Photoinduced formation of metal nanoparticles in γ-irradiated sodium-fluoride crystals

It is established that sodium nanoparticles with sizes of several hundreds of nanometers, several tens of nanometers, and several nanometers are formed in γ-irradiated photobleached NaF crystals. Along with randomly scattered particles, areas in which nanoparticles with sizes of tens of nanometers are grouped around a particle with a size of hundreds of nanometers are revealed. Mechanisms for color-center aggregation and nanoparticle formation are discussed.     

Free-radical saturation at high doses in γ-irradiated glycine

In this work the apparent decrease of radical yield in irradiated dry glycine at very high doses of radiation is interpreted as an effect of measurement inaccuracy due to the spatially inhomogeneous distribution of the radicals and to the presence of a mixture of different types of radical species.     

Polymorphic transformations in γ-irradiated amino acids and dipeptides

There is an unexpected decrease in infra-red absorption band intensities of amino acids and dipeptides on irradiation with γ-rays at very high dose rates. The infra-red evidence together with X-ray crystallographic studies leads to the postulation of weak bond formation which increases the degree of molecular association in the irradiated material. A marked increase in infra-red absorption at low dose rate earlier reported⁽¹⁾ has not been observed.     

EPR study of free radicals in γ-irradiated thiazide compounds

The aim of this paper was to identify the type of radicals formed by γ-irradiation in powdered chlorothiazide (CTZ), hydrochlorothiazide (HCTZ), althiazide (ATZ) and trichloromethiazide (TCTZ) on the basis of analysis of their electron paramagnetic resonance spectra with enhanced resolution. In TCTZ, HCTZ and ATZ the radical was formed by abstraction of a hydrogen atom from the carbon atom C-3, and in the case of CTZ by addition of a hydrogen atom to the nitrogen atom N-4. The hyperfine structure is found. The electron densities at nitrogen atom positions in the N-C-N group in HCTZ, ATZ and TCTZ depend on a single 3-position substitution and are in line with their diuretic potency.     

Annealing of deffects in γ-irradiated LiF studied by positron annihilation

Positron lifetime spectra and Doppler broadened spectra have been measured for LiF single crystals gamma-irradiated at room temperature. Isothermal and isochronal annealings of the samples have been performed in a temperature range of 20–600°C.     

Electron spin resonance spectrum for a radical in γ-irradiated N-iodosuccinimide

A radical exhibiting a very large hyperfine coupling to ¹²⁷I, together with a small coupling to ¹⁴N, formed in γ-irradiated N-iodosuccinimide at 77 K is identified as a σ* radical anion in which the added electron is accommodated primarily in the N-I antibonding σ-orbital.     

Electron spin-lattice relaxation time and spectral diffusion in γ-irradiated l-alanine

We performed continuous (CW) wave and pulsed ESR experiments to obtain information on the relaxation behavior of the l-alanine radical in an irradiated single crystal. The analysis of the CW saturation behavior gives a relaxation time of 2.8 μs. The echo detected saturation recovery was obtained for a number of different experimental conditions. In any case only a portion of the 120 G wide ESR spectrum can be affected by the microwave (MW) pulses, spectral diffusion is active and a multi-exponential decay is therefore obtained. We measured characteristic spectral diffusion times of 1–10 and 20–50 μs. We found that a long time of about 200 μs can be measured only by using a train of long selective saturating pulses and short detecting pulses. The stimulated echo decay is bi-exponential, and the characteristic times are very short. A variable temperature investigation in the range 200 to 290 K showed that the decay is governed by the spectral diffusion and by the transverse nuclear spin relaxation timeT _2n of the methyl protons.     

Thermally stimulated transformation of the EPR spectra in γ-irradiated bone tissue

γ-irradiated bone tissue annealed at different temperatures is studied by EPR. In powder samples the annealing-induced changes of the EPR spectra are mainly determined by sharp growth of a signal caused by the products of thermal decay of an organic component in the tissue. This signal considerably complicates the analysis of the EPR spectrum shape for the annealed samples. On the other hand, in the spectra of the plates of bone tissue a change in the lineshape of the EPR signal from CO₂⁻ radicals after annealing is more pronounced than in powder, and it is attributed to the change in the contributions from axial and orthorhombic CO₂⁻ radicals. The analysis of different radicals concentrations vs. annealing temperature revealed above 210 °C the temperature-induced transformation of orthorhombic CO₂⁻ radicals into axial ones in bone tissue which (together with organic component) is responsible for the changes of EPR lineshape at annealing.     

On interpretation of EPR spectrum of free radicals in γ-irradiated methanol

Some authors interpret the EPR spectrum in-irradiated methanol at 77K either by the radical H₂OH or by ⁺ H₂. In order to contribute to this question we have calculated the values of the hyperfine splitting constants of this EPR spectrum as a function of the valence angle H-C-H in a CH₂ fragment. The comparison of the experimental and calculated values of the hyperfine splitting constant and a discussion of the possible valence angles leads us to the conclusion that the EPR spectrum in irradiated methanol originates from the radical H₂OH.The author thanks J. Teplý for valuable remarks which helped this work.     

Electron spin resonance identification of phosphorus-centred radicals in γ-irradiated dialkyl phosphites

Potential curves have been calculated by the ab initio MRD CI method for states of OH⁺ correlating with O(³ P, ¹ D, ¹ S) + H⁺ and O⁺(⁴ S, ² D, ² P) + H. Spectroscopic constants derived from the calculated potential curves are in good agreement with the available experimental data. The calculations support the experimental assignment of vibrational quantum numbers for levels perturbing the A ³Π state.     

