A. G. I. Dalvi

Trap level spectroscopy of actinide-doped alkaline-earth sulphates. I. SrSO4:239Pu and CaSO4:239Pu

Trap level spectroscopy studies of alkaline-earth sulphate (CaSO4 and SrSO4) phosphors doped with 239Pu were carried out using electron paramagnetic resonance (EPR) and thermally stimulated luminescence (TSL) techniques. Internal (in situ) alpha -irradiation (from the alpha -decay of 239Pu) and external gamma -irradiation studies carried out using EPR revealed the formation of radicals SO2-, O-, O3-, SO4-, etc, in these matrices under different conditions. SO2- dimer formation is detected for the first time in alkaline-earth sulphates on gamma -irradiation at 77 K. The thermal stabilities of the radical ions (monitored using EPR) and their correlation with TSL glow peaks helped to identify the thermally stimulated free-radical reactions which result in luminescence and were characterised by the activation energy and frequency factor obtained from the analysis of TSL glows.

Trap-level spectroscopy of actinide-doped phosphors. II. SrSO4:241Am

For pt.I see ibid., vol.17, p.5851 (1984). Trap-level spectroscopic studies of SrSO4 phosphor doped with 241Am were conducted using ESR and thermally stimulated luminescence (TSL) techniques. The formation of electron and hole traps due to internal alpha -irradiation (from the decay of 241Am) and external gamma -irradiation were distinguished by carrying out the studies on pure SrSO4 and also on SrSO4 doped with europium (lanthanide analogue of Am). The ESR studies on these samples have shown that the paramagnetic radicals SO4-, SO3-, O3-, S5+, SH2- were stabilised in SrSO4 under different dopant and irradiation conditions. The radical SH2- is detected for the first time. From the ESR studies of thermal stabilities of radical ions produced and their correlation with TSL peaks, the role of paramagnetic molecular species in the electron and hole trapping and thermally stimulated free radical reactions were identified and the corresponding activation energies and frequency factors were determined.

Absence of unusual sequence of commensurate-incommensurate phase transitions in LiKSO4: an EPR study using an SO4- probe

The structural phase transitions in LiKSO4 have been examined by EPR, at X band, using a paramagnetic SO4- probe. The orientation of the SO4- probe ion is modified with respect to that of the parent SO42- ion. The authors show that this modified orientation and its temperature-dependent motion has misled earlier workers into suggesting an unusual sequence of commensurate-incommensurate transitions in LiKSO4. Their measurements also support the occurrence of another transition in this compound at 130 K, as predicted by neutron diffraction work. This transition appears to trigger an anti-ferro-distortion resulting in the rotation of SO4- by +or-10 degrees about the c axis; all of the sulphates remain chemically equivalent. LiKSO4 exists below 130 K as a mixed-phase compound down to 77 K.

Traplevel spectroscopic studies of BaCO3: Eu and BaCO3: 241Am phosphors

Abstract With a view to understanding the defects due to self-irradiation in 241Am (α-active with T ½=433 years) doped BaCO3 and their role in thermally induced free radical reactions/electron-hole recombination, trap level spectroscopic studies were conducted on BaCO3: 241Am and BaCO3: Eu (lanthanide analogue of Am) using Thermally Stimulated Luminescence (TSL) and Electron Spin Resonance (ESR) techniques. In the case of 241Am-doped BaCO3 phosphor, three glow peaks at 357, 420 and 500 K (for rate of heating β=2.5 K sec−1) were observed and their spectral character has shown that Am2+ acts as the luminescent centre. The TSL glow pattern and the ESR spectrum arising due to internal α-irradiation was unaltered with further (external) γ-irradiation of the phosphor. The ESR studies on these samples have shown that the carboxy CO2- radicals are produced due to α-irradiation and their thermal instabilities are responsible for triggering the processes responsible for the observed TSL peaks. In the γ-irradiated B...

Intermolecular energy transfer from UO2+2 to Eu3+ in solutions

Abstract The quenching constants for the UO 2+ 2 ion fluorescence by the Eu 3+ ion in H 2 O, D 2 O, potassium formate and acetic acid media were determined by measuring the decrease in intensity of the 5050 A fluorescence peak and the lifetime of the UO 2+ 2 ion fluorescence. The energy transferred to the Eu 3+ ion was found to be a small fraction of the energy lost by the UO 2+ 2 ion by the non-radiative processes. The variations of the quenching constants of the UO 2+ 2 ion and the fluorescence lifetimes were determined for different concentrations of potassium formate and acetic acid. These results indicate that the UO 2+ 2 ion forms inner sphere complexes with the two ligands mentioned.

Spectrographic estimation of impurities in selenium

ZusammenfassungFolgende Verunreinigungen werden in hochreinem Selen in Konzentrationen von <1 ppm bestimmt: Al, As, Ba, Bi, Ca, Cd, Co, Cr, Cu, Fe, Hg, Mg, Mn, Mo, Ni, Pb, Sb, Sn, Te, Ti, V, Zn und Zr. Das Selen wird von den Verunreinigungen durch Verdampfen abgetrennt (Lösen einer 1 g-Probe in HNO3/H2SO4). Der Rückstand wird in 6 M HCl gelöst und zusammen mit einem Graphit/NaCl-Gemisch (90∶10) in die Elektrodenbohrung gefüllt. Die Anregung erfolgt in einem Gleichstrombogen von 13 A. Die Nachweisgrenzen liegen im Bereich von 0,005–0,5 ppm, die Genauigkeit beträgt 7–18%.SummaryAn emission spectrographic method for the estimation of impurities of Al, As, Ba, Bi, Ca, Cd, Co, Cr, Cu, Fe, Hg, Mg, Mn, Mo, Ni, Pb, Sb, Sn, Te, Ti, V, Zn and Zr in high purity selenium at concentrations less than 1 ppm has been developed. The impurities were separated from 1 g of selenium by volatilizing Se from its solution in nitric acid and sulphuric acid. The residue containing impurities was dissolved in small amounts of 6 M HCl and loaded along with the washing on 10 mg mixture containing graphite (90%) and sodium chloride carrier (10%), in the electrode crater. The spectra were excited in a d.c. arc carrying 13 A. The detection limits lie in the range 0.005–0.5 ppm for the different elements. The precision of the method ranges from 7–18% for these elements.

