(A) study on spectral gamma response of a plastic scintillator

Abstract

The plastic scintillator has been used for gamma-ray detection in the fields of dosimetry and security because of their advantages including a fast decay time, a low production cost, an easy fabrication method, availability in various shapes and large scale, dose linearity, and tissue-equivalence. Nevertheless, the fundamental characteristics of the plastic scintillator limit its applicability in spectral analysis. Energy calibration and analysis of the spectrum measured with plastic scintillators are not as simple as those on the spectrum measured with inorganic scintillators because only a Compton maximum is observed on the spectrum, and even its energy is not obvious. Several methods have been suggested for energy calibration and description of a spectrum in plastic scintillators but they required additional measurement equipment and many iterations in analyzing processes. In this study, an improved method to describe spectral gamma response in the plastic scintillator is suggested. The proposed method is based on the linear correlation between the energy resolution $(\sigma_R)$ and the estimated energy broadening at a Compton maximum $(\sigma_CM)$. The measured gamma spectra of known sources are calibrated first with the assumption on the energy of Compton maxima. After initial calibration, the energy broadening at a Compton maxima $(\sigma_CM)$ is estimated by Gaussian fitting and the corresponding energy resolution $(\sigma_R)$ is computed. The Compton spectra for each gamma-ray energy are calculated with the computed energy resolution and compared to the measured spectra. Then, the energy of the Compton maxima are deter-mined and used with the FWHM values for the computation of input parameters for GEB-treated MCNP6 simulation. Through this GEB-treated MCNP6 simulation, the detailed gamma spectra can be described, and the energy information required to the energy calibration can be provided by only the calculation of Compton spectra. The proposed method has been applied to three cases: the $1cm^3$ polystyrene scintillator for dosimetry, the 2-inch EJ200 scintillator which is the most common size, and the large PVT scintillator for the radiation portal monitor. The effectiveness of the proposed method was verified by showing a great agreement between measured gamma spectra and simulated spectra. This method can describe the gamma spectrum accurately without many iterations so that it is expected to provide a direct way for the energy calibration and spectral analysis in the applications of plastic scintillators.