Dosimetry of low-energy protons and light ions

For the vertical beam facility at the 14 MV Munich tandem accelerator, various techniques for dosimetry were tested for radiation fields of low-energy protons and light ions (4He, 12C and 16O). A reference dose was determined from the fluence of particles by counting individual particles. A parallel-plate Markus chamber with a small sensitive air volume was used for beam dosimetry applying the ICRU protocol. The doses measured with the ionization chamber were compared with doses evaluated from the fluence measurements. Alternative dose measurements were performed using MTS-N LiF:Mg, Ti thermoluminescence detectors (TLDs) and a photometrically evaluated Fricke chemical dosimeter. An uncertainty of 8% was found in the determination of the dose relative to the reference method. Effects of an inhomogeneous energy loss and a finite track length of the projectiles in the sensitive detector volume of the dosimeters had to be taken into account.