| Research Abstract |
Gamma-ray emission probabilities have been precisely measured by a4πβ-γ coincidence apparatus using a live-time two-dimensional data-acquisition system, and the certainties of those for ^<76>As, ^<159>Gd, ^<169>Yb, ^<182>Ta, ^<186>Re, ^<187>W and ^<188>Re have been improved by two factors or more. Furthermore, it becomes clear that the reported values for ^<76>As and ^<169>Yb are overestimated by 10% and 2%, respectively, and that those for ^<159>Gd, ^<187>W and ^<188>Re are underestimated by 5%, 20% and 3-10%, respectively.
Highly precise determination of γ-ray detection efficiency curve for an HPGe detector with relative efficiency of 25% have been tried Standard sources emitting two cascade γ-rays with high probabilities were measured at 30 cm of source-detector distance under the condition of small correction for absorption and cascade summing. The sources were ^<24>Na, ^<46>Sc, ^<48>Sc, ^<60>Co, ^8Y, ^<94>Nb, ^<108>Ag and ^<111>In. The relation between energy and detection efficiency was analysed and the least-squares method using covariance matrix was applied for normalised those data. The relative detection efficiency curve was obtained with uncertainty of 0.1% between 171 and 2754 keV, whereas the uncertainty was about 0.3% in the range of lower energy and near 2754 keV.The relative γ-ray intensity of the 1643 to 2167 keV γ-rays for ^<38>Cl was very precisely determined to be 0.7496±0.0011 by using this curve. Also, the emission probabilities of the 844 and 1014 keV γ-rays for ^<27>Mg were measured to be 0.7186±0.0008 and 0.2820±0.0008, respectively. Furthermore, the highly precise relative detection efficiency curve was converted to the highly precise absolute detection efficiency curve by determining the disintegration rate of ^<60>Co source with uncertainty of 0.03%. By using this curve, γ-ray emission probabilities of ^<134>Cs and ^<152>Eu used as multi-γ ray standard source are measured and will be compared to the evaluated values.
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