Dosimetric and microdosimetric characteristics of 9.6 to 30-MeV proton beams

High and intermediate energy protons are not able to directly form a track in an etch detector (TED). Such detectors can, however, be used for the detection and dosimetry of beams of these particles through the registration of secondary charged particles with sufficiently high values of linear energy transfer (LET). Intermediate energy protons (10 to 30 MeV) with low LET values ranging from 5.87 down to 2.40 keV/μm are considered. Although the LET values are low, this energy range seems to be sufficient to create secondary particles with much higher LET values through nuclear reactions in the irradiated matter. This phenomenon can modify the characteristics of the energy transfer process due to these particles, and it should be taken into account when such particles are used for radiobiology and/or radiotherapy studies. The importance of these secondary particles was studied experimentally by means of a LET spectrometer based on a chemically etched track detector, in which the tracks of the primary protons are not revealed. These studies were performed with protons whose primary energies were in the range of about 10 to 30 MeV, which are available at the Cyclotron Accelerator Department of Nuclear Research Center for Agriculture and Medicine (NRCAM) in Karaj, Iran. The microdosimetric distributions of the secondary particles mentioned above are presented, and their contributions to the absorbed dose of the primary protons are estimated. The contribution of the secondary particle dose increases with decreasing proton energy. The importance of this phenomenon in some applications is discussed. The origin of the secondary particles in interactions with protons having high and intermediate energies due to various nuclear reactions was calculated by using the Alice computer code. There is good agreement between the experimentally obtained and theoretically calculated results.