Gillian Robertson

Three-dimensional spectral studies of the bleaching of the thermoluminescence of feldspars

Abstract Alkali feldspars, either extracted or as a component of an undifferentiated mixture, are important in thermoluminescence and optical dating. The present work describes measurements of three-dimensional thermoluminescence spectra, in which emitted light intensity is displayed as a function of both temperature and photon energy (or wavelength), for feldspars of a range of composition. In consideration of the increased role of TL/OSL in dating sediments, a particular emphasis has been an assessment of the way in which bleaching by visible and ultra-violet light affects the spectrum. Generally speaking, prolonged bleaching is necessary to remove TL from feldspars but most high-sodium feldspars in the study have a readily bleached component in the ultra-violet emission. We have not found spectral evidence for any other readily bleached peak at high glow-curve temperatures similar to the 325°C peak found in quartz. For some samples, bleaching results in increases of emission in the temperature region of interest for TL dating, and these increases appear across the emission spectrum.

The 100°C thermoluminescence emission from high-fired ceramics: A three dimensional view

Abstract The thermoluminescence emission of two high-fired ceramic samples which show sensitisation of the 100°C peak is described. The emission bands are compared with those seen in a sedimentary quartz sample and the luminescence centres responsible for the various emission bands are discussed.

Bleaching of the thermoluminescence of feldspars by sunlight

Abstract Feldspars are an important component of materials used for thermoluminescence (TL) and photoluminescence (PL) dating of sediments; and successful dating implies a knowledge of the degree of re-setting by exposure to sunlight of the stored luminescence energy. We have studied the bleaching by full sunlight of the TL of six alkali feldspars of representative composition and of one oligoclase. The high potassium and high sodium feldspars are the brightest, and are also the least easily bleached, whereas those of intermediate (K-Na) composition bleach quickly. On a time scale of upwards of 16 h, all samples would have bleached enough for them to be useful for TL dating. A search was made for individual glow curve peaks that bleach particularly quickly (and are thus similar to the well-known 325°C peak used in the TL dating of quartz). In the samples studied, there was only one glow curve peak that was selectively susceptible to bleaching: the 280°C peak in oligoclase.

Bleaching of the thermoluminescence of feldspars by selected wavelengths present in sunlight

Abstract Feldspars occur in many sediments, and dating them by thermoluminescence (TL) requires a knowledge of how efficiently sunlight bleaches these minerals. The relative bleaching efficiencies of various wavelengths have been investigated for four alkali feldspars and an oligoclase, using the natural TL of the samples and the artificial TL induced by laboratory irradiation, bleached by wavelengths in the range 322–350 nm. Ultraviolet wavelengths are more efficient than the longer wavelengths at bleaching all the glow-curve peaks and are responsible for most of the phototransfer from high-temperature peaks to low-temperature peaks. Some feldspars show an initial increase in TL intensity with bleaching. Two sanidines of similar bulk composition but different TL glow curves different dependences on bleaching wavelength. In a sodic sanidine with a dominant 240°C peak the energy required to bleach to 50% was a thousand times greater at 550 nm than at 322 nm. In contrast, another sanidine with a complex glow curve between 150 and 450°C showed a much slower change in the 330°C peak with wavelength—a factor of 10 between 322 and 550 nm—with a region between 400 and 500 nm which was almost independent of wavelength. This behaviour is explained by competing mechanisms of phototransfer and bleaching which depend on wavelength in different ways.

The THAI Ceramics Archaeological Project: TL characteristics of the artifacts

Abstract This project concerns the history of the ceramics industry in North Central Thailand, dating back perhaps a thousand years. Excavations at ancient kiln sites are in progress and scientific investigations are an important part of the work. TL dating is particularly important as C-14 and paleomagnetic measurements have limitations at these sites. The most interesting artifacts are of stoneware which is suitable for pre-dose dating. Kiln bricks are a plausible alternative but have proved to have unsuitable characteristics. In this paper we describe the TL properties of the various types of artifact as they reflect the firing conditions to which the artifacts were subjected. Most of the ages obtained are in the range 600–800 years.

MARKING RED-SCALE WITH CARBON-14 AND ITS EFFECT ON REPRODUCTION AND SURVIVAL

The possibility of using 14C to mark red‐scale for ecological studies has been investigated. Citrus leaves were labelled with 14C to have an activity in the range 3–300 μ Ci gm−1. All insects feeding on these leaves became radioactive. Mature females had an activity of 5000–160,000 c.p.m., mature males an activity of 1000–16,000 c.p.m. and the progeny of the females labelled to the level of 10,000 c.p.m. had an activity of 10–30 c.p.m. Higher levels of activity affected the development and fecundity of the insects. High mortality was observed in first‐instar larvae which had an activity ≥10,000 c.p.m. and in second‐instar larvae which had an activity ≥20,000 c.p.m. Fertilized females which had an activity of 30,000 c.p.m. did not reproduce.

Evidence for a new type of regenerated thermoluminescence in an albite

Abstract While recording the natural thermoluminescence (TL) of a feldspar (Amelia albite) it has been found that if the heating is not sufficient to clean out the high-temperature peak which occurs around 550–575°C, a new peak at about 300°C occurs on the next heating. This new observation of regeneration of TL is different from the regenerated TL reported in the literature, and seems to be due to a localized, thermally assisted mechanism.

A RADIOISOTOPE TECHNIQUE FOR LABORATORY STUDIES OF THE DISPERSAL OF RICE WEEVIL IN GRAIN

Adult rice weevils (Sitophilus oryzae (L.)) were marked with paint containing Scandium‐46 and detected in a column of wheat 4.5 cm diam by means of a γ‐scintillation counter. The radioactive paint had no effect on the mobility and longevity of the insects. Two weevils marked with Sc‐46 could be located if they were more than 2.5 cm apart. An account is given of the use of the technique to follow the movements of a single pair of male and female weevils over 8 days.

Effects of carbon-14 on the survival and reproduction of red scale males

The technique of producing sterile male red scale (Aonidiella aurantii (Mask.)) by treatment with 14C has been further investigated. In a group of males with a mean count rate of 6300 c.p.m., 75% emerged and mated normally with control females, but these females produced only 10% of the number of larvae produced by females mated with untreated males. In another group of males with a mean count rate of 14200 c.p.m., only 31% emerged but there was no further reduction in fertility. A count rate of 6000 c.p.m. is suggested as the optimum 14C content for producing viable sterile males in laboratory conditions. The prospect of using this method of sterilization in a sterile‐male project is rejected because of the difficulty of producing males with a predictable level of 14C, and the high variability in the numbers of larvae produced by females mated with them.

THE DISTRIBUTION OF CARBON‐14 IN PLANTS LABELLED AS A SOURCE OF FOOD FOR RED SCALE

Citrus leaves, banana squash and lemon fruit, labelled by photosynthesis, have been used as a source of 14C for red scale, Aonidiella aurantii (Mask.). The distribution of the isotope amongst the constituents of these plants has been studied using chemical methods of separation and chromatography.