Search

A high-energy mass spectrometer based on the XTU Tandem accelerator of the Laboratori Nazionali di Legnaro is described. Preliminary measurements on standard samples with known10Be/9Be atom ratio show the capability of the system to measure natural concentrations of10Be for geological and cosmochronological studies. The modifications necessary to improve sensitivity and precision of the measurements are discussed.

A variable cosmogenic-production rate model is proposed which takes account of the changes in galactic-cosmic-ray irradiation conditions arising from the vertical oscillation of the solar system about the galactic plane. The model incorporates and substantiates several ideas and suggestions previously put forward in the literature. The time distribution of the10Be concentration predicted by the model appears to be consistent with the data of the deep-sea sediment core RC 12-65. A comparison of our model with the conventional constant-production rate model is carried out, especially with reference to time-integrated concentrations in meteorites.

An easy and rapid method for preparing biological targets for trace element analysis using nuclear techniques involving charged particle beams is described. The targets are thin, homogeneous and uniform. They withstand 100 nA of 1–2 MeV proton beams and of 5–10 MeV alpha beams for about 10 hrs.

The importance of selenium in biological and organic matrices is well established; a very sensitive and fast analytical method is necessary to investigate its role deeply. A preconcentration technique is described that allows selenium detecting at the ppb level in biological samples in a short time. It involves first the decomposition of the organic matrix and then the precipitation of selenium using tellurium both as the coprecipitant and as the internal standard. For serum samples the optimal range of volume to be used is 0.1–2 ml. The sensitivity is obtained at the ppb level after about 10 min irradiation time. The accuracy of the method is checked by comparison with the direct palletization method and by using a standard reference material.

A study of neutron and gamma interaction (in the low dose range) with L-phenylalanine in aqueous solutions shows that the main radiolytic pathway occurs through the attack of OH radicals. The products of the interaction are essentially tyrosine, Dopa and melanine in both cases. However, for gamma radiation there is a complete utilization of the OH radicals and the reaction pathway mainly proceeds by the sequence: phenylalanine»tyrosine»Dopa»melanine. On the contrary, for neutron radiation, the OH recombination is a rather efficient process and the prevailing pathway is: phenylalanine»Dopa»melanine.

The accelerator mass spectrometry system based on the 16 MV tandem accelerator at the Laboratori Nazionali di Legnaro is described. A high-resolution electrostatic deflector rejects isotopic background and other unwanted beams transmitted with the same magnetic rigidity as the rare isotope. Use of this system for 10 Be and 36 Cl measurements in enriched and natural samples is presented.

Nuclear techniques are very useful in the simultaneous determination of many trace elements in biological samples; the sensitivity depends on the method and on the elements in study and in many cases is better than 0;1 ppm. Proton-induced X-ray fluorescence and alpha-particle elastic diffusion techniques are described; the methods of sample preparation, the sensitivity obtained and some experimental results are included.

Summary. The red blood cell (RBC) glutathione peroxidase (GSH-Px) activity and routine haematological parameters were measured in 38 healthy north Italian full-term pregnant women and in their newborn infants. In 31 pairs the serum selenium concentration was also measured. Data were compared with those of 20 normal adult controls (10 males and 10 females). Newborn infants exhibited significantly lower RBC GSH-Px activity and serum selenium concentrations than adult controls. Pregnant women had serum selenium values intermediate between those of adult female controls and their newborn infants. In both the pregnant women and newborns the RBC GSH-Px activity correlated with the level of selenium in serum which suggests that the neonatal RBC GSH-Px deficiency may be partially due to insufficient availability of selenium during pregnancy. Factors other than selenium concentration, e.g. hormonal and genetic, might also affect the RBC GSH-Px activity as suggested by sex differences and mother/child concordances in enzyme activity found in our cases.