The slow component of quartz optically stimulated luminescence

The slow component of quartz OSL displays a number of properties that clearly distinguish it from the main (‘rapidly bleachable’) part of the quartz OSL signal traditionally used for dating. These properties include an extremely high thermal stability, dose saturation level and a charge concentration dependence in both signal form and decay rate. The physical mechanism responsible for the slow component is thought at present to involve a direct donor–acceptor recombination component, possibly associated with competing pathways below, and possibly up to, the conduction band. The thermal stability and high dose saturation characteristics of the slow component suggest much potential for long-range dating exists although at present it is uncertain whether difficulties associated with partial resetting may preclude routine use of the slow component for dating sedimentary deposits. A single-aliquot additive dose method was however used to obtain an estimate of D_e from the slow component for an Egyptian quartz sample that was in broad agreement with previous estimates based on the standard multiple-aliquot additive dose method.The slow component is often small in magnitude compared to the initial portion of the quartz OSL decay. However, this is not always the case and for some samples significant inaccuracies in D_e estimation may occur when deriving ages from the initial ‘rapidly bleaching’ portion of the OSL decay if the effect of the slow component is ignored or taken to be constant.     

Effect of the initial excitation energy on the average fission lifetime of nuclei

The dependence of the fission time on the initial nuclear excitation energy E _{tot 0} ^* is studied on the basis of a refined combined dynamical and statistical model. It is shown that this dependence may be nonmonotonic, in which case it features a broad maximum. It turns out that the form of the average fission time 〈t _f 〉 as a function of E _{tot 0} ^* depends greatly on the orbital angular momentum L _n carried away by prescission neutrons.     

Acoustic emission and thermal expansion of Pb(Mg<Subscript>1/3</Subscript>Nb<Subscript>2/3</Subscript>)O<Subscript>3</Subscript> and Pb(Mg<Subscript>1/3</Subscript>Nb<Subscript>2/3</Subscript>)O<Subscript>3</Subscript>-PbTiO<Subscript>3</Subscript> crystals

The temperature dependence of the elongation per unit length for Pb(Mg_1/3Nb_2/3)O₃ crystals unannealed after growth and mechanical treatment is investigated in the course of thermocycling. It is revealed that this dependence deviates from linear behavior at temperatures below 350°C. The observed deviation is characteristic of relaxors, is very small in the first cycle, increases with increasing number n of thermocycles, and reaches saturation at n≥3. In the first cycle, a narrow maximum of the acoustic emission activity is observed in the vicinity of 350°C. In the course of thermocycling, the intensity of this maximum decreases and becomes zero at n>3. For (1?x)Pb(Mg_1/3Nb_2/3)O₃-xPbTiO₃ crystals, the dependence of the temperature of this acoustic emission maximum on x exhibits a minimum. It is assumed that the phenomena observed are associated with the phase strain hardening due to local phase transitions occurring in compositionally ordered and polar nanoregions.     

Nonlinear dose dependence of TL and LM-OSL within the one trap-one center model

In a recent paper, it has been shown that strong sub-linearity of the occupancy n₀ of trapping states far from saturation can be explained by the simplest model of one trap-one recombination center (OTOR). In the present work we report on results of numerical simulation of dose dependence of the TL maximum under similar conditions. In some cases, the TL maximum is found to be strictly proportional to the filling of the traps, but this is not always the case. Different sublinear dose-dependence functions of the trap occupancy and the maximum TL are demonstrated. With the same sets of parameters, curves of LM-OSL have also been simulated; superlinear as well as sublinear dependencies on the excitation dose have been found.     

