6 Other Individual-Person Radiation Dose Assessments

Abstract

In this section, we discuss assessment techniques for individuals who may have been exposed to neutrons or to radioactive materials, leading to contamination of the body externally and/or internally. In the case of bodily contamination, exposure implies more than simply receiving a radiation dose from an external source. It also includes those conditions leading to persons becoming contaminated with radioactive materials and/or debris. Contamination of the external surface of the body is likely to be very heterogeneous in most circumstances. The degree of contamination will depend on the situation in which contact with radioactive contamination took place and also on the physical attributes of that part of the body that is contaminated, attributes of clothing worn at the time of contamination, whether internal contamination took place, and the chemical or physical form of the contaminants. Contaminated debris can manifest itself in many forms, although particulates are likely to be the most common physical form for many accidents or intentional exposure situations. Knowledge of the form of the contamination is usually helpful in deciding the best type of assay and instrumentation to be used. Unlike the situation of body contamination, dose distribution within the body when exposure to neutrons occurs is always highly heterogeneous, even for a whole-body irradiation. This is due to the high values of the cross sections for neutron interaction with the light atoms composing living tissue, especially hydrogen and nitrogen. In the energy range of fission neutrons (0.0025 eV to 12 MeV), which may be encountered in a criticality accident, for example, most of the dose would be deposited close to that portion of the body surface where neutrons are incident. This section briefly discusses methods and issues related to assessing contamination and/or internal deposition in the body, as well as some dosimetry techniques that are of interest in these situations. References provided give information on converting the results of contamination assays to absorbed dose. We also discuss dosimetry due to neutron exposure using the method of neutron activation.