Trap level spectroscopy of actinide-doped alkaline-earth sulphates. III. SrSO4:UO22+

For pt.II see ibid, vol.21, p.5913 (1988). Electron paramagnetic resonance (EPR) and thermally stimulated luminescence (TSL) studies were conducted on gamma -irradiated SrSO4:UO22+ to elucidate the role of electron and hole traps in thermally stimulated reactions and to obtain the trap parameters (the trap depth and frequency factor). For samples annealed at 970 K (samples A), intense hydrogen atom signals were seen in EPR, and it was found that the thermally stimulated reaction between H0 atoms and SO4- is responsible for the luminescence glow at 380 K. In the close vicinity of this temperature, the EPR spectrum of hydrogen exhibited features of chemically induced dynamic nuclear polarisation, suggesting that this reaction proceeds through pair formation. The hydrogen atom intensities were considerably smaller for samples quenched at 1170 K (samples B) but appeared to have participated in the formation of SH2. In both samples A and samples B, a trapped hole centre with g=1.995 formed owing to gamma -irradiation at 300 K. The temperature stability of this crucially depended on the presence of H0 and also SO4u-. The intense glow peak at 420 K present in both samples was identified as due to the reaction between SO4SuS- and UO2+.

Trap level spectroscopy of actinide-doped phosphors. I. LiF:UO22+ and LiF:241Am

Trap level spectroscopic investigations have been carried out on LiF doped (separately) with uranium and americium using EPR, TSL and TSL-spectral techniques. These studies, apart from obtaining trap parameters-trap depths and frequency factors-helped in elucidating the processes that occur in electron and hole trapping and their subsequent recombination on thermal stimulation. In the uranium-doped sample the electron trapping by U6+ complexes (UO6-)6- and (UO5F)5- at (LiF6-)5- sites and subsequent electron-hole recombination at U6+ has been identified as the predominant mode of TSL. In 241Am-doped sample americium has been found to be stabilised in the divalent state. Whereas in the high-temperature region F-centre production and Am2+ to or from Am3+ were found to be the dominant modes of electron and hole trapping, respectively, in the region below room temperature Am2+ to or from Am+ and production of U3 centres (hydrogen atoms at F- sites) were found to be the dominant modes of electron and hole trapping, respectively. In both high-temperature and sub-room-temperature regions electron-hole recombination results in the creation of electronically excited Am2+ resulting in the luminescence of Am2+ on thermal stimulation.

Thermally stimulated luminescence studies in plutonium- and americium-doped alkali halides

Abstract Thermally stimulated luminescence (TSL) studies were conducted on 239 Pu- and 241 Am-doped NaCl and KCl. Both self-irradiated (by α-particles) as well as externally γ-irradiated samples were investigated. In general, the TSL glow curves were found to be similar under these two irradiation conditions for both types of samples. In addition to the intrinsic emission of the host lattices, characteristic emissions of Pu 3+ /Am 3+ were also observed in the 239 Pu/ 241 Am doped alkali halides. The main glow peaks observed above room temperature are associated with the partial thermal destruction of radiation-induced F -centres and the total destruction of F - and M -centres. The trap parameters for the different glow peaks have been determined.

Spectrographic Determination of Trace Impurities in Sulphur

SummaryAn emission spectrographic method for the estimation of traces of some common impurites viz., Al, Ba, Bi, Ca, Cd, Cr, Cu, Fe, Mg, Mn, Ni, Pb, Sn, Ti and V in high-purity sulphur is described. The impurities separated from 1-g sample, after removing sulphur as SO2 by heating it in air at about 300° C, were dissolved in a small amount of 6M hydrochloric acid and loaded on 10 mg of carrier mixture containing 90% graphite and 10% sodium chloride in the 1/4″ electrode crater. The spectra were exited in a D. C. arc carrying 13 A current for 45 seconds. Cobalt was used as an internal standard and sodium chloride as a carrier. The lowest detection limits lie in the range 0.005 to 0.05 ppm for the different elements. The precision of the method ranges from 6–19% for the elements analysed.ZusammenfassungEine emissionsspektrographische Methode zur Bestimmung üblicher Spuren-Verunreinigungen in hochgereinigtem Schwefel, wie Al, Ba, Bi, Ca, Cd, Cr, Cu, Fe, Mg, Mn, Ni, Pb, Sn, Ti und V, wurde beschrieben. Die aus 1 g Schwefel, nach dessen Entfernung als SO2 durch Erhitzen an der Luft bei etwa 300° C, abgetrennten Verunreinigungen werden in wenig 6-m Salzsäure gelöst und mit 10 mg Trägergemisch, bestehend aus 90% Graphitpulver mit 10% Natriumchlorid, in die Vertiefung einer 1/4″-Elektrode eingebracht. Das Spektrum wird im Wechselstrombogen von 13 A für 45 sec angeregt. Kobalt dient als interner Standard mit Kochsalz als Träger. Die unterste Nachweisgrenze liegt bei 0,005–0,05 ppm für die verschiedenen angegebenen Elemente. Die Genauigkeit beträgt 6–19%.