FAST SHUTTER FOR LOW-BACKGROUND RADIATION ENVIRONMENTS AT SPR-III

A fast shutter system has been developed to isolate experiments from t he radiation emitted after the main pulse of the Sandia Pulsed Reactor , SPR III. In about 15 ms the system moves a 20 kg shield in front of the beam port aperture in the facility shield wall. A second gravity-d riven shutter is dropped into place in about 200 ms. The total attenua tion achieved in the delayed beam intensity is about a factor of one h undred. The shutter assembly was used, along with a sensitive detectio n system, to observe the gamma ray flux emitted by various materials a ctivated by the neutron beam at levels nine orders of magnitude smalle r than the gamma dose rate at the target during the reactor pulse.