Sirin, Murat; Kaya, Selim; Aktarer, Semih Mahmut; Baltas, Hasan; Küçükömeroglu, Tevfik

In this study, the computationally predicted gamma-ray attenuation behavior and fast-neutron removal cross-section characteristics of micrometre-scale CrN, AlCrN, and AlTiCrN ceramic coatings produced via cathodic arc evaporation were investigated. The shielding parameters were not measured by direct gammaor neutron-transmission experiments; instead, mass attenuation coefficients (MAC, mu/rho) in the 0.05-2.50 MeV range were obtained from EGS4 Monte Carlo simulations and Phy-X/PSD calculations, and the agreement between the two computational datasets was evaluated. Energy-dependent attenuation parameters, including half-value layer (HVL), mean free path (MFP), effective atomic number (Zeff), radiation protection efficiency (RPE), and kerma coefficients, were calculated. Statistical comparison showed good consistency between EGS4 and Phy-X/PSD for MAC, RPE, HVL, MFP, and kerma coefficients, whereas Zeff exhibited larger method-dependent deviations. All coatings showed higher attenuation at low photon energies due to the photoelectric effect, while Compton scattering dominated at intermediate energies. Among the investigated coatings, CrN exhibited the most favorable calculated gamma-ray attenuation indicators, with lower HVL and MFP values and higher RPE values. The macroscopic fast-neutron removal cross-section (Sigma R) was also calculated as a first-order neutron attenuation indicator, and CrN showed the highest Sigma R value. Considering their limited thickness of approximately 2.3-2.8 mu m, these coatings should not be regarded as replacements for conventional bulk radiation shields. Instead, nitride-based ceramic coatings may serve as secondary or multifunctional surface layers in space-restricted components requiring local radiation attenuation and mechanical durability.

Çelik, Necati; Ali, Ahmed H.; Apaydin, Gokhan; Çevik, Ugur; Açikel, Selami

The radionuclide 152Eu presents a significant challenge in gamma-ray spectrometry due to its complex decay scheme and significant true coincidence summing (TCS) effects, especially in close-measurement geometries. This study presents a comprehensive investigation into TCS correction factors for the principal gamma-ray lines of 152Eu using tripartite methodology: a custom Monte Carlo (MC) simulation based on the EGS4 system, an established analytical method, and direct experimental measurements. The MC simulation explicitly models the complete decay process, including branching ratios, gamma emissions, internal conversion, and subsequent X-ray emissions for both decay branches (beta-minus to 152Gd and EC to 152Sm). Experimentally, correction factors were derived using a well-characterized point source measured at multiple distances with a coaxial HPGe detector. The analytical, method based on probabilistic analysis of the decay scheme, served as an examination. Results demonstrate that the analytical method underestimated the TCS correction factors, particularly for low-energy lines such as 121.78 keV, where it predicted a mere 0.78 % correction compared to 25.5 and 23.5 % from MC and experiment, respectively. This discrepancy is attributed to the analytical method's neglect of gamma-X ray coincidences and the internal conversion effects. In contrast, the MC simulation showed remarkable agreement with experimental results across all energies, validating its capability to accurately model the full complexity of TCS effects. The study concludes that while analytical methods offer rapid estimates, MC simulations, especially when experimentally validated, are essential for achieving metrological accuracy in the gamma-ray spectrometric analysis of complex radionuclides like 152Eu.

Kaya, Ali; Çelik, Necati; Kaya, Selim

Compton suppression systems are widely used to enhance gamma-ray spectral quality in applications such as nuclear safeguards and environmental radioactivity measurements. Although optimization of high-purity germanium (HPGe) detectors has been extensively reported, the geometric optimization of secondary sodium iodide [NaI(Tl)] scintillation detectors remains less studied. This work investigates the influence of annular and plug NaI(Tl) detector geometry—length, thickness, and radius—on Compton suppression performance using Monte Carlo simulations. Performance is evaluated in terms of the peak Compton suppression factor (CSFpeak) and total Compton suppression factor (CSFtotal). The results show that CSFpeak and CSFtotal increase with plug length (2–10.2 cm) and annular thickness (1–5.85 cm), with saturation observed beyond approximately 8–10 cm and 4–5 cm, respectively, due to reduced incremental photon absorption. The plug detector radius (3.72–5.1 cm) exhibits a nonlinear effect, with optimal performance achieved at 4.55–4.83 cm, beyond which gains are marginal (<5%). Suboptimal geometries (plug length <6 cm, annular thickness <3 cm, plug radius <4.28 cm) result in 20–60% lower suppression performance, increasing Compton continuum contributions in 662 keV spectra. The optimal configuration—plug length of 8–10 cm, plug radius of 4.55–4.83 cm, and annular thickness of 4–5 cm—achieves more than 90% of maximum CSFpeak and CSFtotal while maintaining a balance between performance and detector volume. These results provide quantitative design guidelines for optimizing NaI(Tl)-based Compton suppression systems for improved gamma-ray spectrometry performance.

