[en] In this editorial, recent developments in the preparation of various doped calcium sulphates and barium sulphates as thermoluminescence (TL) dosimetry materials and improvements in their TL sensitivity are briefly outlined. (UK)

[en] CaSO₄:Dy phosphor prepared by a new recipe (denoted as N) is nearly 50% more sensitive than the presently used one (denoted as P). N consists of needle shaped crystals while P is mostly quadrilateral. In P most of the grains in as-grown condition are >75 μm in size while in N most of the grains are <75 μm. While the sensitivity of P increases with grain size, an exactly opposite trend is seen with N since higher sized grains (>105 μm) in N are agglomerates of particles and hence are opaque. The detection threshold of N (14.4 μGy) is nearly 4 times lower than that of P (54.2 μGy). The major glow peak(s) in both the phosphors occur in the 460-490 K (187-217 deg. C) region. But the low temperature peak near 390 K (117 deg. C) is very prominent in P while its presence is insignificant in N. The post-irradiation storage stability of N at ∼30 deg. C was tested up to a period of 25 d and found to be better than that of P. The emission spectra of P and N are characteristic of Dy³⁺. In P, the 480 nm to 570 nm emission intensity ratio varies slightly with glow peak temperature, unlike that of N. The Dy concentration quenching effect in N is less serious than that in P. The intrinsic UV sensitivity of N is nearly a factor of 20 times lower than that of P. (author)

[en] The behaviour of CaSO₄:Dy embedded Teflon (PTFE) thermostimulated luminescent dosimeters (TLDs) at high annealing temperatures (500-800 deg. C) has been studied for the first time. The study reveals the complete evaporation of Teflon at annealing temperatures above 500 deg. C. The residual powder weighed only half that of the CaSO₄:Dy powder contained originally in the disc. X-ray diffraction study indicates that this is due to the conversion of CaSO₄ to CaF₂ and DyF₃ during the breakdown of Teflon polymer. As a result, the weight and TL sensitivity of the residual powder, say after a 700 deg. C, 1 h annealing treatment, were only 50 and 29% respectively of that of the virgin CaSO₄:Dy phosphor powder of similar grain size

[en] High level gamma irradiation is employed for several applications including food processing, sterilization of medical products etc. It is necessary to confirm if a product is irradiated or not and also the exact irradiation dose. Presently, no simple radiation dosimeter system exhibiting linear and stable response exists in this dose region. Electro spin resonance of alanine dosimeter recommended by IAEA is quite complex. In food irradiation of perishable commodities radiation is delivered in sub-ambient temperatures such as chilled (0±4C), frozen (-20±2C) atmosphere and radiation doses are required to be measured at these low temperatures. Available chemical dosimeters in liquid state are not suitable for subambient dosimetry. To address this issue, several luminescence phosphors were synthesized at Saveetha Engineering College, Chennai in collaboration with Dr. Bhaskar Sanyal and Dr. Bhusan Dhabekar from BARC, Mumbai

[en] Optical absorption (OA) and thermoluminescence (TL) studies in LiF TLD-100 single crystals at high gamma-ray dose levels tend to support the validity of the mobile interstitial model in explaining the dependence of the glow curve shape with gamma-ray dose. Especially the disappearance of the dosimetric peak (peak no. V) at about 225 C and other low temperature peaks above 25 C at high gamma-ray dose levels (>10⁵ Gy) is accompanied by the disappearance of the respective OA bands at 310 and 380 nm. At the highest dose studied, LiF TLD-100 exhibits a TL peak at about 350 C (peak no. VIII) whose annealing step coincides with that of the 250 nm OA band which confirms the composite nature of this band. Dose levels greater than 7.2x10³ Gy result in the growth of F-aggregate centres with their characteristic OA bands at 448 nm (M centre) and at 378 nm (R₂ centre). However, detailed studies on the OA spectra of TLD-100 indicate that the mobile interstitial model in its present form does not explain satisfactorily the supralinearity in the response of different TL peaks seen in the medium dose range (10-10³ Gy). OA results tend to support the competing nonluminescent centre model at least for peak V which envisages a part of the charge released during TL readout to be trapped by these competitors, and indicate that more than one TL process operate simultaneously in this material. (orig.)

[en] Radiation safety status in fabrication of uranium oxide and MOX fuel at Nuclear Fuel Complex and Bhabha Atomic Research Centre are presented. (author)

[en] Criticisms are given of a paper concerning the microdosimetric analysis of the response of lithium fluoride thermoluminescent detectors for radiations of different qualities. These criticisms are levelled at target size, the role of impurities even in trace quantities, track integration effects, and the linearity of such dosemeters. A reply is given by the Consultant Editor. (UK)

[en] A new technique of non-violent and fast dissolution of sodium metal in a concentrated aqueous solution of Epsom salt (MgSO₄.7H₂O) at room temperature (RT) has been developed. The dissolution process is mildly exothermic but could be carried out even in a glass beaker in air under swift stirring condition. The reaction products consist of mixed salts of MgSO₄ and Na₂SO₄ as well as Mg(OH)₂ which are only mildly alkaline and hence are non-corrosive and non-hazardous unlike NaOH. A 50 mL solution having Epsom salt concentration of 2 M was found to give the optimal composition for disposal of 1 g of sodium. Supersaturated (>2.7 M), as well as dilute (<1.1 M) solutions, however, cause violent reactions and hence should be avoided. Repeated sodium dissolution in Epsom solution produced a solid waste of 4.7 g per g of sodium dissolved which is comparable with the waste (4 g) produced in 8 M NaOH solution. A 1.4 M Epsom solution sprayed with a high-pressure jet cleaner at RT in air easily removed the sodium blocked inside a metal pipe made of mild steel. The above jet also dissolved peacefully residual sodium collected on the metal tray after a sodium fire experiment. No sodium fire or explosion was observed during this campaign. The Epsom solution spray effectively neutralized the minor quantity of sodium aerosol produced during this campaign. This novel technique would hence be quite useful for draining sodium from fast breeder reactor components and bulk processing of sodium as well as for sodium fire fighting

[en] Since the ICRU Report 39 in 1985 on Determination of Dose Equivalent Resulting from External Radiation Sources, a number of reports have been published dealing with various aspects of ionising radiation. Measurement of these quantities is agreed by many to be the aim of personnel dosimetry. They are, however, sufficiently new, and their detailed interpretation sufficiently subtle, to warrant frequent and continued exposition and examination. Those who are involved in routine personnel and environmental monitoring services would therefore like to know in simple terms: (i) how to measure the new ICRU quantities and whether the present dosemeters (or instruments) can be used for this purpose or whether any major modification in their design will be needed; (ii) what are the differences and relative merits between these quantities and those that are being measured currently; and (iii) whether the new quantities will undergo any further change in the near future. These questions are discussed with specific reference to individual monitoring for photons. (author)

[en] The CaSO₄:Dy thermoluminescence dosemeter (TLD) badge used for countrywide beta, X and gamma ray personnel monitoring has been found capable of measuring simultaneously the peak voltage, half-value layer thickness and exposure to diagnostic X rays. (author)