AN INTERCOMPARISON STUDY OF NP-237 DETERMINATION IN ARTIFICIAL URINE SAMPLES

An intercomparison study of low-level Np-237 determination in artifici al urine samples has been carried out. The purpose of this study was t o find the ''optimal'' method presently available for use in a routine in-vitro radiobioassay program for occupationally exposed workers. Fo ur synthetic urine samples with differing Np-237 concentrations were p repared: (1) 3 mBq kg(-1) of Np-237; (2) 3 mBq kg(-1) of Np-237 with n atural uranium, Pu-239 and Am-241 as interferences; (3) 50 mBq kg(-1) of Np-237; and (4) a matrix blank. The solutions mere submitted to 10 alpha-particle and 10 inductively coupled plasma-mass spectrometry (IC P-MS) laboratories of which six and four laboratories, respectively, r eturned results. Two laboratories performed assays using both techniqu es. The radiochemical method of choice used Np-239 as the tracer, whic h utilized a combination of coprecipitation and anion-exchange separat ion. The best results obtained by ICP-MS were comparable with but not better than the most accurate results obtained by alpha-particle spect rometry. Alpha-particle spectrometry measurements overall gave consist ently better agreement with known values.