Effect of gamma energy, temperature and shelf life on the response of gamma and BD-100R neutron bubble detectors

The use of commercially available bubble detectors for gamma and neutron detection has been reported by several groups. We have carried out systematic investigations to study the response of gamma bubble detector as a function of energy, the effect of waiting time on sensitivity of BD-100R neutron bubble detector and the effect of shelf life on both types of bubble detectors. Our results show that the response of the gamma bubble detector is energy dependent. Waiting time of up to 260 hours for BD-100R neutron detector has no significant effect. Both the detectors have a limited shelf life. These factors must be taken into account while using these detectors.     

Angular and dose dependence of CR-39 neutron response for shape-selected tracks

A shape selection method corresponding to an energy discrimination was used to eliminate unwanted events disturbing evaluation of CR-39 detectors in detecting tracks induced by particles both of perpendicular and oblique incidence. The angular dependence of the response was examined, detecting fast neutrons from ²⁵²Cf with shape selection technique at various angles and distances. Also, the CR-39 track detectors with the ²⁵²Cf source were exposed to high γ-intensity of a ⁶⁰Co irradiation facility in the range 0.1 to 4.5 kGy, similar to the exposures inside spent fuel assemblies. Using the two functions the lower limit of burnup could be determined by the method.     

Registration temperature effect on sensitivity of CR-39(DOP) and SR-90 polymer track detectors

The samples of CR-39(DOP) and SR-90 polymer track detectors have been exposed to -particles from ²⁴¹Am source in an exposure unit. The temperature of the detectors during irradiation has been varied from −30°C to 70°C. These exposed samples have been etched in 6.25 N NaOH solution at 60°C for various etching times. The variation of sensitivity of these detectors as a function of registration temperature has been studied. It has been observed that at the fixed registration temperature, the sensitivity of SR-90 is more than CR-39(DOP) polymer track detector. However, the enhancement in sensitivity with the decrease in registration temperature is more pronounced in case of CR-39(DOP) than SR-90.     

Intercomparison of the response of different photon and neutron detectors around a spent fuel cask

An intercomparison of the response of different photon and neutron detectors was performed in several measurement positions around a spent fuel cask (type TN 12/2B) filled with 4 MOX and 8 UO₂ 15 × 15 PWR fuel assemblies at the nuclear power plant Gösgen (KKG) in Switzerland. The instruments used in the study were both active and passive, photon and neutron detectors calibrated either for ambient or personal dose equivalent.The aim of the measurement campaign was to compare the responses of the radiation instruments to routinely used detectors.It has been shown that especially the indications of the neutron detectors are strongly dependent on the neutron spectra around the cask due to their different energy responses. However, routinely used active photon and neutron detectors were shown to be reliable instruments.     

Thermal stability of the structural features in the superhydrophobic boehmite films on austenitic stainless steels

Boehmite thin film with 50–100 nm surface flake structure has been synthesized on AISI 316 type austenitic stainless steel by immersing boehmite gel film into boiling water. When further coated with hydrolyzed (heptadecafluoro-1,1,2,2-tetrahydrodecyl) trimethoxysilane (FAS), the boehmite film becomes superhydrophobic with a contact angle for water of 152°. The superhydrophobic property results from both the nanoscale surface flake structure and the low surface energy of the FAS top layer. The topography of such film was revealed by atomic force microscope (AFM) and a set of roughness parameters of such film was discussed. The degradation of superhydrophobicity of the surface was studied as a function of the heat-treatment temperatures. Below 600 °C, the surface remained to be superhydrophobic with the FAS top layer. Above 700 °C, the surface was not superhydrophobic anymore due to a gradual loss in surface roughness which was revealed by field emission scanning electron microscope (FESEM). A phase change from boehmite to γ-Al₂O₃ occurred during the heat-treatments from 700 to 900 °C which was studied by the selected area electron diffraction (SAED) patterns from the transmission electron microscope (TEM) measurement.     

Comparison of blue and red TL from quartz

Following a suggestion by Scholefield and Prescott that blue and red emissions in quartz may involve the same electron traps, we have made a detailed study of blue and red TL glow peaks in some Australian sedimentary quartz samples (Scholefield, R.B., Prescott, J.R., 1999. The red thermoluminescence of quartz: 3-D spectral measurements. Radiat. Meas. 30, pp. 83–95). Allowing for thermal quenching of the blue TL, the Rapidly Bleaching Peak (at 325°C for a ramp rate of 20 K s⁻¹) and the low temperature peaks at 140–220°C appear to be identical in the blue and red. We conclude that the electron traps are the same, but that the blue and red luminescence centers probably do not occur in the same grains. On present evidence we cannot determine whether or not the Slowly Bleaching Peak (at 375°C for 20 K s⁻¹) involves the same traps in the blue as in the red. As did Scholefield and Prescott, we find no evidence of a red peak at 100°C.     

