A Cesium-137 Irradiator for Small Laboratory Animals

A 137Cs internal irradiator for small animals is described. The irradiator is loaded with two opposing sources of 2,660 Ci each, yielding 1100 rads∕min. to a tightly-collimated 3-cm diameter field. The front faces of the sources are separated by 27 cm. Vertical uniformity of dose rate is ±1.4%; horizontal uniformity is ±4%. Leakage outside the defined beam is less than 1%. The absorbed dose rate is relatively independent of irradiated sample size. Dose rate to the skin is maintained at tumor dose rate. Beam alignment is accurately reproduced by a mechanical alignment pin. Irradiation time is controlled by an electronic logic package coupled to a punched card reader. Provision is made for hyperbaric and anoxic treatment conditions.