S. V. Moharil

Thermoluminescence in LiNaSO4

Abstract Thermoluminescence characteristics of a new phosphor, LiNaSO4:Eu, are reported. The phosphor has a prominent glow peak around 405 K, emission around 412 nm, which lies in the most sensitive region of the common photomultiplier tubes, good sensitivity, excellent reusability and moderate fading. It is suggested that the phosphor can be used in dosimetry of ionizing radiation using thermoluminescence.

Preparation and characterization of magnesium-borate phosphor

Thermoluminescence is now extensively used for monitoring exposures to personnel. A high-sensitivity, tissue-equivalent phosphor is desirable in such applications. LiF:Mg,Ti is a widely accepted thermoluminescence dosimetry (TLD) phosphor. However, its sensitivity is low compared to that of many other phosphors which are unsuitable for personnel monitoring due to their other drawbacks. The magnesium borate activated with Dy having an effective atomic number (8.4) close to that of human tissue (7.4) reported by Kazanskaya et al. [1] is a promising material in this respect. Paun et al. [2] have reported the thermoluminescence of several activators in this host. Magnesium-borate phosphors were extensively studied by Prockic [3-5]. Despite its good tissue equivalence and sensitivity, use of this phosphor has not been widespread; this is most probably due to its severe fading. In a later work [6], Prockic described an improved phosphor, containing three impurities, which does not show considerable fading. Details of the preparation, however, are not available. Fukuda et al. [7, 8] have described the preparation of magnesium-borate phosphors, but the dosimetric characteristics of these phosphors were not given. This letter describes the preparation and the dosimetric characteristics of a Dy-doped magnesium-borate phosphor of high sensitivity and low fading. The phosphor was prepared by a solid-statechemistry method. Magnesium-nitrate hexahydrate (AR, S. de fine chemicals, 10.00 g), ammonium tetraborate tetrahydrate (AR fluka, 10.27 g) and dysprosium oxide (99.99%, Indian Rare Earths, 14.5 rag) were thoroughly mixed and heated at 80 °C for 12 h and then at 800 °C for 24 h. The resulting compound was slowly cooled to room temperature, crushed to a fine powder, and again heated at 500 °C for 1 h and then quenched to room temperature. The formation of MgB40 7 was confirmed by obtaining a powder diffraction pattern and comparing it with standard data (JCPDS file No. 31-787). Use of ammonium tetraborate instead of boric acid, as recommended in the conventional methods, was found to yield a crystalline phosphor with the desired characteristics. Exposures to gamma rays were given using a Co 6° source. Thermoluminescence-glow curves were recorded with the usual set-up consisting of a small metal plate heated directly using a temperature programmer, a photomultiplier (931 B), a direct current (d.c.) amplifier and a millivolt recorder. Each time, 5 mg of the phosphor was heated at the rate of 150 K min -~. Fig. i shows a glow curve of the phosphor exposed to 0.26 Cikg -1 (1 Ci-3.7 x 10 l° Bq). The glow curve for CaSO4:Dy is also given for comparison. There is a strong peak at 460 K and other weak

Colour centres in microcrystalline powders of alkali halides

Abstract Powders of twelve alkali halides have been coloured in an electrodeless discharge. Due to the simultaneous production and bleaching of F centres, F aggregate centres could be produced in an adequate concentration. From their study it has been concluded that powders behave as deformed single crystals. It could also be shown from this study that the interaction between colour centres and dislocations is lattice dependent and varies regularly as cation changes from Li+ to Rb+, and anion changes from F −to I−.

Growth of colloids in microcrystalline powders of coloured KCl: particle size dependence

It is shown that colloids can be formed much more easily in microcrystalline powders than single crystals. The colloids can be formed at lower and lower temperatures with decreasing particle size of the powders. The ease of colloid formation is attributed to the dislocation-aided motion of F centres.

Effects of selective dissolution on thermodulminescence of extended-chain crystals of polyethylene

Augmentation de la teneur en cristaux a chaine etiree, par rapport aux cristaux en chaine plissee (I) par dissolution selective de (I) par le melange benzene-toluene

Deformation coloration of KF

Abstract Results on optical absorption and thermoluminescence of KF coloured by γ rays are reported in this paper. With optical bleaching, F centre absorption maxima shifted from 455 nm to 475nm. The shift was accompanied by the appearance of additional peaks in glow curves. These changes are attributed to deformational effects.

Spontaneous colloid formation in microcrystalline powders of synthetic NaCl in electrodeless discharge: particle size dependence

Abstract Colloids can be formed much more easily in microcrystalline powders than in single crystals. They can be formed at lower and lower temperatures with decreasing particle size of the powders. Here, the particle size dependence of spontaneous colloid growth in electrodeless discharge is reported. It is shown that adequate concentration of colloids can be formed during lower and lower discharge times with decreasing particle size of the powders. The ease of colloid growth in finer particles is attributed to the increase of dislocations, which are the nucleation sites for the aggregation of F centers. It is further shown that addition of K (potassium) impurity decreases the observed ease in these powders.

The nature of the defects in NaF:LiF

Abstract Most of the alkali halides are freely miscible with one another. The solid solubilities of fluorides, however, exist over a limited range. Thus, not more than 1.5 mol.% NaF can be added to LiF, and the maximum amount of LiF that can be accommodated substitutionally in NaF is about 8.5 mol. 96. Fate of LiF added in excess to these amounts is unknown. It has been suggested that Li+ may enter interstitially. The coloration of the solid solutions provide a clue to the position of the foreign alkali ion in the host lattice. The optical and TSL measurements on the coloured NaF:LiF samples are presented in this paper, which show that Li+ partially goes to interstitial sites, and the remaining amount forms colloids.