Radiation Physics and Engineering
Volume:3 Issue: 1, Winter 2022

Boron Neutron Capture Therapy (BNCT) is one of the promising treatment methods for some malignant tumors such as Glioblastoma Multiforme (GBM). One of the requirements of BNCT treatment is the accurate and real-time boron-concentration monitoring to ensure the efficacy of treatment and no leakage of boron. An accurate method for real-time calculation of the boron dose distribution mapping during irradiation is Single Photon Emission Computed Tomography (SPECT), in which the determination of boron distribution is based on the detection of 478 keV prompt gamma-rays generated through thermal neutron capturing by B-10. Tehran Research Reactor (TRR) is the only possible source for BNCT in Iran, so as the first approach, this BNCT-SPECT system has been evaluated for TRR. In this paper, an imaging system of BNCT-SPECT including four arrays of collimator/detector has been designed for real-time dosimetry as well as boron-10 concentration distribution map in the phantom that placed in front of the therapeutic neutron beam using the Monte Carlo simulation code MCNP6. Maximum Likelihood Expectation Maximization (MLEM) method has been used for image reconstruction which results 1 cm spatial resolution.

Selecting a genuine objective function in the fuel management optimization (FMO) of newly developed reactors is fundamentally important. The FMO problem becomes harder when a multi-objective fitness (cost) function (MOCF) is in use. Usually, when undertaking a MOCF fuel management optimization problem, it is transformed into the summation of objective functions, which are related to weighting factors. Different parameters can be chosen as the main fitness function in an optimization problem. In the case of a nuclear reactor, the cycle length, the multiplication factor and power peaking factor are the most significant. The value of the weighting factors and/or the method with which the cost function has been formulated may affect the final result of optimization. In this paper, the effect of the selection of the cost function has been analyzed in order to reach an optimum in core fuel management of a typical pressurized water reactor, PWR. It is understood from the results that finding a loading pattern that results in a better power peaking factor (lower PPF) is stricter than that of a longer cycle length. Indeed, the obtained loading pattern strongly depends on the selected fitness function. Finally, the flattening function is proposed instead of minimizing the PPF to attain better loading patterns.

An immobilized hybrid biosorbent (IHB) was prepared by hybridizing two biosorbents and evaluated for its ability to remove thorium ions from aqueous solution. The combined effect of the initial pH of solution (2 to 6), initial Th(IV) ion solution concentration (50-300 mg.L-1), IHB dose (0.5-5 g.L-1), and sorption duration (10 to 180 min) was investigated using central composite design (CCD). Experimental data were analyzed using Design Expert 8.0.6 software and fitted to a second order polynomial model with logarithm transform function. The adequacy of the model was verified using three indices, model analysis, coefficient of determination (R2) and the lack-of-fit test. The initial pH of solution was determined as the most effectual factor on Th(IV) ions biosorption removal by using the analysis of variance (ANOVA). According to the obtained results, pH value of 4.5, initial metal ion concentration of 210 mg.L-1, IHB dose of 5 g.L-1, and sorption duration of 95 minutes were proven to be the optimum conditions, for maximum biosorption removal of Th(IV) ions from aqueous solutions. Thermodynamic parameters have been evaluated, and it has been determined that the sorption process is feasible in going forward with more products than reactants, exothermic in nature and the reaction is entropy-driven. The equilibrium data were analyzed by the Langmuir, Freundlich, and Temkin sorption isotherms. Maximum monolayer sorption capacity of the IHB was found to be 142.86 mg.g-1. Pseudo-second-order kinetics model provided the better fit for all the biosorption processes which let suppose a physical rate-limiting step for the process.
Highlights
An immobilized hybrid biosorbent (IHB) was prepared for Th(IV) ions removal from aqueous solution.
RSM was employed for modeling the Th(IV) ions biosorption on IHB.
The Langmuir maximum monolayer Th(IV) ions sorption capacity of the IHB was found to be 142.86 mg.g-1.
Th(IV) ions biosorption on IHB followed the pseudo-second-order kinetics model.

Among the approaches commonly used to extend the sharp peak of the deposited dose in proton therapy, passive scattering is widely used and also is of concern because of the potential for generating secondary particles, especially neutrons, which can damage the non-target healthy tissues. The present simulation-based study investigates the effect of using the passive method for different primary proton energies on the dose delivered to the tissue compared with those of the pencil beam scanning method. The results show that the generation of secondary neutrons strongly depends on the material used in the beam design. Also, it was found that the passive method would lead to the physical neutron dose higher than that of the beam scanning method for various primary proton energies.

In this work, the impact of magnetic field presence on the central axis depth-dose curves of helium ion beams inside a heterogeneous phantom with air and bone layers was investigated. According to the calculations, presence of the magnetic field has a considerable impact on the dose distribution of helium beams depending on the field strength and beam energy. A 32.3% abrupt increase and 92.5% reduction in dose were observed at the boundary between the water-air and the water-bone layer insert, respectively. The accuracy of the simulation was evaluated by verifying the depth dose curves of helium ion beams in a water phantom with experimental data.

‎Irradiation of agricultural products is used to optimize properties and pest control and also increase the storage time of products‎. ‎The desired irradiation result is obtained when the required dose is given to the sample‎. ‎Dosimetry is a method for separating and classifying materials and equipment that is provided to the user to confirm the acceptance of irradiation and control the performance‎. ‎In this work‎, ‎Chromium Nitrate solutions with concentrations of 0.16‎, ‎0.24‎, ‎and 0.32 mM have been prepared and irradiated with gamma rays between 100 to 1000 Gy‎. ‎The purpose of this study is to investigate the dosimetry of these samples in the range of irradiation of agricultural products‎. ‎Results show that the higher concentration sample is linear in about 100 to 1000 Gy dosimetry range and the optimal concentration must be found to achieve a stable sample in about 3 weeks periods‎. ‎Also‎, ‎samples that are in a darker environment are more stable than samples that are in a lighter environment‎.