This paper analyzes 96 samples of cement, 55 samples of chamotte, and 21 refractory products (4 refractory cement, 5 refractory bricks, 10 refractory mass, and 2 refractory sand) using low-level gamma spectrometry. Radiological risk is estimated through absorbed dose rates and annual effective dose, while results were compared with similar studies and discussed. Results indicate the need for radioactivity control of these building materials, since high dispersion of the activity concentrations of naturally occurring radionuclides is present, as well as high activity concentrations of 226Ra and 232Th compared with other building materials.

One of the major demands in gamma spectrometry of environmental samples is the accurate determination of activity concentration of present radionuclides (naturally occurring and those of artificial origin), due to the fact they are commonly of relatively low content. Thus, all these measurements have in common that the detection limit, in the spectral region of interest should be as low as possible. For this reason, the construction of a good passive, as well as active shield requires a detailed knowledge of the origin of the background events in the absence of an environmental sample. In addition, an analysis of the impact on detection limits due to the presence of the sample itself is also important. Also, the knowledge of the statistical basics for low-level counting is helpful to enable the best choice of detector characteristics (relative efficiency, peak to Compton ratio, resolution), measuring time, and required level of precaution against the different background contributions.In this paper, the background spectra of several gamma spectroscopy systems (with passive and active veto shields) are analyzed and discussed, regarding their capabilities for measurements of environmental samples. Furthermore, various environmental samples are analyzed by low-level gamma spectrometry, including the sample measurements in the presence of an active veto shield against cosmic-ray muons. The disturbance of radioactive equilibrium between members of radioactive series in the samples is commented on, together with the possibility of use of certain gamma lines (including their interference and the corresponding intensities) for radionuclide activities determination.

Low-energy continuous gamma radiation with a maximum energy distribution at similar to 70 keV reaches the Earth's surface from the upper hemisphere. In addition to components resulting from cosmic-origin low-energy gamma radiation, there is also a prominent contribution arising from gamma photons emitted by environmental ra-dionuclides, which are backscattered by air above ground (commonly referred as "skyshine" radiation). Since both components are covering the same energy region of gamma radiation (mainly 30 keV-350 keV), it is not simple to determine the separate contributions of each radiation component to the total gamma flux. The effi-cient way to solve this long-standing problem is to study the backscattering of gamma radiation on the atmo-spheric air by Monte Carlo simulations. In this work, the simulations were performed in order to obtain air-backscattered spectra, as well as gamma photon fluxes which can be expected for specified activity concentra-tions of natural radionuclides (K-40, Ra-226, Th-232) distributed in the ground. The simulation results were compared with experimental measurements of low-energy photon flux in the open area from the upper hemi-sphere. Furthermore, the influence of height above ground and distance from the shore on the skyshine intensity reduction is explored.

Diatomaceous earth is a natural material used in the food and beverage industry for filtration. In this paper, the radioactivity analyses and radiological risk estimation for 73 DE samples were conducted. The activity concentration of 226Ra, 232Th, and 40K was found to be in the range (5–164) Bq kg−1, (2–120) Bq kg−1, (19–1480) Bq kg−1, respectively. Absorbed gamma doses were in the range (8–172) nGy h−1. The total annual effective dose for workers was found to be in the range (0.011–0.217) mSv. Results indicate there is no particular radiation risk for workers and the public.

Detailed studies of background events provide information necessary for the planning of active and passive shielding of the detector in all experiments, especially ones searching for rare nuclear events. An effective approach in understanding the contribution of cosmic rays to the background of the HPGe detector is the use of Monte Carlo simulations. In this study, the Monte Carlo simulations were performed in order to obtain the time spectrum of the events induced by cosmic-ray muons and neutrons in the materials in the vicinity of the detector system and the detector itself. In order to reject background events originating from environmental radionuclides (from U-238 and Th-232 series, 40K, etc.), a coincidence system based on a large-volume HPGe detector and plastic scintillation detector was developed and the same setup was constructed in simulations. The experimental spectrum was compared with the simulated one. The possibility to distinguish these events based on the time was presented and illustrated through the selection of several time intervals of the time spectrum obtained in the simulation and corresponding spectra. Furthermore, the contribution of the muon-induced neutrons and cosmic-ray neutron-induced events to the background spectrum of the large-volume HPGe detector was analyzed. It was found that neutrons produced in the interaction of cosmic-muons with detector shielding and the detector itself are relatively small contributors to the overall neutron-induced events (i.e. low-energy region up to 100 keV originating dominantly from recoils and gamma lines originating from inelastic neutron scattering) registered in coincidence spectrum of HPGe detector compared to the contribution of cosmic-neutron themselves. The share of neutron components in this low-energy region of the coincidence spectrum of the HPGe detector was estimated to be asymptotic to 88%. In experiments searching for hypothetical dark matter particles, expected signals are in this energy region, thus in this type of experiment, it is essential to perform rejection of events induced by neutron interaction, in order to avoid misidentification of registered signals.