A new treatment for the interpretation of radical decay in γ-irradiated polyethylene

The decay of polymer radicals in γ-irradiated polyethylene as measured by EPR is discussed from the viewpoint of a continuous but not constant distribution over the activation free energy and of the kinetic constants. The possibility of determining this distribution from experimental results alone is shown. In addition, the new treatment enables us to obtain more clearly the various temperature regions in which radical decay takes place most rapidly, and this allows a distinction by EPR, for instance, even between several kinds of low-density polyethylene.     

Kinetics of accumulation and decay of paramagnetic centers in γ-irradiated doped phosphate glasses

The dose dependences and decay kinetics of PO ₄ ^2? and PO ₃ ^2? paramagnetic centers and radiation-reduced europium Eu^(3+)? in γ-irradiated phosphate glasses of composition 4Na₂O · La₂O₃ · 7P₂O₅ doped with europium are studied. The data obtained are discussed within the trapping volume model in the approximation of short irradiation duration. It is shown that the trapping volume parameter v decreases with increasing irradiation dose. A physical interpretation of the parameter v is proposed.     

Study of fission track registration efficiency of γ-irradiated polyester track detector in solution medium

The fission track registration efficiency (K _wet) of the Garware polyester track (GPF) detector in solution has been determined with respect to the Lexan detector whose K _wet is very well known in the literature. The K _wet is found to be (1.2 ± 0.1) 10⁻³ cm. The track registration efficiency of the GPF detector in solution is better than the efficiencies of other nuclear track detectors reported in the literature. This implies that the threshold energies for track registration are different for different detectors and that GPF detector has a lower threshold-energy value. The effects of gamma irradiation in the dose range of 5–51 Mrad on the fission track registration efficiency (K _wet) of this track detector from the solution medium are also investigated. The results show that the K _wet values for the gamma-irradiated detectors in the above dose range in 2M HNO₃ solution medium decreases by ∼7–15%. The changes induced in the gamma-irradiated detectors as a function of gamma dose have also been studied by bulk-etch rate measurements.     

Critical behaviour in the commensurate-incommensurate phase transition of pure and γ-irradiated LiRbSO4 crystals

The effect of γ-irradiation on the incommensurate phase of LiRbSO₄ crystals has been studied by measuring the specific heat C_p . As a result of γ-irradiation, the values of C_p decreased and the transition temperature T_c shifted to lower values. The values of ΔH and ΔS decreased with increasing dose rate. The results are explained on the basis of an energy change due to induced lattice defects.     

E.S.R. spectra of the radicals produced in γ-irradiated diborane in the solid state

The hopping and Coulomb repulsion integrals of the Hubbard model, as applied to the NMP-TCNQ charge-transfer crystal, are found by an INDO calculation of the neutral and charged monomer and dimer of TCNQ. The ratio of these integrals is in satisfactory agreement with experiment, although the calculated integrals themselves are very different from the effective ones for electronic transport, due to renormalization, caused largely by counter-ion polarizability.     

The electron spin resonance spectrum of NH(SO3 -) in γ-irradiated potassium sulphamate

The electron spin resonance spectrum of the radical NH(SO₃ ^- trapped in a single crystal of potassium sulphamate is interpreted. The hyperfine couplings for the hydrogen and nitrogen nuclei are given. The radical is planar, the unpaired electron occupying an orbital of π symmetry being predominantly a nitrogen 2p orbital.     

Radiation-induced changes in electrical conductivity and structure of BaPbO3 after γ-irradiation

Several barium plumbate (BaPbO₃) solid samples, made from PbO and BaCO₃ powder by chemistry liquid-phase coprecipitation, were investigated before and after γ-irradiation. The solid samples were irradiated by a ⁶⁰Co γ-irradiation source whose dose rate is about 0.7?kGy per hour. The irradiation times were 0, 72, 144, 216, 288 and 360?h. Then, the four-probe method, X-ray diffraction (XRD), scanning electron microscope (SEM) and X-ray photoelectron spectroscopy (XPS) were used to indicate the changes in electrical conductivity and microstructure of BaPbO₃ after γ-irradiation. The XRD results indicated that the content of PbO was reduced as the irradiation dose was increased and eventually vanished from the surface of samples. However, there was no new obvious substance phase found from the XRD atlas. It seems that the PbO transformed into nearly amorphous Pb₅O₈. The conjecture could be proved by the results of annealing experiment and SEM. The XPS results seem to show that the microstructure of BaPbO₃ was slightly changed.     

Rapid scan electron paramagnetic resonance at 1.0 GHz of defect centers in γ-irradiated organic solids

The radicals in six ⁶⁰Co γ-irradiated solids: malonic acid, glycylglycine, 2,6 di-t-butyl 4-methyl phenol, l-alanine, dimethyl malonic acid, and 2-amino isobutyric acid, were studied by rapid scan electron paramagnetic resonance at L-band (1.04 GHz) using a customized Bruker Elexsys spectrometer and a locally-designed dielectric resonator. Sinusoidal scans with widths up to 18.2 mT were generated with the recently described coil driver and Litz wire coils. Power saturation curves showed that the rapid scan signals saturated at higher powers than did conventional continuous wave signals. The rapid scan data were deconvolved and background subtracted to obtain absorption spectra. For the same data acquisition time the signal-to-noise for the absorption spectra obtained in rapid scans were 23–37 times higher than for first-derivative spectra obtained by conventional continuous wave electron paramagnetic resonance.