Thermoluminescence Peak Temperature Research Articles

A Comparative Study of the Dosimetric Characteristics of BaSO4:Eu and CaSO4:Dy Teflon TLD Discs

Thermoluminescence (TL) characteristics of BaSO 4 :Eu Teflon discs (punched out from BaSO 4 :Eu Teflon sheet received from Nemoto and Co. Ltd, Japan) were compared with CaSO 4 :Dy Teflon discs (BARC make) of similar dimensions. The TL sensitivity of BaSO 4 :Eu discs was 5.8 and 11.0 times that of the CaSO 4 :Dy discs when they were compared on two TL readers, developed locally, having EMI 9524A and EMI 6255S photomultiplier tubes. The TL peak temperature of BaSO 4 :Eu Teflon discs occurs at about 220°C which is nearly the same as that for CaSO 4 :Dy discs. The photon energy dependence factor of these BaSO 4 :Eu Teflon discs at 52 keV as compared to that at 60 Co gamma energy was about 52: the corresponding photon energy dependence factor for CaSO 4 :Dy discs was about 9 at 32 keV. The dose vs TL response for 60 Co gamma radiation was studied in the dose range 1.0 mGy to 1.0 Gy and was found to be linear. The intrinsic UV (253.7 nm) response of these BaSO 4 :Eu discs was 3378 times that of CaSO 4 :Dy. TL fading of the exposed discs due to direct exposure to room light (at an intensity of 300 lux) for 8 h was 14% as compared to 5% for CaSO 4 :Dy.

Applicability in Dosimetry of Thermoluminescent Li2B407 Doped with Cu or Eu Impurities

Thermoluminescence properties of Li2B4O7 polycrystalline powder undoped and doped with Cu or Eu impurities are investigated. Glow curves of ß irradiated samples are recorded and the dependences of their shapes and of the peak intensities on the dopant concentrations are determined. The results obtained for Li2B4O7:Cu show, besides a very good agreement with previously reported data for slightly doped samples, the appearance of extra TL peaks with increasing Cu concentration. In the case of Li2B4O7:Eu, a high temperature thermoluminescence peak caused by the impurity is observed at any dopant concentration. Comparison with data concerning undoped Li2B4O7 allows for identification of the contributions of impurities to the glow curves. As an important dosimetric feature, the linearity of the TL response of all dosemeters is determined: a satisfactory behaviour is found for appreciably doped Li2B4O7:Cu, whereas samples doped with Eu or with low concentrations of Cu exhibit supralinearity and sub-linearity phenomena.

Thermoluminescence from a distribution of trapping levels in UV irradiated calcite

Both geological and synthetic calcite samples exhibit a low temperature thermoluminescence (TL) peak around 80°C; this TL peak has been the subject of several investigations since it is believed to involve localized transitions in the crystal rather than the more usual electronic transitions through the energy bands. We performed a detailed study of the kinetics of this TL peak in a high purity synthetic calcite powder. Annealing of the samples at temperatures above 500°C causes the TL peak at 71°C to become more narrow and the TL intensity to change dramatically between 400 and 700°C. Our experimental results are consistent with the presence of a distribution of activation energies and a first order TL process associated with this TL peak. Several commonly used methods of analysis such as the initial rise, heating rate, whole glow, isothermal decay and peak shape methods were used to evaluate the activation energy E, the frequency factor s and the order of the kinetics b. Good agreement was obtained between all methods except the isothermal decay method. The kinetic parameters associated with this low temperature TL peak were found to be E = 0.78 ± 0.03 eV, s = (1–7) × 10 10 s −1 and b = 1. A theoretical model based on a Gaussian distribution of energies provides a self-consistent description of the TL glow curves and the dose dependence of the observed TL height. When the calcite sample is annealed at temperatures above 500°C, the width of the Gaussian distribution of energies becomes more narrow. Two possible mechanisms are suggested for the observed changes in the TL glow curves.

Billion-year age dependence of luminescence in granitic quartz

Quartz grains from granites of known age ranging from 25 to 1040 million years old (Ma) that were previously studied using electron spin resonance (ESR), have been further studied using thermoluminescence (TL) and optically stimulated (green light) luminescence (OSL). Both inadvertently light-exposed quartz grians (Q1 samples) and the same quartz grains after further controlled light exposure (Q2 samples) plus gamma dose yielded signal characteristics strongly correlated with the crystallization age of the host granite. TL peak temperature in Q1 samples was positively correlated with age, whereas an anticorrelation with age was found for the OSL response after beta dose and standard preheating to Q1 samples. Regenerated TL sensitivity was found to decline in linear fashion with age ( R 2=0.998) for Q2 samples. The various correlations with age appear better than those found previously in these samples using ESR signals. It is concluded that luminescence pathways are altered over geologic time in a similar way for all the granites, and these changes may be potentially useful as a long-ranging quartz geochronometer.