Akbulut Özen, Songül; Özen, Murat; Çelik, Necati

CsPbBr3 single-crystals were synthesized using a hydrobromic acid–based temperature-lowering method, and their structural and optical properties were confirmed by XRD, DSC, and UV–Vis analyses. A solubility curve was established to optimize growth conditions, enabling enlargement of the seeded crystals. The radiation detection potential of CsPbBr3 was evaluated using EGS4 Monte Carlo simulations across photon energies ranging from 10 keV to 1 MeV. Simulated full-energy peak efficiencies and resolution values were compared with conventional detectors (Si(Li), NaI, and HPGe) and with alternative perovskite derivatives (CH3NH3PbBr3, Cs4PbBr6, CsPb2Br5). CsPbBr3 exhibited efficiency scaling with detector volume and resolution behavior consistent with the statistical 1/√E dependence typical of direct-gap semiconductors. While HPGe maintained superior intrinsic resolution, CsPbBr3 offered promising room-temperature performance without cryogenic requirements. These results demonstrate that the temperature-lowering method provides a viable route to scalable CsPbBr3 single-crystals and confirm their potential as cost-effective, high-Z semiconductor detectors for X- and γ-ray applications. The findings establish a foundation for the further optimization of perovskite-based radiation detection technologies.

Kaya, Ali

This study investigates the distribution of natural radionuclides (226Ra, 232Th, and 40K) and the artificial radionuclide 137Cs in soil samples collected from the Aktutan hydrothermal alteration zone in Gümüşhane, Türkiye. Hydrothermal systems are known to enhance radionuclide mobility and enrichment due to fluid–rock interactions, making them important environments for radiological assessment. However, no previous comprehensive radiological study has been conducted in this region. A total of 12 soil samples were collected and analyzed using high-purity germanium (HPGe) gamma-ray spectrometry. The measured activity concentrations ranged from 16 to 58 Bq·kg−1 for 232Th, 5 to 282 Bq·kg−1 for 226Ra, and 246 to 647 Bq·kg−1 for 40K, while 137Cs was detected in several samples with a maximum value of 5.7 Bq·kg−1. The elevated 226Ra concentrations observed in specific locations may be associated with localized hydrothermal alteration and possible uranium enrichment. Radiological hazard parameters, including absorbed dose rate, annual effective dose, radium equivalent activity, and hazard indices, were calculated. Most values were within internationally recommended limits; however, two sampling sites exhibited elevated radiological risk indicators, particularly in terms of excess lifetime cancer risk. Although the number of samples is limited, the selected locations represent areas of intense hydrothermal alteration and provide preliminary insight into radionuclide distribution in the region. The findings highlight the importance of localized geological controls on radioactivity and suggest the need for continuous environmental monitoring in areas with elevated radionuclide concentrations.

