Photopeak Efficiency Research Articles

Monte Carlo simulation of photo-peak efficiency response function and calculation of total efficiency for a NaI (Tl) scintillator detector

Abstract NaI (Tl) scintillation detectors are widely used in laboratories and in the field of gamma-ray spectrometry where detector efficiency is a key factor for successful quantitative γ ray analysis. In this work, Monte Carlo simulations using MCNPX code have been performed in order to evaluate energy resolution as a full width at half maximum (FWHM) of the peak and absolute efficiency of NaI detectors. Also, the detection efficiency and energy resolution for the NaI (Tl) scintillation detector of Tehran Research Reactor (TRR) pollution monitoring laboratory was measured. Simulation results were compared to experimental data and good agreement are obtained. In radioactive analyzing laboratory, precise determination of the detector efficiency according to any different gamma energy is a very important parameter whereas it uses in daily laboratory work.

Discerning Transuranic Sub-Concealments in Nuclear Waste Barrels Using γ-Ray Spectrometry: A Non-Invasive Assay Strategy To Combat the Threat of Nuclear Diversion.

Insufficient inventory control arising from inadequate monitoring procedures can lead to vulnerabilities in nuclear security. In addition, insider threats, by either malicious intent or negligence, can pose a substantial risk by exploiting such deficiencies to perform unlawful actions, such as theft or diversion, which may lead to compromised nuclear security. Interim storage barrels, intended for temporary containment of low-density nuclear waste, require special attention in this regard. In certain scenarios, the inadequacy of the existing waste barrel assay methodologies to identify and correctly measure any undesirable transuranic subconcealment present inside may pose a risk of nuclear diversion. The present work aims to establish an absolute waste barrel assay procedure to mitigate such risks by offering a robust method for the detection and assay of transuranic subconcealments in nuclear waste barrels using high-resolution γ-ray spectrometry. Challenges related to the varying amounts of attenuation experienced by the γ-rays within the subconcealments, low-density matrix, and the steel barrel wall have been addressed by an iterative photopeak efficiency transfer approach. The methodology has been verified for the assay of seven mock-up samples mimicking nuclear diversion attempts using waste barrels, for which conventional barrel scanning would be inadequate and tomographic scanning would be highly time-consuming. Using this methodology, Pu and 241Am isotopes have been assayed within <10% of the expected value for the majority, with the measurement uncertainty of <10%. The present method, which is simple and noninvasive, can identify inconsistencies with the labeled inventory and detect potential diversion attempts.

Simplified efficiency calibration methods for scintillation detectors used in nuclear remediation

Our study introduces innovative methods to address waste reduction and enhance resource efficiency in nuclear cleanup processes. We focus on sustainable nuclear technology, aligning with goals for cleaner production and environmental protection. We developed two novel methods, termed “oversimplified” and “simplified,” for easily determining the photopeak efficiency of NaI(Tl) scintillation detectors. These methods, along with a “general” solution method, were validated with calibrated radioactive sources such as 241Am, 57Co, 133Ba, 137Cs, and 60Co, and were used to commission a NaI(Tl) scintillation detector system at Chalk River Laboratories (CRL) for nuclear remediation. The system demonstrated high accuracy, making it suitable for screening unstable isotopes at contaminated sites. This screening tool significantly reduces the number of soil samples requiring detailed characterization, thereby lowering operational costs. The NaI(Tl) detector system was calibrated for near-contact geometry, which is commonly used at CRLs. Detection limits were established for this configuration. By improving the efficiency calibration of scintillation detectors, our study advances sustainable nuclear remediation practices, promoting environmental sustainability and cleaner production processes.

