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VI.C.2General Requirements of Screening Methods
Any method of screening that is used to draw conclusions about the significance of potential radiation doses, or lack thereof, incorporates two basic elements:
A model to estimate dose in an assumed exposure scenario.
A dose criterion to define a level of exposure below which there is no concern.
If the dose estimated with the model is below the dose criterion, potential doses in the assumed scenario are considered to be so low that the associated health risks are insignificant.
Given the basic elements listed above, a method of screening must satisfy two conditions to meet its intended purpose:
The model used to estimate dose must tend to overestimate doses for any exposure conditions that could be encountered.
The dose criterion must correspond to a dose that clearly is insignificant with regard to potential health risks to an exposed person.
It also is helpful if the model used to estimate dose is simple and transparent, so that others can understand that it is likely to overestimate dose.
VI.C.3Assumptions Used in Internal Dose Screen
The methods used to estimate inhalation doses to participant groups for purposes of screening are the same as those described in Section IV.C.2. That is, the same four basic exposure scenarios and the same methods of estimating inhalation dose in each scenario were used in screening. For example, when a participant group was assumed to be exposed to resuspended fallout that had been deposited on the ground, the inhalation dose to an organ or tissue of concern is estimated on the basis of (1) estimates of the relative activities of radionuclides produced in shots of concern combined with an assumption of no fractionation of radionuclides in fallout except for the removal of noble gases, which are used to estimate the relative activities of radionuclides in fallout deposited on the ground; (2) measurements of external photon exposure or exposure rate due to the deposited fallout with film badges or field instruments combined with calculations of the exposure rate per unit activity concentration for the assumed mixture of radionuclides, which are used to estimate the absolute activity concentrations of radionuclides on the ground; and (3) an assumed resuspension factor, which is applied to the estimated concentrations of radionuclides on the ground to obtain an estimate of the concentrations in air.
The dose criterion used in screening of potential inhalation exposures of participant groups is a 50-year committed equivalent dose of 0.15 rem to bone,