Radiation Physics and Engineering

Abstract The vital radioisotope 99mTc, used in approximately 80-85% of diagnostic radiopharmaceuticals, is mostly obtained from the decay of Mo-99. To provide 100 Ci Mo-99 (6 days) per week for Iran's domestic nuclear medicine centers, an industrial plan of Mo-99 production via fission of Low Enrichment Uranium targets in the Tehran Research Reactor has recently been evaluated. In this regard and with the aim of better conceptual knowledge for the site's solid waste management, two holders made of Al-Alloy 6061 and Stainless Steel-316, which will be used to irradiate the targets, were investigated in this paper. The gamma spectrum emitted from the irradiated holder device and the corresponding dose rate were calculated by a proposed method that had been verified experimentally. When the Al-Alloy 6061 holder device was used, the calculation results indicated that the 99Mo activity produced in the mini-plates was higher and the gamma dose rate of the activated holder device decreased faster.

Abstract In this research, by using the Seyler-Blanchard (SB) interaction, we present the Thomas-Fermi statistical approach in the simplest possible form in order to study the thermodynamic properties of nuclear matter with special attention to symmetry energy and its role in the thermodynamic instabilities. Our results show that the symmetry energy and symmetry free energy for the SB interaction are stiffer than those for the Myers-Swiatecki (MS) interactions. It can be seen that the temperature plays a prominent role in eliminating the unstable regions of the phase diagrams so that the unstable region shrinks with increasing temperature until it disappears at the critical temperature. Furthermore, the thermodynamic instabilities of asymmetric nuclear matter (ANM) occur simultaneously in both the chemical and mechanical modes, while the mechanical instabilities play a dominant role, as can be observed more significantly in the SB interaction than in the MS interactions due to the stiffer behavior of the symmetry energy and the symmetry free energy. This work paves the way for in-depth research on the liquid-gas phase transition, considering that the other theoretical predictions are consistent with the results of this model.

Abstract Some prominent and well-known companies or institutes recently developed a new Micro Modular Reactors (MMR) generation. Such a new design mainly includes the monolith core structure, heat pipes, Stirling engines, and very tiny or compact designs. MARVEL is one of the most miniature and innovative designs as well. Undoubtedly, such a compact and innovative design has a lot of strategic or multi-purpose applications. Despite their advantages and applications, each new design should be accurately analyzed and checked against different aspects. In this paper, MARVEL, one of the most advanced emerging technologies, is selected for neutronic simulations and in-depth analyses using MCNP. Moreover, the reactor core design is analyzed and evaluated by loading four advanced nuclear fuel types. They are UZRH, UO₂, Uranium Nitride, and MOX. Parameters include the effective multiplication factor, neutron flux distribution, power peaking factor, reactor kinetics, fuel burn up, and consumption. Results are quite promising in utilizing such advanced nuclear fuels for such an advanced compact reactor. Finally, each type may have its advantages and disadvantages as well.

Abstract Fluid transmission pipelines are prone to corrosion and sediment deposition due to the nature of the materials they carry. Deposits inside of the pipeline may worsen corrosion, leading to micro-cracks and pitting. Neglecting to assess these factors can lead pipelines to failures with catastrophic consequences. Various methods have been developed for this purpose, with techniques using penetrating X-rays and gamma rays being the most accurate and non-destructive. In this study, gamma-ray dual-energy computed-tomography was utilized as a precise and non-destructive method for detecting corrosion in pipeline walls. Projections were obtained using the Limited-Number-Detector Computed Tomography (LNDCT) technique for pipeline phantoms. Dual-energy techniques were employed, emitting gamma rays from suitable radioactive isotopes such using two radioisotopes, Am-241 and Cs-137. Projections at different angles were recorded using 15 NaI(Tl) 2-inch detectors, and the corresponding full-energy-peak were separated and organized in the sinogram matrix. Subsequently, image reconstruction was performed using the Filtered-Back-Projection (FBP) algorithm, and the quality of the reconstructed image was assessed. The reconstructed images demonstrate the effectiveness of the dual-energy method in distinguishing between light and heavy materials, potentially leading to higher image quality compared to single-energy methods. Detailed analysis of the data obtained from dual-energy tomography enables precise identification of defects, failures, and sedimentation, without damage to pipeline structures. This research contributes to enhancing the evaluation and monitoring methods for pipelines, improving the efficiency of these systems, and ultimately advancing safety and productivity in the oil and gas industry.

