Radioluminescence (RL) behaviour of Al2O3:C-potential for dosimetric applications

The radioluminescence (RL) of carbon doped aluminium oxide (Al₂O₃:C) TL dosimeter material (TLD-500) was investigated using a ¹³⁷Cs conversion electron source (which also emits β and γ) for simultaneous irradiation and luminescence excitation. Furthermore, RL dosimetry characteristics of this material were studied. The main RL emission occurs at 420 nm. That matches the known main TL and OSL emissions for this material as well as an emission that was investigated in earlier RL studies, excited at higher energies (4 MeV electrons) and very high pulse delivered doses (≈800 kGy·s⁻¹). Furthermore, the saturation dose for the main peak is reached at the dose level of ≈80 Gy as known from TL and earlier RL investigations. Other peaks at 700 and 790 nm and broad emission bands at photon energies higher than 3.00 eV and others between 2.00 and 2.50 eV were observed. The 700 nm emission shows growth also at higher dose levels, and saturates at an estimated dose of ≈800 Gy. The 790 nm emission reaches its maximum intensity at ≈10 Gy absorbed dose. The reported results give an outlook to the usability and the potential of Al₂O₃:C combined with RL measurements for radiation dosimetry as well as for beta source calibration, using radioluminescence.     

TL response of a natural fluorite

A batch of a naturally occurring fluorite (CaF₂) from the Middle Benue Valley region of Nigeria has been studied in some detail for its thermoluminescence (TL) properties. TL glow peaks are observed at 119, 144 and 224°C at a heating rate of 10°C s⁻¹. The TL response is observed to increase with increasing dose, as expected, over the dose range examined. Variations are observed in the decay curves of the various glow peaks with storage at room temperature. While the lower temperature peaks are observed to decay, enhancement of the TL signal is observed for the 224°C glow peak when stored for four weeks. A low-level radioactivity measurement showed no evidence of self-irradiation from naturally occurring radionuclides. UV exposure was suppressed by storage in a black sealed container to exclude sunlight contribution to the observed TL response. A scheme involving the formation of large defect complexes, from smaller ones, during storage, as possible route leading to loss of signal in low temperature glow peaks and a corresponding enhancement at higher temperature, is suggested.     

Growth of aligned carbon nanotube arrays on metallic substrate and its application to supercapacitors

Aligned carbon nanotube arrays (ACNTAs) with lengths up to 150 μm were fabricated on metallic alloy (Inconel 600) substrates by pyrolysis of iron (II) phthalocyanine (FePc) in the presence of ethylene (C₂H₄). The as-grown ACNTAs, formed by aligned multi-walled carbon nanotubes with high purity, were characterized by scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM), and Raman spectroscopy techniques. The ACNTAs were used directly as electrode materials in supercapacitors with (Et)₄NBF₄ + propylene carbonate (PC) as electrolyte, and their electrochemical properties were investigated. A rectangular-shaped cyclic voltammetry (CV) curve was observed even at a sweep rate of 1000 mV s⁻¹. The specific capacitance measured at 1000 mV s⁻¹ was about 57 % (47 F g⁻¹) of that obtained at 1 mV s⁻¹ (83 F g⁻¹), and an equivalent series resistance (ESR) of 0.55 Ω was measured for the ACNTA and activated carbon pair electrodes embedded in a coin cell. The results indicated that the ACNTAs could be a promising candidate as electrode materials in supercapacitors.     

Upper limit on the decay Σ(1385)→Σγ and cross section for γΣ→Λπ

Coherent Λπ⁻ production on Pb of 600 GeV Σ⁻ hyperons has been studied with the SELEX facility at Fermilab. Using the Primakoff formalism, we set a 90% CL upper limit on the radiative decay width Γ[Σ(1385)⁻→Σ⁻γ]<9.5 keV, and estimate the cross section for γΣ⁻→Λπ⁻ at  GeV to be 56±16 μb.     

The ‘110°C’ TL peak in synthetic quartz

The thermoluminescence (TL) of synthetic quartz has been investigated in the temperature region 275–475 K. These measurements have revealed a more complicated structure of the 110°C TL peak and thermal activation energies and frequency factors have been estimated for a number of peaks within the glow curve. The results obtained after annealing samples in different atmospheres indicate that oxygen-related defects play an important role in the luminescence process, involving both the charge traps and recombination centres.     

