Vol.32,

The aim of this study was to design a cage-like radiotherapy system (CRTS) to further promote the clinical application of noncoplanar radiotherapy. The CRTS comprises two stands, two O-rings, several arc girders, an X-ray head, an imaging subsystem, and a treatment couch. The X-ray head rotates with O-rings around the patient’s body and slides along the arc girder. Compared with the C-arm linear accelerator (C-Linac), the clinically available spatial irradiation angle ranges (SIARs) of the CRTS for the head, chest, and abdomen were 33%, 63.6%, and 62.6% larger, respectively. Moreover, according to a preliminary planning comparison based on the dose distribution simulation method, the CRTS achieved much better protection of normal tissue than the C-Linac. Furthermore, the CRTS enabled accurate noncoplanar irradiation without movement of the body being irradiated, allowed automatic control of the movements of different parts without risk of collisions, and provided continuous radiation over an angle that considerably exceeded a full turn. These advantages make CRTS very promising for noncoplanar radiotherapy.

461

Reactivity measurement is an essential part of a zero-power physics test, which is critical to reactor design and development. The rod drop experimental technique is used to measure the control rod worth in a zero-power physics test. The conventional rod drop experimental technique is limited by the spatial effect and the difference between the calculated static reactivity and measured dynamic reactivity; thus, the method must be improved. In this study, a modified rod drop experimental technique that constrains the detector neutron flux shape function based on three-dimensional space-time dynamics to reduce the reactivity perturbation and a new method for calculating the detector neutron flux shape function are proposed. Correction factors were determined using Monte Carlo N-Particle transport code and transient analysis code for a pressurized water reactor at the Ulsan National Institute of Science and Technology and Xi'an Jiaotong University, and a large reactivity of over 2000 pcm was measured using the modified technique. This research evaluated the modified technique accuracy, studied the influence of the correction factors on the modification, and investigated the effect of constraining the shape function on the reactivity perturbation reduction caused by the difference between the calculated neutron flux and true value, using the new method to calculate the shape function of the detector neutron flux and avoiding the neutron detector response function (weighting factor) calculation.

352

Cross-section homogenization for full-core calculations of small and complex reactor configurations, such as research reactors, has been recently recognized as an interesting and challenging topic. This paper presents the development of a PARCS/Serpent model for the neutronics analysis of a research reactor type TRIGA Mark-II loaded with Russian VVR-M2 fuel (known as the Dalat Nuclear Research Reactor or DNRR). The full-scale DNRR model and a supercell model for a shim/safety rod and its surrounding fuel bundles with the Monte Carlo code Serpent 2 were proposed to generate homogenized few-group cross-sections for full-core diffusion calculations with PARCS. The full-scale DNRR model with Serpent 2 was also utilized as a reference to verify the PARCS/Serpent calculations. Comparison of the effective neutron multiplication factors, radial and axial core power distributions, and control rod worths showed a generally good agreement between PARCS and Serpent 2. In addition, the discrepancies between the PARCS and Serpent 2 results are also discussed. Consequently, the results indicate the applicability of the PARCS/Serpent model for further steady state and transient analyses of the DNRR.

393

A liquid fueled thorium molten salt reactor (TMSR-LF), one of the Generation IV reactors, was designed by the Shanghai Institute of Applied Physics, Chinese Academy of Sciences. This study uses the Monte Carlo N-Particle Transport code to calculate the neutron and gamma dose rate distributions around the reactor. Multiple types of tallies and variance reduction techniques were employed to reduce calculation time and obtain convergent calculation results. Based on the calculation and analysis results, the TMSR-LF radiation shield with a 60 cm serpentine concrete layer and a 120 cm ordinary concrete layer is able to meet radiation requirements. The gamma dose rate outside the reactor biological shield was 16.1 mSv∙h^-1; this is higher than the neutron dose rate of 3.71×10^-2 mSv∙h^-1. The maximum thermal neutron flux density outside the reactor biological shield was 1.89×10³ cm^-2∙s^-1, which was below the 1×10⁵ cm^-2∙s^-1 limit. This means that the radiation effect caused by neutron activation can be disregarded.

416

A new detector array characterized by compact structure and large solid-angle coverage was designed for radioactive ion beam (RIB) experiments and measuring multi-nucleon correlation. A Monte Carlo simulation was performed to explore the effects of beam drifts in different directions and distances on the angular distribution of the Rutherford scattering, as measured by the detector array. The results indicate that, when the beam drift distance is less than 2.0 mm, the symmetry of the detector array can maintain a count error of less than 5%. This confirms the property of the detector array for RIB experiments. Furthermore, the simulation was validated through the elastic scattering angular distributions of ^6,7Li measured by the detector array in ^6,7Li + ²⁰⁹Bi experiments at different energies.

346

Based on the Monte Carlo approach and conventional error analysis theory, taking the heaviest doubly magic nucleus ²⁰⁸Pb as an example, we first evaluate the propagated uncertainties of universal potential parameters for three typical types of single-particle energy in the phenomenological Woods-Saxon mean field. Accepting the Woods-Saxon modeling with uncorrelated model parameters, we found that the standard deviations of single-particle energy obtained through the Monte Carlo simulation and the error propagation rules are in good agreement. It seems that the energy uncertainty of the single-particle levels regularly evoluate with certain quantum numbers to a large extent for the given parameter uncertainties. Further, the correlation properties of the single-particle levels within the domain of input parameter uncertainties are statistically analyzed, for example, with the aid of Pearson’s correlation coefficients. It was found that a positive, negative, or unrelated relationship may appear between two selected single-particle levels, which will be extremely helpful for evaluating the theoretical uncertainty related to the single-particle levels (e.g., K isomer) in nuclear structural calculations.

