U-238 DECAY CHAIN DATA

BNFL Springfields Works and the MAFF Fisheries Radiological Inspectorate regularly monitor silt from the River Ribble and its estuary to assess the radiological impact of the BNFL liquid discharges on the local environment. It is generally accepted that due to its short half-life, Pa-234m should be in secular equilibrium with its precursor Th-234. Measured results do not support this theory but show instead an average factor of 1.8:1 to exist between Pa-234m and Th-234. Both laboratories use the United Kingdom Chemical Nuclear Data Library as the basis for their gamma line identification process and would expect better agreement. A search of current nuclear data libraries has identified some inconsistencies in reported gamma line intensities for this decay chain. This paper is a report on the work carried out at BNFL and MAFF to confirm the correct intensities for Th-234 and Pa-234m.