Journal of Nuclear Research and Applications
Volume:4 Issue: 4, Autumn 2024

The nuclear fission of protactinium nuclei is a complex process influenced by an intricate interplay of nuclear components and microscopic details. This study presents a comprehensive analysis of the fission mechanism for 231-232Pa, emphasizing the role of parameters of fission barriers, static and dynamic deformations, predictions of nuclear level densities (NLD) models at the fission saddle points and its change compared to the ground state, fission models and fission dynamics. Through a combination of theoretical modeling and advanced simulation techniques using nuclear reaction and evaporation codes, the neutron induced fission cross sections of 231Pa are calculated and the profound impact of NLD on the static and dynamic deformations are illustrated. Our findings can be confirmed with experimental data which serve as benchmarks for the veracity of the proposed models. It is shown that the NLDs at saddle points have a significant effect on reaction results and fission path determination. It is shown that the effect of nuclear dynamic deformations should be included in the nuclear level density on the fission barriers so that the modeling can reproduce the experimental data. This study can be considered an essential roadmap for understanding the behavior of nuclear reactors and the development of nuclear energy.

In this work, the feasibility study on using a Coded-Aperture Imaging based on a Modified Uniformly Redundant Array coded mask in Single Photon Emission Computed Tomography (SPECT) was investigated for boron dose measurement in Boron Neutron Capture Therapy (BNCT). In this preliminary study, a MURA rank 13 with a 2×2 mosaic configuration, and a CZT detector array mounted in a single mask were investigated using Monte Carlo Simulation Code, MCNPX2.7. This is the first investigation on the use of Coded-Aperture Imaging for BNCT purposes for boron dose measurement during treatment. Also, the Maximum Likelihood-Expectation Maximization method was used for image reconstruction for boron dose estimation in the tissue. The results were examined for the recommended therapeutic neutron beam in the Tehran research reactor. Preliminary results show that SPECT with Modified Uniformly Redundant Array masks can be an efficient and precise tool for boron dose measurement in BNCT, and results show the superiority of this method in comparison to the conventional SEPCT in BNCT.

Radiation pressure acceleration (RPA) and target normal sheath acceleration (TNSA) are the two most significant methods in laser-accelerated proton beam (LAP) planning systems. LAP has inspired innovative applications that can benefit from proton bunches, distinguishing them from conventionally accelerated proton beams.The secondary neutrons and photons produced during the collision of protons with beamline components are significant concerns in proton therapy. Various Monte Carlo studies have evaluated beamline and shielding considerations for the TNSA method but there are no studies that directly address secondary neutron and photon production from the RPA method in LAP. The purpose of this study is to calculate the flux distribution of secondary neutron and photon radiation in the initial area of LAP and to determine the optimal thickness and radius of the energy selector in a LAP planning system based on the RPA method. Additionally, we present Monte Carlo calculations to identify the appropriate beam pipe for shielding in a LAP planning system. The Monte Carlo calculations for this research were conducted using the GEANT toolkit.Results show, energy selector is the most important source of secondary neutron and photon particles in the LAP beamline. According to the calculations, a pure tungsten energy selector is not the proper case, and using Tungsten+Polyethylene or Tungsten+Graphite composite selectors will reduce the production of neutron and photon intensities by approximately ~10% and ~25% respectively. Also, the optimal radiuses of energy selectors were found to be ~4 cm and ~6 cm for 3-degree and 5-degree proton deviation angles respectively.

Concrete is commonly used to shield gamma rays and neutrons. The effectiveness of concrete shielding for neutrons depends on the moisture content in the concrete. Moreover, the strength and durability of concrete structures are influenced by the moisture content in the concrete specimen. Therefore, determination of the moisture content in concrete is very important. The gamma ray attenuation technique is a potentially attractive non-destructive method for determining the concrete moisture content due to its high accuracy and speed. In this study, gamma attenuation in concrete shields of different thicknesses and moisture levels was simulated using the Monte Carlo method. Two separate artificial neural networks (ANN) were trained with simulation data to accurately estimate results and decrease calculation time. The thickness of concrete is predicted in the first ANN. Then, the count in full energy peak and thickness is applied to the second ANN to determine the concrete moisture. The trained neural network can estimate the thickness of concrete with a main relative error (MRE) of 0.42%. The findings indicate that the suggested approach can accurately determine the concrete moisture with an MRE error of 4.6% for test data.

Radon is a radioactive gas that nowadays is considered one of the most harmful natural factors in residential areas all over the world. After cigarettes, radon gas is considered to be the biggest cause of lung cancer. Therefore, it is very important to study the measurement of radon concentration in different parts of the building. In this research, by choosing a sample building, the distribution of radon concentration in different regions is modelled by using Computational Fluid Dynamics (CFD) in two conditions, non-ventilation and natural ventilation. Then the results measured by a continuous work radon detector have been compared in a similar condition. Also, to confirm the results, the average radon concentration in the building and for different conditions was compared with the data obtained from the analytical method. The results show that the modelling performed in a non-ventilation method with an error of less than 16% is consistent with the experimental data. Also in natural ventilation conditions, the experimental results confirm the numerical modelling results. On the other hand, the results derived from the analytical solution in both non-ventilation and natural ventilation conditions confirm the results obtained from the simulation of the distribution of radon concentration. Our emphasis on this study is to determine the proper location of sleeping, sitting, and standing in a building, to reduce the dose received from radon gas.

Zr-1 wt% Nb is extensively utilized as a structural material for fuel rod cladding in nuclear power plant reactors. The microstructural refinement of the cladding alloy in the hot manufacturing stage not only increase its mechanical properties but also influences the fuel rod's performance and integrity. In the present study, the hot compressive behavior and microstructural evolution with the aim to identify the recrystallization mechanism type in Zr-1 wt% Nb was investigated. Hence, the hot compression test was conducted at different temperature range of 600-900 ◦C and strain rates of 0.001-1 s-1. At the hot deformation temperature of 600 ◦C, the compressive stress was monotonically increasing with straining due to the occurrence of the work-hardening mechanisms in the deformation process. At the high deformation temperatures of 700 ◦C and above, the compressive strength initially increased until it reached the peak stress, after which it gradually decreased and settled into the steady state region. Investigating the hot deformed microstructures imply that significant grain refinement was obtained through the dynamic recrystallization occurrence. It was concluded that the continuous dynamic recrystallization and dynamic recovery were among the first softening mechanisms activated up to strains of 0.3 and then the discontinuous dynamic recrystallization completes the grain refinement in the microstructure.