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Register a new userQuantum-tail effect in low energy d+d reaction in deuterated metals
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The Bochum experimental enhancement of the d+d fusion rate in a deuterated metal matrix at low incident energies is explained by the quantum broadening of the momentum-energy dispersion relation and consequent modification of the high-momentum tail of the distribution function from an exponential to a power-law.
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The investigation of the d+d fusion reactions in metallic environments at sub-Coulomb energies demands especially adapted techniques beyond standard procedures in nuclear physics. The measurements which were performed with an electrostatic accelerator at different self-implanted metallic target materials show an enhancement of the reaction cross-section compared to the gas target experiments. The resulting electron screening energy values are about one order of magnitude larger relative to the gas target experiments and exceed significantly the theoretical predictions. The measurements on deuterium inside metals are heavily affected by the interference of two peculiarities of this system: the possibly very high mobility of deuterium in solids and the formation of surface contamination layers under ion beam irradiation in high vacuum systems. Thorough investigations of these processes show their crucial influence on the interpretation of the experimental raw data. The differential data acquisition and analysis method employed to it is outlined. Non observance of these problems by using standard procedures results in fatal errors for the extraction of the screening energies.
Results of numerical simulations of fusion rate d(d,p)t, for low-energy deuteron beam, colliding with deuterated metallic matrix (Raiola et al. Phys. Lett.B 547 (2002) 193 and Eur. Phys J. A 13 (2002) 377) confirm analytical estimate given in Coraddu et al. nucl-th/0401043, taking into account quantum tails in the momentum distribution function of target particles, and predict an enhanced astrophysical factor in the 1 keV region in qualitative agreement with experiments.
We theoretically investigate a possibility of an $eta ^{prime} d$ bound state and its formation in the $gamma d to eta d$ reaction. First, in the fixed center approximation to the Faddeev equations we obtain an $eta ^{prime} d$ bound state with a binding energy of 25 MeV and width of 19 MeV, where we take the $eta ^{prime} N$ interaction with a coupling to the $eta N$ channel from the linear $sigma$ model. Then, in order to investigate the feasibility from an experimental point of view, we calculate the cross section of the $gamma d to eta d$ reaction at the photon energy in the laboratory frame around 1.2 GeV. As a result, we find a clear peak structure with the strength $sim$ 0.2 nb/sr, corresponding to a signal of the $eta ^{prime} d$ bound state in case of backward $eta$ emission. This structure will be prominent because a background contribution coming from single-step $eta$ emission off a bound nucleon is highly suppressed. In addition, the signal can be seen even in case of forward $eta$ emission as a bump or dip, depending on the relative phase between the bound-state formation and the single-step background.
A model for the p d --> p d eta reaction published earlier, including the final state interaction (FSI) of all particles, is revisited to investigate the low energy data on this reaction. The three body problem of p-d-eta scattering in the final state is approximated in terms of pairwise interactions between the three particles in the final state. Apart from a comparison with some preliminary data, two new findings relevant to the near threshold data analysis are reported. The first one points toward the limitations of an FSI factor used conventionally to extract the eta-deuteron scattering length and infer subsequently on the existence of eta-mesic states. The second result emphasizes the role of the $p-d$ FSI and the strong Coulomb repulsion near threshold. Finally, a comparison of the above model calculation with low energy data, excludes very large eta-nucleon scattering lengths.
An enhancement of antiprotons produced in p+d reaction in comparison with ones in p+p elementary reaction is investigated. In the neighborhood of subthreshold energy the enhancement is caused by the difference of available energies for antiproton production. The cross section in p+d reaction, on the other hand, becomes just twice of the one in elementary p+p reaction at the incident energy far from the threshold energy when non-nucleonic components in deuteron target are not considered.
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