Abstract A boiling model, specifically the Rensselaer Polytechnic Institute (RPI) model, is utilized by Computational Fluid Dynamics (CFD) code to calculate the pool boiling behavior on surfaces with varying wettability characteristics. The RPI model is an accurate method for predicting the heat transfer coefficient of nucleate boiling, which is based on a component-by-component heat flux analysis. With some modifications, the RPI model can also be employed to simulate pool boiling heat transfer and CHF. To validate the modeling approach, the calculated heat flux for the pool boiling regime is compared to experimental data from the literature. The results indicate that the modified RPI model has a good ability to accurately predict the heat flux for the pool boiling stage. Furthermore, this modified RPI model demonstrates close agreement with the experimental results obtained for surfaces exhibiting diverse wettability properties. This suggests the model's capability to effectively capture the impact of surface wettability on pool boiling heat transfer. The successful application and validation of the modified RPI model for pool boiling simulations, particularly its ability to account for varying surface wettability characteristics, represents a valuable contribution to the existing knowledge on computational modeling of boiling heat transfer phenomena.

Abstract The neutron source at the Shahid Bahonar University of Kerman employs an Americium-Beryllium (Am-Be) source with an activity of 5 Ci. This study aimed to calculate neutron tracks from this source using experimental and simulation approaches. The PTRAC command of the MCNPX code was utilized to determine the neutron spectrum incident on the Digital Video Disc (DVD) converter layer. Advances in neutron detection methods have introduced significant innovations, including the use of converter layers combined with DVD layer as nuclear track detector. In this technique, a boron oxide layer with a thickness of 0.1 millimeters was put on the DVD surface to convert neutrons into alpha particles, allowing for nuclear track recording. Empirical results demonstrated that the number of tracks depended on the boron concentration in the converter layer. The angular spectrum of the DVD converter layer indicates that the highest particle collision angle occurred near 60°. Simulation result confirmed the feasibility of this method for neutron detection.

Abstract Radon gas is a significant source of natural radiation exposure in humans. In this research, the responses of three different radiation detectors are compared by preliminary test results for Radon gas detection. First detector is a pulse-mode counter developed by using a BPW34 photodiode. To amplify and read out the output signal of the photodiode, a charge-sensitive preamplifier, based on a two-stage TLC272 operational amplifier is designed. In the following, a pulse counting circuit is implemented by using an ATmega32 microcontroller. The second developed detector is a current-mode air ionization chamber working at low applied voltages, with output signal enhanced by a current amplifier BC517 Darlington transistor, read out by an Arduino UNO module. Additionally, an alpha-sensitive Geiger-Mueller counter (model NT-960, Novin Teyf) with a mica entrance window is employed as the third detector. Soil samples containing natural Uranium, in companion with all three detectors were sealed in a chamber to study the detector responses to different concentrations of Radon gas. Findings indicate that all three detectors exhibit an increasing response as the concentration of Radon gas is increased. In the viewpoint of measurement accuracy, the Geiger-Mueller counter provides more accurate results due to a higher count rate and lower statistical fluctuations, with a concentration curve giving the half-life of Radon acceptably. The ionization chamber is shown to suffer from low sensitivity due to its current-mode operation.

Abstract Radiolabeled monoclonal antibodies have shown great promise for cancer diagnosis and therapy. Approximately 15% to 20% of breast cancers exhibit an overexpression of a growth-promoting protein known as HER2. In the present study, trastuzumab was conjugated with CHX-A-DTPA (Macrocyclics B-355), the average number of the chelator conjugated per mAb was calculated and total concentration was determined by spectrophotometrically. CHX-A-DTPA–trastuzumab was labeled with ⁶⁷Ga (10 mCi, 375 MBq) then Radiochemical purity and immunoreactivity by SKBR₃ cell line and serum stability of ⁶⁷Ga-CHX-A-DTPA-trastuzumab were determined. The biodistribution studies was performed in female Sprague Dowley rat (⁶⁷Ga–CHX-A-DTPA–trastuzumab i.v., 200 microl, 200±20 mCi, 35±5 μg mAb , 4, 24, 48 and 72 h). ⁶⁷Ga-CHX-A-DTPA-trastuzumab was prepared (RCP>98% ± 0.5, Specific activity 4.1±0.7 μCi/μg). Conjugation reaction (c/a) was 4.1±1.2. Labeling yield was 92.5% ± 2.1. Immunoreaction of ⁶⁷Ga-CHX-A-DTPA- trastuzumab complex towards HER2 antigen was determined by RIA and the complex showed high immunoreactivity towards HER2. In vitro stability showed more than 91%±2.6 in the PBS and 81%±1.8 in the serum over 24 h. The Immunoreactivity of the radiolabeled anti-HER2 towards SKBR3 cell line was done by using Lindmo assay protocol which was found to be 0.84. The biodistribution of ⁶⁷Ga–CHX-A-DTPA-trastuzumab complex in normal Sprague Dowley rat at 4, 24, 48, and 72 h after intravenous administration, expressed as (%ID/g). Biodistribution studies at 24 and 48 h post-injection revealed the similar pattern to the other radiolabeled anti-HER2 immunoconjugates