PD Sahare

Nanocrystalline samples of Mn-doped CaF2 were synthesized by chemical coprecipitation method. The
impurity concentration was varied in the range of 0.5e4.0 mol%. The structure of the synthesized material
was confirmed using powder XRD analysis. TEM images of the nanoparticles show their size
occurring mostly in the range of 35e40 nm, with clusters of some impurity phases formed on annealing
of the material at higher temperatures. Detailed studies on TL showed that the structures of glow curves
depend on Mn concentrations and annealing temperatures. Optimization of the concentration and
annealing temperature showed that the sample (doped with 3.0 mol% and annealed at 673 K) has almost
a single dosimetric glow peak appearing at around 492 K. EPR and PL spectra were further studied to
understand the reasons for changes in the glow curve structures. All detailed studies on TL, PL and EPR
showed that the changes in glow curve structures are caused not only by the stress connected with the
difference in ionic radii of host Ca2þ and the guest impurity Mn3þ/Mn2þ, but are also governed by other
reasons, like diffusion of atmospheric oxygen and formation of impurity aggregates, such as, MnO2,
Mn3O4, etc. This is true not only for nanocrystalline CaF2:Mn but could also be so for the bulk CaF2:Mn
(TLD-400) and would thus help in understanding complex glow curve structure, high fading and the loss
of reusability on annealing beyond 673 K.

ABSTRACT A new high sensitivity Na2LiPO4:Eu optically stimulated luminescence dosimeter (OSLD) material was prepared by a simple solid-state diffusion method. The formation of the material was confirmed by comparing the experimental data with that available in the literature (JCPDF # 80-2110). The dosimetric properties of the phosphor material using a continuous wave-optically stimulated luminescence (CW-OSL) technique were studied. The material was studied for different concentrations of the impurity and also for different heating treatments. The material doped with 1.0 mol% and annealed at 873 K was found to be the most sensitive. The phosphor was found to have all the good dosimetric characteristics, such as tissue equivalence (low-Z, Zeff 10.8), high sensitivity (3 times less than the commercially available Al2O3:C, Landauer Inc., USA and BeO, Thermalox® 995, Materion Inc., USA), low fading (6.2% in 40 days), wide range of dose response (0.1–1.0 kGy), excellent reusability, easy optical bleaching (annealing) for its reuse, etc., which makes the material useful for dosimetry of high-energy radiations using OSL. The advantages of our OSLD phosphor are the easily available and inexpensive ingredients and a very simple method of preparation that makes it cost effective as compared to the commercially available OSLD phosphors. Also, it is easy to handle, unlike the Thermalox® 995 (BeO) dosimeters which are very toxic, and require a special method of preparation and handling.

ABSTRACT A new highly sensitive, low-Z (Zeff ≈ 10.8) TLD phosphor, Eu3+ doped NaLi2PO4, was successfully synthesized via solid state diffusion method. The formation of the single phase compound was confirmed by Powder X-Ray diffraction (PXRD) analysis. Variation of the doping level has shown that the impurity (Eu3+) concentration for maximum TL sensitivity is 0.5 mol%. Heat treatments given to achieve the high TL sensitivity of this phosphor also showed that it needs to be annealed at 973 K for 1 h. Incorporation of the impurity in the Eu+3 states was confirmed by the PL emission peaks. The TL glow curve consists of a prominent dosimetry peak at around 458 K besides small shoulders on both sides at around 400 and 500 K. The dose response of the phosphor was found to be sub-linear up to 10 Gy of the dose and later it becomes linear till it start saturating beyond 1 kGy. The TL sensitivity of the newly developed NaLi2PO4:Eu3+ phosphor to γ radiation from 137Cs (in the linear dose range) was compared to some standard commercially available phosphors, such as, TLD-100, TLD-400, TLD-700H and TLD-900. It was found to be much more sensitive than these phosphors except TLD-700H, which is ∼2 times more sensitive. Easy method of synthesis, simple glow curve structure, high sensitivity, low fading, wide range of doses and very good reusability make the phosphor a suitable candidate for the TL dosimetry.

