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Segmented gamma scanning (SGS) is a fast and effective method for measuring radioactive waste drum. The efficiency calibration is directly related to the accuracy of reconstructed radioactivity. An efficiency function model and SGS efficiency calibration method are proposed for solving existing SGS efficiency calibration problems such as time lag, limited by experimental sources or difficult to effectively combine with SGS system. The SGS system model is established by the Geant4 to calculate the segment efficiency under different linear attenuation coefficients of medium and gamma energies. The efficiency calibration function is established with the function model and parameters. Waste drum samples are constructed with the polyethylene and point sources 137Cs/60Co to complete SGS experimental measurement, efficiency calibration and radioactivity reconstruction. The result shows that the relative deviation of the reconstructed activity of a single point source at different locations in the drum is −50.48% to 43.69% and it of multi-point sources in a segment or a drum is −27.88% to 3.57%. Experimental results verify the effectiveness of this efficiency function model and SGS calibration method. • An efficiency function model is proposed for the SGS efficiency calibration. • The relative deviation of reconstructed activity is −50.48% to 43.69% for a single point source placed in the drum. • This method can conveniently and quickly calculate the SGS efficiency. [ABSTRACT FROM AUTHOR]

An algorithm based on moment estimation is presented to determine the initial parameters of the particle spectrum peak shape function for the iteration fitting procedure. The algorithm calculates the mean value, variance, and third-order central moment by using the spectrum peak data, solves the parameters of the fitting function, and then provides them as the initial values to the Levenberg–Marquardt algorithm to ensure convergence and optimized fitting. The effectiveness of the proposed algorithm was tested by gamma and alpha spectra. The algorithm can be used in automated peak curve fitting and spectral analysis. [ABSTRACT FROM AUTHOR]

Abstract: An online automatic Ti-grade analyzer (OATGA), consisting of a 238Pu source and a proportional counter, is designed for assuring product quality. The advantage of this system was its time-effectiveness; the entire monitoring process can be finished within approximately 5min. This system has successfully solved some key analysis issues in titanium ore concentrate production process. The results obtained by feature measurements and chemical analysis were in agreement with each other. After two-year usage of OATGA at PANGANG, southwestern China, it was proved as a reliable method for online quality control in the production process of titanium ore concentrate. [Copyright &y& Elsevier]

Neutron activation analysis is a highly sensitive non-destructive testing technique with important applications in industry, geoscience, medical therapy, etc. This work designed and optimized a thermal neutron device that utilized a portable D-D neutron generator, and the Monte Carlo method with the Geant4 toolkit was applied to simulation. The objective of the optimized design is to maximize the thermal neutron flux at the output surface and increase the utilization efficiency of the neutron generator. A parameter K was defined as a measure of the device's slowing capacity for neutrons and was used to determine the optimized device geometry. The simulation considered the contribution of different types and sizes of moderators and reflectors to the thermal neutron intensity to obtain the optimal size. The shielding protection of the device was then designed. The effectiveness of shielding with different thicknesses was evaluated using three dose reference points. The results indicated that the optimized device can achieve a maximum thermal neutron flux of 1.97 × 105 n∙cm−2∙s−1 at the output surface by using high-density polyethylene (HDPE) as the moderator and nickel as the reflector. It was determined that using 45 cm of HDPE and 9 cm of lead protection in sequence along the neutron head axis would reduce the dose rate at the reference point, located 5 cm from the surface of the device, below the safety limit of 2.5 μSv/h. • Geant4 was used to optimize the design of a thermal neutron activation analysis setup based on a DD neutron generator. • A maximum thermal neutron flux of 1.97 × 105 n∙cm−2∙s−1 at the output surface. • The reference point dose rate is reduced to below the safe limit of 2.5 μSv/h. [ABSTRACT FROM AUTHOR]

Coded-aperture imagers typically have a smaller field-of-view (FOV) than in un-collimated gamma imaging systems. However, sources out of the fully coded field-of-view (FCFOV) can cause pseudo hotspots on the wrong side of an image reconstructed using the cross-correlation method. In this work, we propose a neural network method to identify and localize the sources within the partially coded field-of-view (PCFOV). The model was trained using Monte Carlo simulation data and evaluated with both simulation and experimental data. The results showed that the proposed model can identify and localize sources with good classification accuracy, low positioning error, and strong robustness to the statistical noise. • Sources localization within a partially coded field-of-view was investigated. • A neural network model was proposed to identify and localize sources. • The model was trained using Monte Carlo simulation data. • Both simulation and experimental results demonstrate the feasibility of the method. [ABSTRACT FROM AUTHOR]

