Enhancement of deuteron-fusion reactions in metals and experimental implications
A. Huke · K. Czerski · P. Heide · G. Ruprecht · N. Targosz · W. Żebrowski
Abstract and summary · read the original at the source
In one page
Armin Huke, Konrad Czerski and colleagues in Berlin, Szczecin and at TRIUMF fired slow deuterons into metal targets to measure the quantity the whole lattice-fusion story rests on: how much easier a metal makes it for two deuterons to reach each other. Electrons in a metal crowd around a nucleus and partly cancel its charge, so a colliding pair behaves as though it had been handed a small energy bonus — the screening energy. In gas targets that bonus is about a tenth of what these metals give. Here they measure 322 electronvolts in tantalum, 313 in palladium, 297 in zirconium, 190 in aluminium, and none at all in pure carbon films. Much of the paper is about how easy it is to fool yourself: deuterium migrates inside a hot target and oxide layers grow on its surface, and both change the counting rate without changing any cross-section, so the team built an analysis that watches the deuteron density live and rejects the runs where it drifts. Their numbers are floors, not ceilings.
Why it matters hereChapter 12 turns on one measurable quantity — how much a metal lattice lowers the effective barrier between two deuterons — and this is the careful, published number for it, several hundred electronvolts, with the systematic traps that inflate or deflate it named and controlled. It is also chapter 1’s evidence ladder in action: the authors show which runs count and why.
What it claims
01Electron screening energies for the deuteron-deuteron reaction inside metals, measured by the discontinuities in the reduced yield rather than by absolute yields, come out at 322 plus or minus 15 electronvolts in tantalum, 313 plus or minus 2 in palladium, 297 plus or minus 8 in zirconium and 190 plus or minus 15 in aluminium, while carbon films show no screening enhancement at all.Section IV A, Table I and Figure 7
Published and peer-reviewed02Because unavoidable contamination layers can only diminish an inferred screening energy, the values reported here — the range 190 to 320 electronvolts — are lower limits on the real effect; the differential analysis behind them is independent of the imprecise stopping-power coefficients and of the absolute deuteron number density, and it monitors the density online so that runs with shifting depth profiles are recognized and rejected.Section III, end; Section VI, Conclusion
Published and peer-reviewed03The enhancement is carried by the conduction electrons: screening energies measured in insulating materials are much smaller, under about 50 electronvolts, while the contributions from polarization of bound host electrons and from cohesion should be similar in both cases — so what a metal adds is its free-electron gas.Section IV B, discussion accompanying Figures 8 and 9
Published and peer-reviewed04Subtracting the calculated cohesion contribution and the bound-electron part leaves a free-electron polarization screening energy that follows a smooth law — the product of the two nuclear charges times 250 plus or minus 20 electronvolts, divided by the square root of the electron-gas parameter — which can be used to estimate the free-electron contribution for other reacting nuclei in a metallic environment.Section IV B, parameterization of the free-electron polarization
Published and peer-reviewed05The measurements select the degenerate-electron-gas picture over the classical plasma one: the Debye-Hückel description applies only above the Fermi temperature, typically around a hundred thousand kelvin and far above the evaporation temperature of a metal, so no temperature dependence of the screening energy should appear in this regime — and the follow-up radioactive-decay measurements the authors survey agree with that expectation.Section V; Section VI, Conclusion
Published and peer-reviewed06The size of the effect is still open: the experimental screening energies exceed the self-consistent dielectric-function calculation by a factor of about two, which the authors state plainly as an unidentified contribution still to be found, and they name what would settle it — precise determination of the screening energies in an ultra-high vacuum system where the contamination-layer problem is removed.Section IV B, comparison with theory; Section VI, Conclusion
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Read it · abstract
Abstract
Recent measurements of the reaction d(d,p)t in metallic environments at very low energies performed by different experimental groups point to an enhanced electron screening effect. However, the resulting screening energies differ strongly for divers host metals and different experiments. Here, we present new experimental results and investigations of interfering processes in the irradiated targets. These measurements inside metals set special challenges and pitfalls which make them and the data analysis particularly error-prone. There are multi-parameter collateral effects which are crucial for the correct interpretation of the observed experimental yields. They mainly originate from target surface contaminations due to residual gases in the vacuum as well as from inhomogeneities and instabilities in the deuteron density distribution in the targets. In order to address these problems an improved differential analysis method beyond the standard procedures has been implemented. Profound scrutiny of the other experiments demonstrates that the observed unusual changes in the reaction yields are mainly due to deuteron density dynamics simulating the alleged screening energy values. The experimental results are compared with different theoretical models of the electron screening in metals. The Debye-Hückel model that has been previously proposed to explain the influence of the electron screening on both nuclear reactions and radioactive decays could be clearly excluded.
The way in
https://doi.org/10.1103/physrevc.78.015803Published as Physical Review C 78, 015803 (2008) under the APS default licence. The preprint is on arXiv as 0805.4538, filed May 2008 under arXiv’s non-exclusive distribution licence, which does not grant redistribution — so this page carries the summary, the claims and the authors’ own abstract, and sends the reader to the full text at the source.
How to cite it
A. Huke, K. Czerski, P. Heide, G. Ruprecht, N. Targosz, W. Żebrowski (2008) Enhancement of deuteron-fusion reactions in metals and experimental implications. doi:10.1103/physrevc.78.015803
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