Modification of the 50% maximum dose depth for 41-MeV (p+,Be) neutrons by use of filtration and/or transmission targets.

Several target configurations for the 41-MeV (p+,Be) reaction have been evaluated for the characteristics of the radiation field produced; depth dose, dose rate per microA, From analysis, it is concluded that to achieve the desired 13.2-cm depth for 50% of maximum dose and acceptable dose rate at a target-to-skin distance (TSD) of 125-150 cm, the neutron spectra must be filtered to preferentially absorb the lower-energy neutrons. Further increases in depth of 50% of maximum dose and a significant reduction in beryllium heating problems result if a partial transmission target is used with the terminal 30% of proton energy being deposited in a copper target backing.