331

The discrimination of neutrons from gamma rays in a mixed radiation field is crucial in neutron detection tasks. Several approaches have been proposed to enhance the performance and accuracy of neutron-gamma discrimination. However, their performances are often associated with certain factors, such as experimental requirements and resulting mixed signals. The main purpose of this study is to achieve fast and accurate neutron-gamma discrimination without a priori information on the signal to be analyzed, as well as the experimental setup. Here, a novel method is proposed based on two concepts. The first method exploits the power of non-negative tensor factorization (NTF) as a blind source separation method to extract the original components from the mixture signals recorded at the output of the stilbene scintillator detector. The second one is based on the principles of support vector machine (SVM) to identify and discriminate these components. In addition to these two main methods, we adopted the Mexican-hat function as a continuous wavelet transform to characterize the components extracted using the NTF model. The resulting scalograms are processed as colored images, which are segmented into two distinct classes using the Otsu thresholding method to extract the features of interest of the neutrons and gamma-ray components from the background noise. We subsequently used principal component analysis to select the most significant of these features from the training and testing datasets for SVM. Bias-variance analysis is used to optimize the SVM model by finding the optimal level of model complexity with the highest possible generalization performance. In this framework, the obtained results have verified a suitable bias–variance tradeoff value. We achieved an operational SVM prediction model for neutron-gamma classification with a high true positive rate. The accuracy and performance of the SVM based on the NTF was evaluated and validated by comparing it to the charge comparison method via figure of merit. The results indicate that the proposed approach has a superior discrimination quality (figure of merit of 2.20).

444

Using the source imaging technique in two-pion interferometry, we study the image of the hydrodynamic particle-emitting source with the HIJING initial conditions for relativistic heavy-ion collisions on an event-by-event basis. It is shown that the initial-state fluctuations may give rise to bumpy structures of the medium during hydrodynamical evolution, which affects the two-pion emission space and leads to a visible two-tiered shape in the source function imaged using the two-pion Bose-Einstein correlations.@@This two-tiered shape can be understood within a similar but more analytic granular source model and is found to be closely related to the introduced quantity ξ, which characterizes the granular inhomogeneity of the source. By fitting the imaged source function with a granular source parametrization, we extract the granular inhomogeneity of the hydrodynamic source, which is found to be sensitive to both the Gaussian smearing width of the HIJING initial condition and the centrality of the collisions.

613

Liquid-based detectors are widely used in particle and nuclear physics experiments. Because fixed method is used to construct the geometry in detector simulations such as Geant4, it is usually difficult to describe the non-uniformity of the liquid in a detector. We propose a method based on geometry description markup language (GDML) and a tessellated detector description to share the detector geometry information between computational fluid dynamics (CFD) simulation software and detector simulation software. This method makes it possible to study the impact of a liquid flow and non-uniformity on the key performance of a liquid-based detector, such as the event vertex reconstruction resolution. This will also be helpful in the detector design and performance optimization.

323

The nuclides inhaled during nuclear accidents usually cause internal contamination of the lungs with low activity. Although a parallel-hole imaging system, which is widely used in medical gamma cameras, has a high resolution and good image quality, owing to its extremely low detection efficiency, it remains difficult to obtain images of inhaled lung contamination. In this study, the Monte Carlo method was used to study the internal lung contamination imaging using the MPA-MURA coded-aperture collimator. The imaging system consisted of an adult male lung model, with a mosaicked, pattern-centered, and anti-symmetric MURA coded-aperture collimator model and a CsI(Tl) detector model. The MLEM decoding algorithm was used to reconstruct the internal contamination image, and the complementary imaging method was used to reduce the number of artifacts. The full width at half maximum of the I-131 point source image reconstructed by the MPA-MURA coded-aperture imaging reached 2.51 mm, and the signal-to-noise ratio of the simplified respiratory tract source (I-131) image reconstructed through MPA-MURA coded-aperture imaging was 3.98 dB. Although the spatial resolution of MPA-MURA coded aperture imaging is not as good as that of parallel-hole imaging, the detection efficiency of PMA-MURA coded-aperture imaging is two orders of magnitude higher than that of parallel hole collimator imaging. Considering the low activity level of internal lung contamination caused by nuclear accidents, PMA-MURA coded-aperture imaging has significant potential for the development of lung contamination imaging.

333

To study vertical sag requirements and factors affecting the stretched wire alignment method, the vertical sag equation is first derived theoretically. Subsequently, the influencing factors (such as the hanging weight or tension, span length, temperature change, elastic deformation, and the Earth’s rotation) of the vertical sag are summarized, and their validity is verified through actual measurements. Finally, the essential factors affecting vertical sag, i.e., the specific strength and length, are discussed. It is believed that the vertical sag of a stretched wire is proportional to the square of the length and inversely proportional to the specific strength of the material.

406