Seema Shinde

A thermoluminescent fast-neutron dosemeter based on pellets of CaSO4:Dy mixed with sulphur

The fast neutron activation reaction 32S(n, p) 32P in CaSO4: Dy has been used in the measurements of fast neutron dose by employing a post-irradiation TL accumulation method. In order to increase the efficiency of the method CaSO4: Dy powder was mixed with sulphur powder in various proportions from which pellets weighing each were made. After neutron irradiation these pellets were each burnt in an aluminium planchette and the phosphor residue with 32P beta activity on it was allowed to undergo self-irradiation for TL accumulation. The fast neutron efficiency of the system employing 10 pellets of 0.1% CaSO4: Dy was found to be about 100 times that of bare CaSO4: Dy powder.

Photo transfer thermoluminescence in CASO4:Dy — grain size dependence

Abstract The grain size dependence of PTTL (photo transfer TL) and RTL (residual TL) in CaSO 4 : Dy TL phosphor has been studied. For unground phosphor the PTTL was found to decrease as a function of grain size and for 53–37 μm grain size range the PTTL was found to be higher by a factor of 7.5 compared to the phosphor of grain size range 840–420 μm. When this unground phosphor in different grain size ranges were ground separately to 53–37 μm grain size, the PTTL in each case was found to increase. However, this increased PTTL was always less than that of the unground phosphor of 53–37 μm grain size but increased with the decrease in the original grain size range from which it was obtained. The residual glow curves of smaller grain size phosphor have an additional glow peak at 520 ° C which has been also found to contribute to the PTTL besides the 420 ° C glow peak. The PTTL was found to increase with Dy-concentration initially upto 0.05 mole %, thereafter it steadily decreased with the Dy-concentration.

Growth and optical properties of partially transparent Eu doped CaF2 ceramic

Partially transparent ceramic of 2 at.% Eu doped CaF2 have been grown preferentially towards [111] direction. For this purpose, Eu doped CaF2 nanoparticles (size∼12 nm) obtained by a low temperature solution growth method has been pressed at 1000°C under vacuum. The preferentially grown ceramic shows 15% transparency within the visible range of spectrum. As confirmed by the X-ray diffraction result, the hot pressed ceramic exhibits reduced lattice volume than the nanopowder. It indicates Eu3+ as the dominant substituting ions at the Ca2+ sites of CaF2 lattice in the hot pressed ceramic material. It is corroborated by the photoluminescence results of hot pressed ceramic which shows strong red emission corresponding to Eu3+ sites. However, photoluminescence of nanopowder exhibits intense peak in the blue region of the spectrum which is characteristics of Eu2+ sites.

Synthesis of gadolinium silicate by hydrothermal method

A simple method based on hydrothermal synthesis of materials to prepare gadolinium silicate has been prescribed. It is found that molar ratio of Gd(NO3)3: TEOS plays a crucial role in the formation of Gd2SiO5. The effect of calcinations, concentration of the precipitating agent and dopant atoms on composition and morphology of the synthesized materials has been investigated. The desired phase of Gd2SiO5 can be synthesized from hydrothermally grown powder after annealing at 1400°C.

Synthesis of optically transparent ceramic of CaF2 doped with Mn and Ce for thermoluminescent dosimetry

Nano-particles of CaF2: Mn were synthesized by a co-precipitation method. Optically transparent ceramics were obtained by vacuum hot-pressing at 1000°C under 20 MPa pressure for 2 h. The duration of pressure and dehydration of the initial powder was found important to achieve the transparency. 50% transparency was observed for a polished disc of 1 mm thickness. SEM micrographs revealed the absence of voids in hot pressed samples. These samples were found to be highly sensitive and linear for TLD and can measure doses from mGy to kGy.

Band-gap modulation via gallium substitution in cerium doped gadolinium aluminum garnet using a mixed fuel combustion approach

Cerium doped Gadolinium garnets (Gd3AlxGa5−xO12 where 0≤x≤5) are synthesized via combustion synthesis using mixture of urea and glycine fuels. A 4h Post annealing at 1400 oC is found to be necessary for pure phase formation. Lattice spacing variation as a result of partial or total Ga substitution at Al site was mapped by X-ray diffraction. Photoluminescence emission of Ce shifts as a consequence of Ga substitution and therefore suggests a local re-adjustment of crystal field around activator site.

Scintillation yield uniformity studies on single crystals of Tl doped CsI

Single crystals of 0.1% Tl doped CsI (50 mm φ and 50mm L) have been grown using the Bridgman melt growth technique. Scintillation yield uniformity of radiation detector made from the as-grown crystals was checked using an 243Am α (5.25 and 5.5 MeV) source. It was found that yield variation along the radial direction was within 2% over 0-15 mm and was less than 5% for the whole crystal. A correlation between radial temperature profile of furnace and yield uniformity was observed.

Size dependent absorption kinetics of sedimenting nanoparticles

Nanoparticles (NPs) beyond a certain size suspended in a lighter fluid medium, fall under gravity after attaining terminal velocity. This velocity is higher for larger particles. Thus absorption kinetics of ZnO NPs reflecting a change in the particle density with time exhibit different slopes for different sizes. A model based on Stoke’s law of viscous drag can predict the size distribution of NPs having negligible inter-particle correlations. However, distinct slopes of the absorption kinetics provide a rough idea of the average size of as grown NPs.

Effect of film thickness on luminescence property of CsI: Tl

Thin films of thallium activated cesium iodide (CsI: Tl) have been deposited on silicon substrates using a thermal evaporation technique. The films were found to have similar luminescence properties as bulk single crystals and the Tl ion concentration could be controlled by varying the film thickness. These can be used with P-I-N photodiodes in the radiation detection applications.

Epitaxial growth of Eu doped CaF2 thin film on CaF2 (111)

Epitaxial films of 2 at.% Eu doped CaF2 have been grown on (111) plane of CaF2 by a low temperature solution growth method. The CaF2: Eu films when grown on Si (111) and glass substrate show random orientation having higher degree of surface roughness. As confirmed by the X-ray diffraction and photoluminescence results, Eu (II) ions substitute the Ca sites of CaF2 lattice. Excitation spectrum shows two broad peaks at 282 and 366 nm, which correspond to the allowed transitions of 4f7 to 4f65d1 (eg) and 4f65d1 (t2g) of Eu2+, respectively. Photoluminescence of Eu (II) doped CaF2 films exhibit intense and sharp peak in the blue region of the spectrum.