Growth and characterization of highly efficient Cs[formula omitted]Cu[formula omitted]I[formula omitted] single crystal for [formula omitted]-ray detection

Metal halide perovskites, particularly zero-dimensional (0D) variants, have garnered significant attention as scintillator materials for various applications such as γ-ray spectroscopy, X-ray imaging, and security. Among these, Cs3Cu2I5 has emerged as a promising candidate owing to its exceptional characteristics, such as good energy resolution, high light output, and high stopping power. Although there is sufficient data available on the scintillation properties of Cs3Cu2I5 Single Crystal (SC) grown using various methods, there still remains a scarcity of data on the scintillation properties of SCs grown using solvent evaporation method at room temperature. In the present work, Cs3Cu2I5 SCs have been grown using the solvent evaporation method at room temperature and characterized for their structural, optical, and scintillation properties. The SC shows an orthorhombic structure with a bandgap of 3.58 eV. The optical properties of the SC reveal the existence of Self-Trapped Exciton (STE). The SC exhibits an energy resolution of 5.80 ± 0.05% at 662 keV and a light output of 41,000 photons/MeV, making it suitable for γ-rays detection. The intrinsic photopeak efficiencies of Cs3Cu2I5 SC for γ-rays are reported for the first time. GEANT4 simulation toolkit has been used to perform realistic simulations, and the simulated and experimental efficiencies are compared. Simulations show that Cs3Cu2I5 scintillator has twice the efficiency of the NaI:Tl scintillator.

Geant4 simulations for the [formula omitted]-ray detectors of gSPEC at GSI/FAIR

A design study for the γ-ray detector array of the gSPEC project, which aims at measuring nuclear moments at GSI/FAIR, is presented. Foreseen setups, involving DEGAS and the new gDEGAS triple cluster detectors for γ-ray spectroscopy are simulated using the Geant4 framework. The main characteristics associated to these detector assemblies with the envisaged configurations, namely the photo-peak efficiency and the angular resolution, are discussed. A new correction procedure for a better reconstruction of the time-perturbed angular distribution is proposed.

To Reconstruct or Discard: A Comparison of Additive and Subtractive Charge Sharing Correction Algorithms at High and Low X-ray Fluxes.

Effective X-ray photon-counting spectral imaging (x-CSI) detector design involves the optimisation of a wide range of parameters both regarding the sensor (e.g., material, thickness and pixel pitch) and electronics (e.g., signal-processing chain and count-triggering scheme). Our previous publications have looked at the role of pixel pitch, sensor thickness and a range of additive charge sharing correction algorithms (CSCAs), and in this work, we compare additive and subtractive CSCAs to identify the advantages and disadvantages. These CSCAs differ in their approach to dealing with charge sharing: additive approaches attempt to reconstruct the original event, whilst subtractive approaches discard the shared events. Each approach was simulated on data from a wide range of x-CSI detector designs (pixel pitches 100-600 µm, sensor thickness 1.5 mm) and X-ray fluxes (106-109 photons mm-2 s-1), and their performance was characterised in terms of absolute detection efficiency (ADE), absolute photopeak efficiency (APE), relative coincidence counts (RCC) and binned spectral efficiency (BSE). Differences between the two approaches were explained mechanistically in terms of the CSCA's effect on both charge sharing and pule pileup. At low X-ray fluxes, the two approaches perform similarly, but at higher fluxes, they differ in complex ways. Generally, additive CSCAs perform better on absolute metrics (ADE and APE), and subtractive CSCAs perform better on relative metrics (RCC and BSE). Which approach to use will, thus, depend on the expected operating flux and whether dose efficiency or spectral efficiency is more important for the application in mind.

Conceptual design and simulated performance of the Barrel part of gamma array for the experimental terminal at HFRS of HIAF

The Barrel of γ array, consisting of 640 CsI(Tl) crystals and covering a polar angle range from 36.4° to 135.6°, has been designed for the experimental terminals at High energy FRagment Separator of High-Intensity heavy-ion Accelerator Facility in Huizhou. Together with the existing Endcap, consisting of 1024 CsI(Tl) crystals and covering a polar angle from 15.6° to 36.4°, at the External Target Facility in Lanzhou to form a new γ array, it is expected to meet the experimental requirements for in-beam γ-ray spectroscopy technique. A Monte Carlo code based on Geant4 was implemented to study the performance of the new γ array. Taking into account the Doppler correction and the intrinsic energy resolution of the detector, the energy resolution is 5.4% (FWHM) for the Endcap and 9.8% (FWHM) for the Barrel when the energy of the emitted γ-ray is 1 MeV in the Center-of-Mass frame with the beam energy of 500 MeV/u (beam velocity β = 0.759). The full-space photopeak efficiency is greater than 40% when the energy of the emitted γ-ray is less than 5 MeV in the Center-of-Mass frame and the beam energy is less than 700 MeV/u (β = 0.821). Such performance can satisfy most of the physics requirements for in-beam γ-ray spectroscopy experiments.

