div dir="ltr">Abstract:
The organic scintillators are used in a wide range in nuclear physics field due to its high efficiency and good response for different nuclear radiations. In the present work, a plastic scintillator NEl04 (2" x 2") was designed and constructed. The effect of the designed parameters in the characteristics of the scintillator, which are the pulse rise time. and the response of the detector to different nuclear radiations, was investigated. A Monte Carlo methed was applied to simulate the neutron interaction with the present scintillator for calculating the response function and the detection efficiency. The detection efficiency for neutron energy range (0.1- 6.0) Me.V was found to be about (57%- 60%) for a bias of (0.2 and 0.4) Me V respeclively. The following design parameters were studied: - 1. The effect of reflector and light guide on the scintillator characteristics. Two types of reflectors were used, Al foil and TiO2 and the results were compared to that in the case without using reflector. 2. The effect of light guide thickness between the scintillator and photomultiplier tube. Five Perspex light guide thicknesses were used, which have 5. 1 cm in diameter and 1,2, 3, 4 and 5 cm in thickness. 3- The effect of photomultiplier tube and voltage divider electronics. Two types of photomultiplier tube were used with three associated dividers have currents of 1.43, 1.7 and 2 m.A. This study shows the the following conclusions: 1.The output pulse rise time from the
detector is improved as the reflector is removed. A pulse rise time of 1.75 ns was obtained, however, the detector counting efficiency was decreased by about 10% to 15%. 2-The Al reflector is more efficient when used with high and medium voltage dividers current. A best pulse rise time of (2 - 2.5) ns was obtained using Al reflector, and (2.25 - 2.5) ns when using TiO2 reflector. 3The use of light guide highly improves the time response of me detector. The thickness of 4 cm of the light guide was found to be sufficient for this purpose. The pulse rise time is improved when using a light guide. The rise time was decreased from (3 - 3.5) ns to (2- 2.25) ns. 4- In the design of the voltage divider associated with me photomultiplier tube of the detector, the output current should be kept as large as possible to increase me dynamic range of me detector and to decrease the operating voltage and thereby reducing me detector noise. 5. The designed and constructed detector is found to be suitable in use for detection of gamma-rays, beta -particles as well as neutrons. This study gives conclusions and answers for several problems concerning the effect of the different design parameters on me detector performance.