Electron paramagnetic resonance and thermally stimulated luminescence studies of uranyl doped calcium sulphate

Electron paramagnetic resonance (EPR) and thermally stimulated luminescence (TSL) studies were conducted onγ-irradiated CaSO₄:UO ₂ ²⁺ to elucidate the role of the electron/hole traps in thermally stimulated reactions and to obtain the trap parameters (trap depth and frequency factor). Intense TSL glow peaks around 140, 375, 400 and 438±2K are observed and their spectral characteristics have shown that UO ₂ ²⁺ and UO ₆ ⁶⁻ act as luminescent centres. EPR studies have shown the peaks at 140 and 400/438K to be associated with the thermal destruction of O⁻ and SO ₄ ⁻ radical ion in two stages respectively. The maximum rate of thermal destruction of SO ₄ ⁻ ions (as seen by EPR) in various alkaline earth sulphate matrices investigated in our laboratory is also summarized. The activation energy which characterizes the electron transfer reaction between SO ₄ ⁻ and the dopant ion lies in the range of (0.95±0.15 eV). This value is independent of the dopant and therefore seems to be characteristic of the binding energy of hole in the SO ₄ ⁻ radical ion.     

Electron paramagnetic resonance study of impurities and point defects in oxide crystals

In this topic review the results of the X-band electron paramagnetic resonance (EPR) measurements of Mn, Co, Cr, Fe ions in YAlO₃ (YAP) crystals and Fe ions in LiNbO₃ (LNO) crystals and of chromium doped Bi₁₂GeO₂₀ (BGO) and Ca₄GdO(BO₃)₃ single crystals, are presented. It is well known that the oxide crystals (for example:YAP, LNO, BGO) are one of the most widely used host materials for different optoelectronic applications. The nature of point defect of impurities and produced in the oxide crystal after irradiation by bismuth ions and after irradiation by the ²³⁵U ions with energy 9.47 MeV/u and fluency 5?×?10¹¹?cm^?1 is discussed. The latter is important for applications of these oxide crystal as laser materials.     

Electron paramagnetic resonance of Ce3+ ions in lead thiogallate single crystals

The results of electron paramagnetic resonance (EPR) studies of Ce³⁺ impurity ions in single crystals of lead thiogallate PbGa₂S₄ have been reported. The Ce³⁺ ions substitute for Pb²⁺ ions in the crystal lattice of PbGa₂S₄. A number of paramagnetic cerium centers in lead thiogallate have been observed. The spectra are described by the spin Hamiltonian of rhombic symmetry with the effective spin S = 1/2. The g factors of the main cerium centers have been determined. A large number of paramagnetic centers are due to both nonequivalent positions of lead and local charge compensation under the substitution Ce³⁺ ?? Pb²⁺.     

Electron paramagnetic resonance of Dy3+ ions in lead thiogallate single crystals

The results of electron paramagnetic resonance (EPR) studies of Dy³⁺ ions in lead thiogallate PbGa₂S₄ single crystals have been presented. It has been shown that the ground state of these ions corresponds to the lowest Stark sublevel Γ₆ of the term ⁶ H _15/2. The spectra are well described by the axially symmetric spin Hamiltonian with the effective spin S = 1/2 with the factors g _‖ = 15.06 and g _⊥ = 2.47. The Dy³⁺ ions substitute Pb²⁺ ions in the crystal lattice of PbGa₂S₄. The observed hyperfine structure has allowed to unambiguously interpret the EPR spectra. The hyperfine interaction constants of two odd isotopes of dysprosium in lead thiogallate single crystals have been found to be A _‖ = 675 × 10^?4 cm^?1 and A _⊥ = 111 × 10^?4 cm^?1 for ¹⁶³Dy and A _‖ = 472 × 10^?4 cm^?1 and A _⊥ = 77 × 10^?4 cm^?1 for ¹⁶¹Dy.     