Development of wide range photon detection system for muonic X-ray spectroscopy

We have developed a photon detection system for muonic X-ray spectroscopy. The detector system consists of high-purity germanium detectors with BGO Compton suppressors. The signals from the detectors are readout with a digital acquisition system. The absolute energy accuracy, energy and timing resolutions, photo-peak efficiency, the performance of the Compton suppressor, and high count rate durability are studied with standard γ-ray sources and in-beam experiment using 27Al(p,γ)28Si resonance reaction. The detection system was demonstrated at Paul Scherrer Institute. A calibration method for a photon detector at a muon facility using muonic X-rays of 197Au and 209Bi is proposed.

Estimation of photopeak efficiency for IAEA gamma standards of different geometries using HPGe and 3″x3″ NaI(Tl) gamma spectrometry systems

The IAEA certified reference gamma standards of primordial radionuclides, such as K-40, U-238, and Th-232, are analysed using gamma spectrometry systems, namely High Purity Germanium (HPGe) and 3″x3″ NaI(Tl) scintillation detectors. The analysis aims to estimate and compare the Full Energy Photopeak Efficiencies (FEPE) of these detectors for the respective gamma emission energies. Additionally, to assess the impact of sample geometry and volume on the FEPEs of the detectors, the study is extended to gamma counting of the aforementioned IAEA standards using two commonly employed sample geometries: flat-cylindrical (∼ 150 ml) and elongated-cylindrical (∼ 250 ml), usually chosen based on the sample quantity. Furthermore, the study calculates and compares the Minimum Detectable Activities (MDA) of the two detectors for the primordial radionuclides in these sample geometries. The study reveals that for both detectors, the calculated efficiency values are higher for the flat-cylindrical geometry compared to the elongated-cylindrical geometry. In contrast to FEPE, the MDA values are observed to be higher for the elongated-cylindrical geometry. The results also indicate that the values of FEPE and MDA for the 3″x3″ NaI(Tl) scintillation detector are higher than those of the HPGe detector for both geometries, in line with the expectations. This study on FEPEs and MDA of gamma detectors are crucial because precise measurements using efficient detectors with low MDAs are vital for obtaining accurate data and drawing valid conclusions.

Radionuclide concentrations in agricultural soil and lifetime cancer risk due to gamma radioactivity in district Swabi, KPK, Pakistan

This study focuses on measuring the levels of naturally occurring radioactivity in the soil of Swabi, Khyber Pakhtunkhwa, Pakistan, as well as the associated health hazard. Thirty (30) soil samples were collected from various locations and analyzed for 226Ra, 232Th, and 40K radioactivity levels using a High Purity Germanium detector (HPGe) gamma-ray spectrometer with a photo-peak efficiency of approximately 52.3%. The average values obtained for these radionuclides are 35.6 ± 5.7 Bqkg−1, 47 ± 12.5 Bqkg−1, and 877 ± 153 Bqkg−1, respectively. The level of 232Th is slightly higher and 40K is 2.2 times higher than the internationally recommended limit of 30 Bqkg−1 and 400 Bqkg−1, respectively. Various parameters were calculated based on the results obtained, including Radium Equivalent (Raeq), External Hazard (Hex), Absorbed Dose Rate (D), Annual Gonadal Equivalent Dose (AGDE), Annual Effective Dose Rate, and Excess Lifetime Cancer Risk (ELCR), which are 170.3 ± 24 Bqkg−1, 0.46 ± 0.06 Bqkg−1, 81.4 ± 2.04 nGy h−1, 582 ± 78.08 μSvy−1, 99.8 ± 13.5 μSv Gy−1, and 0.349 ± 0.04, respectively. These values are below the limits recommended by the United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) in 2002. This study highlights the potential radiation threats associated with natural radioactivity levels in the soil of Swabi and provides valuable information for public health and safety.

