Development of a whole body counter with Compton suppression factor for small animals

The basic operation, design and construction of the plastic scintillator detector is described. In order to increase the sensitivity of this detector, two blocks of plastic scintillator have been assembled to act as an anticomptom system. The detectors were produced by polymerization of styrene monomer with PPO (2,5 diphenyl-oxazole) and POPOP (1,4 bis(-5 phenyl-2-oxazoly)benzene) is in proportions of 0.5 and 0.5% respectively. Four radioactive sources: 22 Na, 54 Mn, 137 Cs and 131 I were used to evaluate the performance of this system. The Compton reduction factor, determined by the ratio of the energy peak values of suppressed and unsuppressed spectra, was 1.16. The Compton suppression factor determined by the ratio of the net photopeak area to the area of an equal spectral width in the Compton continuum, was approximately 1.308 ± 0.109. The sensitivity of the system, defined as the least amount of a radioactivity that can be quantified in the photopeak region, was 9.44 cps. First, the detector was assembled, to be applied in biological studies of whole body counter measurements of small animals. Using a phantom (small animal simulator) and a punctual 137 Cs source, located in the central region of the well counter the geometrical efficiency detector was about 5%. (author)