Optically stimulated luminescence (OSL) study of synthetic stishovite

Optically stimulated luminescence (OSL) of synthetic stishovite was investigated for a future dating technique of meteor impact craters. Luminescence around 330 nm was measured on the γ-ray irradiated stishovite under two stimulating light sources of infrared laser (830 nm) and blue light emitting diode set (470 nm). Thermoluminescence (TL) studies before and after the OSL measurements showed the intensities around 100–200°C and 220–350°C to increase and those around 350–450°C to decrease. This indicates that a part of deep-trapped charges excited during the OSL measurements were retrapped by shallower traps. The infrared stimulated luminescence (IRSL) after the TL measurement up to 450°C could not be detected, while the blue light stimulated luminescence (BLSL) after TL had about one-tenth of the intensity before TL. This indicates that a part of the charges in shallower traps were detrapped thermally and returned to the deeper traps which were related to BLSL. The result implies that some of the BLSL-related traps are quite stable at room temperature and could be used for geological dating. In addition, two paramagnetic centers produced by sudden release of high pressure in synthesis process were found in the unirradiated stishovite by electron spin resonance (ESR). Their g-factors are g=2.00181 and g=2.00062 for an axial signal and g=2.00305 for the other isotropic signal. These signals could be used for an evidence of impacts if those signals could be stored in geological time.     

Structure of the Si(011)-(16 × 2) surface and hydrogen desorption kinetics investigated using temperature-programmed desorption

D₂ temperature-programmed desorption (TPD) was used to probe the structure of the Si(011)-(16 × 2) surface. Deuterium was adsorbed at 200°C to coverages θ_D ranging up to complete saturation (approximately 1.1 ML) and the sample heated at 5°C s⁻¹. TPD spectra exhibited three second-order desorption peaks labelled β₂, β*₁ and β₁ centered at 430, 520 and 550°C. Of the proposed models for the Si(011)-(16 × 2) reconstruction, the present TPD results as a function of θ_D provide support for the adatom/dimer model with the β₂ peak assigned to D₂ desorption from the dihydride phase, while the β*₁ and β₁ peaks arise from adatom and surface-atom monohydride phases.     

Radiation induced luminescence processes in c-BN

Spectral properties of cubic boron nitride have been studied using methods of photoluminescence (PL), X-ray excited luminescence (XL), thermoluminescence (TL) and optically stimulated luminescence. It is found that emission of cubic boron nitride is presented by 4 subbands, their relative yield is determined by the excitation type: blue, green (dominant) and red bands are observed in PL, ultraviolet, blue (dominant), green and red bands—in XL. Three thermal peaks are found in TL curves in the 0–700°C temperature range, their presence and intensity depend on radiation type used. A tentative correspondence between thermal peaks and emission bands is found.     

Characteristics of TL and PTTL glow curves of gamma irradiated pure Li2B4O7 single crystals

The TL glow curve of X-ray irradiated pure and Cu-doped Li₂B₄O₇ shows that the most intense TL peak is at 160°C. In the present work the characteristics of the TL and PTTL glow curves from gamma irradiated pure Li₂B₄O₇ single crystal samples (prepared by Mitui Kinzoku Kougyo, Japan) have been studied. The samples were irradiated with different gamma doses (from 0.5 up to 500 Gy) using a ⁶⁰Co gamma ray source at a dose rate of 78 Gy h⁻¹. The TL glow curve shows three intense peaks (at 160°C, 260 and 305°C) and three weak ones (at 110, 140 and 220°C). The most intense TL peak is at 160°C, which agrees with the TL glow curve from X-ray irradiated samples [Kutomi Y. and Tomita A. (1990) TSEE and TL of Li₂B₄O₇:Cu single crystals. Radiat. Prot. Dosim. 33, 347–350]. The 305°C peak in gamma irradiated samples also appears to be very intense, which indicates its possible use in high-dose high-temperature dosimetry. Further, the characteristics of the PTTL glow curve have been studied as a function of ultraviolet exposure and number of repeated PTTL cycles.     