Electron paramagnetic resonance of deep boron acceptors in 4H-SiC and 3C-SiC crystals

EPR spectra of deep boron in 4H-SiC and 3C-SiC crystals have been observed and studied. Two sites in 4H-SiC produced deep-boron EPR signals, quasi-cubic k and hexagonal h. In both cases the deep-boron center symmetry is close to axial along the c crystal axis, and the g factor anisotropy is about an order of magnitude larger than that for shallow boron centers. In the 3C-SiC crystal, the deep-boron symmetry is also close to axial along one of the four 〈111〉 directions. The model proposed for the deep boron center with acceptor properties is B_Si-v _C, where B_Si is the boron substituting for silicon, and v _C is the carbon vacancy, with the B_Si-v _C direction coinciding in 4HSiC with the hexagonal axis of the crystal for both k and h positions. In the cubic 3C-SiC crystal, there are four equivalent deep boron centers, which represent B_Si-v _C pairs with the bond directed along one of the four 〈111〉 crystal directions. Fiz. Tverd. Tela (St. Petersburg) 40, 36–40 (January 1998)     

Effects of the interaction of electron paramagnetic resonance transitions of copper and gadolinium centers in lead germanate single crystals

This paper reports on the results of investigations into the temperature and orientation dependences of the electron paramagnetic resonance spectrum in the vicinity of accidental coincidence of the spectral lines attributed to the signals (homogeneously broadened or with an antisymmetric arrangement of the spin packets) from Cu²⁺ and Gd³⁺ impurity centers in the ferroelectric lead germanate Pb₅Ge₃O₁₁. The parameters of the broadening and coupling of the spectral components are determined using computer simulation of the electron paramagnetic resonance spectra involving coupling (exchanging) components.     

Thermally stimulated luminescence and electron paramagnetic resonance studies of actinide doped calcium chloro phosphate

Electron paramagnetic resonance [EPR] and thermally stimulated luminescence [TSL] studies were conducted on self [α]-irradiated²³⁹Pu doped calcium chloro phosphate andγ-irradiated²³⁹Pu/²³⁸UO ₂ ²⁺ doped calcium chloro phosphate to elucidate the role of the electron/hole traps in thermally stimulated reactions and to obtain trap parameters from both TSL and EPR data. TSL glow peaks around 135 K (# peak 1), 190 K (# peak 2), 435 K (# peak 5) and 490 K (# peak 7) were observed and their spectral characteristics have shown that Pu³⁺ and UO ₆ ⁶⁻ act as luminescent centres in calcium chloro phosphate with respective dopants. EPR studies have shown the formation of the radical ions H⁰, PO ₄ ²⁻ , O⁻, O ₂ ⁻ and [ClO]²⁻ under different conditions. Whereas the [ClO]²⁻ radical being stable up to 700 K, was not found to have any role in TSL processes, the thermal destruction of other centres was found to be primarily responsible for the TSL peaks observed. The trap depth values were determined both by using the TSL data and also the temperature variation of EPR spectra of these centres.     

Electron paramagnetic resonance in Kondo insulators

This review is devoted to the application of electron paramagnetic resonance (EPR) in the study of fluctuating-valence materials, which are characterized by a narrow gap in the electron energy spectrum (Kondo insulators or Kondo semiconductors). The authors’ papers on studying classical objects of this field of solid-state physics, SmB₆ and YbB₁₂, are considered as an illustration of the potentiality of the EPR method. Temperature dependences of the gap width in these materials were obtained, the static and dynamic Jahn-Teller effects on Sm³⁺ ions in SmB₆ were detected, and the formation of Yb³⁺ ion pairs and the spontaneous breaking of cubic symmetry in YbB₁₂ were observed. The results obtained indicate that preference should be given to the exciton-polaron model developed by Kikoin et al. for the ground state of Kondo insulators.     

Nuclear polarization by electron paramagnetic resonance in paramagnetic crystals

The possibility of the polarization of nuclei in paramagnetic salts by saturation of electron paramagnetic resonance is theoretically analyzed. The proposed method assumes saturation of the forbidden transition of the typeM=±1, m=±1, ±2, for mutually perpendicular external magnetic and high-frequency fields. The analysis is carried out for the case of a large quadrupole moment of the nucleus. The degree of orientation attained is comparable in order of magnitude with Overhauser's method. This method is particularly suitable for the polarization of nuclei of transuranium elements.

---

. M=± 1, m==±1, ±2 . . . .

---

---

In conclusion the author would like to thank J. Burget, J. ajko, M. Kolá and M. ott for helping in the laborious solution of system (16).     