Standard reference sources, used for efficiency curve calibration of detector, often contain radionuclides with complex decay schemes (such as 60Co, 88Y, 152Eu …), introducing a potential problem in gamma-ray spectrometry, due to the appearance of coincidence summing of detected photons, in particular at a low source-detector distance. In this paper, a set of Monte Carlo simulations of an identical experimental setup were performed in order to obtain the efficiency curve of coaxial p-type HPGe detector for energy region (0-2) MeV, with the effect of true coincidence summing and without it. Obtained efficiency curves are compared with the experimental curve after applied EFFTRAN corrections. Fairly well agreement (between simulated and experimental curves with EFFTRAN corrections (with a relative deviation of 10%) proved the reliability of EFFTRAN corrections, as well as the possibility of Monte Carlo simulations for efficiency curve determination.

Apart from the continuous exposure of humans to background ionising radiation, an increased level of radiation may also originate from the use of building materials with an enhanced level of radioactivity. Thus, it is necessary to examine the content of radionuclides present in building materials, as well as the corresponding dose which may be received by residents from these materials. In this paper, particular attention was dedicated to finding the absorbed dose rate and annual effective dose caused by the presence of naturally occurring radioisotopes 226Ra, 232Th, and 40K in granite, a widely used building material, by means of Monte Carlo simulations. In addition, the obtained dose rate simulation results were compared with values estimated from commonly used simple equations, relating to the dose rate emitted by granite plates, covering the interior of a standard room. In the simulation, a room was constructed with standard dimensions (4 m × 5 m × 2.8 m), and with floor and walls covered with 3 cm thick granite. A water cylinder (approximate mass 65 kg) was positioned in the center of the room, representing a human body. The emission of the most intense gamma rays from 226Ra and 232Th progenies, as well as from 40K, emanating from the granite matrix, was simulated. The number of generated photons in each simulation (typically it was an order of magnitude of ~106) precisely represented actual activity concentrations of 226Ra, 232Th, and 40K in granite samples. All processes playing a role in the interactions of gamma photons with the granite matrix itself, the outer concrete shell, the air within the room, and the water cylinder, were taken into account by GEANT4 simulation software, after which the spectra of deposited energy inside of the water cylinder were obtained. Based on the deposited energy, the absorbed dose rate and annual effective dose were calculated for 6 analysed granite samples, each with different 226Ra, 232Th, and 40K contents. Furthermore, the effect of the position of the water cylinder in the simulated room on the absorbed dose rate was considered, as well as the distribution of the deposited energy within the water cylinder. The absorbed dose rates, and consequently annual effective dose, obtained in the simulations were found to be 30%-40% higher than the values obtained from using a standard formula.

Muography is a well established method to obtain 3D images of large objects (e.g. volcanoes and large buildings) without any additional particle source, taking advantage of the presence of cosmic muons. The underlying principle of muography is the measurement of individual muon tracks and the determination of their absorption or scattering. These processes depend on the material that they have travelled through. The novel method discussed is based on the measurement of the muon tracks and of the corresponding particles that were produced by the muons themselves in the investigated target. As muons pass through matter they interact with matter by ionization, bremsstrahlung, pair production and nuclear interactions. Our experimental setup is designed in a way to measure both the primary muons and the created secondaries (mostly electrons and gammas). The tracks of the muons are determined by a special kind of Multi-Wire Proportional Chambers (MWPC) called CCC (Close Cathode Chamber). The secondary particles produced in the target are measured by four plastic scintillators placed around the target. The CCC chambers and the scintillators are used in coincidence in order to gather data about muons that passed through the target. As cross sections of the described processes vary by the density and the atomic number of materials this technique could be used to investigate the material content of the target.

Exploration of possible anomalies in the decay of different radionuclides is an active research area in the fields of astrophysics and nuclear physics. The most significant changes in decay rates can be expected for beta(-), beta(+) or electron capture decay nuclides, due to the proposed influence of the solar neutrino flux by some research groups. In this work, the nuclear decay rate of beta(+) decay of Na-22 was investigated during the time interval of (similar to)33 days. For this purpose, a coincidence system based on a planar high purity germanium detector and a plastic scintillation detector was designed and used for the acquisition of experimental Na-22 coincidence spectrum. The corresponding experimental conditions: temperature, atmospheric pressure, and relative humidity, which may affect the measurement system, were monitored. In addition, Monte-Carlo simulations of this system were performed in order to obtain the Na-22 simulated coincidence spectrum. The time-dependent coincidence spectra in 0.5 h bins were collected by the multiparameter MPA-3 system. The fluctuations in the decay rate (i.e. possible variations of the decay constant) were analyzed by Fourier and Lomb-Scargle algorithms. No significant evidence for periodic behavior in decay rate or aperiodic anomalies was found during the acquisition period.

