Luminescence from NaCl for application to retrospective dosimetry

The alkali halide NaCl (Common salt) is an environmentally-abundant phosphor of considerable potential for retrospective dosimetry and radiological event analysis due to its high sensitivity to ionising radiation when analysed by Thermoluminescence (TL), Optically-stimulated luminescence (OSL) or Infrared-stimulated luminescence (IRSL). We report here aspects of luminescence from NaCl relevant to the development of valid protocols for measurement of recent ionising radiation exposure. The timescale of interest in this application is from days to decades, hence our emphasis is on detection and characterisation of TL emission in the 100–300 °C range, and of OSL and IRSL emissions measured following only low temperature preheating (160 °C). A collection of 19 salt samples was assembled, including samples of rock salt and domestic salt produced by evaporation from brine. Analysis of TL emission spectral changes, together with previously reported TL, OSL and IRSL sensitivity changes, confirmed activation of sensitivity change by exposure to temperatures exceeding 160 °C. Kinetic analysis using Chen's method found E = 0.943 eV and s = 5.1 × 10¹¹ s^?1 for the 100 °C TL peak, giving a lifetime at 20 °C consistent with previous calculations and in the range of 7–14 h.     

Identification of irradiated rice noodles by electron spin resonance spectroscopy

Electron spin resonance (ESR) spectroscopy has been applied to the identification of the irradiation of a wide variety of foods. In this study, ESR was applied to identify irradiated rice noodles. A detailed ESR investigation of irradiated noodles was carried out in the dose range 0.5–3 kGy. The stability of the radiation-induced ESR signal at cold (?4 °C) and room (25 °C) temperatures was studied over a storage period of 24 weeks. Irradiated rice noodle samples exhibited a strong, symmetric doublet ESR signal centered at g = 2.0, whereas unirradiated noodle exhibited a very weak signal. The ESR signal intensity increased linearly with radiation dose ranging from 0.5 to 3 kGy. Keeping the samples at ?4 °C and 25 °C for 24 weeks caused decreases of 50% and 90% in the ESR signal intensities, respectively. However, long-term decay data at room temperature showed that the ESR technique could be used to identify irradiated rice noodles up to 24 weeks following irradiation.     

Effects of the experimental conditions on the growth of crystalline ZnSe nano-needles by pulsed laser deposition

Crystalline ZnSe nano-needles have been grown by pulsed laser deposition on Ni-coated substrates. In order to study the mechanism for the growth of ZnSe nano-needles, the experiment conditions including catalyst layer, substrate material, substrate temperature and deposition duration were changed respectively. The catalyst layer plays an important role in the growth of ZnSe nano-needles. The substrate material and substrate temperature also strongly affect the morphologies and structures of the as-grown ZnSe nano-crystals. On 300–400°C Ni-coated silicon (100) substrates, the crystalline ZnSe nano-needles can be grown densely with the middle diameters of about 20–80 nm, and the lengths of 100–400 nm. Two models for the growth of the ZnSe nano-needles and sphere-leading nano-wires under different substrate temperatures are proposed and verified experimentally.     

Acoustic anomalies and relaxation dynamics of relaxor ferroelectric Na1/2Bi1/2TiO3 single crystals studied by using Brillouin spectroscopy

Acoustic anomalies of relaxor ferroelectric Na_1/2Bi_1/2TiO₃ single crystals were investigated over a wide temperature range from −196 °C to 900 °C by using Brillouin spectroscopy. The longitudinal sound velocity, the acoustic absorption coefficient and the elastic constant C₁₁ were determined for the acoustic phonon mode propagating in the [100] direction. Two acoustic anomalies, weaker ones at the cubic-tetragonal phase transition temperature of ~540 °C and more pronounced ones at temperatures near 315 °C near the dielectric maximum temperature, were investigated and discussed in relation with the relevant order parameters coupled to the acoustic waves. The relaxation dynamics in the cubic phase were studied based on the flattening of the mode frequency and the half width, which was observed for the first time, and a modified Arrhenius law.     

