A directional gamma ray detector using a single chip computational sensor

This paper presents the design and test results of a computational radiation sensor system based on a single chip solution that can determine the direction of gamma rays emitted from a radiation source. The overall system is formed by merging a sensor section with a compact and low power computational radiation sensor section. The sensor section houses three NaI gamma ray detectors arranged in a spatial configuration that allows for direction finding. The computational sensor is based on a single chip solution developed by authors that houses multiple low power sensor front ends, event driven analog-to-digital converters, and a dedicated microcontroller on the same die. The presented system is capable of gathering the pulse height spectra from the gamma isotope data received from the three separate NaI detectors. Further processing of the data is possible by executing software algorithms using the computation resources available on chip. To that end, a compact fixed-point program was developed to perform on-chip real-time gamma ray collection and direction estimation. The single chip solution was fabricated in a 0.18 μm CMOS technology with field tests demonstrating the validity of the approaches taken. The total computational sensor system power consumption is less than 20 μW, excluding the detector power consumption. The gamma isotope direction finding program executes in less than 1 ms with 5° accuracy.