Calculation of energetic positron beam produced from a 45MeV LINAC

On the basis of a help of Monte Carlo Simulation Code EGS4, we calculated the yields of bremsstrahlung X-rays which was essential to produce the positron beam. We also calculated the yield of monoenergetic gamma photon formed by the annihilation of a fast positron as well as positronium. The simulation has shown that the yield of the bremsstrahlung increases in high Z materials. In the case of Pt, the yield is the largest at near of one radiation length and the total energy of bremsstrahlung amounts to about 8 MeV per incident electron of 45 MeV. The yield of the positron becomes maximum at near of 1.5 radiation length, in the case of Ta target, and the calculation shows that 6 x 108 positrons are produced by one pulse from the linac installed at Hokkaido University. Moreover, it is seen that thin Be target is available to yield the monoenergetic annihilation gamma which is one of the applications of fast positrons. (author)