Committed doses

Adams, N., Dependence on Age at Intake of Committed Dose Equivalents from Radionuclides, Phys. Med. Biol. 26 1019-1034 (1981). 

Schlenker RA. 1986. Comparison of intake and committed dose equivalent permitted by radiation protection systems based on annual dose equivalent and committed dose equivalent for a nuclide of intermediate effective half-life. Health Phys 51 207-213. 

Kendall, G.M., Kennedy, B.W., Greenhalgh, J.R., Adams, N. Fell, T.P. (1987) Committed doses to selected organs and committed effective doses from intake of radionuclides. Report GS7. National Radiological Protection Board. Chilton, Oxon. 

Current federal and state regulations limit radiation workers doses to a total effective dose equivalent (TEDE) of 5 rem/year and a committed dose equivalent to any organ, other than the lens of the eye, of 50 rem/year (EPA 1988c USNRC 1995a). These limits apply to the sum of external and internal doses. The limits are upper limits, and an important philosophy in radiahon protection is to keep radiation doses as low as reasonably achievable (ALARA). 

The ALI is the activity of a radionuclide that can be taken into the body in a year, by inhalation or ingestion, without exceeding a committed effective dose equivalent (CEDE) of 5 rem/year or a committed dose equivalent to any organ of 50 rem/year, whichever is more limiting. The total effective dose equivalent TEDE is the sum of the CEDE and any penetrating external dose (10 CFR 20). If any external dose is present the ALI must be reduced by a proportional amount to ensure that the dose limits are not exceeded. For example, if a worker received an external dose of 1 rem/year, the ALI would have to be reduced by 20% to ensure that the TEDE did not exceed 5 rem/year. 

The DAC is simply the inhalation ALI divided by the volume of air that a worker is assumed to breathe in a year (2,400 m ). Thus, if the average air concentration is controlled so as not to exceed the DAC, a worker will not take in more than an ALI, and the worker s dose will not exceed 5 rem CEDE or 50 rem committed dose equivalent to any organ (ICRP 1977). 

In the committed dose concept, also introduced by ICRP, the total dose contribution to the population over all future years due to a specific release or exposure is considered. The committed dose is defined as the time integral per capitem dose rate between the time of release and infinite time, and is measured in Sv... 

Similai ly, a collective committed dose is obtained by integrating the collective dose. 

F. Radiation Dose (committed dose equivalent, committed effective dose)... 

The intake by inhalation, ingestion or through the skin of a given radionuclide in a year by the reference man which would result in a committed dose equal to the relevant dose limit. 

The dose limits apply to the sum of the relevant doses from external exposure in the specified period and the relevant committed doses from intakes in the same period the period for calculating the committed dose shall normally be 50 years for intakes by adults and to age 70 years for intakes by children. 

Kobis de Saint-Chamas et al. (1991) have described the monitoring programme which included monitoring of Cs contents in coconuts from the whole French Polynesian territory. The methodology is described and the results of the 2589 samples collected for 1967 to 1988 are presented. The maximum content found since 1967 is 52 Bq kg for coconut water and 289 Bq kg for coconut copra. The decrease of Cs content is constant without discontinuity, whatever the distance from the explosion sites. The committed dose equivalent from Cs delivered by coconut water and copra consumption represents only a few microsieverts a year. 

Committed dose equivalent (//t,5o) is the dose equivalent to organs or tissues of reference (T) that will be received from an intake of radioactive material by an individual during the 50-year period following the intake. 

Effective dose equivalent (He) is the sum of the products of the tissue weighting factors (Wr) applicable to each of the body organs or tissues that are irradiated and the committed dose equivalent to the corresponding organ... 

The annual occupational dose limit to an adult radiation worker is the more limiting of (1) total effective dose of 5 rem (0.05 Sv) or (2) the sum of deep-dose equivalent and the committed dose equivalent to any individual organ or tissue, other than the lens of the eye, being equal to 50 rem (0.5 Sv). 

The Food and Drug Administration (FDA) develops standards for radioactive material concentrations in food (FDA 1998), and medical devices used in radiation therapy (FDA 1997). The FDA recently updated its guidance document that presents recommended action levels for radionuclides in foods, both domestic and imported (FDA 1998). These derived intervention levels (DILs) are estimated levels in food that could lead to individuals receiving a radiation equivalent dose equal to the FDA protection action guide (PAG) that is set as the more limiting of either 0.5 rem (5 mSv) for committed effective dose or 5 rem (50 mSv) committed dose equivalent to any individual tissue or organ. Table 8-2 presents the most restrictive DILs for strontium. 

Annual limit of intake (ALI) the amount of a radioactive material taken into the body of an adult worker in one year, by inhalation or ingestion, that would result in an effective committed dose equivalent of 0.05 Sv (5 rem) or a committed dose equivalent of 0.5 Sv (50 rem) to any single tissue or organ. 

The ICRP and the IAEA regularly issue recommendations for proper handling of radiation sources. The purposes of the recommended system of dose limitations are to ensure that no exposure is unjustified in relation to its benefits, that all necessary exposure is kept as iow as is reasonably achievable (the ALARA principle), and that the doses received do not exceed the specified limits. The ICRP stresses the values given in Table 18.11 they apply to the sum of the relevant doses from external exposure in die specified period and the SO-year committed dose (for children 70 years see also next ) in the same period. These values must be respected. They are intended to limit somatic effects in individuals, hereditary effects in the immediate offspring of irradiated individuals, and hereditary and somatic effects in the population as a whole. 

In order to relate the emissions of radioactivity from nuclear power installations or the accumulation of radioactivity in the body from fall-out to a resulting dose to the population, the ICRP has introduced the committed dose concept (equival t or effective), S... 

A substance which represents a hazard within the body due to its radioactivity is referred to as radiotoxic. The radiotoxicity depends on the properties of the radiation and on a number of physical, chemical, and biological conditions such as mode of intake (via air, in water or food, through wounds, etc.), the size of the ingested or inhaled particles, their chemical properties (e.g. solubility), metabolic affinity, and ecological conditions. Most of these conditions are considered in the ALI concept. ALI Annual Limits of Intake) and D AC Derived Air Concentrations, from the ALI value) and other relevant data are presented in Table 18.12. An annual intake of 1 ALI corresponds to an annual committed dose equivalent of 50 mSv. 

Radiotoxicity depends on energy deposition in tissue or organs by the radionuclide, the specific tissue exposed to the radionuclide, and the tissue radiation sensitivity. Energy deposition by a radionuclide is a function of its emitted radiations and half-life. Biokinetic studies have identified for most radionuclides of interest the pattern of movement through the body and the effective turnover rate (the sum of the biological and radioactive turnover rates). Biokinetic information also identifies the appropriate type of sample to be collected among blood, urine, feces, saliva, breath, hair, teeth, nasal swipes, and tissue obtained incidental to unrelated operations, and collection frequency. The measured radionuclide concentrations are combined with biokinetic information to calculate the committed dose equivalent, the indicator of radiation impact on the subject (NCRP 1987b). 

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