Standardised growth curves for optical dating of sediment using multiple-grain aliquots

The single aliquot regenerative dose (SAR) protocol offers the opportunity of exploring, relatively simply, the existence of a ‘universal’ growth curve for use in dating using optically stimulated luminescence (OSL). A test dose is used in the SAR procedure to monitor and correct for sensitivity change occurring either over the burial period, or as a result of thermal pretreatments during the measurement procedure. However, this test dose can also be used to correct for variations in signal intensity between individual aliquots, thus enabling the comparison of growth response with dose for many different aliquots and samples, even for measurements made using different instruments.In this paper, the growth characteristics of coarse-grained quartz and polymineral fine-grains are examined using data obtained as part of the SAR procedure. Following standardisation of these data for differences in the test dose response and the magnitude of the test dose used, distinct and reproducible patterns of growth are observed and mineral-specific standardised growth curves (SGCs) are defined for multiple-grain aliquots. An equivalent dose for a sample can then be determined based only on measurements of the natural luminescence signal intensity (L_n) and the response to an artificial irradiation dose (T_n). This equivalent dose, determined using the SGCs defined for quartz and polymineral fine-grains, is compared to that determined using a conventional SAR measurement procedure, for a large number of samples and aliquots. Using an SGC, accurate estimates of equivalent dose may be made based solely on measurements of L_n and T_n, thus potentially speeding up the measurement process. This has obvious benefits where it is necessary to examine a large number of aliquots.     

Thermoluminescence and optically stimulated luminescence studies on LiMgPO4 crystallized by micro pulling down technique

LiMgPO₄ (LMP) crystals were grown by micro pulling down technique. Samples were irradiated with different β-particle doses of the ⁹⁰Sr/⁹⁰Y source. Thermally and optically stimulated luminescence spectra were measured with the automatic Risø TL/OSL-DA20 reader under the different modes of stimulation. The dose–response dependence, reproducibility, the lowest measurable dose and short-time fading were investigated. TL and OSL dose–response of LiMgPO₄ crystals was found to be linear up to around 1 kGy, what makes this material suitable for high dose measurements. Discrepancies between successive measurements did not exceed 10%, regardless of the applied growth parameters. The lowest measurable dose, defined as three standard deviations of the signal of unexposed detector, was determined around 0.5 mGy. About 73% of the initial OSL signal value was measured 24 h after the irradiation. For longer periods of time the level of signal stabilizes so that there was no further loss of signal observed. In case of TL, the level of signal does not stabilize and decreases to 69% within 2 weeks after the irradiation. The obtained results tend to suggest that LiMgPO₄ crystals may be considered as promising dosimeters for both personal and high dose dosimetry.     

Na-rich feldspar as a luminescence dosimeter in infrared stimulated luminescence (IRSL) dating

One of the challenges in dating rock surfaces is the choice of the luminescence mineral. Although quartz is the preferred dosimeter in sediment dating, it is often not sufficiently sensitive when extracted from solid rocks. The intensity of signals from feldspars tends to be much less dependent on geological origin and erosion history, but the dosimetry of K-rich feldspar grains extracted from rocks is complicated because the internal dose rate is very dependent on the original feldspar grain size. The in situ grain size information is lost during the crushing process used to separate the grains for measurement. This latter problem does not apply to Na-rich feldspar because of the absence of internal radioactivity.The potential application of Na-rich feldspar as a luminescence dosimeter for the IRSL dating of rock surfaces is investigated using a variety of sediment samples from different geological settings for which independent age control is available. The blue and yellow luminescence emissions are measured for IR stimulation at 50 °C (IR₅₀), and post-IR IR stimulation at 290 °C (pIRIR₂₉₀). Thermal stability experiments imply that the corresponding signals in both emissions have comparable thermal stabilities and that all signals have similar recombination kinetics and are thermally stable over geological timescales. The IR₅₀ doses measured using blue and yellow emissions are similar to or lower than quartz doses while pIRIR₂₉₀ blue doses are higher than those from yellow emission and quartz doses. The fading rates measured for the IR₅₀ signals are ∼3%/decade larger than those measured for the pIRIR₂₉₀ signals in both yellow and blue emissions. Furthermore the average fading rates of both yellow signals are ∼3%/decade higher than the corresponding fading rates of the blue signals. However, there is no detectable correlation between fading rates and the measured D_e values. The residual doses measured from the laboratory-bleached samples and a modern analogue suggest that the IR₅₀ signals in both blue and yellow emissions bleach to the same degree, as do the corresponding pIRIR₂₉₀ signals, and that there is no significant naturally-unbleachable residual dose observed using these signals. Neither anomalous fading nor incomplete bleaching explains the observed dose discrepancy between the two emissions. Eight uncorrected and fading-corrected ages are calculated for each sample based on all four signals, using the dose rate relevant to Na-rich feldspar extracts (i.e. ∼3% K). The IR₅₀ and pIRIR₂₉₀ blue ages were also calculated assuming a dose rate based on 12.5% internal K (i.e. assuming that the blue signals were mainly derived from contamination by K-rich feldspar). The latter pIRIR₂₉₀ blue ages are in agreement with the expected age control, raising the possibility that this signal originates mainly from K-rich feldspar contamination in our Na-rich fractions, and thus is not so useful in the luminescence dating of rock surfaces. On the other hand, the pIRIR₂₉₀ fading-corrected ages based on the yellow emission are consistent with the independent age controls; higher preheat and stimulation temperatures may result in more stable yellow signals from Na-rich feldspar extracts from rocks, and so reduce the size of the fading correction. We conclude that, because this signal avoids the dosimetry difficulties of K-rich feldspar extracts, it has considerable potential in the IRSL dating of rock surfaces.     

