Characterization of germanium detectors for the first underground laboratory in Mexico

Abstract

This article reports the characterization of two High Purity Germanium detectors performed by extracting and comparing their efficiencies using experimental data and Monte Carlo simulations. The efficiencies were calculated for pointlike γ-ray sources as well as for extended calibration sources. Characteristics of the detectors such as energy linearity, energy resolution and full energy peak efficiencies are reported from measurements performed on surface laboratories. The detectors will be deployed in a γ-ray assay facility that will be located in the first underground laboratory in Mexico, Laboratorio Subterr'aneo de Mineral del Chico (LABChico), in the Comarca Minera UNESCO Global Geopark [1].

Gamma-ray flux measurement and geotechnical studies at the selected site for the LABChico underground laboratory

“…(meter water equivalent) overburden. LABChico is focused on the development of research and educational programs through the establishment of a γ-ray assay facility initially consisting of two High Purity Germanium detectors [27]. A dedicated program in fundamental and applied science is devised, where γ-ray assay of detector components for underground astroparticle physics will be developed, in addition to environmental radiation monitoring applications, see [2,3,4,5,6,7,8].…”

Contextual Isotope Ranking Criteria for Peak Identification in Gamma Spectroscopy Using a Large Database

“…The results in sections V-A and V-B below were obtained with spectra from a set of radioactive sealed calibration sources (Table III) and they were acquired with an EG&G-ORTEC Hyper Pure Germanium detector in the Detectors Laboratory at the Institute of Nuclear Science of the National Autonomous University of Mexico (UNAM), hereafter referred to as ICN-HPGe detector, whose characterization has been reported elsewhere [44]. The data acquisition system (DAQ) was a PX5-HPGe multi-channel analyzer (MCA) and a digital pulse processor (DPP) software analyzer provided by Amptek [45].…”

“…Nonetheless, no significant improvements were observed when efficiency corrected spectra were used as input. Therefore, identification could be achieved without knowing the detector's efficiency [44]. Besides, a test was implemented to find the dependence of the ranking results against the peakto-background ratio (PBR) defined as the ratio of the area enclosed by a peak to the area of the background beneath it, in an interval ±3σ around the peak, and calculated using an exponential plus second order polynomial fit.…”

“…To explore the capability of the program to identify isotopes in spectra that may contain an arbitrary combination of isotopes, various test were performed using previously studied samples [46], [47]: one had traces of 210 Pb (sample A) and the other contained 177 Lu and 131 I (sample B) and a rock sample taken from the inside of LabChico's site (sample C). It was known that sample A was spiked with lead and it was acquired with the high purity germanium detector of the Institute of Physics of the UNAM (IF-BEGe detector) [44] with a exposure time of 24 h, spectrum of sample B was acquired inside the Boulby Underground Germanium Suite (BUGS) facility [48] at Boulby Underground Laboratory [49] and a previous analysis of sample B identified 177 Lu and 131 I [46] and sample C is a rock taken during geotechnical studies [47] and assayed with the ICN-UNAM HPGe [44].…”

Volume reduction of water samples to increase sensitivity for radioassay of lead contamination

“…In addition to the assay conducted at Boulby using the RosebeRRy BEGe detector, the 210 Pb water samples were also characterised at the Institute of Physics of the National Autonomous University of Mexico (IF UNAM) using the BEGe detector described in Aguilar-Arevalo et al (2020a). The measurements and calibration with both IF UNAM and Boulby Germanium detectors were consistent as described in Aguilar-Arevalo et al (2020a) and shown in Table 4. For the Boulby measurements, the statistical and systematic effects described for Table 3 also apply here.…”