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- Author or Editor: S. Durrani x
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Abstract
The leaching behavior of 
-emitter radionuclides (uranium and americium) from zeolite-L and the zeotype (SAPO-34) in a Flexcrete-cement matrix were examined by static and dynamic methods using 0.005M CaCl2 and synthetic ground water as leachants. The leaching rates of UO
2
2+
were found to be higher by about ten orders of magnitude than those of Am3+ for both zeolite-L and SAPO-34 in the cement matrix. The static and dynamic leaching rates of UO
2
2+
for SAPO-34 in CaCl2 and synthetic ground water were ten orders of magnitude lower than those for L. SAPO-34 showed good selectivity for uranium at pH 2–3.5 and L was usefully selective for Am3+. Distribution coefficients of Am3+ and UO
2
2+
increased with equilibrium pH.
Abstract
This paper describes a new version of the measurement of the calibration factor, K, between radon activity concentration and track density. The use of Solid State Nuclear Track Detectors (SSNTDs) is one of the most convenient techniques to assess the radiation level of 
-activities in the environment. Exposed plastic films are chemically and electrochemically etched in an alkali solution and the -tracks are evaluated under an optical microscope. The detailed procedure for this study and the caliabration of the etched films for conversion of track density to radon exposure in (Bq·m–3) are given in this paper. It was found the experimental and theoretical values of K were 1.37 and 1.27 (track·cm–2·kBq–1·h–1·m3), respectively, for plastic detectors CR-39.
Abstract
The effects of barium substitution for Bi or Sr sites on the growth of superconducting phases have been studied. The sol spray process has been used to synthesis the Bi-Sr-Ca-Cu-O (BSCCO) and Ba-BSCCO homogeneous ceramic powders. Thermogravimetric (TG), differential thermal analysis (DTA), X-ray diffraction (XRD), scanning electron microscopy (SEM) techniques were employed to characterize the synthesized materials. The electrical resistance was measured by classical d.c. fourprobe technique. It has been observed that sol spray process has affected the physico-chemical properties of the materials and also avoid the use of chelating agent as in the case of sol gel process. In addition to the Bi2Sr2CaCu2O8 (2212) phase Ba doped specimens also contained Bi2Sr2Ca2Cu3O10 (2223), BaBiO3, BaCuO2 and CuO phases. The results revealed that the specific effect of barium-doping on either sites (Bi or Sr) seems to avoid the formation of higher volume fraction of the low T c phase and promoting the formation of BiBaO3, BaCuO2 and CuO along with formation of a high T c 2223 phase. The substitution of Ba on either sites (Bi or Sr) lower the sintering temperature for the formation of high T c (small volume fraction) however, the Ba doped specimens also contained non-superconducting phases.
Abstract
Some plastic sheets manufactured or commercially available in Pakistan have been tested as radiation dosimeters for cobalt-60 
-rays. Radiation induced colouration in the plastics have been measured spectrophotometrically. The results show that 2 mm thick clear poly(methyl methacrylate) (PMMA) can be used as radiation dosimeter up to 45 kGy when absorption measurements are made at 305 nm and 314 nm; whereas 1 mm thick clear poly(vinylchloride) (PVC) is useful up to 30 kGy when measured at 396 nm. The response of PMMA dosimeter is stable for at least 15 days and that for PVC for 30 days, when stored under ambient conditions after irradiation. Post-irradiation stability at various temperatures (–10 to 55°C) has also been studied.
Abstract
Sol-gel process was employed to synthesize the Pb-BSCCO system having general composition Bi2−xPbxSr2Ca2Cu3O10−δ, where x=0.2, 0.4 and 0.8. Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), dilatometry and vibrating sample magnetometer (VSM) were employed to study the materials produced at different stages. Two-stage heating firstly at 300 and then 800°C was adopted in order to avoid the burning of the materials and formation of carbonates. The carbonate formation was avoided by heating the materials firstly at 300°C for 2 h and without intermediate cooling moved to the furnace having temperature 800°C and hold for 2 h. The sintering behaviour of samples was studied by dilatometry and the results revealed that the sample having x=0.4 was stabled up to a temperature of 700°C while samples having x=0.2 and 0.8 to a temperature of 625°C. The maximum shrinkage was observed at 850°C in all the samples. On the basis of dilatometry results, the samples were sintered at 845°C for 60 h to observe the superconducting phases. The highest volume fraction of high superconducting phase (2223) was noticed in the sample containing x=0.4 having onset T c=110 K.
Abstract
Yttrium aluminum garnet (YAG) and neodymium-doped yttrium aluminum garnet (Nd-YAG) nano-crystalline powders were successfully grown using cost effective sol spray process without the addition of any chelating agent or organic templates. Thermal decomposition behavior was studied by thermogravimetry (TG) and differential thermal analysis (DTA). Results revealed that crystallization of YAG started around 920 °C. The shrinkage/expansion behavior of synthesized powder was examined by dilatometer and revealing that sintering kinetics of these materials can be related to the evaporation of binder and formation of crystalline phases. Nano-crystallinity and garnet structure of YAG and Nd-YAG specimens were analyzed by Raman, fourier transform infra red (FTIR), and X-ray diffraction (XRD) techniques. XRD patterns were indexed using Rietveld refinement method. Smaller lattice parameter and a small change in atomic position of oxygen were found in Nd-YAG when compared with YAG structure. Scanning electron microscope (SEM) results indicated that particle size of Nd-YAG was <150 nm. The morphology of Nd-YAG nanosized powder was rounded in shape.
