Development of laboratory standards for AMS measurement of Np-237

A new method for the preparation of Np-237/U-238 laboratory standards for accelerator mass spectrometry (AMS) measurement was developed at China Institute of Atomic Energy (CIAE). Np-237 was generated by beta-decay (6.75 days) of U-237 produced via fast neutron induced U-238(n,2n)U-237 reaction. The Co-58(n,2n)Co-59 and Nb-93(n,2n)Nb-92m reactions were used to monitor the integral incident neutron flux. The cross-section of U-238(n,2n)U-237 was determined by measuring the emission rate of 208.0 keV gamma-rays from U-237 decay with a calibrated HPGe gamma-ray spectrometer at CIAE. In order to correct for the self-attenuation of 208.0 key gamma-ray in the U sample, a Lu-177-U method was introduced. The new correction method provided effective and high quality measurements of the cross-section for the U-238(n,2n)U-237 reaction; and the Np-237/U-238 ratio. A series of AMS standards for Np-237/U-238 (10(-9)-10(-13)) can be obtained by successive dilution of the original standard sample. (C) 2010 Elsevier B.V. All rights reserved.