The maximum proton energy is 160 MeV which corresponds to a depth of penetration of 17 cm of water. Degraders are used in the external beam to reduce proton energy as required, down to about 20 MeV. Energy resolution is typically 2 to 5 MeV for energies above 100 MeV and it is 10 MeV for lower energies. The time structure of the external beam can be varied but consists typically of a 200 micro second burst of protons every 5 milliseconds. Internal beam current is about 0.5 microamps. Beam diameter can be adjusted from less than 0.1 cm to a maximum of 30 cm.
Most irradiations take place in air in the external beam.
Due to the low beam current it is possible to have unusually quick access to the experimental areas for adjustment of apparatus and targets. Irradiations can take place in the internal beam but are limited to small foil targets. In this case the irradiations take place in vacuum and the proton energy is selected by the choice of target probe position. Selected Publications Clinical use of protons and ion beams from a worldwide perspective. J.M. Sisterson, Nucl.