[en] The reduction of the Compton continuum can be achieved using a Compton suppression shield. For the first time, an experimental method is purposed for estimating the optimum dimensions of such a shield. The method can also provide information on the effect of the air gap, source geometry, gamma-ray energy, etc., on the optimum dimension of the active shield. The method employs the measurements of the Compton suppression efficiency in two dimensions using small size scintillation detectors. Two types of scintillation materials; NaI(Tl) and NE-102A plastic scintillators, were examined. The effect of γ-ray energy and source geometry were also investigated using ¹³⁷Cs and ⁶⁰Co sources with three geometries; point, cylindrical, and Marinelli shapes. The results indicate the importance of both NaI(Tl) and NE-102A guard detectors in surrounding the main detector rather than the distance above it. The ratio between the part of the guard detector above the surface of the main detector to that below it should be about 1:3 for NaI and 1:4 for NE-102A. The optimum dimensions for NaI(Tl) detector were found to be 12.5-20 cm for the height and 15-20 cm for the thickness. The corresponding values for NE-102A are 17.5-25 cm for the height and 25-30 cm for the thickness. (author)

[en] A NaI-NaI coincidence low background counting system has been constructed to be used in radioenvironmental measurements. The slow timing technique, using the constant fraction timing single channel analyzer and coincidence unit, was used in the present system. The coincidence efficiencies of systems employing two and four NaI(Tl) detectors have been evaluated. A scintillation preamplifier with multiple inputs was constructed for summing the outputs of PM tubes. The performance of the system was tested using radioactive point sources and environmental samples. The detection efficiency of the NaI-NaI coincidence system employing four NaI(Tl) detectors was found to be high enough to measure low-level γ-ray activity of desired isotope in environmental samples with neither high background contribution nor interferences from other isotopes. (author)

[en] The concentrations of ¹³⁷Cs and ⁴⁰K in some Egyptian foodstuffs have been measured. The results of this study can be considered as a first step towards calculating the baseline levels of radioactivity in foodstuffs in Egypt. Furthermore, the data presented herein can be used as a reference level for future food radioactivity monitoring after the possible operation of the planned nuclear power plants, as well as to screen imported foodstuffs that are suspected of being contaminated. The overall intake of ¹³⁷Cs is quite low and no significant radionuclide contamination was found. The highest contents of ¹³⁷Cs and ⁴⁰K among the tested foodstuffs were in Jew's mallow and roquette. Calculations were also made to determine the potential dose to an individual consuming vegetables

[en] A 4πβγ-coincidence system has been prepared for the identification of new isotopes with low fission yields and short half-lives. The β-detector of this system consists of a large solid-angle scintillation detector, which works in coincidence with X- and γ-ray detectors. The system performance was tested with sources of ⁴²K and ¹⁶⁶Ho as off-line test and with sources of ⁹⁴Rb, ⁹⁴Sr, ⁹⁴Y and ¹⁴⁶La as on-line test. The system was found to work satisfactorily with high β-detection efficiency. (author)

[en] The anticoincidence shield is one of the active shield forms. This shield is used mainly to reduce the cosmic-ray component of detector background. A cosmic-ray veto detector was designed and constructed to operate in anticoincidence mode with the 5^x5^Nal(TI) or 204 cm3 HPGe detectors. An NE-102A plastic scintillator with the thickness of 7.5cm and area of 69x45 cm2 is used to construct this veto detector. A fast-slow coincidence circuit for anticoincidence operation was used in the present gamma-ray spectrometer. The veto detector is placed over the gamma-ray detector and its low-background lead shield. Background reduction of both gamma-ray detectors used with the arrangement employing the active (veto detector) and passive (low-background lead) shields is studied. The gamma-ray spectrometer employing the large-volume detector shielded with the veto detector and low-background lead shield was found to be a powerful tool for the low-level radio environmental measurements. The possible improvements to enhance the performance of the veto detector are discussed

[en] High-purity germanium (HPGe) detectors are widely used to determine quantitatively the concentrations of natural and artificial radionuclides in environmental samples. Even with detectors of high performance, it is difficult to measure environmental samples with small activity concentrations. In the case of low-level radioenvironmental measurements at close geometry, much care has to be dedicated to the efficiency calibration of the spectrometer used. This is because the full-energy-peak efficiency is a complicated function of many parameters, such as the energy of gamma-ray, the dimension of the detector, the dimensions of the source, the geometrical arrangement of the detector and source, and the density of the sample. In the present work, the relative efficiency curves for the 10% p-type HPGe detector for environmental samples placed in a cylindrical container were constructed using ⁶⁰Co, ¹³³Ba and ¹⁸²Ta solutions. (author)

[en] A Nal-Nal coincidence low background counting system has been constructed to be used in neutron activation analysis and radioenvironmental measurements. The slow timing technique, using the Constant Fraction Timing Single Channel Analyzer and Coincidence unit, was used in the present system. To improve the coincidence counting efficiency of the system, four 3.8cm x 2.5cmNaI(Tl) detectors were used. A special scintillation preamplifier with three inputs and one output was constructed for summing the outputs of three PM tubes. The performance of the new system was tested using radioactive point sources and some environmental samples. The system characteristics and its special features are discussed

[en] Short communication

[en] For the purpose of identifying new isotopes using the KUR-ISOL, preparation is made to increase the ion yield of the ISOL as much as possible through many ways. One of them is to use a N₂ jet or a He+N₂ mixture jet system instead of a He jet system. The use of N₂ gas may have some advantages over He because of its larger stopping power. Therefore, the characteristics of the N₂ jet system in the KUR-ISOL were studied by varying the parameters of the system, such as the pressure in the target chamber and the distance between the end of the capillary and the skimmer plate. In this report, the preliminary results obtained for the N₂ jet system are presented. It was found that He and N₂ gases have almost the same transport time, and their induced activities are negligible. The use of N₂ as the transport gas enables the use of a smaller target chamber, which results in a shorter sweeping-out time. For comparing the He and N₂ jet systems, the efficiency of fission product transport was measured before and after mass separation. Also ion yield was measured, and these results are reported. The mixture of N₂ and He gases was used, and the good results were obtained. (K.I.)

[en] The basic characteristics of a N₂-jet system coupled with a surface-ionization type ion source have been investigated at KUR-ISOL. The yields of transported activities and ionized ions have been measured under various conditions for both the He- and N₂-jets. The effects of N₂ gas upon the ionization and skimmer efficiency have been investigated. It was found that N₂ gas has almost no effect upon the ionization efficiency, but causes poorer skimmer efficiency than He gas owing to the large opening angle of aerosol particles at the outlet of a capillary. A mixture of He and N₂ gases was also tested. (orig.)