Influence of sintering temperatures on LiF:Mg,Cu,P with various magnesium concentrations

The dependence of LiF:Mg,Cu,P samples with various concentrations of Mg on sintering temperatures was investigated to find a new dosimeter. The influence of high sintering temperatures on LiF:Mg,Cu,P chips depends strongly on Mg concentrations. The height of the main peak versus the sintering temperatures exhibits a maximum, the position of which varies between 690 °C and 750 °C, depending on the Mg concentration in the range studied. The high temperature peaks of LiF:Mg,Cu,P for various Mg concentrations reduce basically when the sintering temperature is increased. LiF:Mg,Cu,P is much less sensitive than LiF:Mg,Cu,Si to sintering temperature. LiF:Mg,Cu,P with 0.6 mol% of Mg can be re-used at annealing temperature of 260 °C, regardless of the sintering temperature. It was found that the optimum concentration is Mg: 0.6 mol%, the optimum sintering temperature is 750 °C, considering that LiF:Mg,Cu,P with a low residual signal and good sensitivity can be re-used at annealing temperature of 260 °C and produced in a large scale. The new optimum LiF:Mg,Cu,P formation has 52 times higher than that of the TLD-100, and an extremely low residual signal of 0.07% without an initialization readout procedure.     

Synthesis and study of optical and electrical characteristics of a hybrid structure of single wall carbon nanotubes and silver nanoparticles

Ag nanoparticles of average size 20 nm have been deposited on SWCNT surfaces following a very lucid wet chemical process. The SWCNT/Ag nanohybrid material has been characterized using scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDAX), X-ray diffraction (XRD) analysis and Raman spectroscopy. Both optical and electrical properties of the hybrid have been studied. The hybrid material has been synthesized at 60 °C and treated to higher temperatures. About three-fold increase in photoluminescence (PL) emission intensity has been achieved when the hybrid sample has been treated to 500 °C. DC conductivity at varying temperatures from 77–473 K has been studied. The conductivity of Ag-decorated SWCNTs increased up to 1.76 times of that of pristine SWCNT at a low temperature of 180 K. This hybrid material can find wide application as conducting filler in polymer composite which other filler materials seldom possess.     

Radiation hardening in Zircaloy-2

Annealed Zircaloy-2 was exposed to fast neutron fluences in the range 0.46 to 6.71 × 10¹⁹ nvt, E > 1 MeV, at temperatures of up to 450°C. The level of radiation hardening, as measured by the change in yield stress after irradiation, increased with irradiation temperature at least up to 380°C.

Post-irradiation annealing treatments showed that radiation anneal hardening occurred after irradiation at temperatures up to 325°C. After irradiation at 375°C, annealing treatments did not produce a further increase in the yield stress above that produced by the irradiation, however the radiation hardening persisted to 450°C. The uniform strain tended to decrease as the amount of radiation anneal hardening increased and as the fast neutron fluence increased above ～5 × 10¹⁸ nvt, E > 1 MeV.

The effects of irradiation temperature and post-irradiation annealing on the yield stress and on uniform strain are explained in terms of the strengthening of radiation damage defect clusters and their increased effectiveness to impede dislocation movement.     

Structure and properties of ZnSe nanocomposite thin films

The structure and electrophysical and optical properties of semiconductor ZnSe nanocomposite thin films are studied. These films are obtained by discrete thermal evaporation in an ultrahigh vacuum. ZnSe films are synthesized in various structural states in the condensation temperature range 2–200°C. The optical spectra of these films are studied in the visible region.     

Impedance spectroscopy and dielectric analysis in KH2PO4 single crystal

Optical observation, differential scanning calorimetry, thermogravimetric analysis, and differential thermogravimetric measurements have been carried out on KH₂PO₄ single crystals. As compared with the optical observation of crystal under polarizing microscope, the dehydration process occurred gradually over the crystal surface at temperatures above 195 °C and then the interior of the sample. The ac impedance measurements were performed as a function of both frequency and temperature. The electrical conduction and dielectric relaxation have been studied. The activation energy of migration is 1.02 eV in the temperature range between 150 and 179 °C. The conduction mechanism in this temperature range is attributed to the hopping of proton among hydrogen vacancies. At temperatures above 186 °C, a higher conductivity activation energy with 2.94 eV is obtained. In addition to the proton conduction, the migration of the heavier ions (such as potassium ion) is also suggested.     

