Quantifying the impact of lead doping on plastic scintillator response to radiation.

PURPOSE

Through the addition of high-Z dopants, the sensitivity of plastic scintillators to low-energy radiation can be increased. This study quantifies this change in sensitivity as a function of dopant concentration.

METHODS

Measurements were conducted using four different lead-doped scintillators (0%, 1%, 1.5%, and 5% Pb) in high-energy electrons (6 to 15 MeV) and low-energy photon (100 to 300 kVp) radiation fields. High-energy and low-energy irradiations were done using a clinical linear accelerator and an orthovoltage unit, respectively. Light emitted by the scintillator was quantified using a photosensor module. The experimental setup was replicated in Geant4.10.3 Monte Carlo and scintillator parameters (Quenching parameter: kB and the light yield: L ) were varied until agreement between measured and simulated results was reached. Monoenergetic electrons were used to simulate the high-energy electron beam while a spectrum generated using SpekCalc software was used in the low-energy simulations. Light produced by the scintillator was quantified using a flux scorer sensitive only to photons in the visible wavelength range. In order to compare measured and simulated results, the light produced by the scintillator was normalized to the absorbed dose-to-water at the point of measurement.

RESULTS

At high lead dopant concentrations, the scintillator's sensitivity to the 100 kVp beam increased by 474% relative to the 15 MeV electron beam; the scintillator's kB parameter increased from 0.126 to 0.27 mm/MeV. A model quantifying the change in kB and L as a function of Z was derived; presenting a modified Birks' Law for metal-doped plastic scintillators.

CONCLUSION

The impact of high-Z doping on plastic scintillator response was quantified; this can allow for the controlled induction of energy dependence in plastic scintillator detectors.