Electron paramagnetic resonance of radiation-induced paramagnetic centers in an aerogel

Silicon oxide aerogel samples irradiated with x rays at room temperature have been analyzed using the electron paramagnetic resonance method. It has been found that three types of paramagnetic centers appear: paramagnetic centers with a g factor of 2.0035, centers associated with the presence of protons in SiO₂ globules, and centers in the adsorbed film on the aerogel surface. The fast (T _fast = 30 h) and slow (T _slow = 70 d) processes have been revealed in the recombination of these centers.     

Electron paramagnetic resonance of hydrogen in silicon

A review of the investigations by means of electron paramagnetic resonance (EPR) of hydrogen and hydrogen-related defects in crystalline silicon is presented. The main features of the EPR center Si-AA9 (bond-centered hydrogen), which is known as the hydrogenic analogue of the anomalous muonium (Mu^*) in silicon, are discussed. It was found that the process of annealing the AA9 center is characterized by an activation energy, E = 0.48 ± 0.04 eV with a second-order pre-exponential factor, K₀ = (1.25 ± 2.5) × 10^-7 cm³/s.

A detailed investigation by EPR of the defect (Si-AA1), which we identify as the hydrogen-related shallow donor in a positive charge state, is also presented. In particular it is shown that the H-related shallow donor is a helium-like center and its wave function has C_2v symmetry. Moreover, the main features of the series of EPR spectra in silicon characteristic for the implantation of hydrogen are presented.     

Electron paramagnetic resonance spectroscopy of Cr 3+ in hexagonal Cs 2 NaGaF 6 crystals

Powder samples of hydrothermally grown Cr 3+ -doped Cs 2 NaGaF 6 crystals have been investigated with electron paramagnetic resonance spectroscopy at X - (9.5 v GHz) and Q -band (34 v GHz). Analysis of the spectra clearly demonstrates that there are two distinct Cr 3+ centres in the Cs 2 NaGaF 6 crystal, having nearly identical g factors, but differing largely from the viewpoint of their zero field splitting. By using the 53 Cr hyperfine spectra observed with electron nuclear double resonance spectroscopy, it is deduced that these centres have opposite signs for the zero field splitting. The spectroscopic properties of the Cr 3+ centres in the isostructural Cs 2 NaGaF 6 and Cs 2 NaAlF 6 crystals are compared and discussed.     

Electron paramagnetic resonance radiation dosimetry in fingernails

There is now an increased need for accident dosimetry due to the increased risk of significant exposure to ionizing radiation from terrorism or accidents. In such scenarios, dose measurements should be made in individuals rapidly and with sufficient accuracy to enable effective triage. Electron paramagnetic resonance (EPR) is a physical method of high potential for meeting this need, providing direct measurements of the radiation-induced radicals, which are unambiguous signatures of exposure to ionizing radiation. For individual retrospective dosimetry, EPR in tooth enamel is a proven and effective technique when isolated teeth can be obtained. There are some promising developments that may make these measurements feasible without the need to remove the teeth, but their field applicability remains to be demonstrated. However, currently it is difficult under emergency conditions to obtain tooth enamel in sufficient amounts for accurate dose measurements. Since fingernails are much easier to sample, they can be used in potentially exposed populations to determine if they were exposed to life-threatening radiation doses. Unfortunately, only a few studies have been carried out on EPR radiation-induced signals in fingernails, and, while there are some promising aspects, the reported results were generally inconclusive. In this present paper, we report the results of a systematic investigation of the potential use of fingernails as retrospective radiation dosimeters.     

Electron paramagnetic resonance in deuterated nickel fluosilicate

Electron paramagnetic resonance measurements in single crystals of NiSiF₆. 6D₂O were made at K, Ku and Ka bands at 4.2 K and between 77 K and 300 K. The measured g values were in the range 2.23–2.26, while the zero-field splitting parameter D varied from ?(0.185 ± 0.005) cm^?1 at 4.2 K to ?(0.53 ± 0.01) cm^?1 at 298 K. The parameters of the trimolecular hexagonal unit cell were determined to be approximately a = 9.28 Å, c = 9.58 Å from powder X-ray diffraction measurements at room temperature.     

Electron paramagnetic resonance in Nd-Ag amorphous alloys

We have studied the EPR of Nd³⁺ ions in Nd_16.7Ag_83.3 amorphous alloys between 4.2 K and room temperature. The resonance observed above 100K at a field corresponding to a g ? 2.3 indicates the existence of sites having a non-axial crystal field of the form J²_x-J²_z.