Natural radioactivity in bioassay by alpha-spectrometry measurements

Personnel of nuclear facilities are checked regularly for internal contamination by bioassay measurements. Although these persons are generally not involved in any incident, natural radioactivity from U, Th and Ra can be found in their urine or faeces. Uranium total activity in urine has been found with a range of 0.051 to 3.0 mBq/24 h and in faeces from 14.5 to 380 mBq/d. 234U/238U ratio for urine is 1.48 but this ratio varies from 0.47 to 19. By comparison, the 234U/238U ratio found in urine from workers in volved with natural uranium or 4.5% enriched uranium is 1.0 and around 4.0 respectively. 230Th, 228Th and sometimes 232Th have also been detected. The total thorium activity varies from 0.137 to 5.6 mBq/24 h in urine and from 9 to 183 mBq/d in faeces. 228Th has generally been found in excess of 232Th. All these measurements were performed by alphaspectrometry. The few 226Ra results have been measured using the Lucas or emanation method. (author)