NKS-NORCMASS reference material for analysis of Pu-isotopes and ²³⁷Np by mass spectrometry

The aim of the reference material in the Norcmass-project was to produce a lowlevel (<<1mBq/g of ²³⁹Pu) sample of sufficient amount to allow individual laboratories to perform several tests without risk of using up the material. Although there are several reference materials available (eg IAEA) few have ²³⁹Pu/²⁴⁰Pu data and almost none have ²³⁷Np/²³⁹Pu-data. Those who have (eg IAEA-384) have very high concentrations and are not useful for testing analytical methods designed for low-level measurements where a large sample mass may be required. The reference material consist of the top 10cm of 2mm sieved soil pooled together from 12 different Danish locations collected during 2003. The Soil was blended and sieved through 0.6 and finally through a 0.4 mm sieve. A total amount of 17 kg soil was produced. Several aliquots of the material was subject to analysis by alpha spectrometry and ICP-MS. The material contain ^239+240Pu at a concentration of 0.24 ± 0.01 mBq/g and a ²⁴⁰Pu/²³⁹Pu atom ratio of 0.19 ± 0.006. The ratio ²³⁷Np/²³⁹Pu was determined to 0.32 ± 0.01.