Düzgün, İbrahim; Kaya, Selim; Gül, Osman

This study reports on the structural characterization, radiation shielding assessment, and magnetic-field response of holmium-substituted Y3-xHoxBa5Cu8O18+δ superconducting ceramics synthesized by the conventional solid-state reaction route. X-ray diffraction measurements on five compositions (x = 0, 0.75, 1.5, 2.25, 3) supported the formation of a dominant orthorhombic Y358-type matrix across the substitution range. Scanning electron microscopy (SEM) combined with energy-dispersive X-ray spectroscopy (EDS) revealed a progressive microstructural evolution with increasing Ho content, including SEM–BEC/EDS-detectable Ho-rich inclusions consistent with Ho2BaCuO5-type secondary particles at higher substitution levels. XCOM-based mass attenuation coefficients, half-value layer, mean free path, effective atomic number, radiation protection efficiency, gamma-ray kerma coefficients, and fast-neutron removal cross-sections were calculated for all five compositions over 50–2000 keV. EGS4 Monte Carlo simulations independently verified the XCOM results for three representative compositions (x = 0, 1.5, and 3). Ho-containing specimens exhibited a significant enhancement in photon absorption near 60 keV, associated with the increased photoelectric contribution of holmium in the vicinity of its K-absorption edge. Among the full five-composition series, the x = 2.25 specimen (ρ = 5.531 g cm−3) exhibited the best calculated shielding performance across the full energy range, owing to its highest bulk density combined with substantial Ho incorporation. The x = 1.5 specimen provided the most balanced calculated radiation-attenuation and hysteretic magnetic response among the three representative compositions examined by EGS4 and M–H measurements at 20 K, retaining approximately 93% of the reference M–H hysteresis area while full substitution reduces it by roughly 67%. These findings establish a multi-parametric reference dataset for Ho-substituted Y358 ceramics and demonstrate the promise of rare-earth-engineered superconducting ceramics as multifunctional materials in radiation-intensive environments.

Şirin, Murat; Kaya, Selim; Temiz, Cengiz; Çağlar, Seyit

This study investigates the gamma-ray and fast-neutron shielding performance of Al–Cu–Sc/B4C nanocomposites containing 0–20 wt% boron carbide (B4C). The composites were produced using melt spinning, high-energy ball milling, and vacuum sintering techniques. Their structural and microstructural characteristics were examined by X-ray diffraction and scanning electron microscopy. Gamma-ray attenuation properties were measured experimentally at photon energies of 0.662, 1.173, and 1.333 MeV using a high-purity germanium detector. In addition, theoretical calculations were carried out in the 0.05–2.50 MeV energy range using Monte Carlo simulations together with the Phy-X/PSD calculation platform. Several radiation shielding parameters were evaluated, including the mass attenuation coefficient, half-value layer, mean free path, radiation protection efficiency, effective atomic number, and fast-neutron removal cross-section. The results show that the incorporation of B4C improves the fast-neutron shielding capability of the composites. The sample containing 20 wt% B4C exhibits an increase of approximately 32% in fast-neutron removal cross-section compared with the reference alloy. A slight reduction in gamma-ray attenuation is observed at low photon energy, whereas the shielding performance at medium and high energies remains nearly unchanged. These findings indicate that Al–Cu–Sc/B4C nanocomposites are promising lightweight and lead-free candidates for shielding against mixed gamma and neutron radiation. Their low density and the absence of toxic lead support potential applications in medical radiation facilities, nuclear technology systems, aerospace platforms, and industrial radiation environments where both radiation protection and weight reduction are important.

Çelik, Necati

High Purity Germanium (HPGe) detectors are essential instruments in gamma-ray spectrometry, offering high sensitivity and exceptional energy resolution. The full-energy-peak (FEP) efficiency is a critical parameter that influences the accuracy of activity concentration measurements of radionuclides. This study examines the FEP efficiency of a coaxial HPGe detector, focusing on variations in crystal length, crystal radius, and crystal hole dimensions. For varying crystal lengths, the efficiency values show negligible differences at low energy (50 keV) but significant increases at higher energies, indicating that longer crystal lengths enhance efficiency. Similarly, the efficiency increases with larger crystal radii across all energy levels suggesting substantial efficiency gains even at low energies. However, variations in crystal hole radius and depth, exhibit minimal impact on FEP efficiency across all tested energy levels. These findings highlight that optimizing crystal length and radius is more crucial for changing detector efficiency compared to modifying hole dimensions, providing valuable insights for optimizing Monte Carlo models and detector design.

Celik, Necati; Altin, Duygu; Cevik, Ugur

In the presented study, a code was created for the purpose of true coincidence summing (TCS) correction factors for 134Cs. The created code was implemented in EGS4 Monte Carlo simulation package. TCS factors were determined for nine different energies for different detector-source geometries. The calculated results were successfully validated by an empirical method using a point 134Cs radioactive source and a p-type HPGe detector having 55% relative efficiency. Although the code created gives TCS factors only for 134Cs, the technique presented can be used to obtain the factors for any radionuclide used in gamma-ray spectrometry.