Plastic scintillator detector for qualitative and quantitative measurements of gamma radiation

Background Plastic scintillator detectors are rugged and easily manufactured in desired shape, sizes and response time to gamma radiation is prompt as compared with any other scintillator detectors. Being popular these detectors are used in radiation monitors one of the application to restrict radioactive material movement. These are used in gross counting mode to know the presence of radioactivity. Therefore secondary survey is required to know the nature of the radionuclides. Purpose The feasibility study of Cylindrical Plastic Scintillator Detector (CPSD) was carried out for the qualitative and quantitative assessment of gamma emitting radionuclides. Methods In this work limited gamma spectrometry was carried out using NE110 equivalent cylindrical plastic scintillating material of 5.1 cm diameter and 100 cm long. CPSD is optically coupled to photomultiplier tube (PMT). The detector signal is processed using preamplifier, shaping amplifier and further analysed by a multi channel analyser (MCA). CPSD gamma spectrum consists of Compton continuum and Gaussian shaped Compton edge energy (λ e ) appearing as Compton maxima energy (λ max ). Photon transport simulation is used to characterize λ max as a signature for radionuclides emitting gamma energy/energies. In case of unresolved gamma energies, it appears as weighted effective Compton maxima energy. The prominent gamma energies observed across nuclear industries are in the energy range 0.03–3 MeV. It is grouped as low energy, intermediate energy, high energy and ultra-high energy window. The simulated spectrum is obtained suing Gaussian broadening parameters deduced from experimentally measured spectrum. The efficiency response function is developed from simulated response of detector to standard gamma sources under known source detector configurations. Results The mono energetic gamma emitting radioisotopes are identified against λ max from data library. Qualitative analysis of spectrum is used to discriminate artificial radioactive material from naturally occurring radioactive material using gamma photon, corresponding Compton edge and expected Compton maxima in each energy window. The provisional quantitative assessment is carried out using efficiency deduced from response function. The detection efficiency varies within 1%–0.2% for 0.03 to 3 MeV gamma energies. In this study efficiency for 137 Cs source is 0.26% with FWHM 0.092 MeV and the results re within 15% for the measured activity. Estimated sensitivity and spectral dose rate coefficient for CPSD are 77 cps/µR/h and 44.29 nGy/kcps respectively. The MDA or MDL of the most prominent radioisotopes used in nuclear industry are estimated. CPSD showed an ability to detect 149 kBq, 137 Cs radioisotope at 1 m distance. Conclusion CPSD can be utilised for gamma isotope identification with limited gamma spectroscopy tool in contamination and dose rate measurements monitors.