A single chip computational sensor system for gamma isotope identification

This paper presents the design and test results of a computational radiation sensor system based on a single chip solution that can perform standalone gamma isotope identification. A low power sensor front end with a charge sensitive amplifier, an event driven analog-to-digital converter, and a dedicated microcontroller are integrated on the same chip to process and bin the isotope data from a NaI gamma ray detector according to gathered pulse height. This combination effectively implements a single chip multichannel analyzer with the capability to do further processing of the data in software. To that end, a compact fixed-point program was developed to further analyze the pulse height spectra gathered from a variety of gamma ray sources and perform on-chip real-time gamma isotope identification. The design 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 30 μW, excluding the detector power consumption. The gamma isotope identification program executes in 70 ms.