Calibration HPGe detector using IAEA-U source for CBRNe

Eur. Phys. J. Plus (2024) 139:654 https://doi.org/10.1140/epjp/s13360-024-05417-3 Regular Article Calibration HPGe detector using IAEA-U source for CBRNe Debora Siqueira Nascimento1,2,a Massimo Chiappini1,f , Andrea Chierici2,b , Riccardo Ciolini2,c , Stefano Chiappini1,d , Francesco d’Errico2,e , 1 National Institute of Geophysics and Volcanology, Via di Vigna Murata, 00143 Rome, Rome, Italy 2 Department of Civil and Industrial Engineering, University of Pisa, L.go Lucio Lazzarino, 56122 Pisa, PI, Italy Received: 31 March 2024 / Accepted: 1 July 2024 © The Author(s) 2024 Abstract Detecting and preventing the illicit movement of radioactive materials within a country is crucial, requiring the identification of radiologic anomalies against the normal radiation background. High-purity germanium (HPGe) detectors, known for their precision and sensitivity, have become popular for analyzing radioactive materials in CBRNe scenarios. This study focused on calibrating an HPGe detector for CBRNe applications, using gamma-ray spectra from an IAEA-U reference source. Energy calibration involved identifying peaks in the spectra and creating a calibration curve for energy and channel number data. Efficiency calibration, determined using the known activity of the source, revealed a linear relationship between energy and detector response. Over four years, systematic efficiency calibrations showed a deviation of only 3% well below the recommended limit of 5%. These findings underscore the reliability of the system as a reference spectrometry method for accurate detection of radioactive materials. 1 Introduction Gamma-ray spectrometry is a widely utilized technique for assessing the presence of radionuclides in environmental samples. In the context of CBRNe (Chemical, Biological, Radiological, Nuclear, and explosive) scenarios, the accurate identification of radioactive materials is crucial for ensuring the safety and security of affected areas. Gamma spectroscopy plays a pivotal role in this mission, enabling the precise detection and quantification of radionuclides [1, 2]. Comprehensive energy and efficiency calibration are fundamental components of gamma spectroscopy, ensuring the accuracy needed for distinguishing between natural and anthropogenic sources [2]. Moreover, the capability of gamma spectrometry to provide real-time data and spatial mapping of radioactive contamination holds immense significance in environmental monitoring. Gamma spectroscopy is employed in various environmental monitoring approaches [3]. Spectrometers can be utilized in aircraft or motor vehicles for aerial and ground measurements, respectively [3]. Portable spectrometers are a practical choice for on-the-go applications, while borehole spectrometers cater to down-hole measurements. For analyzing rock and soil samples, laboratory spectrometers are highly reliable. Worldwide studies covering extensive areas have utilized ground and air gamma-ray measurements, and their findings are typically presented in gamma-ray dose rates or concentrations of radioelements [4–6]. To achieve accurate results, proper calibration of instruments is crucial. The International Atomic Energy Agency (IAEA) plays a pivotal role in establishing standards for the calibration of gamma-ray instruments and in preparing geological reference materials for calibration purposes. In consideration of the importance of precise environmental mapping, we are currently preparing our high-purity germanium (HPGe) detector to serve as a reference instrument for field measurements. The initial step in this preparation involves comprehensive energy and efficiency calibrations. Energy calibration is vital to ensure the accurate identification of specific radionuclides, which is essential for precise environmental mapping. By accurately determining the energies of gamma rays emitted by radioactive sources, our detector will contribute to the creation of detailed and reliable environmental maps, allowing us to identify the distribution of radioactive materials with confidence. Efficiency calibration is equally critical, guaranteeing the correct quantification of radionuclide Andrea Chierici, Riccardo Ciolini, Stefano Chiappini, Francesco d’Errico and Massimo Chiappini have contributed equally to this work. a e-mail: (corresponding author) b e-mail: c e-mail: d e-mail: e e-mail: f e-mail: 0123456789().: V,-vol 123 654 Page 2 of 7 Eur. Phys. J. Plus (2024) 139:654 Fig. 1 Electronic setup used for the measurements concentrations in the environment. This calibration process establishes a consistent relationship between the detector’s response and the energy levels of incoming gamma radiation, enabling us to accurately measure the quantity of radioactive material present in the environment. The efficiency curve is influenced by both the characteristics of the detection system and the shape of the sample. Theoretical determination can be achieved through Monte Carlo simulation or semi-empirically using analytical methods. In practical terms, experimental determination involves using standard samples that encompass a range of radionuclides with known activities, covering the energy range of interest. Certified reference materials (CRMs) have been demonstrated to be a suitable source for the determination of the detection efficiency of HPGe [2, 7, 8]. Therefore, the aim of this work is to calibrate our detector HPGe using a CRMs (IAEA-U) source in energy and efficiency. In the future, enable us to better understand the spatial distribution of radioactive contaminants in the environment, supporting efforts to safeguard environmental integrity and public health. 2 Methodology 2.1 HPGe gamma-ray spectrometer Gamma-ray spectrometry measurements were carried out using a coaxial p-type high-purity germanium (HPGe) detector, specifically the Model GEM40P4-76. The cryostat utilized in this research is the CFG-PV4 model. The crystal itself possesses a 64-mm diameter and extends to a length of 66.8 mm, demonstrating a measured relative efficiency of 49% at an energy level of 1.33 MeV. The system is meticulously shielded with a four-layer design. The initial layer comprises 1.8 mm of copper, followed by a 0.81-mm layer of tin. Subsequently, there is a shielding layer of 150 mm of lead, and lastly, an additional 0.8-mm layer of lead is added. This arrangement extends over a total length of 258 mm and serves to effectively minimize interference from laboratory background radiation. The amplifier, multi-channel analyzer and acquisition system is based on an Ortec DSPEC Jr 2.0 [9], configured as reported in Fig. 1. 2.1.1 Certified reference material Certified reference material (CRM) is meticulously certified and supplied by the International Atomic Energy Agency (IAEA) through its Analytical Quality Control Services, serving as a trusted calibration source. These CRMs provide known concentrations of radioactivity measured in becquerel per kilogra (...truncated)