Background Rates Outside the OMEGA-60 Target Chamber Seconds to Minutes After a High-Yield Shot

Inertial confinement fusion may be used to make fundamental nuclear science measurements of low-energy light-ion cross sections also of interest in astrophysics and fusion research. The feasibility of collecting and counting the beta decay of the reaction products (half-life 20 ms to 20 s) in the expanding neutral gas after the ICF shot is being studied using two types of “traps” – a getter and a turbopump. Both of these use phoswich detectors to identify beta particles and count the beta decays of the trapped product nuclei.   One concern with this technique is that the background rate, even relatively long after the shot, may still be too high relative to the small number of detected product nuclei.  An OMEGA ride-along experiment was performed to measure the background rates in these detectors from milliseconds to seconds after the laser shot.