Response of germanium detectors for high-energy γ-rays by 27Al(p, γ)28Si at Ep = 992 keV

Abstract The performance of germanium detectors for high-energy γ-rays was evaluated using a 992-keV resonance in the 27Al(p, γ)28Si reaction. The measurement was conducted at the RIKEN tandem accelerator. The energy of the excited state from the resonance was evaluated as 12540.7(2) keV. Using newly evaluated excitation energy, an energy calibration function and a photo peak efficiency of Ge detectors up to 10.8-MeV photons were deduced. Energy accuracy is achieved at 0.3 keV for the overall energy region. This reaction provides reliable energy and efficiency standards for high-energy γ-rays.

GermanIum array for non-destructive testing (GIANT) setup for muon-induced x-ray emission (MIXE) at the Paul Scherrer Institute

The usage of muonic x-rays to study elemental properties like nuclear radii ranges back to the seventies. This triggered the pioneering work at the Paul Scherrer Institute (PSI), during the eighties on the Muon-induced x-ray emission (MIXE) technique for a non-destructive assessment of elemental compositions. In recent years, this method has seen a rebirth, improvement, and adoption at most muon facilities around the world. Hereby, the PSI offers unique capabilities with its high-rate continuous muon beam at the Swiss Muon Source (SμS). We report here the decision-making, construction, and commissioning of a dedicated MIXE spectrometer at PSI, the GermanIum Array for Non-destructive Testing (GIANT) setup. Multiple campaigns highlighted the outstanding capabilities of MIXE at PSI, e.g., resolving down to 1 at. % elemental concentrations with as little as 1 h data taking, measuring isotopic ratios for elements from iron to lead, and characterizing gamma rays induced by muon nuclear capture. On-target beam spots were characterized with a dedicated charged particle tracker to be symmetric to 5% with an average σ = 22.80(25) and 14.41(8) mm for 25 and 45 MeV/c, respectively. Advanced analysis of the high-purity germanium signals further allows us to improve energy and timing resolutions to ∼1 keV and 20 ns at 1 MeV, respectively. Within the GIANT setup, an average detector has a photopeak efficiency of ϵĒ=0.11% and an energy resolution of σĒ=0.8keV at E = 1000 keV. The overall performance of the GIANT setup at SμS allowed us to start a rich user program with archaeological samples, Li-ion battery research, and collaboration with the industry. Future improvements will include a simulation-based analysis and a higher degree of automation, e.g., automatic scans of a series of muon momenta and automatic sample changing.

Technical note: Simulation of lung counting applications using Geant4

A Geant4 simulation package has been developed to investigate and test detector configurations for lung counting applications. The objective of this study was to measure radiation emitted from the human body and to make a qualitative comparison of the results of the simulation with an experiment. Experimental data were measured from a plastic phantom with a set of lungs containing 241Am activity. For comparison, simulations in which 241Am activity was uniformly distributed inside the lungs of the ICRP adult reference computational phantom were made. The attenuation of photons by the chest wall was simulated and from this photopeak efficiency and photon transmission were calculated as a function of photon energy. The transmission of 59.5 keV gamma rays, characteristic of the decay of 241Am, was determined from the computational phantom as a function of the angular position of the detector. It was found that the simulated detector response corresponds well with that from an experiment. The simulated count rate below 100 keV was 10.0(7) % greater compared to the experimental measurement. It was observed that 58.3(4) % of photons are attenuated for energies below 100 keV by the chest wall. In the simulation, the transmission of 59.5 keV gamma rays varied from 13.8(2) % to 38.0(4) % as a function of the angular position of the detector. The results obtained from the simulations show a satisfactory agreement with experimental data and the package can be used in the development of future body counting applications and enables optimization of the detection geometry.