Oxygen diffusion and surface exchange in La1−xSrxFe0.8Cr0.2O3−δ (x=0.2, 0.4 and 0.6)

Oxygen tracer diffusion (D*) and surface exchange rate constant (k*) have been measured, using isotopic exchange and depth profiling by secondary ion mass spectrometry (SIMS), in La_1−xSr_xFe_0.8Cr_0.2O_3−δ (x=0.2, 0.4 and 0.6). Measurements were made as a function of temperature (700–1000 °C) and oxygen partial pressure (0.21–10⁻²¹ atm) in dry oxygen, water vapour and water vapour/hydrogen/nitrogen mixtures. At high oxygen activity, D* was found to increase with increasing temperature and Sr content. The activation energies for D* in air are 2.13 eV (x=0.2), 1.53 eV (x=0.4) and 1.21 eV (x=0.6). As the oxygen activity decreases, D* increases as expected qualitatively from the increase in oxygen vacancy concentration. Under strongly reducing conditions, the measured values of D* at 1000 °C range from 10⁻⁸ cm² s⁻¹ for x=0.2 to 10⁻⁷ cm² s⁻¹ for x=0.4 and 0.6. The activation energies determined at constant H₂O/H₂ ratio are 1.21 eV (x=0.2), 1.59 eV (x=0.4) and 0.82 eV (x=0.6).

The surface exchange rate constant of oxygen for the H₂O molecule is similar in magnitude to that for the O₂ molecule and both increase with increasing Sr concentration.     

Effect of temperature on the luminescence processes of SrAl2O4:Eu

The UV excited and persistent luminescence properties as well as thermoluminescence (TL) of Eu²⁺ doped strontium aluminates, SrAl₂O₄:Eu²⁺ were studied at different temperatures. Two luminescence bands peaking at 445 and 520 nm were observed at 20 K but only the latter at 295 K. Both Sr-sites in the lattice are thus occupied by Eu²⁺ but at room temperature efficient energy transfer occurs between the two sites. The UV excited and persistent luminescence spectra were similar at 295 K but the excitation spectra were different. Thus the luminescent centre is the same in both phenomena but excitation processes are different. Two TL peaks were observed between 50 and 250 °C in the glow curve. Multiple traps were, however, observed by preheating and initial rise methods. With longer delay times only the high temperature TL peak was observed. The persistent luminescence is mainly due to slow fading of the low temperature TL peak but the step-wise feeding process from high temperature traps is also probable.     

The role of alkali ions in the 190 K TSL peak in quartz

The role of alkali ions in the creation of the thermally stimulated luminescence (TSL) peak at 190 K in quartz has been investigated by wavelength resolved TSL and thermally stimulated current (TSC) measurements performed on synthetic crystals, both as grown and hydrogen swept, characterised by alkali content of about 1–3 and 0.1 ppm respectively. The 190 K peak has been efficiently produced in as-grown crystals by a double irradiation procedure consisting of a first x-ray irradiation at 90 K followed by heating in the 170–300 K temperature range and a second irradiation at 90 K; this effect has not been observed in the hydrogen swept crystal. Moreover, the study of the spectral composition of the emitted light has shown the existence of two emission bands, one peaking at 450 nm (T<150 K) and the second one evidenced for T>150 K and peaking at around 380 nm.

In as grown samples, TSC peaks at 205, 260 and at around 350 K (composite structure) have been detected: their intensities are much stronger in the as grown crystal and with the electric field oriented along the z-axis indicating that they have an ionic character. By taking into account the mechanism of formation of the [SiO₄/M⁺]⁰ (M⁺=Li⁺, Na⁺) traps (previously found to be responsible for the 190 K TSL peak), the 205 K TSC peak can be attributed to the radiation induced dissociation of alkalis from [AlO₄/M⁺]⁰ defect centres and subsequent migration near to Si sites; on the other hand, the 260 K TSC peak can be related to the subsequent disintegration of [SiO₄/M⁺]⁰ defects involving the migration of alkalis to different ionic traps.