Characterization and organic electric-double-layer-capacitor application of KOH activated coal-tar-pitch-based carbons: Effect of carbonization temperature

The present study reports the influence of pre-carbonization on the properties of KOH-activated coal tar pitch (CTP). The change of crystallinity and pore structure of pre-carbonized CTPs as well as their activated carbons (ACs) as function of pre-carbonization temperature are investigated. The crystallinity of pre-carbonized CTPs increases with increasing the carbonization temperature up to 600 °C, but a disorder occurs during the carbonization around 700 °C and an order happens gradually with increasing the carbonization temperatures in range of 800–1000 °C. The CTPs pre-carbonized at high temperatures are more difficult to be activated with KOH than those pre-carbonized at low temperatures due to the increase of micro-crystalline size and the decrease of surface functional groups. The micro-pores and meso-pores are well developed at around 1.0 nm and 2.4 nm, respectively, as the ACs are pre-carbonized at temperatures of 500–600 °C, exhibiting high specific capacitances as electrode materials for electric double layer capacitor (EDLC). Although the specific surface area (SSA) and pore volume of ACs pre-carbonized at temperatures of 900–1000 °C are extraordinary low (non-porous) as compared to those of AC pre-carbonized at 600 °C, their specific capacitances are comparable to each other. The large specific capacitances with low SSA ACs can be attributed to the structural change resulting from the electrochemical activation during the 1st charge above 2.0 V.     

High‐temperature tensile cell for in situ real‐time investigation of carbon fibre carbonization and graphitization processes

A new high‐temperature fibre tensile cell is described, developed for use at the Advanced Photon Source at Argonne National Laboratory to enable the investigation of the carbonization and graphitization processes during carbon fibre production. This cell is used to heat precursor fibre bundles to temperatures up to ～2300°C in a controlled inert atmosphere, while applying tensile stress to facilitate formation of highly oriented graphitic microstructure; evolution of the microstructure as a function of temperature and time during the carbonization and higher‐temperature graphitization processes can then be monitored by collecting real‐time wide‐angle X‐ray diffraction (WAXD) patterns. As an example, the carbonization and graphitization behaviour of an oxidized polyacrylonitrile fibre was studied up to a temperature of ～1750°C. Real‐time WAXD revealed the gradual increase in microstructure alignment with the fibre axis with increasing temperature over the temperature range 600–1100°C. Above 1100°C, no further changes in orientation were observed. The overall magnitude of change increased with increasing applied tensile stress during carbonization. As a second example, the high‐temperature graphitizability of PAN‐ and pitch‐derived commercial carbon fibres was studied. Here, the magnitude of graphitic microstructure evolution of the pitch‐derived fibre far exceeded that of the PAN‐derived fibres at temperatures up to ～2300°C, indicating its facile graphitizability.     

Time-resolved OSL studies on BeO ceramics

Time-Resolved Optically Stimulated Luminescence (TR-OSL) from BeO ceramics was investigated using a blue laser (445 nm) as stimulation light source. It was observed that, at relatively low dose levels (up to ∼25 Gy) the TR-OSL decay curve can be approximated with a single exponential decay function with a lifetime of ∼26 μs at room temperature. Beyond 25 Gy a new decay component with a lifetime of a ∼2 μs was observed in addition to the ∼26 μs component. Thermal stability, radiation dose response, optical bleaching, measurement temperature dependence of the components of the TR-OSL signal were investigated in detail. As result of these studies, a new OSL component which becomes unstable after 150 °C was observed. OSL decay rate of this component was found to be higher than the one which becomes unstable after 300 °C. In order to obtain information about the temperature dependence of the luminescence efficiency, luminescence emission lifetime was determined in the temperature range from 30 to 130 °C with 10 °C steps. Using the temperature dependence of the lifetime, thermal quenching energy was determined to be around 0.56 eV for the 26 μs component. For the ∼2 μs component an enhancement in the component intensity was observed pointing to a thermally assisted process with activation energy of 0.15 eV.     

