Analysis of the EPR spectrum of γ-irradiated barium dithionate

Abstract

An analysis of the experimental EPR spectrum of γ-irradiated barium dithionate is made. Based on the data obtained, a model of this spectrum is constructed. It is shown that the spectrum results from superposition of four individual signals, for which the following values of the g-factor components have been determined: for I g M = 2.0097, g N = 2.0044; for II g M = 2.0069, g N = 2.0023; for III g M = 2.0042, g N = 2.0032; for IV g M = 2.0002 and g N = 2.0032.Introduction. The spin-resonance method of determining an absorbed dose D of ionizing radiation with the aid of barium dithionate (BaS 2 O 6 ⋅2H 2 O) is based on measurement of the concentration C of stable radiation-induced ion radicals, given the known coefficient of the linear function C = f(D). In this case, to determine the concentration with a minimum error, it is necessary to make use of a calculation model of the EPR spectrum of irradiated barium dithionate that would be appropriate for the experimental spectrum. Then it becomes possible, firstly, to most accurately determine the area of the corresponding EPR signal and, secondly, to reduce the threshold of the radiative sensitivity of a dosimeter. First of all, the latter is of current interest for medical radiology, where small doses of ionizing radiation are used and, therefore, there are small-intensity signals often comparable with the noise level. Based on the results of an analysis of the experimental EPR spectrum of irradiated barium dithionate, an attempt is made in the present work to construct a model spectrum that would approximate the experimental one as closely as possible.Experimental Procedure. The technique of producing barium dithionate used in the experiment and the methods of testing the degree of its purity are described in [1,2].Fine-crystalline barium dithionate was exposed to γ-radiation in an air medium at atmospheric pressure and a temperature of 20 o C on a PXM-γ20 ( 60 Co) setup. Doses of 1, 5, 10, 25, 30, 40, 50, and 60 kGy were used. The irradiated samples were heated in air under isothermal conditions at temperatures of 75 and 80 o C. The process was monitored by the EPR method. The spectra were registered on a compact computerized spectrometer (λ = 3 cm) at 20 o C. When the values of g-factors were measured, MgO containing Mn 2+ ions was used as an external standard. The error of measurements was ±0.0004.Results and Discussion. In [3] it is established that the EPR signal of γ-irradiated barium dithionate is complex and consists of four components I-IV that were revealed by us in the course of heating the investigated substance at 80 o C under isothermal conditions (Fig. 1a, curves 1 and 5). The spectrum is also separated into components when the power P of the microwave oscillator of the spectrometer is increased (the interval considered is 10-79 mW, Fig. 1b) The situation of separation is simplified because the dependence of the relative intensity I of central component III on P, unlike the dependences observed for the remaining three components, exhibits an extreme...

EPR spectra of γ-irradiated hydrated barium dithionate single crystals

“…Table 2 gives these distances and the distances between S atoms that were obtained from splitting of the D * lines using Eq. (2). Because the exact position in the crystal of the S atoms of the radical is unknown (due to relaxation of the position of the S atoms in forming the radical), which pairs we observe cannot be shown accurately in the figure.…”

“…The small anisotropy of the g-factor and its off-diagonal components lead to the weak modulation of the off-diagonal components of the g-tensor of the SO 3 − radical by lattice vibrations. We propose that the line of center 1 is due to the SO 2 − radical because the experimental values for this center g max = 2.0101 and g av = 2.007 are close to those for the SO 2 − radical [2]. The structures of centers 2 and 4 have not yet been determined.…”

“…Dipole-dipole coupling parameters of certain pairs are determined. The g av values, anisotropy of the g-factor, and EPR line widths differ for the powder [2] and the single crystal. …”

Radiation-induced radical ions in calcium sulfite

“…As the initial data, we used the experimentally obtained values of the g factors. To determine the shape of the spectral lines, we used the spin model [7] tested previously in [5,6]. Using the same method as in the indicated papers, we determined the parameters of the spin model.…”