氚化水摄入量-尿氚浓度换算因子的估算

EVALUATION OF INTAKE CONVERSION FACTOR FOR TRITIATED WATER

对10名氘化水摄入者的观察结果表明,单位摄入量所致的体内氚滞留量R^I(t)可用两项指数函数之和来描述,即R^I(t)=0.987exp(-0.693(t/10))+0.013exp(-0.693(t/42))。假定人的体水体积为42L,体水氚浓度与尿氚浓度相同,则可推导出摄入量-尿氚浓度换算因子c_u^I(单位摄入量所致的尿氚浓度,以下简称摄入量换算因子),即c_u^I=[0.987exp(-0.693(t/10))+0.013exp(-0.693(t/42))]/42。在摄入后早期,上式给出的摄入量换算因子与ICRP第54号出版物给出的换算因子是一致的。但随着摄入后时间的推移,二者之间的差异将越来越明显,在摄入后第100天,前者较后者高约3.5倍,第200天时高约500倍。因此,在缺乏摄入后早期(约40天)的尿氚监测资料情况下,采用两个指数项之和的滞留函数来估算摄入量更为合适。

Investigation of 10 patiente with an intake of tritiatedwater suggests that the body retention of tritium for a unit intake can beevaluated by a sum of two exponential functions: R^I(t) =0.987exp(-0.693t/10) + 0 .013exp(-0.693t/42). If it is assumed that the volumeof total body Water is 42 L and the concentration of ~3H in urine is thesame as that in body water, the intake conversion factor (the ~3H conce-ntration in urine resulting from unit intake) can be derived with theequation: c_U^I=0 .987exp (-0.693t/10)+0. 013exp (-0.693t/42)/42.At earlystage after an intake,the intake conversion factor estimated with aboveequation is in good agreement with that given by ICRP 54. Howevertheir difference is becoming obvious with increasing days after an intake.For instance,at 100 days after an intake,the former is 3.5 times greaterthan the latter, and 500 times at 200 days. Therefore, it is possible thatthe intake is estimated with the above two exponential functions if lack ofmonitoring information on ~3H concentration in urine at early stage afteran intake.