Search Results
Radiation effects in the transient hot-wire technique
Measurement of the thermal conductivity of n -pentane
Abstract
The transient hot-wire technique is widely used for absolute measurements of the thermal conductivity and thermal diffusivity of fluids. It is well established that fluid radiation effects significantly influence these measurements, especially those for the thermal diffusivity. Corrections for radiation effects are based on the models developed and deviations of the measured data from the ideal line source model. In this paper, the effect of fluid radiation on the measurements of the thermal conductivity of n-pentane is presented. For comparison, the influence of thermal radiation effect on measurement of transparent fluids, such as argon is also shown. The difference between the influence of natural convection and thermal radiation is also demonstrated.
Abstract
The aim of this work is to study the ionizing radiation effects on thermal properties of there cycled polyamide-6. This polymer was irradiated with an electron beam of 1.5 MeV with different doses. The thermal properties of the samples were determined by TG, DSC and DMA measurements. It was observed that the irradiated samples of recycled polyamide-6undergo a crosslinking process.
Abstract
In the field of radiation effects in materials, a detailed and precise description of the radiation environment used to damage samples is often required to make sense of subsequent materials analysis. The types of reactions and extent of damage that occur during irradiation strongly depend on the flux spectrum of the particular facility. Different neutron activation techniques for characterizing neutron flux spectra were performed on the University of Texas at Austin TRIGA research reactor’s in-core facilities. The results were compared in terms of spectral detail and precision. Activation of Au foils with multiple correction factors, and multiple foil activation employing different deconvolution techniques comprise the methods tested.
Fluid radiation effects in the transient hot-wire technique
Measurement of thermal conductivity of propane
Abstract
The transient hot-wire technique is widely used for absolute measurements of the thermal conductivity of fluids. Refinement of this method has resulted in a capability for accurate and simultaneous measurement of both thermal conductivity and thermal diffusivity together with a determination of the specific heat. However, these measurements, especially those for the thermal diffusivity, may be significantly influenced by fluid radiation. The present work investigates the effect of fluid radiation on the measurements of the thermal conductivity of propane. Recently developed corrections have been used to examine this assumption and rectify the influence of even weak fluid radiation. Measurements at 372 K with a hot-wire instrument demonstrate the presence of radiation effects in both the liquid and vapor phase. The influence is much more pronounced in liquid propane at 15.5 MPa than in the vapor phase at 881.5 kPa. The technique employed to obtain radiation-free thermal conductivity measurements is described.
Abstract
Radiation effects on the extraction of Am(III) with di (2-ethylhexyl) phosphoric acid (DEHPA) was studied by exposing DEHPA to gamma rays under various conditions. Gamma irradiation of undiluted DEHPA causes an enhancement of extraction of Am(III) due to the formation of mono (2-ethylhexyl) phosphoric acid (MEHPA) similarly to that of Nd(III). The presence of diluent during irradiation brought about a slight difference from the results in the absence of a diluent. The marked change occurred in Df when the organic solvent was exposed to γ-ray while being mixed with nitric acid solution. An initial slight increase of Df for Am(III) and Nd(III) was followed by a subsequent decrease beyond an absorbed dose of approximately 200 Wh·1−1. This phenomenon was explained by the enhanced decomposition of DEHPA and the subsequent strong hydrolytic and radiolytic decomposition of MEHPA to H3PO4 in the aqueous phase, and the complex forming nature of H3PO4 with Am(III) and Nd(III).
Abstract
Radiation effects on the extraction of americium(III) with several dialkylphosphoric and monoalkylphosphoric acids have been studied comparatively. The extractants were exposed to60Co γ-rays in the absence and presence of diluent and HNO3. The Df of Am(III) was measured and the yield of radiolytic products was determined after γ-irradiation as a function of the absorbed dose. Di(hexoxyethyl)phosphoric acid was the most susceptible to radiation among the extractants studied and its extractability was weakened by radiation regardless of the presence or absence of diluent or HNO3. Diisodecylphosphoric acid itself showed an enhancement upon irradiation but incurred a depressant effect upon intimate contact with HNO3·Mono(2-ethylhexyl)phosphoric acid showed a decrease of the Df of Am(III), similarly to DIDPA in the presence of HNO3 during γ-irradiation. All the above extractants gave H3PO4 as the principal radiolytic product upon γ-irradiation upon intimate contact with HNO3 causing decreasing solely the extraction of Am(III). Di(2-ethylhexyl)phosphoric acid proved to be the most stable extractant to radiation among those studied.