Gamma-ray track reconstruction using graph neural networks

Since the advent of the new generation of germanium detector arrays for low-energy nuclear physics experiments utilizing gamma-ray tracking, the challenges associated with track-reconstruction methods have been extensively studied. In the present work an approach based on recent developments in machine learning was used to address the problem. Here, a graph neural network was constructed and trained on data simulated in Geant4 in order to attempt track reconstruction of gamma rays below 1 MeV in a spherical shell geometry of pure germanium. Using a thick-shell geometry, and simulated data without energy- and position uncertainties the network achieved a reconstruction rate above 80% for complete tracks, and a combined peak-to-total value of 85% for energy spectra with four discrete peaks. For data with added noise, i.e. finite resolution in interaction-point position and energy, the corresponding peak-to-total ratio dropped to 74%. The track reconstruction was stable across multiplicities 1–10 but showed an increased error frequency in the energy range between 50 keV and 250 keV. To specifically study the complication of gamma tracks lost by out-scattering from the detector volume, a thin-shell (9 cm thickness) geometry was used together with a modified version of the GNN framework. By letting the GNN code identify and discriminate the out-scatter events, an improvement of the P/T value from 66% to 75% was found for the packed, noisy data. For the sake of comparison the new GNN model with existing gamma-ray tracking methods, a separate instance of the network was trained on slightly higher energies (up to 1.5 MeV) and multiplicities (up to 15) to evaluate 1.332 MeV photon cascade data in terms of P/T and photo-peak efficiency. The results for this GNN data set, with P/T values at 85% for single tracks and 74% for multiplicity 15, show clear promise when compared to the existing tracking methods.

Design study of a HPGe detector array for β-decay investigation in laboratory ECR plasmas

In the frame of the PANDORA project, a new experimental approach aims at measuring in-plasma β-decay rate as a function of thermodynamical conditions of the environment, namely a laboratory magnetized plasma able to mimic some stellar-like conditions. The decay rates (expected to change dramatically as a function of the ionization state) will be measured as a function of the charge state distribution of the in-plasma ions. The new experimental approach aims at correlating the plasma environment and the decay rate. This can be performed by simultaneously identifying and discriminating—through an innovative multi-diagnostic system working synergically with a γ-ray detection system —the photons emitted by the plasma and γ-rays emitted after the isotope β-decay. In this study, the numerical simulations supporting the design of the γ-ray detector array, including a statistical significance study to check the feasibility of measuring the in-plasma decay rates, are presented. Geant4 simulations focused on the design of the array of γ-ray detectors and the evaluation of total efficiency depending on the detector type and the optimal displacement of detectors around the trap (including collimation systems and shielding). The simulation results showed that, due to technical limitations in the number of apertures that can be created in the magnetic trap, the best compromise is to use 14 HPGe (70% of relative efficiency) detectors surrounding the magnetic trap. The HPGe detectors were chosen for their excellent energy resolution (0.2% @ 1 MeV), since the harsh environment (the background is represented by the intense plasma self-emission) strongly affects the signal-to-background ratio. Once determined the total photopeak efficiency (0.1–0.2%), the sensitivity of the PANDORA experiment was checked in a “virtual experimental run,” by exploring the measurability of isotope decay rates for the first three physical cases of PANDORA: 176Lu, 134Cs and 94Nb. The preliminary results demonstrated the feasibility of the measurement in terms of the signal-to-background ratio and significance that it is possible to reach. The results indicated that experimental run durations could take from several days to 3 months, depending on the isotope under investigation, thus shedding new light on the role of weak interactions in stellar nucleosynthesis.

Simplified efficiency calibration methods for semiconductor detectors used in criticality dosimetry

“Oversimplified” and “simplified” methods based on true coincidence summing effect used in uncomplicated determination of the photo-peak efficiency of the semiconductor High Purity Germanium (HPGe) detector system are suggested and verified. The methods and calibrated 60Co radioactive source may be used to commission any HPGe detector to use during potential criticality event. The determined accuracy of the semiconductor HPGe detector system using this method is a few percent (for the detector system used in this study it was ≃8% for “oversimplified” and ≃5% for “simplified” methods accordingly) reasonable, expected, and good enough to use for estimation of neutron dose from irradiated human blood in a potential criticality event. Moreover, if one can experimentally deduce the photo-peak efficiency for 60Co 1333 keV γ-ray line using the suggested methods, then with a few percent accuracy this efficiency could be also used for 1369 keV γ-ray line in the decay of 24Na isotope.

