Envirogeochemical exploration for "NORM" wastes: Quadrupole inductively coupled plasma mass spectrometric measurements of thorium and uranium isotopes 1

Naturally occurring radioactive material consists of ²³⁸U, ²³⁵U and ²³²Th and series daughters; it is released into the environment from many anthropogenic sources. The use of quadrupole ICP-MS is well-suited to site investigations of releases of naturally occurring radioactive material through measurements of the ratios ²³²Th.²³⁰Th; ²³⁰Th.²³⁸u and ²³⁴U.₂₃₈U Each ratio measurement may potentially indicate the contrast between the geochemical background and the affected environment. ²³²Th : ²³⁰Th was measured in samples prepared by fusion or selective extraction; Th was concentrated using TRU-Spec extraction resin and isotopic measurements were made with 5-10 ng Th. The precision is ≈ 1% (2σ mean) and 10% for ²³²Th : ²³⁰Th of 1 000 and 100000-200000, respectively. Thorium isotopic measurements were applied to studies of accumulation of ²³⁰Th in phosphate-fertilized lawns. The ratio ²³⁰Th:²³⁸U was determined via combining separate measurements of ²³⁰Th.²³²Th and ²³²Th.²³⁵u or ²³²Th.²³⁸U; a ²³⁰Th,. ²³⁸U precision of 1-2% (2σ mean) is reported for a phosphate fertilizer sample. This ²³⁰Th : ²³⁸U measurement scheme requires no synthetic yield tracers, and is applied to studies of deposition of U mill tailings in an affected river basin. The ratio ²³⁴U:²³⁸U was determined in natural waters following a two-stage extraction with Chelex 20 and UTEVA resins; a precision of x 0.3-0.5% (2σmeani) is attained for sample concentrates containing 15-25 ug U. ²³⁴U:²³⁸U measurements are useful in distinguishing between dissolved U from natural weathering versus mining/milling sources.