Properties of Eu-doped zinc oxide thin films grown on glass substrates by radio-frequency magnetron sputtering

Eu-doped ZnO (EZO) thin films were prepared on glass substrates at various growth temperatures by radio-frequency magnetron sputtering. The properties of deposited thin films showed a significant dependence on the growth temperature. The preferential growth orientation of all the thin films was occurred along the ZnO (002) plane. The maximum crystallite size and the minimum average transmittance in the wavelength range of 450–1100 nm were observed for the EZO thin film deposited at 25 °C. A red shift of the optical band gap was observed in the growth temperature range of 25–300 °C. The highest figure of merit, an index for evaluating the performance of transparent conducting thin films, was obtained at 200 °C of growth temperature. These results indicated that the high-quality EZO film was obtained at a growth temperature of 200 °C.     

High-dose high-temperature emission of LiF:Mg,Cu,P: Thermally and radiation induced loss & recovery of its sensitivity

Highly sensitive LiF:Mg,Cu,P (MCP) detectors enable measurements of radiation doses from tens of nanograys up to a few kilograys, where the saturation of the signal of the main dosimetric peak occurs. Thanks to the recently observed high-dose high-temperature emission of MCP detectors heated to temperatures up to 600 °C after exposures to radiation doses ranging from 1 kGy to 1 MGy, a new method of thermoluminescent measurement of radiation doses has been recently developed at the Institute of Nuclear Physics (IFJ). This method can measure doses ranging from micrograys up to a megagray. So far, high dose measurements were performed on fresh MCP samples and each detector was used only once, because as a result of these measurements, the detectors lose their sensitivity to a large extent. In this study, a specific thermal treatment intended to fully restore the loss of MCPs TL sensitivity was sought. We have investigated several annealing procedures, applying different temperatures (from 400 °C up to 700 °C) for different periods of time (10–30 min) in argon atmosphere. In this way we were able to recover MCP sensitivity fully, allowing for reuse of the samples after high-dose irradiation and high-temperature measurement.     

Correlation between sintering temperature and properties of ZnO ceramic varistors

The effect of sintering temperature on ZnO varistor properties is investigated in the range of 700–1400 °C. The increase of sintering temperature does not influence the well-known peaks related to hexagonal wurtzite structure of ZnO ceramics, whereas the average grain size is increased from (1.08 to 2.1 μm). With increasing sintering temperature up to 1200 °C, the nonlinear region is clearly observed in the I–V characteristics, whereas this region is completely absent only for the sample sintered at 1400 °C. As the sintering temperature increased, the breakdown field decreased over a wide range from 2838.7 to 6.41 V/cm, while the nonlinear coefficient is increased in the range of (23.86–47.76). Furthermore, the barrier height decreased from 1.76 to 0.974 eV, whereas electrical conductivity is improved. On the other hand, the optical band gap is gradually decreased in the range of 3.08–2.70 eV with increasing sintering temperature. These results showed a strong correlation between sintering temperature and the properties of ZnO ceramic varistor.     

Effect of Temperature on Cononsolvency of Polyvinylpyrrolidone in Water/Methanol Mixture

The behavior of polyvinylpyrrolidone in mixed water/methanol solvents was studied by rheoviscosimetry over a temperature range of 20°C–40°C. For the lower temperatures of this range, the intrinsic viscosity variation of the polymer vs. methanol molar fraction shows structural transitions (coil–globule–coil). This transition, which is usually attributed to the cononsolvency phenomenon, agrees with our previously published results obtained by dynamic light scattering. For higher temperatures, near 40°C, the intrinsic viscosity increase shows an expansion of the polymer over the alcohol molar fraction range 0.2 < X _A < 0.5. This last result can be attributed to the water/alcohol complex destruction under temperature increase. The “excess viscosity” of the polymer-mixed solvents vanishes with increasing temperature and becomes positive at 40°C. So, the polymer chain tends to transit from a globular to an ideal chain in the middle composition range of the mixed solvents.     