Calculation of the carrier concentration dependence of the Auger lifetime in degenerate n-type (Hg,Cd)Te

The Auger 1 lifetime expression for degenerate n-type (Hg_1?xCd_x)Te has been derived by replacing the Fermi-Dirac distribution functions for the pair of Auger collision electrons with step functions. The lifetime is calculated as a function of carrier concentration, _n0 for several values of energy gap and temperature using a non-parabolic band structure. We find that for strong degeneracy, the lifetime, τ_AlsuD varies as n₀^?γ where 0.7 ?γ? 1 and that γ is dependent upon the energy gap. The relatively slow dependence of τ_Al^D upon n₀, compared to the non-degenerate case () is due to the dependence of τ_Al on the threshold energy which for the degenerate case is a linear function of the Fermi energy, hence, a function of n₀.     

Vector analysis vs. regions of integration ratio method for determination of gamma and neutron contributions in a mixed field

The different ratios of the dosimetry peaks and the high temperature peaks after gamma and neutron irradiation can be employed for mixed field dosimetry, after performing proper analysis. In the present work the results obtained by the vector analysis method were compared to those obtained by the regions of integration (ROI) method for TLD600 chips irradiated by different combinations of gamma rays and thermal neutron doses. When applying the ROI method, the calculated neutron to gamma dose ratios (D_n/D_γ) were in good agreement (differences up to about 20%) with the actual experimental values in the D_n/D_γ range from 0.033 to 20. When applying the vector analysis method, the range of the D_n/D_γ ratio with differences up to about 20% is reduced to 0.033–4, and the uncertainties are generally higher. Thus, no advantage is expected when using the vector analysis method compared to the ROI method for evaluation of the dose ratio D_n/D_γ in a mixed field.     

Nucleon-content effect on the fission lifetime of excited nuclei

It was shown previously that the fission lifetime of a nucleus excited to about 100 MeV depends strongly and nonmonotonically on the initial value of its angular momentum L ₀. This result was obtained on the basis of a refined version of the combined dynamical and statistical model. The present study is devoted to a theoretical analysis of the dependence of the fission time on the nucleonic composition of the nucleus involved. The respective calculations were performed within the same model. The dependence of the average fission time 〈t _f 〉 on the initial fissility parameter (Z ²/A)₀ appears to be of a resonance type and is similar to its dependence on L ₀. This dependence of the average fission time on (Z ²/A)₀ stems both from statistical calculations and from a dynamical simulation of the fission mode with allowance for friction. The conditions under which the average fission time reaches a maximum are specified. The dependence of the average fission time on (Z ²/A)₀ remains nonmonotonic in the fusion-fission reaction as well, in which case the distribution of compound nuclei with respect to the initial angular momentum is broad.     

