T.K. Seshagiri

Application of ICAP-AES for the determination of Dy, Eu, Gd, Sm and Th in uranium after chemical separation.

A method has been developed for the determination of Dy, Eu, Gd, Sm and Th in uranium (after chemical separation) by use of an inductively-coupled argon plasma in conjunction with a direct-reading spectrometer. The method can be used for the determination of Dy and Eu down to 0.02 mug ml , Gd to 0.05 mug ml , Sm to 0.1 mug ml and Th to 0.20 mug ml .

SO4−–SO3− radical pair formation in Ce doped and Ce, U co-doped K3Na(SO4)2: EPR evidence and its role in TSL

Abstract Thermally stimulated luminescence (TSL) and electron paramagnetic resonance (EPR) studies were carried out on cerium doped and cerium–uranium co-doped K 3 Na(SO 4 ) 2 samples after γ -irradiation. Three glow peaks around 352, 415 and 475 K were observed and their spectral characteristics have shown that Ce 3+ and UO 2 2+ act as the emission centres in K 3 Na(SO 4 ) 2 :Ce and K 3 Na(SO 4 ) 2 :Ce, U, respectively. In Ce–U co-doped sample, energy transfer from cerium to uranium takes place. The commonly occurring radiation-induced centres in sulphates, viz SO 3 − and SO 4 − were observed by EPR and SO 4 − radical ion was found to take part in the TSL emission at 415 K . The hitherto unknown information, however, is the formation of SO 4 − –SO 3 − radical pair creating deep traps in these lattices, apparently assisted by the dopants. This is the first observation of such radical pair formation leading to the identification of deep traps in this lattice. The radical pair, (SO 3 − –SO 4 − ) which is stable up to 970 K , decreases the intensity of the peak at 415 K due to the depletion of SO 4 − centres.

Thermally stimulated luminescence and electron paramagnetic resonance studies of doped K3Na(SO4)2

Abstract Rare earth and actinide doped alkali and alkaline earth sulphates, exhibit a variety of point defects stabilized due to the charge imbalance/self-irradiation and they play an important role in luminescence properties. In this paper, we report the point defects formed in the mixed sulphate K3Na(SO4)2 on doping with the radio-active rare earth element 147 Pm as studied by TSL and EPR techniques. EPR studies on self and gamma irradiated samples showed the signal due to the radical pair, SO4−–SO3− in addition to the signals from SO4−, SO3− and O2− ions. However EPR spectra of electron beam irradiated (undoped) K3Na(SO4)2 samples did not show the presence of the radical pair SO4−–SO3−, indicating the importance of dopant per se, in stabilizing the radical pair. EPR studies of 147 Pm doped samples annealed at different temperatures after gamma irradiation showed that SO4−–SO3− radical pair gets destroyed around 550 K , whereas SO4− ion gets annealed in the temperature range 375– 450 K . SO3− ion was found to be stable upto 600 K . From TSL–EPR correlation, it is inferred that the release of trapped hole at SO4− ion on heating leads to the formation of SO 4 2− ∗ and energy transfer to Pm3+ ion, results in the glow peak at 415 K .

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.

Thermally stimulated luminescence and electron paramagnetic resonance studies of 237Np doped alkaline earth sulphates

Abstract Thermally stimulated luminescence (TSL) and electron paramagnetic resonance (EPR) studies were carried out on samples of 237 Np 4+ doped CaSO 4 /SrCO 4 . TSL glow peaks with T max around 395 and 425 K in CaSO 4 , and 425 K in SrSO 4 , were observed on samples gamma-irradiated at 300 K. The prominent TSL around 425 K in CaSO 4 /SrSO 4 was found to coincide with the temperature at which the EPR signals of SO 4 − radical ions diasappear. The trap depth value for this process has been determined from both TSL and EPR data. A comparison is made of the trap depth values obtained for “hole” detrapping at the sulphate site in various actinide doped CaSO 4 /SrSO 4 lattices studied in our laboratory. The average activation energy was found to be in the range 0.8–0.9 eV.

Thermally stimulated luminescence and electron paramagnetic resonance studies on uranium doped K2Ca2(SO4)3

Thermally stimulated luminescence (TSL) studies of gamma-irradiated uraniumdoped K2Ca2(SO4)3 revealed two glow peaks around 400 K and 435 K. Electron paramagnetic resonance (EPR) studies carried out on these samples have shown the formation of the radical ions SO4−, SO3−, SO2− and O3−. From the study of the thermal stabilities of these radical ions, it was found that the thermal destruction of SO2− and SO4− radical ions are associated with the glow peaks observed around 400 K and 435 K respectively. Uranate ion was identified as the luminescent centre for the observed TSL glow. The trap depth values for the glow peaks have been determined from TSL data.

Nitrate anion effects on the trap formation and thermally stimulated luminescence of Np4+-doped BaCO3

Abstract Thermally stimulated luminescence (TSL) and electron paramagnetic resonance (EPR) studies were conducted on self-irradiated as well as gamma irradiated BaCO 3 co-doped with 237 Np 4+ and NO 3 − ions. EPR studies of the irradiated samples revealed that the electron transfer process between iso-electronic carbonate and nitrate groups is the dominant effect of ionizing radiation, forming CO 3 − and NO 3 2− ions. This facilitated the radiation stability of the valence of Np in the tetravalent state. TSL spectral studies showed that Np 4+ ion acts as the luminescence centre. TSL–EPR correlation studies revealed the role of CO 3 − ion in the glow peak at 413 K .

Radiation stabilization of U5+ in CaO matrix and its thermal stability: Electron paramagnetic resonance and thermally stimulated luminescence studies

Electron paramagnetic resonance (EPR) evidence is presented for the radiation stabilization of pentavalent uranium in CaO matrix. From the theoretical predictions ofg value for U5+ in axial symmetries, it was concluded that U5+ at Ca2+ site is associated with a second neighbour charge compensating Ca2+ vacancy. EPR measurements also revealed the presence of Mn2+, Mn4+ and Cu2+ impurities in the samples. The thermal stability of U5+ was investigated using EPR and thermally stimulated luminescence (TSL) techniques. The TSL and EPR studies on gamma irradiated uranium doped calcium oxide samples had shown that the intense glow peak at 540 K is associated with the reduction in the intensity of EPR signal of U5+ ion around this temperature. This peak is associated with the process U5++hole→U6+*→U6++hv. The activation energy for this process was determined to be 1.4eV.

Radiation effects in plutonium and carbonate co-doped calcium hydroxy apatite: An EPR study

Electron paramagnetic resonance studies were conducted on synthetic calcium hydroxy apatite samples co-doped with 239Pu and carbonate ion. These investigations were carried out to assess the self-irradiation effects in bone and teeth on exposure to plutonium, as calcium hydroxy apatite is the major constituent of bone and teeth. On self-irradiation, in addition to the signal from O- ion arising from the radiolysis of hydroxide ion, EPR signals due to CO2-, PO22- and another signal assigned to surface O- ions were observed in the samples. In freshly quenched gamma irradiated samples, signals from CO3-, O- , PO22- and O2- ions were observed. The EPR signal of O2- ion shows a doublet splitting suggesting that O2- ion gets preferentially stabilized close to Pu4+. The radiation damage due to Pu4+ at Ca2+ sites, in the sample appears to be lower as compared to that due to external gamma-irradiation. Moreover, the alpha-dose in 239Pu doped samples has self-annealing effects. These are attributed to localized radiation damage due to alpha-particles compared to evenly distributed radical ions produced due to gamma-irradiation.