An aluminum capsule 2⅛ in. in diameter and 9 in. long completely contains the high-order detonation of 3.6 g of explosive. This was approved for insertion in the General Electric Test Reactor and successfully used to irradiate a series of explosive and propellant samples. Modifications were also made to permit continuous measurement of pressure and temperature of the sample during irradiation when desired. Methods used to measure gamma flux, neutron dosages, and temperature limits are also described.