F. Raiola

Enhanced electron screening in d(d, p)t for deuterated Ta

Abstract:The recent observation of a large electron screening effect in the d(d, p)t reaction using a deuterated Ta target has been confirmed using somewhat different experimental approaches: Ue = 309±12 eV for the electron screening potential energy. The high Ue value arises from the environment of the deuterons in the Ta matrix, but a quantitative explanation is missing.

Electron screening in d(d, p)t for deuterated metals and the periodic table ✩

The electron screening effect in the d(d, p)t reaction has been studied for 29 deuterated metals and 5 deuterated insulators/semiconductors. As compared to measurements performed with a gaseous D2 target, a large effect has been observed in the metals V, Nb, and Ta, which belong to group 5 of the periodic table, as well as in Cr, Mo, and W (group 6), Mn and Re (group 7), Fe and Ru (group 8), Co, Rh, and Ir (group 9), Ni, Pd, and Pt (group 10), Zn and Cd (group 12), and Sn and Pb (group 14). In contrast, a comparatively small effect is found in group 4 (Ti, Zr, Hf), group 11 (Cu, Ag, Au), group 13 (B, Al), for the insulator BeO, and for the semiconductors C, Si, and Ge. An explanation of this apparently novel feature of the periodic table is missing.  2002 Elsevier Science B.V. All rights reserved.

Electron screening effect in the reactions 3He(d, p)4He and d(3He, p)4He

The cross section of the reactions 3He(d, p)4He and d(3He, p)4He has been measured at the center-of-mass energies E=5 to 60 keV and 10 to 40 keV, respectively. The experiments were performed to determine the magnitude of the electron screening effect leading to the respective electron-screening potential energy Ue=219±7 and 109±9 eV, which are both significantly higher than the respective values from atomic physics models, Ue=120 and 65 eV.

Electron screening effect in the reactions 3 He(d, p) 4 He and d( 3 He, p) 4 He ☆ ☆ Supported in part by INFN, BMBF (06BO812), DFG (436UNG113-146) and OTKA (T025465).

The cross section of the reactions 3He(d, p)4He and d(3He, p)4He has been measured at the center-of-mass energies E=5 to 60 keV and 10 to 40 keV, respectively. The experiments were performed to determine the magnitude of the electron screening effect leading to the respective electron-screening potential energy Ue=219±7 and 109±9 eV, which are both significantly higher than the respective values from atomic physics models, Ue=120 and 65 eV.

Electron screening in d(d, p)t for deuterated metals: temperature effects

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.

Experimental study of proton-induced nuclear reactions in 6,7 Li

The 6Li(p,α)3He and 7Li(p,α)4He reaction cross sections were obtained for E = 90–580 keV and E = 90–1740 keV, respectively. R-matrix and polynomial fits to the bare astrophysical S-factor confirmed, with improved accuracy, previous work data, yielding Sb(0) = 3.52 ± 0.08 MeV b, and 55.6+0.8−1.7 keV b for the 6Li and 7Li reactions, respectively. Therefore, the astrophysical consequences related to these two isotopes remain essentially unchanged. With the present work Sb(E) data, a reanalysis of the low energy data for different environments—Li2WO4 insulator, Li metal, and PdLix alloys—confirms that the large electron screening effects can be explained by the plasma model of Debye applied to the quasi-free electrons in the metallic samples.

Electron screening: A review

Understanding the electron screening effect in the laboratory is critical for a correct interpretation of low‐energy nuclear reactions in stars. Extensive studies of the electron screening effect in deuterated metals (54 metals) and other environments have been carried out in Bochum in the last 4 years. Experimental results of anomalous enhancements have been interpreted in terms of the Debye plasma model applied to quasi‐free metallic electrons. For the d(d,p)t reaction in metallic environments, the variation of hydrogen solubility in the samples as a function of temperature has also been measured, showing an anti‐correlation with screening enhancement as expected. Within this model, the deduced number of valence electrons per metallic atom also agrees with the corresponding number from the Hall coefficient. Recently, the expected temperature dependence of the screening potential has been verified together with the expected Zt scaling (with the metallic host) of the Debye radius. Preliminary results on the 7Li(p,α) and 6Li(p,α) reactions in Li2WO4 insulator, Li metal and PdLi alloys confirm the expected behaviour of the screening effect and further supports the applicability of the Debye model. Indeed, the proposed model also accounts for the high screening potential (Ue = 900±50 eV) observed in previous studies of the reactions 9Be(p,α) and 9Be(p,d), which was not understood at the time. A review of all these results will be presented.

Electron screening in d(d, p)t for deuterated metals

Abstract Experimental studies on the electron screening effect in the d(d,p)t reaction for 26 deuterated metals have shown a surprisingly high enhancement factor as compared to measurements performed with a gaseous D2 target. In comparison, a comparatively small effect is found for 11 deuterated insulators/semiconductors and for the noble metals (Cu, Ag, Au). An explanation of these observations is missing.