The aim of this work was to determine the efficiency of the detectors. For this purpose, the experimental investigations using a neutron generator and a Pu-Be source were combined with Monte Carlo computations using the Geant4 code.
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