AN INTENSE PROTON-BEAM DIAGNOSTIC USING THE LI-7(P,GAMMA)BE-8-DOUBLE-RIGHT-ARROW-PR-141(GAMMA,N)PR-140(BETA(+)) NUCLEAR-REACTION SEQUENCE

An indirect nuclear activation diagnostic was developed to measure the proton fluence onto a thick target of lithium metal located in the diode region of pulsed power accelerators. This diagnostic uses the nuclear reaction sequence 7Li(p, γ)8Be→141Pr(γ,n) 140Pr(β+) to relate the proton fluence to induced 140Pr activity. This diagnostic was calibrated using a Van de Graaff accelerator. Energetic protons were focused onto a thick lithium target driving the 7Li(p,γ)8Be reaction. The resulting prompt gamma rays activated a secondary 141Pr target via the reaction 141Pr(γ,n)140Pr(β+). A NaI gamma-gamma coincidence detector system was used to measure the induced 140Pr activity as a function of proton energy and proton fluence. These data yielded a calibration curve for proton energies ranging from 2 to 12 MeV. Since deuterium impurities can interfere with this diagnostic by driving the reaction sequence 7Li(d,n)8Be→141Pr(n, 2n)140Pr, a similar calibration experiment was conducted using deuterium ions. These data yielded a correction factor that can be used to determine the deuterium contribution to the 140Pr activity, providing that the deuterium beam fraction is known. © 1995 American Institute of Physics.