Typical industry set-up, used for material thickness inspection and process monitoring of different manufactured products, is based on the detection and counting of particles emitted by the radioactive source after passing the inspected material. The sensitivity of this method for determining material thickness in the flooring industry is assessed in this paper with Monte Carlo method by simulating a simplified typical industrial set-up used for this purpose. From the results of the Monte Carlo simulations, the sensitivity corresponding to the changes in the number of the detected electrons for the thickness material in range 2-2.2 mm was obtained. It was found that it is possible to distinguish the number of detected electrons in the 3 sigma region for the thickness changes of order of 0.1 mm, proving the necessary sensitivity of the presented method and adequacy as a part of quality assurance procedure. Furthermore, due to radioactive source use in this type of measurements, it is necessary to estimate the dose received from ionizing radiation. Thus, ambient dose equivalent was measured several times during the production line, at the nearest position to the radioactive source reachable by hand, but also at the position of the operator. Measured dose equivalent rate was compared with absorbed dose rate to the extremities obtained by Monte Carlo simulations showing good agreement. Estimated annual equivalent dose to the extremities and annual effective doses confirmed the safe use of the radioactive source Sr-90 for the thickness inspection and production process monitoring in the flooring industry.

The sum-peak method is a technique for measuring the absolute activity of gamma cascade emitting sources with a single gamma spectrometer. The effects of angular correlations and random coincidences, if not taken into account, can significantly reduce the accuracy of the method. However, we show that Monte Carlo simulations can reproduce the spectral data with a sufficient quality to perform the required corrections. In this work, we introduced a novel approach for data corrections for angular correlations and pile-up using Monte Carlo simulations. Furthermore, the new method for forming the count rate equations leads to a new formula for the sum-peak method, including random coincidences of any order.

To investigate the accuracy of the calibration of the HPGe detectors using an uncalibrated complex gamma cascade emitting source and the sum-peak method, Monte Carlo simulations were conducted. It was shown that accuracy below 5% is achievable for a 133Ba source, only if the spectral data are corrected for angular correlations even at short distances from the detector endcap.

Changes in cosmic-ray intensity can significantly influence the search for rare events or processes in nuclear and astroparticle physics through corresponding variations in detector background count rate. In this work, we present an approach to explore cosmic-ray intensity and corresponding cascade production of secondary particles in the detector vicinity using low-energy photon background spectra induced by cosmic rays at the earth’s surface. The coincidence system based on a plastic scintillator and an extended range HPGe detector, including a multiparameter device, was used for the acquisition of low-energy photon spectra. This system was also simulated by the GEANT4 toolkit, and the simulated and experimental spectra were compared. Single aperiodic events, as well as possible periodic behavior of low-energy photon emission were searched for.

The selection of appropriate materials and their thicknesses, which should be used for germanium spectrometer shielding, is an important and complex task with the aim to reduce the contribution of background events to detector spectra. These background events have origin in the radioactive decay of environmental radionuclides, and also are produced by cosmic-ray muon induced secondary particles within shielding materials. In this work, the emission of gamma rays arising from members of U-238 and Th-232 series, as well as from K-40, distributed in the surroundings of the cylindrically-shaped shields was simulated, together with cosmic-ray muons of average energy 2 GeV, interacting with the shields. Different types of materials (Pb, Fe, Cu) including variations of the shield thickness were considered in simulations based on Geant4 software, while internal contamination of shielding material and radon buildup inside the shielding were not taken into account. The simulated spectra for germanium detector were analyzed and mutually compared. The results obtained were useful to provide optimal parameters for the shielding of germanium detectors against the external radiation - cosmic-ray muons and environmental gamma rays.

Most studies focused on thoron have shown that indoor thoron originates mainly from building materials and that thoron concentrations exponentially decrease with a distance from a wall surface. On the contrary, due to longer half-lives of thoron progenies, Pb-212 and Bi-212, which are mainly responsible for the bronchial dose, it is expected that their spatial distribution is homogeneous. Therefore, direct measurements of thoron progeny concentrations or direct thoron measurement and determination of thoron equilibrium factor are necessary for accurate dose assessment. In this paper, we have optimized and validated a reliable and inexpensive method for direct measurement of thoron progenies concentrations based on an air filtration followed by gamma spectrometry measurements. With simultaneous measurements of indoor thoron by the RAD7 active device, the equilibrium factor for thoron in 15 different investigated dwellings was estimated. Obtained results for the equilibrium equivalent thoron concentrations in the range from 0.277 Bq/m(3) to 11.34 Bq/m(3) and thoron equilibrium factor in the range from 0.0047 to 0.098 with arithmetic mean value of 0.034 are in good agreement with already published results.