Development of a miniature silicon dosimeter for proton beam dosimetry in several media

A miniature silicon dosimeter for proton beam dosimetry has been developed by improving our p-n junction silicon dosimeter for electron and X-ray dosimetry. The detecting element of the dosimeter has the form of a 1.48 mm diameter by 0.22 mm thick disk. The characteristics of the dosimeter were investigated with 52 MeV and 35 MeV proton beams at the FM cyclotron. It was found out from this measurement that the effective thickness of the sensitive layer to protons is about 77.2 μm and that the range where the dosimeter response is nearly linear to the proton number is from about 3 x 103 protons s-1, that is, 1.2 x 102 rad h-1 to about 5 x 107 protons s-1, that is, 1.9 x 106 rad h-1. We have measured the expansion of 52 MeV protons injected into carbon, aluminum, iron, mylar and water due to multiple scattering and also the central-axis and the lateral depth-dose distributions deposited in water by the 52 MeV proton beam. The beam width gradually increases with the depth in media and its increment rate increases with the atomic number of the medium. (orig./HP)