The electron screening in the d(d, p)t reaction has been studied for the deuterated metal Pt at a sample temperature T = 20 • C-340 • C and for Co at T = 20 • C and 200 • C. The enhanced electron screening decreases with increasing temperature, where the data agree with the plasma model of Debye applied to the quasi-free metallic electrons. The data represent the first observation of a temperature dependence of a nuclear cross section. We also measured the screening effect for the deuterated metal Ti (an element of group 4 of the periodic table) at T = −10 • C-200 • C: above 50 • C, the hydrogen solubility dropped to values far below 1 and a large screening effect became observable. Similarly, all metals of groups 3 and 4 and the lanthanides showed a solubility of a few per cent at T = 200 • C (compared to T = 20 • C) and a large screening also became observable. Within the Debye model, the deduced number of valence electrons per metallic atom agrees with the corresponding number from the Hall coefficient, for all metals investigated.

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for converting on the lathe, my blueprints into pieces for the target chamber, and for his valuable help in mechanical issues.Jorge Rocha for doing the lithium implantations and for helping with his expertise in vacuum technology.Eng. Hugo Marques and Prof. Dr. Orlando Teodoro for taking the SIMS and XPS spectra and helping me in the analysis. Palavras chaveLítio primordial, reacções nucleares induzidas por partículas carregadas, secção eficaz, factor astrofísico S , distribuições angulares, blindagem electrónica, modelo de Debye. AbstractThis work presents the results of the experimental study of proton induced nuclear reactions in lithium, namely the He reactions were measured concurrently with seven and four targets, respectively. These targets were produced in order to obtain adequate and stable lithium depth profiles.In metallic environments, the measured electron screening potential energies are much higher than the predictions of atomic-physics models. The Debye screening model applied to the metallic conduction electrons is able to explain these high values. It is a simple model, but also very robust. Concerning primordial nucleosynthesis and stellar evolution models, these v vi results are very important as they show that laboratory measurements are well controlled, and the model inputs from these cross sections are therefore correct.

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