Measurement of 237Np in environmental water samples by accelerator mass spectrometry

Abstract

Accelerator mass spectrometry (AMS) was used to measure 237Np in environmental water samples extracted from Irish Sea sediments. The samples were of limited volume (approximately 700 ml) and of low activity (0.06-0.79 mBq l-1; 2.30-30.3 pg l-1). AMS proved to have the required sensitivity for measuring these samples, and was in principle capable of measuring much smaller amounts, as low as 0.4 microBq (3.9 x 10(7) atoms). However, the background level in the procedural blanks showed that there was a systematic low level 237Np contamination of each sample, arising from the 239Np yield monitor used in the separations procedure, which effectively increased the detection limit of these analyses.

Critical comparison of radiometric and mass spectrometric methods for the determination of radionuclides in environmental, biological and nuclear waste samples

“…Due to the low concentration encountered in environmental samples, a pre-concentration and completely separation from interfering radionuclides are necessary. Ion exchange, extraction chromatography and solvent extraction, are normally used for the separation of 237 Np [255][256][257][258][259][260][261][262][263] 3 , it has to be therefore reduced to Np 4+ before hydroxide precipitation. Solvent extraction using tri-n-octylphosphine oxide (TOPO) in toluene or thenoyl trifluoroacetone (TTA) in oxylene has been used to separate Np from metals, uranium, thorium and other transuranics.…”

“…Due to the long half-life of 237 Np, mass spectrometric methods are sensitive for its determination, AMS [260], ICP-MS [261], and GDMS [117] have been used for the determination of 237 Np. In AMS, the separated Np is mixed with Fe 2 O 3 and used as a target; NpO -ions are sputtered by ion source, separated in the mass spectrometer and counted by an ionization chamber.…”

“…In AMS, the separated Np is mixed with Fe 2 O 3 and used as a target; NpO -ions are sputtered by ion source, separated in the mass spectrometer and counted by an ionization chamber. A sensitivity of 0.024 μBq was measured, considering the procedure blank count rate; a detection limit of 7 μBq was reported [260]. A GDMS method was reported for the direct determination of 237 Np in sediment from the Irish Sea [117].…”

Determination of the gamma emission probabilities of 239Np

“…It can be produced by disintegration of 243 Am. 239 Np is of great importance as a chemical yield tracer for the radiochemical determination of 237 Np in samples [1]. The absence of standardized solutions and the poor quality of the associated decay scheme data inhibited the use of 239 Np.…”

AMS Measurement of 237Np at China Institute of Atomic Energy (CIAE)

“…The 237 Np/ 238 U atomic ratio in nature is expected to be 10 12 or even lower (Peppard et al 1952;Myers and Lindner 1971;Zhang 1978), but it may be significantly higher in high-grade uranium ore (Zhang 1978), depending strongly on the integral neutron flux received by the material. The low 237 Np present in the environment means that it has been of less immediate concern to humans than the other transuranium elements, Pu and Am, and it has therefore been studied to a lesser extent (Keith-Roach et al 2001). However, the study of Np in the environment is now of increasing interest because of its relatively high mobility, its ingrowth in the environment, and the timescales involved.…”