Monte Carlo simulation of a BEGe 6530 detector in GAMOS

A Mirion Technologies BEGe 6530 detector was used to validate the use of the GEANT4 scripting language GAMOS for performing source-less full-energy gamma ray photopeak efficiency calibrations. The detector model was developed using a combination of manufacturer specifications, experimental measurements of the detector’s physical dimensions and comparisons of experimental and simulated response to a 137Cs point source. The resulting simulation files were short and concise (containing only eighty lines of code in total), reflecting the user-friendliness of GAMOS.Experimental efficiency data were then collected from point sources emitting gamma rays spanning an energy range of 26.3keV to 1408.0keV at a distance of 250mm, corresponding to a typical in-situ measurement geometry. These data were used as the basis of a three-way comparison with GAMOS estimates and Mirion Technologies’ proprietary LabSOCS source-less efficiency calibration software. GAMOS was able to reproduce experimental efficiency values to within about 1% across the entire energy range (the same accuracy achieved by LabSOCS), whilst providing insights into model limitations that are not available from LabSOCS outputs.This study demonstrates that GAMOS can produce reliable source-less efficiency calibrations for industry-relevant measurement geometries whilst offering a unique combination of ease-of-use and extensive user control over the simulation process and outputs.

Experimental and simulated methods to characterize the response of a scintillator detector

The NaI(Tl) detector is one of the most used in gamma ray spectrometry because it presents high counting efficiency for gamma rays in a wide energy range. This study presents the modeling of a real 1¼ x ¾" NaI(Tl) scintillation detector + photomultiplier using computational simulations carried out by the MCNP6 code, which considers energy resolution. In the mathematical model, the sensitive volume of the detector was adjusted using 241Am and 137Cs radiation sources by means of the absolute photopeak efficiency. Moreover, the MCNP6 code was used to calculate the effective solid angle of the detector in order to obtain the intrinsic efficiency response function. The mathematical model was experimentally validated using calibrated radioactive sources (241Am, 133Ba, 137Cs and 60Co) and the response functions - efficiency curve and energy resolution - were obtained. In addition, an experimental evaluation of the crystal homogeneity of the detector was made using a137Cs radiation source and a 3D printed device developed without stepper motors. The proposed methodology is able to obtain absolute photopeak efficiency in agreement with experimental data with maximum relative error of 5.64%. The gamma scanning procedure indicated that the crystal of the detector remained homogeneous.

Energy response and fast timing characteristics of 1.5[formula omitted] x 1.5[formula omitted] CeBr[formula omitted] scintillator

The present work reports the performance of 1.5′′ x 1.5′′ CeBr3 cylindrical fast scintillator detectors, coupled to the Photomultiplier Tube (PMT) Hamamatsu R13089-100. The detectors are characterized with respect to the energy linearity response, energy resolution, absolute photopeak efficiency and time resolution, using standard radioactive sources. The energy spectra recorded for different radioactive sources and the absolute photopeak efficiency at different source-to-detector distances are compared with the GEANT4 Monte Carlo simulation. The best time resolution of 141(1) ps, measured for the 1173–1332 keV prompt γ-ray cascade for a single 1.5′′ x 1.5′′ CeBr3 detector, is reported from the present work. The results are compared with the values reported for similar detectors of different sizes.

UCGretina geant4 simulation of the GRETINA Gamma-Ray Energy Tracking Array

UCGretina, a geant4 simulation of the GRETINA gamma-ray tracking array of highly-segmented high-purity germanium detectors is described. We have developed a model of the array, in particular of the Quad Module and the capsules, that gives good agreement between simulated and measured photopeak efficiencies over a broad range of gamma-ray energies and reproduces the shape of the measured Compton continuum. Both of these features are needed in order to accurately extract gamma-ray yields from spectra collected in in-beam gamma-ray spectroscopy measurements with beams traveling at v∕c≳0.3 at the National Superconducting Cyclotron Laboratory and the Facility for Rare Isotope Beams. In the process of developing the model, we determined that millimeter-scale layers of passive germanium surrounding the active volumes of the simulated crystals must be included in order to reproduce measured photopeak efficiencies. We adopted a simple model of effective passive layers and developed heuristic methods of determining passive-layer thicknesses by comparison of simulations and measurements for a single crystal and for the full array. Prospects for future development of the model are discussed.