Development and Characterization of a Directional Gamma-ray Detector

Abstract

Background: This work characterizes the first generation of detectors from the Hanna Laboratory to implement Silicon Photomultipliers and a heptagonal scintillator conguration. The purpose of the device is to determine the angle at which a radioactive source is located.

Methods: The development of the detector consisted of three phases: construction(September 2012- December 2012), simulation and characterization (April 2013). The experimental portion of the work consisted of placing a 137 Cs source at an arbitrary location, measuring the count rates in each scintillator panel and analysing the results.

Results: The detector’s function was validated by confirming the inverse square law with a radioactive source moving away from the detector. Furthermore, with a x2 summation method of analysis the angular position of a source was determined with an accuracy of 10˚ and a precision of 12˚. With a normalisation method of analysis the angular position of a source was found with an accuracy of 2˚ and a corresponding precision of 2˚.

Limitations: The quality of the electronics handling the signal from the silicon photomultipliers limited our resolution. Occasional double counts occur when a large amount of energy is imparted to the scintillator. Furthermore, the custom-built circuitry lowered the signal-to-noise ratio such that large distances were not feasible due to electronic noise constraints. Finally, simulation data analysis showed that the break of one circuit only had a small effect on the x2 method of analysis.

Conclusions: In conclusion, the design of the detector and the analysis techniques were shown to be suitable for short range angular resolution of a gamma-ray source. Both distance trials and a simulation of the detector prototype confirmed the validity of our design and of the analysis methods used. These promising results at short distances motivate further work in electronic circuit design to improve the range while maintaining both accuracy and precision.