Temperature Dependence Of Electron Screening In D(d,p) T Reaction For Deuterated Metals

The experimental and theoretical studies of the electron screening effects in charged-particle induced reactions at energies of astrophysical interest are systematically reviewed, and the theoretical discussions on the electrostatic screening effects are also summarized briefly.The electron screening in D(d, p)T was studied previously for deuterated metals, insulators, and semiconductors. As compared to measurements performed with a gaseous D₂ target (U_e = 25 eV), a large screening was observed in the metals, while a small screening was found for the insulators and semiconductors. An exception was found for the metals of groups 3 and 4 of the periodic table and the lanthanides, which showed a small screening; this is related to their high hydrogen solubility y. For the metals with high U_e values, the solubilities were small (a few percent) leaving the metallic character of the samples essentially unchanged. An explanation of the large screening was suggested by the plasma screening of Debye applied to the quasi-free metallic electrons.For a deep understanding of the electron screening effects, we cooperated with the astrophysics group of Ruhr University to study the electron screening in the D(d, p)T reaction, using the 100kV accelerator of the Dynamitron-Tandem- Laboratorium, for the deuterated metal Pt at a sample temperature T = 20℃ to 340℃, and for Ta and Co at T = 20℃ and 200℃. 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℃ to 200℃: above 50℃ the hydrogen solubility dropped to values far below one and alarge screening effect became observable. Similarly, all metals of groups 3 and 4 and the lanthanides showed a solubility of a few percent at T = 200°C (compared to T = 20°C) and a large screening became also 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. As another application of the Debye model, the possible enhancement of the a-decay rate in a metallic environment is discussed.