Emission probabilities of the main γ-rays of 237 Np and 233 Pa

Due to the needs in environment monitoring and nuclear waste survey, there has been increasing interest over recent years, for measuring the activity of 237 Np. Thus, in order to improve the standardization and the knowledge of the decay scheme of this radionuclide, an EUROMET project (No. 416) has been proposed by National Physical Laboratory (UK). In the frame of this project and of a collaboration between LNHB and IFIN-HH, the emission probabilities of the main gamma-rays following the decay of 237 Np (in equilibrium with its daughter 233 Pa) have been precisely measured. Two calibrated Ge-HP detectors were used: one planar (for low energies) and the other coaxial (optimum for energies above 50 keV). The 237 Np/233 Pa solution (produced by IRMM, in cooperation with NPL) was standardized at LNHB, by using absolute measurement methods; from this solution, five point sources were prepared and measured. For each source, a periodical check of the equilibrium between 237 Np and 233 Pa, was performed. The measured gamma emissions were in the range 28-415 keV. The uncertainty values obtained for the emission probabilities are competitive, almost half of them being 1% or less. These results were presented at the Conference of the International Committee for Radionuclide Metrology (ICRM), Prague, 1999. This work will be completed this year with the analysis of the KαX and KβX regions of the 237 Np/233 Pa spectra. This study is performed in collaboration with two Russian scientists: Dr. S. Sepman (D.I. Mendeleyev Institute for Metrology (VNIIM), St. Petersburg) and Dr. G. Shchukin (V.G. Khlopin Radium Institute (KRI), St. Petersburg). (authors)