Laser-Excited Volume Secondary Radiation in Wide-Gap Semiconductors and Dielectrics

Studies of the volume secondary radiation (photoluminescence and Raman scattering) in wide-gap semiconductors (GaP, ZnSe) and condensed dielectrics were carried out at various temperatures. The low-temperature variations of the dielectric constants were evaluated. The anti-Stokes photoluminescence from the sample bulk, resulting from interband and impurity recombination, was observed for the first time when exciting the spectra of secondary radiation by the continuous radiation of a low-power helium--neon laser with the lasing line in the transparency region of gallium phosphide. A similar effect was observed at low temperatures in zinc selenide excited by an argon laser. Photoluminescence from the sample bulk was also found for a number of condensed dielectrics (hydrocarbons and oil) at room temperature. The results obtained allow analysis of impurities in the bulk of semiconductors and dielectrics based on recording the volume photoluminescence spectra.     

Structural characterisation of the silica and alumina Zener pinning phases in nanocrystalline CeO2 by 29Si and 27Al nuclear magnetic resonance

Nanocrystalline CeO₂ samples have been manufactured using sol-gel techniques, containing either 15 % silica or 10 % alumina by weight to restrict growth of the ceria nanocrystals during annealing by Zener pinning. ²⁹Si and ²⁷Al MAS NMR have been used to investigate the structure of these pinning phases over a range of annealing temperatures up to 1000 °C, and their effect on the CeO₂ morphology has been studied using electron microscopy. The silica pinning phase resulted in CeO₂ nanocrystals of average diameter 19 nm after annealing at 1000 °C, whereas the alumina pinned nanocrystals grew to 88 nm at the same temperature. The silica pinning phase was found to contain a significant amount of inherent disorder indicated by the presence of lower n Qⁿ species even after annealing at 1000 °C. The alumina phase was less successful at restricting the growth of the ceria nanocrystals, and tended to separate into larger agglomerations of amorphous alumina, which crystallised to a transition alumina phase at higher temperatures.     

Reliability of single aliquot regenerative protocol (SAR) for dose estimation in quartz at different burial temperatures: A simulation study

The single aliquot regenerative protocol (SAR) is a well-established technique for estimating naturally acquired radiation doses in quartz. This simulation work examines the reliability of SAR protocol for samples which experienced different ambient temperatures in nature in the range of −10 to 40 °C. The contribution of various experimental variables used in SAR protocols to the accuracy and precision of the method is simulated for different ambient temperatures. Specifically the effects of paleo-dose, test dose, pre-heating temperature and cut-heat temperature on the accuracy of equivalent dose (ED) estimation are simulated by using random combinations of the concentrations of traps and centers using a previously published comprehensive quartz model. The findings suggest that the ambient temperature has a significant bearing on the reliability of natural dose estimation using SAR protocol, especially for ambient temperatures above 0 °C. The main source of these inaccuracies seems to be thermal sensitization of the quartz samples caused by the well-known thermal transfer of holes between luminescence centers in quartz. The simulations suggest that most of this inaccuracy in the dose estimation can be removed by delivering the laboratory doses in pulses (pulsed irradiation procedures).     

Gamma ray induced sensitization of 110°C TL peak in quartz separated from sand

We have investigated the gamma ray induced sensitization of the 110°C TL peak in quartz, separated from sand, in the dose range 30–750 Gy. A pre-dose of 100 Gy followed by annealing at 500°C for 1 h yielded an optimum sensitization factor of 14.2 for a test gamma dose of 0.5 Gy; this factor decreases slowly up to the studied pre-gamma dose of 750 Gy. From ESR studies carried out in the temperature range 25–550°C, the formation of E′₁-centres and their subsequent decay (at temperatures >400°C) have been observed. The released charge carriers (electrons) may lead to elimination of competitors (as a result of their filling up). Thus, the radiation-induced sensitization of the 110°C TL peak could be due to elimination of the competing deep traps.