Detection of irradiated frog (Limnonectes macrodon) leg bones by multifrequency EPR spectroscopy.

The free radicals of irradiated frog Limnonectes macrodon leg bones tissue were studied by electron paramagnetic resonance in both X and Q bands. The kinetic behaviour, the activation energy as well as the thermal stability of the radiation-induced radicals in bone tissue were investigated by means of both isothermal and isochronal annealing. Unirradiated bone tissue displayed the presence of Mn(2+) ions at both frequencies, while a week EPR singlet was evidenced only at 34 GHz. When irradiated with (60)Co gamma ray, the EPR spectra completely changed their patterns and intensity, the overall spectra provin, at both frequencies, to be typical axial ones. The 100°C isothermal annealing studies attested the existence of two different free radical species, significantly more labile than in the case of mammal bone tissues. At the same time, the Arrhenius plot of 15 kGy irradiated bones evidenced two different kinetic regimes with two different activation energies.

Standardization of 68(Ge+Ga).

The radionuclide 68Ga is mainly a positron emitter (89.2%), with a half-life of 67.7 min. It is used in nuclear medicine, being chemically extracted from the mixture 68(Ge+Ga); its precursor, 68Ge, disintegrates 100% by electron capture, with a half-life of 270.8d (Table of radionuclides, comments and Evaluation). A 4pibeta-gamma coincidence method was used for standardization, with a 4pi proportional beta-detector and a NaI(Tl) gamma detector. Registration of the capture radiations was avoided using foil absorption and a high beta threshold. Using supplementary foils for positron absorption, extrapolation graphs were obtained, with a mean slope of -4.4%. Care was taken to compensate for the loss of 68Ge during the preparation of solid sources for measurement. A combined uncertainty of 1.1% was estimated.