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.
ASJC Scopus subject areas
- Analytical Chemistry