Characterization of Gamma Knife Perfexion™ source based on Monte Carlo simulation.

This study is aimed at characterizing a single Cobalt-60 source capsule of the Gamma Knife Perfexion™ unit using the BEAMnrc Monte Carlo code. The Gamma Knife Perfexion™ source capsule was modeled using the BEAMnrc user code according to the manufacturer's technical details. The modeled parts include the source, the area around the source, and the capsule. The cylindrical source is 1 mm in diameter and 17 mm in length, with a physical density (ρ) of 8.9 × 103 kg/m3. The simulation parameters were an electron cutoff energy (ECUT) of 0.7 meV and photon cutoff energy (PCUT) of 0.01 meV. Energy fluence was calculated on a 0.25 cm diameter scoring plane located 3.1 cm from the source. Simulations were performed with and without the encapsulation of the source to investigate its effect on the spectrum and fluence of emitted gamma rays. The results showed that the influence of source encapsulation on the gamma rays is an increase in the relative number of particles in each energy bin of aggregate gamma rays by 92.36% at 0.23 meV energy and 66.12% at 1.10 meV energy. The secondary gamma rays were found to increase by 94.17% at 0.23 meV energy and 63.74% at 1.10 meV energy. The encapsulation of the source attenuated the gamma rays, which altered the spectrum. The mean energy of the beam increased, thereby exhibiting a beam-hardening effect.

Radiotracer method for residence time distribution study in multiphase flow system.

[(131)I] isotope in different chemical compounds have been injected into 24in hydrocarbon transmission pipeline containing approximately 95% water, 3% crude oil, 2% gas and negligible solid material, respectively. The system is operated at the temperature around 70 degrees C enabling fluids flow is easier in the pipeline. The segment of measurement was chosen far from the junction point of the pipeline, therefore, it was reasonably to assume that the fluids in such multiphase system were separated distinctively. Expandable tubing of injector was used to ensure that the isotopes were injected at the proper place in the sense that [(131)I]Na isotope was injected into water layer and iodo-benzene, ([131])IC(6)H(5,) was injected into crude oil regime. The radiotracer selection was based on the compatibility of radiotracer with each of fluids under investigation. [(131)I]Na was used for measuring flow of water while iodo-benzene, ([131])IC(6)H(5,) was used for measuring flow of crude oil. Two scintillation detectors were used and they are put at the distances 80 and 100m, respectively, from injection point. The residence time distribution data were utilized for calculation water and crude oil flows. Several injections were conducted in the experiments. Although the crude oil density is lighter than the density of water, the result of measurement shows that the water flow is faster than the crude oil flow. As the system is water-dominated, water may act as carrier and the movement of crude oil is slowed due to friction between crude oil with water and crude oil with gas at top layer. Above of all, this result was able to give answer on the question why crude oil always arrives behind water as it is checked at gathering station. In addition, the flow patterns of the water in the pipeline calculated by Reynolds number and predicted by simple tank-in-series model is turbulence in character.