tailieunhanh - RADIATION PROTECTION MANUAL Episode 3

Tham khảo tài liệu 'radiation protection manual episode 3', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | EM 385-1-80 30 May 97 2 As with all radiation exposures the size of the dose resulting from an external exposure is a function of a the strength of the source b the distance from the source to the tissue being irradiated and c the duration of the exposure. In contrast to the situation for internal exposures however these factors can be altered either intentionally or inadvertently for a particular external exposure situation changing the dose received. 3 The effectiveness of a given dose of external radiation in causing biological damage is dependent upon the portion of the body irradiated. For example because of differences in the radiosensitivity of constituent tissues the hand is far less likely to suffer biological damage from a given dose of radiation than are the gonads. Similarly a given dose to the whole body has a greater potential for causing adverse health effects than does the same dose to only a portion of the body. b. Internal Exposures. 1 Exposure to ionizing radiation from sources located within the body are of concern for sources emitting any and all types of ionizing radiation. Of particular concern are internally emitted alpha particles which cause significant damage to tissue when depositing their energy along highly localized paths. 2 In contrast to the situation for external exposures the source-to-tissue distance exposure duration and source strength cannot be altered for internal radiation sources. Instead once a quantity of radioactive material is taken up by the body for example by inhalation ingestion or absorption an individual is committed to the dose which will result from the quantities of the particular radionuclide s involved. Some medical treatments are available to increase excretion rates of certain radionuclides in some circumstances and thereby reduce the committed effective dose equivalent. 3 In general radionuclides taken up by the body do not distribute equally throughout the body s tissues. Often a radionuclide concentrates