ABSTRACT A new K2Ca2(SO4)3:Cu+ nanocrystalline TLD phosphor was prepared by chemical coprecipitation method using calcium chloride, potassium chloride and ammonium sulphate as reactants and copper chloride (Cu2Cl2, as impurity) in the presence of ethanol. The samples were characterized by X-ray diffraction (XRD), Transmission electron microscopy (TEM), Differential thermal and thermogravimetric analysis (DT-TGA) techniques. XRD and DTA data show that there is a phase transformation from orthorhombic to cubic occurring at around 550 K. The effects of impurity concentration, annealing temperature and γ rays dose on TL characteristics of the material have been studied. Different glow curves have been theoretically deconvoluted using computerized glow curve deconvolution (CGCD method) into simple glow peaks to determine their trapping parameters. The results show that different phases existing in the material on annealing might have reorganized the electron-traps (energy levels) and hole-traps (luminescence centers) and are responsible for changing glow curve structures. This is very important to know as any change in the glow curve structure would cause errors in estimation of doses of high-energy radiations and also may lose its reusability. The photoluminescence (PL) studies show that there are no redox reactions (Cu+ Cu2+) taking place and Cu remains in its Cu+ form after annealing and even after irradiation.

ABSTRACT In the present paper optimized dosimetric characteristics of low-Z magnesium tetra-borate MgB4O7:Mn,Tb using a thermoluminescence (TL) technique have been reported. The phosphor material was synthesized using a conventional high temperature solid-state diffusion reaction. The crystalline structure and phase purity of synthesized powder were confirmed by powder X-ray diffraction (XRD) analysis. The material in the microcrystalline form was found to be in orthorhombic form. The comparative dosimetric properties of the phosphor material have been extensively investigated for its applications in personal and medical dosimetry. It has been found that the codoped MgB4O7:Mn,Tb material, exposed to γ rays, shows better TL sensitivity and has an edge over the Mn and Tb doped samples as it is much more sensitive than the formers (550 and 40 times, respectively, more than the later ones). It has a simple glow curve structure (two well separated TL peaks centered at around 475 and 650 K). They are sufficiently above the room temperature (RT) to show low fading (~10% in a month after storing in dark at RT). However, the fading is much faster, if exposed to sunlight/room light/UV radiation. This has been a serious problem with many borate based phosphors. A detailed study on bleaching to UV–visible light of different wavelengths (energies) has been carried out and a new mechanism based on redox reactions is proposed. Low fading (~10% in a month) at room temperature on storing in dark, high TL sensitivity (3.5 times than that of TLD-100), tissue equivalence (Zeff≈8.23) and linear dose response up to wide range (0.1 Gy to ~5.0 kGy) of γ rays make it a suitable candidate for the radiation dosimetry and monitoring. However, it needs to be protected from sunlight/room light for fast fading.

This paper investigates the optically stimulated luminescence (OSL) response of BaFCl:Eu and K2Ca2(SO4)3:Eu phosphors for different doses and bleaching durations. The results have also been compared with the commercially available Landauer Al2O3:C (Luxel®) dosemeter. Nanocrystalline K2Ca2(SO4)3:Eu is known to be a sensitive thermoluminescent phosphor, but its OSL response is hardly reported. At first, pellets of nanocrystalline K2Ca2(SO4)3:Eu powder were prepared by adding Teflon as a binder. Their OSL signal was compared with that of the material in pure form, i.e. without adding the binder (in 100:1 ratio). It was observed that adding the binder does not appreciably affect the OSL intensity. On comparison with the commercially available Al2O3:C from Landauer, it was found that K2Ca2(SO4)3:Eu is around 15 times less sensitive than Al2O3:C. 'Homemade' BaFCl:Eu phosphor has also been studied. The intensity of BaFCl:Eu was ∼20 times more than the standard Al2O3:C dosemeter and ∼200 times more sensitive than K2Ca2(SO4)3:Eu in the dose range of 13-200 cGy. OSL dosemeters are believed to give luminescence signal even if they are read before, i.e. multiple reading may be possible under suitable conditions after single exposure. This was also checked for all the prepared dosemeters and it was found that Al2O3:C showed the least decrease of <2 %, followed by BaFCl:Eu of 15 % and K2Ca2(SO4)3:Eu with 20 %. Finally, Al2O3:C and BaFCl:Eu phosphors were also studied for their optical bleaching durations to which the respective signals get completely removed so that the phosphor can be re-used. It was observed that BaFCl:Eu is bleached faster and more easily than Al2O3:C.