PACS: 78.60.K–61.72.J–42.70.Ce     

Excess molar heat capacity of isobutyric acid–water binary liquid mixtures near and far away from the critical temperature

The heat capacity of the liquid–liquid mixture isobutyric acid–water has been measured for the first time near and far away from its critical point using an adiabatic calorimeter. The measurements were performed at atmospheric pressure, in the one phase region as a function of three temperatures: (1) T − T_C = 0.055 °C, (2) T − T_C = 3.055 °C, (3) T − T_C = 8.055 °C and of the composition X in acid (IA). The heat capacity C_p decreases rapidly when X increases at the used temperatures. Near the critical composition, C_p is not affected by the correlation of the concentration fluctuations.

The molar excess heat capacity of the system under investigation was analysed along the phase diagram and considered as a structural transformation effect.     

Study of the 110°C TL peak sensitivity in optical dating of quartz

As the 110°C TL emission in quartz uses the same luminescence centers as the OSL emission, the 110°C TL signal from a test dose may be used to monitor the OSL sensitivity change. It is thus important to study the relationship between the 110°C TL peak and the OSL sensitivity in studies related to optical dating from quartz. We have conducted a series of experiments using sedimentary quartz, where the annealing temperatures were varied between 260 and 1000°C before the measurement of OSL and 110°C TL sensitivities. Another series of experiments on two sedimentary quartz samples investigated the 110°C TL peak and OSL dose-dependent sensitivity change after different annealing temperatures. In these experiments, the 110°C TL and OSL signals from the test dose are shown to have similar sensitization characteristics: the 110°C TL sensitivity change is proportional to the OSL sensitivity change if the annealing temperature is lower than 500°C. It is concluded that the 110°C TL signal can be used to correct the OSL sensitivity change in the single-aliquot additive-dose protocol.     

Defect versus nanocrystal luminescence emitted from room temperature and hot-implanted SiO2 layers

Silicon nanocrystals have been synthesized in SiO₂ matrix using Si ion implantation. Si ions were implanted into 300-nm-thick SiO₂ films grown on crystalline Si at energies of 30–55 keV, and with doses of 5×10¹⁵, 3×10¹⁶, and 1×10¹⁷ cm⁻². Implanted samples were subsequently annealed in an N₂ ambient at 500–1100°C during various periods. Photoluminescence spectra for the sample implanted with 1×10¹⁷ cm⁻² at 55 keV show that red luminescence (750 nm) related to Si-nanocrystals clearly increases with annealing temperature and time in intensity, and that weak orange luminescence (600 nm) is observed after annealing at low temperatures of 500°C and 800°C. The luminescence around 600 nm becomes very intense when a thin SiO₂ sample is implanted at a substrate temperature of 400°C with an energy of 30 keV and a low dose of 5×10¹⁵ cm⁻². It vanishes after annealing at 800°C for 30 min. We conclude that this luminescence observed around 600 nm is caused by some radiative defects formed in Si-implanted SiO₂.     

A comparative study of the thermoluminescence properties of several varieties of Brazilian natural quartz

The following varieties of natural quartz, as the blue, the green, the red, the pink, the black, the sulphurous and the milky quartz, have been investigated concerning their thermoluminescence properties. For comparison sake natural colorless alpha quartz has been include. Since X-rays diffraction analysis has shown that all of them have the same crystal structure as the alpha quartz, it is expected that no great change in the TL property should be found, however, that was not the case. The TL peaks at 110, 175, 220, 325 and 375 °C observed in the alpha quartz are not found in all the varieties of quartz, for instance, the sulphurous quartz presented only 110° and 245° peaks, the pink one presented just 110, 220 and 375 °C peaks and so on. In respect to TL response as function of gamma ray dose a quite varied behavior has been observed and discussed.     

