[en] Published in summary form only

[en] Five types of building materials of different quality and from different sources were analysed for uranium and thorium using instrumental neutron activation analysis (INAA). The concentration of thorium was found to be about 3-5 times higher than uranium while the activities were about the same. The total activities of both elements was found to be between 1-4 pCi g^-1. (author) 1 ref.; 1 tab

[en] The natural radiation damage in zircon caused by the decay of uranium and thorium, present as impurities, is studied, the radiation damage is first gauged by etching the fission tracks. It is found that thermoluminescence (TL) sensitivity (defined as light output per unit test-dose) decreases as the radiation damage increases, suggesting a destruction of TL centres. The spacing d of the (112)-plane is also measured. It is also found that d-value increases with radiation damage, suggesting the displacement of atoms from their normal lattice sites. However, as the track density increases beyond ∼ 3X10⁶ tracks/cm², the d-value remains at ∼ 2.52 A. By annealing the crystal, the displaced atoms are found to return to the original lattices sites, and this is followed by a reduction in d-value as well as the recovery of TL sensitivity. The fission track density also decreases and all the tracks disappear at the annealing temperature of ∼ 800⁰C. (author)

[en] Concentrations of uranium and thorium in some West Malaysian limestones have been determined using neutron activation and delayed neutron analyses. These limestones are mainly calcium carbonates and contain uranium and thorium in concentrations of about a few parts per million. (author) 4 refs.; 2 figs

[en] Many of the minerals used for archaeological dating employing thermoluminescence (TL) exhibit anomalous fading to some extent. It is known for zircon that radiation damage, caused by the decay of uranium and thorium present in it as impurities, adversely affects the TL sensitivity as well as its ability to store natural TL. We have investigated the effects of radiation damage on the anomalous fading of TL in zircon, and find that all zircons, whether natural or artificially produced, exhibit anomalous fading of TL. Such fading is aggravated by radiation damage, but is reduced on annealing the damaged crystal, thus providing strong evidence for a link between radiation damage and anomalous fading in zircon. We have measured the spectral composition of the TL, and find that in highly damaged zircons the rate of anomalous fading is a function of the wavelength of the TL glow. The effects of varying the storage temperature and dose-rate have also been investigated. (author)

[en] A radiation dosimeter based on Ge-doped silica fibre is described. Parameters concerning thermoluminescence (TL) induced by ⁶⁰Co irradiation are investigated, including activation energies, frequency factors, and reproducibility with dose and fading. It is concluded that Ge-doped silica fibres provide a good basis for medical radiation dosimetry at therapy levels. In particular, doses are reproducible to within 3%, the fibres are reusable and show linearity of dose versus TL output over the approximate range of dose 1 Gy to in excess of 100 Gy. At room temperatures, fading within the first 30 d following irradiation has been found to be of the order of 7%. (author)

[en] It is found that natural zircon, which has suffered a low degree of damage from the decay of its uranium and thorium impurities, displays a TL spectrum with peaks at approx. 480 nm (blue-green) and approx. 600 nm (yellow-orange); whereas for severely damaged zircon the spectral composition exhibits only a broad peak centred at approx. 600 nm. When annealed, the severely damaged zircon reverts to displaying - in response to a test dose - a TL spectrum similar to that of the less damaged crystals. Moreover, when the completely annealed zircon is subsequently subjected to intense artificial damage, it once again shows a TL spectrum with a broad peak centred at approx. 600 nm. These observations clearly link the TL spectral composition with the degree of radiation damage sustained by zircon. By measuring the TL spectra after various storage times at room temperature, it is found that the long-wavelength parts of the spectra fade faster than the shorter-wavelength parts. (author)

[en] The etching time of zircons with different amounts of radiation damage is measured. It is found that as track density increases, a shorter etching time is needed to reveal the tracks. The change in X-ray diffraction angle (20) of the (112) plane for zircon with different amounts of radiation damage is also studied. A correlation is found between diffraction angle and fission track density. For zircon with natural track density of ≤ 3 x 10⁶ tracks/cm², there seems to be an inverse relation between track density and 20 values suggesting that as the degree of radiation damage of the crystal increases, more atoms are forced into interstitial positions. However beyond the track density of ∼ 3 x 10⁶ tracks/cm², the change in 20 with increasing track density is not as rapid as before, approaching a saturation value of 35.62^o. (author)

[en] The natural radiation damage in zircon caused by the decay of uranium and thorium, present as impurities, is studied. The radiation damage is first gauged by etching the fission tracks. It is found that thermoluminescence (TL) sensitivity (defined as light output per unit test-dose) decreases as the radiation damage increases, suggesting a destruction of TL centers. The spacing d of the (112)-plane is also measured. It is also found that the d-value increases with radiation damage, suggesting the displacement of atoms from their normal lattice sites. However, as the track density increases beyond ≅ 3x10⁶ tracks/cm², the d-value remains at ≅ 2.52 A. By annealing the crystal, the displaced atoms are found to return to the original lattice sites, and this is followed by a reduction in d-value as well as the recovery of TL sensitivity. The fission track density also decreases and all the tracks disappear at the annealing temperature of ≅ 800⁰C. (orig.)

[en] This paper reports on the radiation damage in two types of U-rich minerals, viz, zircon and apatites that has been studied using thermoluminescence (TL) method. In U-rich minerals considerable radiation damage over geological time-periods, mainly through the α-decay of these actinides, but, to some extent, also through their fission decay. Radiation damage is gauged by measuring the track density, caused by fission fragments. A clear inverse relation is found between the natural TL (as well as the TL sensitivity - a light output per unit dose) and the natural fission track density. Annealing out the radiation damage, whether natural or artificial, restores and TL sensitivity progressively as the pre-annealing temperatures is increased. The TL sensitivity seems to recover fully when the crystals was annealed at ∼800 degrees C for 1 hour