Thermal and epithermal neutron flux distributions measurement in thermal column of TRR using an experimental-simulation method.
For designing an appropriate neutron beam, the determination of neutron flux at any irradiation facility is an important key factor. Due to the importance of determining the thermal and epithermal neutron fluxes in a typical thermal column of a reactor, a simple and accurate technique is introduced in this study. Absolute thermal and epithermal fluxes were measured experimentally at a certain point using the foil activation method by neutron bombardment of bare and cadmium covered Au foils. The relative neutron fluxes were also derived simply by means of Monte Carlo simulation by accurate modelling of the reactor components. Finally, by normalization of the relative distribution flux with regard to information about the absolute neutron flux, the accurate thermal and epithermal neutron distributions were derived, separately.
Neutron irradiation tests on B4C/epoxy composite for neutron shielding application and the parameters assay
Abstract In this investigation, epoxy resin with a low viscosity amine-based curing agent was chosen as matrix and additives were added to epoxy resin using low speed stirring with ultrasonic waves approach. The chemical stability of resin during fabrication of composites was studied with Fourier transform infrared spectroscopy (FTIR). The effect of B4C particle size (20 and 150 µm) on neutron shielding was investigated. Besides, in order to develop the high performance composites, the effect of ATH (flame retardant) and WO3 powders (for shielding from against gamma rays) on neutron shielding property is considered. The neutron experiments were based on foil activation analysis in thermal column of Tehran Research Reactor (TRR). According to experimental data, required shield thickness (B4C, 150 µm, 3 wt%) for 80% absorption of neutron fluence was calculated about 9.8 mm. Consequently, data show thermal neutron absorption is dependent also on the size of the boron compound filler and show a significant enhancement in shielding performance when using smaller particle size of B4C filler. Furthermore, data obviously show that the neutron attenuation coefficient of reinforced composites increases to 0.345 cm−1 for B4C (20 µm, 5 wt%)/ Epoxy composite shield. As clearly data indicate, adding WO3 and ATH additive had a significant influence on the thermal neutron attenuation property and hybrid shield shows an enhancement of more than 60% in shielding performance.
A case of treatment-related leukoencephalpathy: sequential MRI, CT and PET findings
SummaryA case of treatment-related leukoencephalopathy is presented. A patient with medulloblastoma was postoperatively treated with craniospinal axis irradiation. One month after irradiation, weekly intrathecal administration of methotrexate was performed 4 times to treat cerebrospinal fluid dissemination of the tumor. Two months after the initiation of intrathecal chemotherapy, the patient became somnolent and developed decerebrate posturing. Magnetic resonance imaging showed diffuse leukoencephalopathy. Positron emission tomography revealed a diffuse decrease in glucose uptake in the deep white matter. Auditory evoked potential also showed diffuse abnormalities, not only in the cerebrum, but also in the brain stem. High dose intravenous leucovorin rescue was attempted without any neurologic improvement.