The natural thermoluminescence of meteorites: 7. Ordinary chondrites from the Elephant Moraine region, Antarctica

We report natural and induced thermoluminescence (TL) measurements for meteorites from the Elephant Moraine region (76°17′S, 157°20′E) of Antarctica. We use our data to identify fragmented meteorites (i.e., “pairings”); our dataset of 107 samples represents at most 73 separate meteorite falls. Pairing groups are generally confined to single icefields, or to adjacent icefields, but a small proportion cross widely separated icefields in the region, suggesting that the fields can be considered as a single unit. Meteorites from this region have high natural TL levels, which indicates that they have small terrestrial surface exposure ages (<12,500 years). There do not appear to be significant differences in natural TL levels (and hence surface exposure ages) between individual blue icefields in the region. The proportion of reheated meteorites from the Elephant Moraine region is similar to that of other Antarctic sites and modern falls, consistent with the uniformity of the meteoritic flux in this regard. An unusual subset of H‐chondrites, with high induced TL peak temperatures, is absent among the data for meteorites collected in the Elephant Moraine region, which stresses their similarity to modern falls. We suggest that the Elephant Moraine icefields formed through shallow ablation of the ice. Unlike the Allan Hills sites to the south, lateral transport is probably less important relative to the infall of meteorites in concentrating meteorites on these icefields.

Breakup and Structure of an H-Chondrite Parent Body: The H-Chondrite Flux over the Last Million Years

Induced thermoluminescence (TL) measurements have identified a subset of Antarctic H chondrites which have significantly higher induced TL peak temperatures than other Antarctic H chondrites or modern falls. This group was not produced by weathering or shock, but appears to have been produced by differences in thermal history. This group also consists of meteorites with ∼8-Myr cosmic ray exposure ages and relatively large 3 He/ 22Ne and 21Ne/ 22Ne ratios suggestive of small degrees of shielding compared to other Antarctic and non-Antarctic H-chondrites. Metallographic cooling rate determinations confirm the unusual thermal history of this subset, H5 chondrites in this subset having cooling rates of ∼100 °C/Myr, compared to ∼10-20 °C/Myr for other H5 chondrites. Possible origins for this unusual subset include formation in a near-surface layer on a H-chondrite parent body, formation on a more rapidly cooling parent body which was not directly related to the parent body currently dominating the H-chondrite meteorite flux, or by impact processing during the 8-Myr event. Thermoluminescence data from meteorites from six Antarctic collection sites indicate that this subset dominated the H -chondrite flux ∼300,000 years ago, but ceased to be represented in the flux ∼20,000 years ago. The generally smaller size of these meteoroid bodies may have allowed them to evolve more rapidly to Earth-crossing orbits but also resulted in their rapid destruction in space. These data show that the H -chondrite flux has changed over a relatively short period of time in terms of average meteoroid size and thermal history.

An Application of Thermoluminescence to Herbicide Studies

Thylakoids of genetically engineered species of Synechococcus PCC7942 were investigated by thermoluminescence (TL), polarographic and herbicide-binding studies. The results were as follows: 1) Deletion of either copy I or copy II/III of the psbA gene family resulted in modified oscillation patterns of flash induced TL and O2 evolution compared to wild type cells. 2) Replacement of Ser264 in psbA I by Ala or Gly inducing strong herbicide resistance leads to a downshift of the TL peak temperature of B-band by 10 C and alters the oscillation pattern of flash induced TL and O2 evolution significantly to exhibit a pattern with comparatively high O2 yield after the 2nd flash. Additional deletion of psbA II III does not lead to significant changes compared to the single mutated strains. 3) Contrary to Ser,M mutants, replacement of Phe255 by Tyr in psbA I alone, which also induces herbicide resistance, is not accompanied by- corresponding changes in TL peak temperature and/or oscillation pattern of flash-induced TL and O2 evolution. However, strongly altered properties are observed after additional deletion of psbA II/III. Based on these data it is inferred that expression of either psbA I or psbA II III genes only gives rise to PS II complexes slightly different in their function. Site-directed muta- genesis of psbA I gene modulates the expression ratio between copies I and II/III. The possible implications are discussed.