Abstract
The thermal decomposition kinetics of irradiated and unirradiated ammonium perchlorate and ammonium perchlorate powder-aluminum particle mixtures has been studied by determining decomposition gas pressurevs. heating time with samples at a controlled temperature Qualitatively the radiation induced changes are similar to those obtained in previous studies on ‘pure’ ammonium perchlorate. The induction period is shortened and the acceleratory and decay period rate constants are increased. The data have been analyzed using Avrami-Erofeev kinetics. The results for pure unirradiated material are in accord with published results. The activation energies for the induction, acceleratory and decay periods for pure pellets were found to be 133.5±6.7, 131.8±6.7 and 127.2±6.7 kJ·mol, respectively. Samples were exposed to either a single gamma-ray irradiation, fission neutron irradiation followed by a gamma-ray irradiation, or to a proton irradiation. When compared on an equal energy deposited basis, the fast neutron induced changes are appreciably larger than the gamma-ray changes. However, the proton induced changes are comparable or slightly more than the gamma-ray effects. Some, or all, of the fast neutron effects can be attributable to the concentrated radiation damage ‘spikes’ along the path of lattice atom recoils. It is likely that these become thermal decomposition sites when the crystals are heated. Protons create fewer spikes than fast neutrons. Overall, the results indicate that any ammonium perchlorate-aluminum propellant mixtures that may be exposed to radiation environments, such as used in this study, should be subjected to a thorough radiation effects analysis if reliable performance is required.
Abstract
Laboratory experiments were performed on the sorption of cesium on gamma-irradiated silica-titania gel. The detrimental effects of absorbed dose on the affinity of the sorbent towards cesium was discussed. Data obtained from sorption studies were fit into heterogeneity based Freundlich isotherm. The empirical parameters, thus obtained were used to arrive at the site distribution function. The potential of site distribution function in foreseeing, the reusability and long-term residence of radionuclides in the sorbent has been highlighted.
Abstract
Thermal decomposition of 
-irradiated (dose: 0–3.6 MGy) ammonium perchlorate was followed. The dynamic heating (range: 100–220 °C) and IR spectral measurements were carried out simultaneously. Temperature and dose brought a lowering in peak intensity of NH
4
+
and C10
4
–
ions. Radiolytic products C103 and NH3 are considered to initiate the decomposition process.
The observation of chromosome aberration frequency in lymphocyte karyotype is the conclusive method to assess the absorbed dose of ionizing radiation. Our study compared the incidence of chromosome aberrations in occupationally exposed healthy medical workers and in not exposed healthy population. We analyzed the effect of working place, dose by thermo luminescence dosimeter (TLD), duration of occupational exposure (DOE) and age on the sum of aberrant cells and aberrations. The four-year study included 462 subjects with a mean age of 42.3 years, who were occupationally exposed to ionizing radiation and 95 subjects with a mean age of 35.2 years, who were not exposed to ionizing radiation, during the same time period and from the same territory. All of them possess TLD which is read by a scanner for thermo luminescence dosimeters. Modified Moorhead’s micro method for peripheral blood lymphocytes and conventional cytogenetic technique of chromosome aberration analysis were used for the analysis of chromosome aberrations. Stained preparations (Gyms) are observed in immersion by light microscope. The karyotype of 200 lymphocytes in metaphase is analyzed; the most characteristic aberration: dicentric, then the ring and acentric fragments. The incidence of chromosome aberrations was found to be 21.6% in the exposed group and 2.1% in the controls, while the “findings within the limits” (non-specific chromosome lesions – gaps, breaks, elongations, and exchanges) were equal in the two groups (22%). Among occupationally exposed medical workers, the highest incidence was found in nuclear medicine workers (42.6%), then in orthopedists (27.08%). There is a highly significant difference of the number of aberrant cells and the sum of chromosome aberrations between the exposed and control groups ( p < 0.001). The sum of chromosome aberrations and the number of aberrant cells were in positive correlation with the duration of exposure ( p < 0.001), and to a less degree of probability with the age ( p < 0.05) in the exposed workers. In the controls, this correlation was negative and insignificant. The group of subjects with a duration of occupational exposure up to 15 years had a significantly smaller number of aberrant cells and chromosome aberrations in comparison to the subjects with longer duration of occupational exposure, over 15 years.
