Long Scintillation Detector Using Composite Light Guide for β-ray Survey Measurement

Abstract

In this paper, we describe a new type of scintillation detector that can be inserted into long, narrow tubes used in nuclear power plants to measure radioactive contamination of their inner surfaces. The sensitive area of the detector needs to cover the entire circumference and extend along the longitudinal axis, and its performance must be equivalent to that of a conventional survey meter. To construct such a sensitive area, we bonded six long, thin plastic scintillator strips around a hexagonal center core. For the hexagonal center core, we proposed a novel light collection structure called a “composite light guide,” using a wavelength-shifting technique to maintain the counting efficiency while achieving better uniformity along the longitudinal axis. We conducted basic experiments, and also established a simple light propagation model of the composite light guide, focusing on the light intensity, and confirmed its effectiveness. Using this light propagation model, we determined the optimum design and incorporated it into the manufacture of a prototype detector. From tests of the prototype detector, we verified that its performance satisfied the design requirements and that the composite light guide functioned effectively.