ABSTRACT
In this research, thermal neutrons albedo coefficients and relative number of excess counts have been measured experimentally for different thicknesses of two-layer reflectors by using 241Am-Be neutron source (5.2Ci) and BF3 detector. Our used reflectors consist of two-layer which are combinations of water, graphite, polyethylene, and lead materials. Experimental results reveal that thermal neutron reflection coefficients slightly increased by addition of the second layer. The maximum value of growth for thermal neutrons albedo is obtained for lead-polyethylene compound (0.72 ± 0.01). Also, there is suitable agreement between the experimental values and simulation results by using MCNPX code.
ABSTRACT
In the present work, thermal properties of low density polyethylene (LDPE) and its nano composites are investigated. For this purpose LDPE reinforced with different weight percents of hydroxyapatite (HAP) powder which was synthesized via hydrolysis method are produced. The samples were irradiated with 10MeV electron beam at doses of 75 to 250kGy. Specific heat capacity measurement have been carried out at different temperatures, i.e. 25, 50, 75 and 100°C using modulated temperature differential scanning calorimetry (MTDSC) apparatus and the effect of three parameters include of temperature, irradiation dose and the amount of HAP nano particles as additives on the specific heat capacity of PE/HAP have been investigated precisely. The MTDSC results indicate that the specific heat capacity have decreased by addition of nano sized HAP as reinforcement for LDPE. On the other hand, the effect of radiation dose is reduction in the specific heat capacity in all materials including LDPE and its nano composites. The HAP nano particles along with cross-link junctions due to radiation restrain the movement of the polymer chains in the vicinity of each particle and improve the immobility of polymer chains and consequently lead to reduction in specific heat capacity. Also, the obtained results confirm that the radiation effect on the specific heat capacity is more efficient than the reinforcing effect of nano-sized hydroxyapatite.
Subject(s)
Durapatite/chemistry , Electrons , Hot Temperature , Nanocomposites/chemistry , Polyethylene/chemistry , Cross-Linking Reagents/chemistry , Molecular WeightABSTRACT
The suitability of nano-structured hydroxyapatite (HAP) for use as a thermoluminescence dosimeter was investigated. HAP samples were synthesized using a hydrolysis method. The formation of nanoparticles was confirmed by X-ray diffraction and average particle size was estimated to be ~30 nm. The glow curve exhibited a peak centered at around 200 °C. The additive dose method was applied and this showed that the thermoluminescence (TL) glow curves follow first-order kinetics due to the non-shifting nature of Tm after different doses. The numbers of overlapping peaks and related kinetic parameters were identified from Tm -Tstop through computerized glow curve deconvolution methods. The dependence of the TL responses on radiation dose was studied and a linear dose response up to 1000 Gy was observed for the samples.
Subject(s)
Durapatite/chemistry , Durapatite/radiation effects , Gamma Rays , Luminescence , Nanostructures/chemistry , Nanostructures/radiation effects , TemperatureABSTRACT
In this paper, the gamma-irradiated EPR responses of hydroxyapatite (HAP) samples were investigated from a dosimetric point of view. For this purpose, nano-structure hydroxyapatite was synthesised via a hydrolysis method. A portion of the produced powder was annealed at 600 °C for 4 h. All the samples were irradiated under the (60)Co gamma-ray source at different absorbed doses from 0.1 to 45 kGy. EPR signal intensities of HAP samples were measured at room temperature in air. Subsequently, the EPR signal intensities were constructed as a function of radiation dose and were compared with the results of bone powder samples. The results show that the EPR responses of non-annealed HAP samples are higher than others for several times.
Subject(s)
Cobalt Radioisotopes/chemistry , Durapatite/chemistry , Absorption , Animals , Bone and Bones/pathology , Cattle , Dose-Response Relationship, Radiation , Electron Spin Resonance Spectroscopy , Gamma Rays , Hydrolysis , Microscopy, Electron, Transmission/methods , Powders , Radiation Dosage , Radiometry/methods , Temperature , Time Factors , X-Ray DiffractionABSTRACT
Micro and nano-structure hydroxyapatite samples were synthesized via several different methods. The samples were characterised utilising the Fourier transmission infra-red, scanning electron microscope and X-ray diffraction methods, to find out the structure most similar to human tooth enamel, and the best method was found. The electron paramagnetic resonance (EPR) signals of the gamma-irradiated samples were measured using an EPR spectrometer system. A calibration curve was established by irradiation of the samples at four doses of 50-500 mGy. The parameters of the calibration curve, slope and intercept with dose axis are determined by linear regression analysis. This calibration curve can be used for human tooth enamel for retrospective dosimetry purposes.
