The Development and Performance of a Prototype Shadow-Shield Whole Body Monitor

A shadow-shield whole body monitor has been developed which is capable of high sensitivity at low cost and which is of suitable design for incorporation in a mobile laboratory. The stages of development and the performance of the final prototype are described so that the shielding requirements and crystal volume can be estimated approximately for a required sensitivity. The prototype, using a 3 in. diameter × 3 in. high sodium iodide detector, has a sensitivity, or minimum detectable activity for iron-59 and cobalt-58 of approximately 4 × 10 −3 μ C. With a detector 11½ in. diameter × 4 in, it is shown that sensitivities comparable with steel-room monitors can be expected. The variation in counting-rate due to redistribution of the isotope in the patient's body has been examined.