Correlation analysis of the shifts of the electronic spectra of anthracene, phenanthrene, and fluorene as functions of the temperature in the gas phase and of the refractive index in n-paraffin solvents

The temperature-induced shifts of the maxima of the longest-wavelength bands of the S ₁ ← S ₀ and S ₂ ← S ₀ transitions in phenanthrene and the S ₁ ← S ₀ transition in fluorene in the gas phase are measured. A correlation analysis of these data and similar data on the S ₁ ← S ₀ and S ₁ → S ₀ transitions in anthracene is fulfilled. The positions of the maxima of analogous bands of the S ₁ ← S ₀ transition in anthracene, S ₁ ← S ₀ and S ₂ ← S ₀ transitions in phenanthrene, and S ₁ ←S ₀ transition in fluorene dissolved in liquid n-paraffins are also measured and analyzed as functions of (n ² ? 1)/(n ² + 2), where n is the refractive index of the solvent. The results confirm the conclusion of the Mirumyantz-Demchuk theory about the linear temperature dependence of the wave number of a band maximum but contradict the prediction that, upon extrapolation to T = 0 K, the positions of the maxima correspond to the electronic transitions in the molecule unperturbed by out-of-plane vibrations of the aromatic core.     

Dielectric and AC conductivity behavior of BaBi2Nb2O9 ceramics

The complex dielectric and AC conductivity response of BaBi₂Nb₂O₉ relaxor ferroelectric ceramics were studied as a function of frequency (100 Hz-10 MHz) at various temperatures. The observed dielectric behavior was characterized by two types of relaxation processes which were described by the ‘universal relaxation law’. The frequency dependence of conductivity which showed a classical relaxor behavior followed the Jonscher's universal law σ(ω)=σ₀+Aωⁿ. The exponent n exhibited a minimum in the vicinity of temperatures of dielectric anomaly while the pre-factor A showed a maximum. The temperature dependence of n followed the Vogel-Fulcher relation with activation energy of about 0.14 eV.     

Characterization of nonlinearities in the dose dependence of thermoluminescence

Nonlinearities often occur in the dose dependence of thermoluminescence (TL). These include sublinearity, usually when there is an approach to saturation in the dose dependence, as well as supralinearity, also termed superlinearity in the literature. Different researchers in the field have viewed the effect of supralinearity/superlinearity from two somewhat different points of view. One point of view has to do with the rate of change with dose of the dose dependence function. The other approach is related more to the applications of TL in dosimetry and archaeological and geological dating, and basically has to do with the correction to be made in extrapolation in cases where supra(super) linearity occurs following an initial linear dose range, or prior to such a linear range. In the present work we propose quantitative methods to characterize these nonlinearities. We suggest the use of two different nonlinearity indices, depending upon how one wishes to describe the nonlinearity. We propose use of the term “supra linearity index”, ƒ(D), in cases where the feature of interest is the deviation from linearity, namely, when the correction in extrapolation is the main issue. We propose the term “superlinearity index”, g(D), in dose ranges where the growth is “more than linear” and when extrapolation is not the main issue. We mathematically define each of these indices and give examples of their use for different dose dependencies.     

The mass of the scalar boson beyond the large- N c limit

Within the framework of the 1/N_c expansion of four-fermion interaction models, we analyse the next to leading 1/N_c corrections to the well known large-N _c result M _S = 2M _Q where M _S is the mass of the scalar boson and M _Q is the constituent quark mass. The calculation is performed in the Extended Nambu-Jona Lasinio (ENJL) model which is suitable for describing low energy hadron properties. We treat the model as fully non renormalizable and discuss the comparison with approaches based on the equivalence with renormalizable Yukawa type models. We consider both the G _V = 0 and the G _V ≠ 0 cases with n _f = 2 flavours and study the dependence upon the regularization scheme. We find that pure next-to-leading 1/N _c corrections are large and negative, while a partially resummed treatment can induce positive and smaller corrections. A triplet-singlet states’ splitting is observed.     

Waveguide structures written in SF57 glass with fs-laser pulses above the critical self-focusing threshold