TL and PTTL in natural fluorite previously irradiated with gamma rays and heavy ions

The effect of annealing temperature on the phototransfer thermoluminescence (PTTL) signal was studied to determine the appropriate annealing temperature for treating the natural powder before irradiation. The temperatures used to anneal virgin natural fluorite samples (only natural dose without giving the samples any artificial doses) were 150, 250, 350, 450, 550, 650 and 750°C for a duration of 1 h in each case. The results show that the PTTL response did not change for anneal temperatures up to 450°C, but at higher temperatures the signal decreased rapidly. The height of the 90°C peak decreased by two orders of magnitude as the anneal temperature increased from 450 to 750°C, whilst the height of the 180°C peak decreased by three orders of magnitude between the same two annealing temperatures. In order to investigate the effect of previous gamma rays and heavy ion irradiation on thermoluminescence (TL) and PTTL signals, powdered samples of natural fluorite from Cornwall, England, were annealed at 500°C and then irradiated (at GSI, Darmstadt, Germany) with ¹⁶¹Dy ions of energy 13 Mev/n; the range of fluences used was from 10⁴ to 10¹² ion cm⁻². Identical samples were given gamma doses in the range 1 Gy to 2.6 × 10⁴ Gy in order to compare the effects of gamma rays and heavy ions. The sensitivities of TL and PTTL were studied by giving the samples a gamma test dose of 1 Gy after annealing the samples at 500°C for 30 min in order to eliminate the TL resulting from previous gamma or heavy ion irradiation.     

Chemically deposited copper oxide thin films: structural, optical and electrical characteristics

Thin films of copper oxide with thickness ranging from 0.05–0.45 μm were deposited on microscope glass slides by successively dipping them for 20 s each in a solution of 1 M NaOH and then in a solution of copper complex. Temperature of the NaOH solution was varied from 50–90°C, while that of the copper solution was maintained at room temperature. X-ray diffraction patterns showed that the films, as prepared, are of cuprite structure with composition Cu₂O. Annealing the films in air at 350°C converts these films to CuO. This conversion is accompanied by a shift in the optical band gap from 2.1 eV (direct) to 1.75 eV (direct). The films show p-type conductivity, 5×10⁻⁴ Ω⁻¹ cm⁻¹ for a film of thickness 0.15 μm. Electrical conductivity of this film increases by a factor of 3 when illuminated with 1 kW m⁻² tungsten halogen radiation. Annealing in a nitrogen atmosphere at temperatures up to 400°C does not change the composition of the films. However, the conductivity in the dark as well as the photoconductivity of the film increases by an order of magnitude. The electrical conductivity of the CuO thin films produced by air annealing at 400°C, is high, 7×10⁻³ Ω⁻¹ cm⁻¹. These films are also photoconductive.     

Kinetics of red, blue and UV thermoluminescence and optically-stimulated luminescence from quartz

The duration over which charge is retained at trapping sites is of fundamental importance for trapped electron dating. Here, we report measurements of the kinetic parameters of the prominent thermoluminescence (TL) glow peaks of quartz, and of the optically-stimulated luminescence (OSL) signal from quartz utilised for optical dating. The similarity in trapping lifetimes of the 325°C TL peak and the dominant component of the OSL signal are taken as further support for the hypothesis of their common origin in the same trapped electron population.     

Concerning infrared-stimulated luminescence from K-feldspars: evidence from heating before stimulating

Repeated heating and stimulation by infrared of feldspar samples causes a reduction in the luminescence signal. Two feldspars were investigated, one microcline and one orthoclase. Empirically the fraction of luminescence signal f(n) remaining after the nth cycle of heating and stimulation is given by f(n)=1−a ln(n) for laboratory dosed samples of both microcline and orthoclase feldspars, for heating temperatures of 150°C, 180°C and 220°C, for heating durations per cycle ranging from 20 s to 2400 s and with the study covering 10 cycles of heating and stimulation. Logarithmic decay of luminescence with time has been explained previously, in other contexts, as due either to quantum tunnelling or to a continuous distribution of states being involved but it is shown that these explanations do not fit the present data. The measured data on f(n) were corrected for the loss of luminescence due to infrared stimulation to ensure that this did not account for the differences between the data and the expectations from models; the functional form f(n)=1−a ln(n) remains valid, although with changed values of a. Numerical simulations of systems involving a limited number of trap depths, from 21 down to 3, were investigated and those with 5 or more trap depths were found to be capable of resembling the data. The simulations could not define a unique pattern of trap depths to match the data, but of the patterns investigated the data were best reproduced by a distribution of at least 5 traps in the energy range from 1.18–1.66 eV. These conclusions augment, and are consistent with, existing information on luminescence mechanisms in potassium-feldspars.