Status of bubble detectors for high-energy heavy ions

Five types of bubble detectors (T-15, T-34, T-12, T-24 and T-14) of large volume and different sensitivities were developed in the China Institute of Atomic Energy for the purpose of heavy ion research. Calibrations were carried out with beams of high-energy protons, He, C, Si, Ar, Fe, Kr and Xe, at accelerators in the energy region 150–650 MeV/u. The bubble detectors were demonstrated to be a family of detectors for recording tracks of high-energy heavy ions with atomic numbers from Z=1 (proton) to all the numbers in the whole periodic table of elements. The threshold levels of the detectors differ from each other with values 0.05±0.01 (T-15), 1.62±0.05 (T-34), 1.68±0.03 (T-12), 2.24±0.06 (T-24) and 6.04±0.80 (T-14) MeVmg⁻¹ cm², respectively, which are about the same or even lower than the levels of plastic track detectors for recording heavy ions. The distinguishing features of bubble detectors are high sensitivity, active recording, real-time display, volume registration and background discriminating capacities. Bubble detectors are a new type of high sensitivity detectors and are very promising for detection of heavy ions, neutrons and exotic particles.     

Thermal annealing of proton tracks with energies of 4 and 6 MeV in CR-39 polymer detectors

In this paper, we study the thermal annealing of proton tracks of 4 and 6 MeV at temperatures ranging from 150 to 240°C in CR-39 polymer detectors. A special experimental set-up for irradiating the detectors was arranged to obtain adequate proton beams from the Cyclotron CV-28 at IPEN/SP, Brazil. We report experimental data on track densities, track diameters, and activation energies based on current annealing models for the annealing of proton tracks in the energy range investigated. A value of (0.20±0.02)eV was determined as the mean activation energy of the annealing process in CR-39 detectors.     

Structural evolution of Sc-containing zirconia electrolytes

A powder of nominal composition (ZrO₂)_0.886(Sc₂O₃)_0.104(Al₂O₃)_0.01 was synthesized by spray drying with the purpose of testing the performance of solid oxide fuel cells containing scandia-stabilized zirconia (ScSZ) as electrolyte. The phases resulting from calcination and sintering at different temperatures were investigated by XRD, impedance and Raman spectroscopy. At sintering temperatures of 1200–1400 °C nearly equal amounts of cubic and rhombohedral ScSZ were detected, whereas heat treatment higher than 1500 °C led to a cubic single-phase material. A preliminary reaction mechanism of phase formation is proposed with respect to the various results depending on heat treatment.     

Electrical properties of calcia-doped ceria with oxygen ion conduction

The electrical conductivity of sintered specimens of (CeO₂)_1−x(CaO)_x was investigated by employing a standard four-probe dc technique as a function of temperature between 400°C and 900°C, composition from 0.10x0.80, and oxygen partial pressure from 10⁻¹⁸ to 1 atm. The temperature and composition dependence of the emf have been carried out with a concentration cell. X-ray diffraction studies indicated that a cubic fluorite crystal remained in all specimens studied, although the solubility limit of CaO in CeO₂ was assumed to lie close to 23 mol% from the change of the lattice constant. The magnitude of the conductivity decreased slightly with increase of the dopant concentrations up to x=0.50. The conductivity of these specimens was about 100 times larger than that of calcia-stabilized zirconia at 600°C with a smaller activation energies of 0.83–0.89 eV. With further increasing dopant concentrations, the magnitude of the conductivity was found to decrease remarkably. With an increase in the dopant concentration, the domain of primarily ionic conduction extended to a lower partial pressure. The conductivity of (CeO₂)_0.50(CaO)_0.50 was found to be primarily ionic down to 10⁻¹² atm even at 900°C. These results indicate that CaO-doped CeO₂ may be more an attractive candidate for fuel cells and other applications.     

The temperature dependence of the short wavelength transmittance limit of vacuum ultraviolet window materials—I. Experiment

The short wavelength transmittance limit or cut-off wavelength, λ_co, of LiF, MgF₂, CaF₂, LaF₃, BaF₂, sapphire, synthetic crystal quartz and fused quartz has been measured from about 100°C to about 10°K. λ_co is not a well denned quantity, so for the purpose of this experiment it has been arbitrarily taken as the wavelength where transmittance could just be measured, usually 0.1-0.5 per cent. With one exception λ_co shifted to shorter wavelengths as the sample was cooled; the shift varied from about 40 to 80 Å over the temperature range from 100°C to 10°K, depending on the material, with the largest shift occurring in BaF₂;. The exception was LaF₃ which showed no measurable change in λ_co wth temperature. Over the temperature range from 20° to 100°C the slope of λ_co, with temperature for all materials was fairly constant, but below 20°C it decreased, approaching zero as the temperature approached 20°-10°K. In the case of synthetic crystal quartz, for example, the slope changed from about 0.28 Å/°K at room temperature to about 0.055 Å/°K at 80°K.     