Waveguide writing with femtosecond (fs) laser pulses in glasses is compromised by uncontrollable non-linear propagation phenomena for powers exceeding a certain threshold, P_cr, which is inversely proportional to the material linear and non-linear refractive indices, n₀ and n₂, respectively. We have studied the behaviour of a commercial glass, Schott SF57, with high values of n₀ and n₂ when it is processed above P_cr with 800 and 1260 nm, 100 fs laser pulses to produce waveguide structures. Two types of structures, longitudinal (l-) and transversal (t-) ones depending on the sample translation, were obtained. In both of them, material damage surrounded by guiding regions was generated. We attribute the formation of the guiding regions of increased refractive index to the high local pressure reached in the focal volume where catastrophic damage occurs. This pressure can be high enough to compress the material nearby thus generating regions with a permanent refractive index increase up to 5 × 10⁻⁴. The efficiency of the guiding region is conditioned by the pulse energy. Mode profile analyses reveal double-sided exponential guided modes in the l-waveguides. As an alternative route to obtain suitable mode shapes and, simultaneously, to increase the coupling efficiency, the use of multiple structures has been investigated. Various l-structures have been written close to each other generating a region of increased refractive index large enough to effectively support a Lorentzian mode at 633 nm.     

On the dependence of equivalent dose on temperature of OSL measurements for sediment quartz grains and its implication in dating practice

The dependence of the equivalent dose (D_e) on the temperature used at stimulation when the standard OSL dating protocol (SAR) is applied has been investigated for sediment quartz samples. A considerable change in this value appears in the temperature region from 80 to 140 °C that is known for high complexity in OSL processes in quartz. Our observations suggest that the variation in the obtained results at least partly is caused by the laboratory procedure used when the natural OSL signal is measured. Directions for further investigations concerning this undesirable effect are indicated.     

Temperature dependence of a Ce3+ doped SiO2 radioluminescent dosimeter for in vivo dose measurements in HDR brachytherapy

Fiber-optic-coupled scintillation dosimeters are characterized by their small active volume if compared to other existing systems, and are therefore particularly suited for internal in vivo dosimetry. Due to possible differences between calibration conditions (i.e., room temperature) and conditions of clinical application (i.e., body temperature), their temperature dependence should be accurately studied. In this work, the temperature dependence of a Ce³⁺ doped SiO₂ scintillation detector coupled to a SiO₂ optical fibre was investigated for high dose rate brachytherapy applications. To this aim, two sets of irradiations with two different Ir-192 sources were performed in a water bath phantom at water temperatures ranging between 17 °C and 40.4 °C (Experiment 1). The relative response of the dosimeter was collected and analyzed. The same experiment was repeated with a second optical fibre which was designed without the active Ce³⁺ doped part at its end (Experiment 2) as well as by changing the length of the passive fibre inserted in water (Experiment 3). The two sets of measurements of experiment 1 were in accordance, indicating a linear increase with temperature of the scintillator sensitivity, with an average increase of 0.27 ± 0.2%/°C. In experiment 2, a 0.5%/°C increase of the collected signal resulted for the passive fibre. No significant difference of the temperature coefficient was found by changing the length of the fibre inserted in water (experiment 3). The obtained results show that a temperature-specific correction factor should be adopted at temperatures different than room temperature (e.g. for in vivo internal dosimetry). Further studies are required to understand the observations.     

Effect of gamma doses on the optical parameters of Se76Te15Sb9 thin films

The effect of γ-radiation dose on the optical spectra and optical energy gap (E_opt.) of Se₇₆Te₁₅Sb₉ thin films was studied. The dependence of the absorption coefficient (α) on the photon energy (hν) was determined as a function of radiation dose. The films show indirect allowed interband transition that is influenced by the radiation dose. Both the optical energy gap and the absorption coefficient were found to be dose dependent. The indirect optical energy gap was found to decrease from 1.257 to 0.664 eV with increasing the radiation dose from 10 to 250 krad, respectively. The results can be discussed on the basis of γ-irradiation-induced defects in the film. The width of the tail of localized states in the band gap (E_e) was evaluated using the Urbach edge method. The refractive index (n) was determined from the analysis of the transmittance and reflectance data. Analysis of the refractive index yields the values of high frequency dielectric constant (ε_∞) and the carrier concentration (N/m^*). The dependence of refractive index on the radiation dose has also been discussed. Other optical parameters such as real and imaginary parts of the dielectric constant (ε₁, ε₂) and the extinction coefficient (k) have been evaluated. It was found that the spectral absorption coefficient is expected to a suitable control parameter of γ-irradiation-sensitive elements of dosimetric systems for high energy ionizing radiation (0.06-1.33 MeV).