ABSOLUTE CALIBRATION OF NUCLEAR ACTIVATION DIAGNOSTICS FOR INTENSE PULSED ION-BEAMS

Absolute calibration of an annihilation-radiation NaI coincidence dete ction system for short-lived ion-induced radioactivity is described. C alibration with a Na-22 radioactive source is compared with an indepen dent calibration using the (12)(p,gamma)N-13(beta(+)) reaction with 1 MeV protons from a Van de Graaff accelerator. These calibrations are c onsistent, provided correction for summing of the 0.51 and 1.27 MeV ga mma rays from the Na-22 source in the NaI detectors is included. This summing correction depends on the total efficiency for detecting 1.27 MeV gamma rays and can alter the calibration by as much as a factor of 2, depending on the size and separation of the detectors. A procedure to determine this correction using Co-60 and Na-22 radioactive source s is described. These two calibrations give a thick-target yield for t he C-12(p,gamma)N-13 reaction at 1 MeV of (8.0 +/- 0.4)x10(-10) reacti ons/proton. Intense pulsed proton fluences of 0.08 to 3.7 cal/cm(2), d etermined by coincidence counting beta(+) annihilation radiation produ ced by the C-12(p,gamma)N-13(beta(+)) reaction, are in agreement with ion-beam fluences measured independently with carbon calorimeters on t he same carbon sample.