Ln1−xSrxCoO3(Ln = Sm, Dy) for the electrode of solid oxide fuel cells

The perovskite-type oxides were synthesized in the series of Ln_1−xSr_xCoO₃(Ln = Sm, Dy). The formation of solid solutions in Dy_{1 − x}Sr_xCoO₃ was limited, compared with that in Sm_{1 − x}Sr_xCoO₃. The electrical conductivities of the sintered samples were measured as a function of x in the temperature range 30 to 1000 °C. The highest conductivity of around 500 S/cm at 1000 °C was found in Sm_0.7Sr_0.3CoO₃. The reactivity of all the samples with YSZ was examined at 800–1000 °C for 96 h. The Sr-doped perovskite oxides were more reactive with YSZ and produced SrZrO₃ at 900 °C after 96 h. However, no reaction product between SmCoO₃ and YSZ was observed at 1000 °C for 96 h. The cathodic polarization of the oxide electrodes, sputtered on yttria stabilized zirconia (YSZ), was studied at 800–1000 °C in air. SmCoO₃ shows no degradation of the electrode performance at higher temperatures. The thermal expansion measurements on the sintered samples were carried out from room temperature to 1000 °C. Large thermal expansion coefficients were found in these samples.     

Sr-doped LaInO3 and its possible application in a single layer SOFC

The effects of dopants on the electrical conductivity of the perovskite-type oxide LaInO₃ have been investigated. Replacement of La by Sr is the most effective way to enhance the conductivity of LaInO₃, whereas Ca substitution for In is rather difficult due to the large difference in the ion radii. The optimum composition is La_0.9Sr_0.1InO_3−δ whose maximum conductivity is 7.6×10⁻³ S cm⁻¹ at 900°C. The electrical conductivity of La_0.9Sr_0.1InO_3−δ has been measured over a wide range of oxygen partial pressure from pO₂=1 to 10⁻²⁵ atm. P-type and n-type behavior at high and low oxygen partial pressure have been observed, respectively, while at intermediate oxygen partial pressures, the electrical conductivity changes only slightly with the oxygen partial pressure. The concept of a single layer solid oxide fuel cell based on a La_0.9Sr_0.1InO_3−δ ceramic pellet has been tested. A maximum power density of 3 mW cm⁻² at 800°C was achieved when dilute H₂ and air were used as fuel and oxidizing agent, respectively.     

Application of quartz glass tubes as the track detectors for chemical identification of short-lived isotopes of elements 104, 105 and 106

The quartz glass open chromatographic columns with thermal gradient, which usually were used for the investigation of chemical properties of short-lived Z104 nuclides, were first used as the track detectors of spontaneously fissioning isotopes of elements 104, 105 and 106. The recoil nuclei of these elements were captured by the flow of gaseous chlorides then go to the quartz tube with reducing thermal gradient 400°C-100°C. The quartz tube was etched in 40% HF. The tracks due to spontaneous fission of isotopes ²⁵⁹104, ²⁶²105 and ²⁶³106 which were etched at the internal wall of quartz tubes were counted under optical microscope.     

Oxygen tracer diffusion in La1 − xSrxCoO3

Tracer diffusion of ¹⁸O in dense, polycrystalline La_1−xSr_xCoO₃ for x = 0.1 has been measured in the temperature range 400 to 600 °C and at 500 °C for x = 0.2 at an oxygen partial pressure of 1 × 10⁵ Pa. Depth profiles were obtained by secondary ion mass spectrometry. The diffusion coefficient for La_0.9Sr_0.1CoO₃ is given by D = (17–247) exp[(−232 ± 8 kJ/mole)/RT] cm²/s. This value is several orders of magnitude lower than D extrapolated from the results for x = 0.2 measured in the 700–900 °C temperature range. One possible explanation for the discrepancy is that the two measurements reflect different diffusion paths. As expected, La_0.8Sr_0.2CoO₃ exhibits a higher diffusivity at 500 °C than does La_0.9Sr_0.1CoO₃.     

