Comparative Study of Plastic Scintillators for Dosimetric Applications

Plastic scintillators are widely studied for radiotherapy dosimetry because of their very interesting properties and especially their water equivalence. Nevertheless, to ensure accurate dose measurements, the properties of the scintillators must be very well known and adapted to this application. We studied six plastic scintillators manufactured by two different companies (Bicron and Amcrys-H) in terms of emission spectrum, light yield, time response, and linearity of the scintillation response with regards to the incident radiation energy. This last data, which is not available for plastic scintillator, is one of the most important in radiotherapy applications because it guarantees the proportionality between the dose deposited in the scintillator and the scintillation intensity. The experimental emission spectra (measured under X-rays) were similar to the manufacturer ones (measured under UV), except for one scintillator which presented incomplete wavelength shifts. This information is important to match the scintillator emission with the photodetector spectral response and to cope with the limiting phenomena of scintillation dosimetry (in particular the Cerenkov radiation). Bicron scintillators showed better scintillation efficiencies (ranging from 64 to 79% of Anthracene) than Amcrys-H ones (ranging from 40 to 63% of Anthracene). On the contrary, the decay times of the scintillators, similar to the ones provided by the manufacturers, were slightly better for the Amcrys-H scintillators (from 4.62 to 9.53 ns ) than for the Bicron ones (from 4.74 to 12.95 ns). This study showed that the response of the scintillation response become linear when irradiated by electrons above 100 keV and photons above 200-250 keV . One of the Bicron scintillators presented a worse criterion of linearity, and one of the Amcrys-H scintillators presented a better criterion. These results clearly show that plastic scintillators are very convenient for radiotherapy where most photons have - - energy higher than a few hundreds of keV.