A dosimetric model is proposed for the gastrointestinal tract based upon the physiological model of EVE (1966a). A general equation describing the kinetics of linear first order phenomena is applied to obtain the burden of radionuclides or disintegrations in the contents of the various segments of the GI tract. The model gives equations for the calculation of the "dosimetric" average dose equivalent and dose equivalent rate to an entire segment as well as instantaneous values at any location within a given segment as applicable to single or continuous uptakes of parent and daughter radionuclides. Allowance is made for both the absorption of radionuclides as well as mass from the contents of all segments; although, this is not always considered significant. The model permits the determination of the quantities of a radionuclide absorbed into the blood, the ratio of daughter to parent disintegrations and the maximum to average dose equivalent rate in a particular segment of the GI tract. Numerical examples are given for various intakes. Maximum permissible daily ingestion rates of fictitious single soluble and insoluble radionuclides with an effective energy term of unity in all segments are given over a large range of half-lives and are compared to values calculated on the basis of current ICRP recommendations. It is proposed that ratios of the maximum to dosimetric average dose equivalent rate be used to define a distribution factor to take into account relatively high dose rates at particular locations within a segment of the GI tract.All equations have been derived using the more fundamental units of atoms or disintegrations and disintegration rates rather than the more popular pCi and pCi-day units. The former units are more fundamentally related to dosimetric quantities of interest.

A battery-powered monitor that uses a miniature Geiger-Muller tube operating in the pulse-counting mode has been constructed. It is used with low-activity cesium-137 sources. The monitor gives a reading within about 1 second, has a standard deviation of 2% of the mean, and is safe, reliable, and stable.