490 TRANSURANIC ELEMENTS IN THE ENVIRONMENT 



Dose and Dose Commitment 



In all the dose-estimation models, the formula for estimating the radiation dose to a 

 critical organ of man, i.e., one of those organs which tends to receive the highest radiation 

 dose , is 



dD E 



^ = my ^30) 



where t = time (days) 



D = dose to the reference organ (rem) 



E = 51.2159e, a dose-rate factor (g • rem idCi^^ day"^^ ) 



e = effective energy absorbed in the reference organ per disintegration of 



radionuclide (MeV/dis) 

 y = plutonium burden in the organ (juCi) 

 m = either the mass of the organ if the organ is not part of the gastrointestinal tract 



or twice the mass of the contents if the organ is part of the gastrointestinal 



tract (g) 



The values of the parameters in Eq. 30 for ^^^Pu and other transuranium elements are 

 given in Table 7. Most of these values were reported by the International Commission on 

 Radiological Protection (1959; 1964). The masses of deep lung and other portions of the 

 respiratory tract are the values used by Snyder (1967) and Kotrappa (1968; 1969). The 

 mass of thoracic lymph nodes was assumed to be the value (15 g) reported by Pochin 

 (1966). The mass of abdominal lymph nodes was assumed to be less than the mass of 

 thoracic lymph nodes and was arbitrarily set at 10 g. The dose accumulated in the organ 

 from the beginning of the exposure period (t = 0) to some later time (t = To) is given by 



E r'D 



D = — I ydt (31) 



m Jo 



If ingestion and inhalation of plutonium were halted at time Tq and the individual were 

 to live to some later time Tl, each organ would accumulate an additional dose from the 

 plutonium already within the body at time Tq. The dose commitment is the sum of the 

 dose accumulated to Tq plus the additional dose, or 



Dc = D + Da (32) 



where D^ is the additional dose (rem) and Dq is the dose commitment (rem). 



ICRP Committee II Model 



The report of the ICRP Committee II (International Commission on Radiological 

 Protection, 1959) contains a model and data that were used to estimate maximum 

 permissible concentrations (MPC's) of radionuclides in air and water. The model, as 



