A "group test" is a simultaneous test on x units selected from a total of N, where 1 5 x 5 N and all N units are to be tested. The result of the test can be that all ( x ) units tested are good or that at least one of the ( x ) units is bad-in which case, a rule must exist for determining the sizes of the subsequent test-subgroups. A prime consideration in adopting such a procedure might be an attempt to reduce the total number of tests required to classify all (N) units in the set.Group testing procedures have found application in such varied areas as (a) blood-testing and (b) testing helium sealed electrical devices. In this paper, it is shown that group testing of large inventories of sealed radioactive sources is more efficient than the other commonly used methods. Further, it is shown that for a given subset of sealed sources containing a single defective source, the "halving" or "binary-batching" approach leads to the least number of tests. Consideration is also given to the case where (a) there is no a priori information on the probability that a source is defective and (b) the result of a single group test indicates at least one defective unit in the group.The efficiency associated with the application of group testing to sealed sources results in a reduction in radiation exposure to personnel. Other possible applications of group testing procedures in radiological health are also discussed.
In a previous report, we proposed a group test procedure that would minimize exposure to personnel leak-testing sealed radium sources by reducing the required number of tests. The procedure was based on two assumptions: (a) there will be at most a single leaking source in any given test group, and (b) the resulting exposure is directly proportional to the number of leak tests performed. Whereas the validity of the first assumption finds its basis in leak test data available in the literature, the requirement of the second assumption may not be readily satisfied.In the present work, this requirement is lifted and consideration is given to the more realistic situation where the exposure is directly proportional to the activity of the group being tested. This leads to a group leak-testing procedure which in many instances results in a considerable reduction in exposure.Consideration is also given to storage arrangements and it is shown that, given an inventory of sealed radium sources, minimum exposure during leak-testing results when the distribution of sources among drawers is as alike as possible with respect to the number, arrangement, and activity of the sources per drawer-assuming use of our recommended leak-testing procedure
It is frequently assumed that radiation measurements in anthropomorphic phantoms yield more accurate dose estimates in humans than can be obtained from water phantoms. As a consequence a realistic phantom consisting of tissue equivalent material, skcleton and air cavities was exposed to X-rays in chest radiographic procedures and dose measurements were made outside the usefil beam. A similar study was performed by another group using a water phantom. Data from these two independent studies were compared at corresponding points.The relative doses at various depths and distances from the edge of the useful beam were plotted together for the trunk and skull regions. I n the trunk region the agreement between realistic and water phantom data was quite good for those points compared (up to 10 cm depth and 45 cm from the edge of the useful beam). In the skull region values for the realistic phantom were as much as 100% higher than those for the water phantom. This was accounted for by the anatomical asymmetry of the body.Results of this study show that water phantom data is comparable to realistic phantom data when applied to the region of the trunk. When applied to the skull region the dose estimates must be modified by appropriate correction factors.
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