DETERMINATION OF TH-232 IN HUMAN TISSUES BY PRECONCENTRATION NEUTRON-ACTIVATION ANALYSIS WITH YIELD DETERMINATION USING TH-227

The accurate and precise determination of Th-232 in biological samples is very important for the development of biokinetic models for thoriu m and for improving our knowledge on its distribution in human tissues . Radiochemical neutron activation analysis has long been one of the m ost sensitive methods for the determination of Th-232. However, these determinations suffer in reliability because recovery information foll owing the separation is not typically available. This information is p articularly important for difficult matrices such as human bone where recoveries may be significantly less than unity. Also, the separation of difficult matrices following neutron activation may involve relativ ely high personal dose from the co-activated matrix. A novel approach for the determination of radiochemical yield has been developed which employs the use of a readily available, gamma-emitting isotope of thor ium, Th-227. Th-227, Obtained by radiochemical separation from Ac-227, is added to each dissolved sample prior to separation and the chemica l yield determined by gamma-ray spectrometry following the separation. This pre-concentration step is then followed by neutron activation an d the Th-232 determined via Pa-233 using gamma-ray spectrometry. Detec tion limits were approximately an order of magnitude lower than obtain ed by alpha-spectrometry.