Simultaneous radiochemical determination of²³⁷Np and²³⁹Np with²³⁵Np as a tracer, and application to environmental samples

Abstract

Neptunium is sorbed, together with plutonium, uranium and iron on Bio Rad AG 1×4 anion exchange resin from 9 mol/1 HCl, eluted with 7 mol/l HNO₃ and 1.2 mol/l HCl, purified on a second, identical column and electrodeposited on stainless steel discs.²³⁷Np is determined by α-spectrometry,²³⁹Np by γ-spectrometry with a Ge detector, or via its 14.3 keV L_αX-rays in a Si(Li) measurement. The neptunium yield is determined from the count rate of the 13.6 keV L_αX rays of the tracer²³⁵Np in a later Si(Li) measurement. The average chemical yield is 78±11%. The detection limit for²³⁷Np is 1 mBq. The procedure allows the sequential determination of neptunium, together with plutonium, strontium, uranium and iron from one sample. The method was applied to air and total deposition samples from Munich-Neuherberg and to sediment samples from the Irish sea.