This study proposes a novel natural environment background model by modeling brief environment conditions. It uses Geant4 program to simulate decays of 238 U, 232 Th, and 40 K in soil and obtains compositions of different-energy gamma rays in the natural environment background. The simulated gamma spectrum of the natural environment background agrees well with the experimental spectrum, particularly above 250 keV. The model is used in the simulation of anticoincidence measurement, indicating that the natural environment background can be decreased by approximately 88%, and the Compton attenuation factor is 2.22. The simulation of anticoincidence measurement can improve the minimum detectable activity (MDA) of the detection system. [ABSTRACT FROM AUTHOR]

The detection speed of the tomographic gamma scanning (TGS) system with a detector array is faster than the single detector system. The NaI(Tl) detector is inexpensive and can work at room temperature, making it ideal for use in the TGS system with a fan-shaped detector array. The collimator of the TGS system is one of the critical elements to ensure the reconstructed image's quality. In addition to providing good detection efficiency of the detector while improving the system's spatial resolution, a proper collimator structure may also reduce cross-interference between segments. We propose a collimator design method for the TGS system with a fan-shaped NaI(Tl) detector array and combine it with the Monte Carlo method to optimize the collimator. We get the collimator aperture size and shape of the TGS system through the simulation results. Simultaneously, according to the detectors' equiangular sector arrangement limitation, we propose setting up a fan-shaped shield with adjustable depth and height at the detector collimator's front. The cross-interference between segments is effectively reduced without reducing the current segment's detection efficiency. The transmission image reconstruction shows that the collimator designed by this method can be used in the TGS system with the fan-shaped NaI(Tl) detector array. • The collimator of the TGS system with the fan-shaped NaI(Tl) detector array is optimized with the Monte Carlo method. • The fan-shaped shield effectively reduces the cross-interference between segments. • A TGS system with a fan-shaped NaI(Tl) detector array is adopted to reconstruct transmission tomography. [ABSTRACT FROM AUTHOR]

The Alxa region (Inner Mongolia, China) is one of the areas preselected for use as a geological repository of high-level radioactive waste in China. Radioactive waste produces radioactive rays during long-term storage, and the cumulative absorbed dose in 1000 years can significantly exceed the maximum of 0.7 MGy, thereby challenging the long-term adsorption stability of clay. This study employed 60Co gamma (γ)-rays to irradiate clay in air under a dose rate of 10 kGy/h. The changes in the internal structure and mechanisms of clay under different gamma radiation doses (1, 2, and 3 MGy) were investigated. Additionally, the adsorption properties of irradiated clay for U(Ⅵ) were tested under different conditions. The clay samples underwent minimal structural changes following high-dose irradiation, and the interlayer spacing was altered due to the fractured framework, dehydroxylation, and radiolysis of water. After irradiation, the Fe (Ⅱ) content in clay was significantly increased, unlike Fe (Ⅲ) content. The adsorption mechanisms of clay before and after the experiments were verified, revealing that the adsorption capacity of irradiated clay to U(Ⅵ) is reduced. [Display omitted] • Gamma irradiation caused H 2 O radiolysis and skeleton fracture in clay samples. • The Fe (Ⅱ) content in clay significantly increased after gamma irradiation. • The uranium adsorption capacity of clay decreased after gamma irradiation. • Uranium adsorbed on clay mainly in the form of UO 2 2+. [ABSTRACT FROM AUTHOR]

This paper proposes a new method to reject pile-up pulse continuous zone. This paper first simulates the differences between three kinds trapezoidal shaping methods of which are trapezoidal shaping without width discrimination, with fixed width discrimination or with changing width discrimination, and then carry out experiment with silicon drift detector (SDD) and 55Fe source in laboratory, and the result of the experiment is that the ratio of peak to background (P/B) increases while the characteristic peaks in high energy section are not affected. Result of the simulation and experiment shows that the method proposed in this paper makes progress in pile-up pulse continuous zone rejection under the circumstance of high-count rates. • The pulse width of the exponential signal with rising edge after the trapezoidal pulse forming increases logarithmically with the increase of the pulse amplitude. • A pile-up pulse continuous zone reject method is proposed. • To verify the simulation result experimentally, 55Fe standard source is used as the measuring object. [ABSTRACT FROM AUTHOR]