Novel coincidence setup using indigenously developed portable USB gamma spectrometer and associated analysis software

Abstract

We present the development of a compact gamma spectrometer that is also capable of coincidence measurements, by connecting two units by a cable. The spectrometer consists of a CsI scintillator mated to a PIN photo-diode as the detector, a charge sensitive pre-amplifier, a shaping amplifier, and a 1024 bin Multi-Channel analyser. The assembly fits on a single PCB of dimensions 55mm x 105mm enclosed in a compact aluminum box. The USB powered plug and play design of the spectrometer makes it a highly portable surveying tool. While the pre-amplifier and shaping amplifier circuits are derived from schematics available in the open source domain, the MCA has been custom built. The data acquisition, analysis cum visualization software has been written in Python and is open sourced. A dual parameter list mode MCA capable of recording time stamped energy data from each of the individual gamma spectrometers including identification of coincident events was also developed for energy-gated coincidence measurements, and algorithms to visualize heat maps and surface plots of the obtained list mode data have been incorporated into the software.An FWHM of 81.2 keV was measured for the 1332 keV peak of 60Co. Two point calibration using the 1173 keV and 1332 keV peaks was carried out. The calculated calibration factors are applied to the 661.7 keV peak of 137Cs. The measured peak is at 661.3 keV, corresponding to 0.1% accuracy. However, a full-range linearity testing with a commercial pulser showed a non-linearity with a maximum value of 0.6%. The dead time of the electronics was measured using a pulse generator, and was found to be less than 20 microseconds. Photopeak efficiency of the detector measured with the 661.7 keV peak of 137Cs was found to be around 29%.In a novel approach, the MCA firmware has been modified to demonstrate non-energy gated gamma-gamma coincidence with no additional circuitry. The coincidence filtering has been verified with a 1μC 22Na source using a timing window of 400 ns.