Roles of Ca 2+ in O 2 evolution in higher plant photosystem II: Effects of replacement of Ca 2+ site by other cations

The properties of the S 2 states formed in Ca 2+-extracted, Sr 2+-substituted, and Cd 2+-substituted photosystem II (PSII) were comparatively studied by means of thermoluminescence (TL) and low temperature EPR spectroscopy. The following results were obtained: (i) Ca-extracted PSII showed neither EPR multiline nor g = 4.1 signals but showed an abnormal TL band with an upshifted peak temperature, which did not oscillate on excitation with two or more flashes. Addition of Ca 2+ to the extracted PSII reversed most of these effects concomitant with marked restoration of O 2 evolution, but the EPR g = 4.1 signal remained lost. (ii) Sr 2+ substitution largely restored the g = 4.1 signal and partly restored the multiline signal in a modified form having a reduced hyperfine line spacing concomitant with partial restoration of O 2 evolution. Sr 2+ substitution also reversed the abnormal TL peak temperature to normal, but the oscillation of the restored TL peak was much damped. (iii) Cd 2+ substitution restored neither of the two EPR signals nor O 2 evolution but reversed the abnormal TL peak temperature to normal. However, the reversed TL peak did not show any oscillatory behavior. Given these results, the function of the weakly bound Ca 2+ in S-state turnovers in higher plant PSII is discussed.

A systematic search of the dopants of calcium sulphide and their effect on the TL spectra above room temperature

AbstractResults on the thermoluminescence following incorporation of a wide range of dopant materials in calcium sulphide are reported. These results are compared with those previously reported in the literature. Factors such as fluxes and preparation technique are varied to determine their effect on the TL spectra. Conclusions regarding the possible source of the traps causing the TL in CaS are drawn with the evidence suggesting natural defects as the source of the traps; the added dopant impurities having only a secondary effect on the thermoluminescence peak temperatures.

Thermoluminescence and the shock and reheating history of meteorites: IV. The induced TL properties of type 4–6 ordinary chondrites

The induced thermoluminescence (TL) properties of 121 equilibrated ordinary chondrites have been measured. The samples were 74 H and 47 L chondrites, of which 33 H and 32 L were from Antarctica. The distribution of TL sensitivities for non-Antarctic L chondrites differs from that of non-Antarctic H chondrites, consistent with a greater proportion of the former class suffering post-metamorphic shock. Data on the effect of laboratory annealing on TL sensitivity, and step-wise Ar release measurements, enable the meteorites to be sorted into three shock-related temperature groups (<800°C, 800–1000°C,1000°C). The distribution of TL sensitivities for Antarctic meteorites suggests that only a few of the present samples have suffered intense shock. Antarctic H chondrites have TL sensitivities typically one third those of non-Antarctic H chondrites; this may reflect a greater proportion of meteorites which have suffered mild shock levels or greater degrees of weathering. On a diagram of TL peak temperature against peak width, L chondrites produce tight clusters with minimal overlap between Antarctic and non-Antarctic meteorites. Antarctic H chondrites also produce a tight cluster, but non-Antarctic chondrites plot in a band in which peak temperature increases with peak width, and there is little or no overlap between the Antarctic and non-Antarctic meteorites. Because TL peak temperature and width reflect the thermal history of the feldspar, and changes in these TL parameters can be produced by laboratory annealing experiments, this implies significant differences in the thermal (probably metamorphic) history of the Antarctic and non-Antarctic ordinary chondrites.

Some quartz thermoluminescence spectra relevant to thermoluminescence dating

A new high-sensitivity spectrometer was used to study the thermoluminescence spectra of several quartzes. It was found that natural quartz extracted from sediments, but otherwise untreated or given a gamma dose, yields two broad emission bands, one centred at 630 nm and the other extending from 350 nm to at least 550 nm. The dependence of the spectra on radiation dose were examined for both laboratory dose and natural dose, which differ by 9 orders of magnitude in dose rate, and no effect due to dose rate was observed. The dose responses of both emission bands were examined in the range 0–1600 Gy and were found to be highly non-linear and different. It is shown that the predose effect in the high temperature thermoluminescence peak is associated with the blue emission and not the red emission. For some sediment samples the presence of zircon in “quartz” extracts was readily identified by its spectrum; in some cases the zircon even dominated the thermoluminescence. Thus it is clearly necessary to remove the zircon if one wishes to study the thermoluminescence of the quartz. For a commercial quartz it was found that annealing at 700°C caused a dramatic spectral change and an increase in sensitivity, thus casting doubt on the applicability of thermoluminescence studies on annealed quartz to TL dating of natural quartz extracted from sediments.