Influence of preheating treatment on the luminescence properties of adularia feldspar (KAlSi3O8)

During the firing of ceramics that contain alkali feldspar grains (up to 900°C in bricks and 1200°C in porcelains) the metastable equilibrium of these natural materials is altered (refractory minerals, neo-formed minerals and new glassy components). Hence, potassium rich feldspar lattices, which are being used in some routines of archaeological dating and retrospective dosimetry, suffer minor modifications by preheating and irradiation treatments (K-self-diffusion, stretching, etc.). In this paper, some pre-heatings of a K-feldspar (adularia) from Saint Gothard (Switzerland) attempted to simulate the temperatures and conditions undergone in brick manufacturing processes (1000°C for 24 h and 1200°C for 240 h). Some changes in the behavior of the TL and RL spectral curves were detected after combinations of thermal pretreatments (at 400°C for 48 h; 500°C for 72 h; 600°C for 96 h and 700°C for 144 h) and irradiations. Comparisons between high temperature annealed (1000 and 1200°C) and non-annealed adularias show spectacular changes in the shape of the TL glow curves: natural-irradiated adularia displays a single large peak at 100°C, whereas annealed adularias show a very complex structure. The observed modifications, probably due to thermal alkali self-diffusion through the lattice interfaces, tilting of the Al–Si crankshafts and phase exsolutions, have been detected by X-ray diffraction.     

The origin of photoluminescence in Ge-implanted SiO2 layers

Ge ions were implanted at 100 keV with 3×10¹⁶ cm⁻² into a 300  nm thick SiO₂ layer on Si. Visible photoluminescence (PL) around 2.1 eV from an as-implanted sample is observed, and faded out by subsequent annealing at 900°C for 2 h. However, PL shows up again after annealing above 900°C at the same peak position. Compared with the as-implanted sample, significant increase of Ge–Ge bonds is measured in X-ray photoelectron spectroscopy, and the formation of Ge nanocrystals with a diameter of 5 nm are observed in transmission electron microscopy from the sample annealed at 1100°C. We conclude that the PL peak from the sample annealed above 900°C is caused by the quantum confinement effects from Ge nanocrystals, while the luminescence from the as-implanted sample is due to some radiative defects formed by Ge implantation.     

Temperature dependence of the calibration factor of radon and radium determination in water samples by SSNTD

The sensitivity of a ²²⁶Ra determination method of water samples by SSNTD was measured as a function of storage temperature during exposure. The method is based on an etched track type radon monitor, which is closed into a gas permeable foil and is immersed in the water sample. The sample is sealed in a glass vessel and stored for an exposure time of 10–30 days. The sensitivity increased more than a factor of two when the storage temperature was raised from 2 °C to 30 °C. Temperature dependence of the partition coefficient of radon between water and air provides explanation for this dependence. For practical radio-analytical application the temperature dependence of the calibration factor is given by fitting the sensitivity data obtained by measuring ²²⁶Ra standard solutions (in the activity concentration range of 0.1–48.5 kBq m⁻³) at different storage temperatures.     

Kinetics of isolated peak 5 in TLD-100 following 165°C post-irradiation annealing

Peak 5 in the glow curve of TLD-100 (at a temperature of approximately 200°C) was studied as a function of post-irradiation annealing at 165°C. Computerized glow peak analysis shows that the order of kinetics of peak 5 increases from 1.2 ± 0.05 (1 SD) following 165°C annealing for five minutes to 1.72 ± 0.07 (1 SD) following annealing at 165°C for thirty minutes. Extrapolation of the results to zero annealing time yields a value of kinetic order consistent with unity. The glow curve analysis also indicates that peak 4 (the satellite peak at approximately 175°C) is undetectable even at the lowest annealing duration of 5 minutes. The high temperature satellite of peak 5 (peak 6 at approximately 225°C) grows with increasing annealing time to 10% of the intensity of peak 5 after annealing for 30 min. Glow curve analysis including peak 6, however, does not significantly change the conclusions regarding the increase in the order of kinetics of peak 5 as a function of annealing time or the consistency of the extrapolated results with kinetic order unity at zero annealing time. Analysis of isothermal decay curves at 165°C shows that the relative intensity of peak 4 to peak 5 decreases with increasing annealing time, from 8% after 5 min annealing to 0.5% after 30 min annealing.     

压水堆核电站燃料组件弯曲对堆芯中子学的影响分析计算

在压水堆核电站中,由于燃料组件装配的压紧力、冷却剂流动、辐射蠕变、燃耗等因素会导致燃料组件的弯曲,燃料组件的弯曲对组件间的水隙分布产生影响,从而影响中子的慢化行为及堆芯的传热性能,进而对反应堆堆芯的运行参数造成影响。本文分析了组件弯曲的成因及机理、影响及后果（包括对堆芯功率分布、径向功率倾斜、焓升因子、热点因子等参数的影响）,并使用蒙特卡罗软件JMCT,对组件弯曲的确定论计算程序的正确性进行了验证。最后通过确定论的计算程序模块,对CPR1000核电站的组件弯曲情况进行了模拟分析,计算结果表明:在某一燃耗下,随着水隙增加或减小,燃料组件功率会随之增加或减小,使堆芯的功率分布发生倾斜,影响核电站的安全运行。