Positron Production with the Usnrl Linac

Positrons produced by electrons peaked at energies of 9.6, 10.8, 11.7, 13.5, 15.0 and 16.6 MeV incident on a 0.8 radiation length gold target, were accelerated to 35 MeV. Their spectra were measured by means of a defining slit system, set for 2 percent energy transmission, located at the focal point of a 90° achronatic deflection system. Experimental values of conversion efficiency were fitted by the expression ¿ = 3.3 × 10-7 (E-4.7), where E is the energy of the incident electrons. The expected positron current for the highest repetition rate (720 pulses per second) is approximately 4 x 10-10 amperes over electron energies from 10 to 14 MeV.