Radiation Physics and Engineering
Volume:3 Issue: 3, Summer 2022

The potential biomedical application of Positron Annihilation Spectroscopy (PAS) for nonstructural characterization of normal and cancer cells was not thoroughly employed and researched. In this paper, the experimental investigation of the oxygen sensing ability of the PAS technique for tumor imaging is presented and discussed. This research is based on the validated hypothesis that tumor cells differ from the normal tissues in their value of oxygen concentrations. The components of Doppler Broadening and positron annihilation lifetime spectra are measured with our homemade spectrometer to determine the mechanism behind the positron annihilation in oxygen content tissue-equivalent samples. The analysis of PAS data shows that the Orbital Momentum Spectrum (OEMS) of the Coincidence Doppler Broadening Spectroscopy (CDBS) and the positronium lifetime components of Positron Annihilation Lifetime Spectroscopy (PALS) are sensitive to the presence of oxygen. The results are applicable in the development of a tumor imaging system based on the PAS technique.

A high-power solid-sate based radio frequency power source is introduced in this paper. Solid-state based amplifiers are much more efficient than microwave tubes and can be used in compact electron cyclotron resonance (ECR) ion sources. A reliable negative bias voltage controller is proposed to drive the power source's main power amplifier, which can deliver up to 300-watt power to the ion chamber. The selected high-power transistor is internally matched on the input side but the output side is matched in this paper to deliver maximum power to the load. The bias circuit was fabricated on FR4 substrate and measurement results were obtained to verify the functionality of the bias sequencer. Analog simulations were done by LTSPICE and high-frequency simulations are performed with the momentum RF simulator of Advanced Design System (ADS). The output power of the proposed structure is tunable with 0.5 dB resolution and can deliver 300 mW to 300 W power to the ion chamber.

To measure excitation functions of particle-induced prompt gamma-ray production reactions on Li, a thin LiF target was fabricated by thermal evaporation technique onto self-supporting Ag film. The thickness and the stochiometric ratio of the thin LiF target was measured using Elastic Backscattering Spectroscopy (EBS), Particle Induced Gamma-ray Emission (PIGE) and Nuclear Reaction Analysis (NRA) techniques. The target was characterized to check uniformity and its stability under beam bombardment. Carbon and Molybdenium contaminations in the target also were examinated. The values of the thickness of the target obtained by EBS, PIGE and NRA techniques are in good agreement with each other , within the estimated uncertainties. Measurements were conducted using the proton/deuteron beams of the 3 MV Van de Graaff electrostatic accelerator of Nuclear Science and Technology Research Institute (NSTRI). All results are presented in an absolute approach by using the experimental cross-section values available through the Ion Beam Nuclear Data Library (IBANDL).

A two-dimensional coincidence technique is carried out to suppress the background for exploring the contribution of positron annihilation with core electrons. The spectrometer is composed of two face-to-face HPGe detectors. To test the performance of the system, the Coincidence Doppler Broadening (CDB) ratio curve of pure well-annealed Copper is investigated. The quality of the annealing process is measured using Positron Annihilation Lifetime Spectroscopy (PALS). For comparison of the ratio curve of different laboratories, an Aluminum sample is considered as a reference due to its simple electronic structure. The element-specific CDBS signature of Copper shows the two peaks around 12.8×10-3 m0c and 19×10-3 m0c at the ratio curve which is dependent on the momentum of Fermi electrons. The presented ratio curve is compared with the reference measurement and simulation. Differences and the similarities in the reported ratio curves are discussed. The comparison shows that our result is more compatible with the theoretical calculations and can be considered as a new reference for future studies on the chemical environment of defects in alloys that include Copper in their contents.

In this study, thermal-hydraulic analysis of a dry storage cask for Bushehr Nuclear Power Plant spent nuclear fuels is carried out. Geometry drawing and mesh generation were completed in SolidWorks and Gambit software, respectively. Three different cases were considered for the cask geometry and design including cask with/without spacers and cask with spacers and fins. Thermal-hydraulic analysis of the cask was performed for steady-state and normal storage conditions in ANSYS CFX solver package. Simulation results indicated a weak thermal-hydraulic behavior of the cask in the geometry without spacer and maximum fuel temperature exceeded the allowable safety limits. However, with the addition of spacers and fins in the geometry of the cask, thermal behavior of the cask was significantly improved and maximum fuel temperature achieved a proper margin compared to the allowable safety limits. As a result, the spent fuel integrity will be maintained in the normal storage conditions. The simulation results were compared with a literature published paper and it showed a good agreement between the calculated results.

In this study, after discretization of the neutron diffusion equation and adjoint with high-order nodal expansion method in two dimensions and two energy groups, calculations with Momentum and Galerkin weighting functions for rectangular geometry (BIBLIS-2D) and hexagonal geometry (IAEA-2D) reactors are performed. The mean of relative power error for Momentum and Galerkin weighting functions was calculated in BIBLIS-2D reactor 0.42% and 0.62%, respectively, and for IAEA-2D reactor 4.96% and 3.52%, respectively. Regarding the results, it was concluded that in order to increase accuracy with the acceptable time of computing (4 Seconds for rectangular geometry and 28 seconds for hexagonal geometry with Intel® Core™ i7-4510U Processor), the Momentum weighting function for rectangular geometry and the Galerkin weighting function for hexagonal geometry can be used to discretize equations without reducing the node size. Therefore, to increase the accuracy while maintaining the speed of calculations, without reducing the size of nodes, the appropriate weighting function can be used in discretization, which can be very useful in performing calculations of different transients.