Historical research guide · 0586 · 2004
Low-Energy Nuclear Reactions in Metals
Jirohta Kasagi
In one minute
Jirohta Kasagi and his colleagues at Tohoku University fired very slow deuterons into metal targets and counted what came out. The question was not whether fusion happens at these energies — it does, rarely — but whether the metal around the nuclei changes the odds. It does, and by a lot. Kasagi summarises two sets of measurements: the deuteron-deuteron reaction that yields a proton and tritium, run in several metals at bombarding energies from 2.5 to 10 kiloelectronvolts, and the lithium-plus-deuteron reactions in palladium and gold from 30 to 75 kiloelectronvolts. At the lowest energies the yield runs well above what bare nuclei predict, and how far above depends on which host the deuterons are sitting in: largest in palladium oxide, then palladium and iron, smallest in gold and titanium. Fitted as a screening potential — an effective softening of the Coulomb barrier — palladium oxide reaches about 600 electronvolts, where the electrons bound to the atoms can supply only a few tens. Something in the metal is doing the rest.
Connection
Chapter 12 rests on a single idea: the barrier two nuclei face is set by the environment they sit in, and the environment is an engineering variable. This is that idea measured with an accelerator rather than a calorimeter — same host metals as the cold fusion experiments, but with the reaction rate read off directly, energy by energy, so the enhancement can be quantified instead of inferred from heat.
From the source
Low-energy nuclear reactions in metals are strongly affected by the metal environment surrounding the nuclei. The reaction rate at a given bombarding energy is not a property of the two nuclei alone; it depends on the host material they are embedded in.Abstract, Prog. Theor. Phys. Suppl. 154 (2004) 365
The programme covers two reaction families: the deuteron-deuteron reaction producing a proton and tritium, measured in several metals for bombarding energies between 2.5 and 10 kiloelectronvolts, and the lithium-6 and lithium-7 plus deuteron reactions producing helium, measured in palladium and gold between 30 and 75 kiloelectronvolts.Abstract, Prog. Theor. Phys. Suppl. 154 (2004) 365
Fitting the enhanced yields as a screening potential gives values that rank cleanly by host: about 600 electronvolts in palladium oxide, 310 in palladium, 200 in iron, 70 in gold and 65 in titanium, each to within a few tens of an electronvolt.Companion ICCF8 report, Section 3, Table 1
Electrons bound to the atoms cannot account for this. Known electron screening supplies at most a few tens of electronvolts for the deuteron-deuteron case and about 0.3 kiloelectronvolts for lithium plus deuteron, while the measured lithium values in palladium come out near 1.55 and 1.76 kiloelectronvolts.Companion ICCF8 report, Section 3 and Section 4
The fitted screening potential tracks the inverse of the deuteron number density in the metal during bombardment, which the authors read as an index of how freely deuterons move. The mechanism they infer is one whose strength grows with deuteron mobility in the host, on top of the ordinary electron screening.Companion ICCF8 report, Section 4, Fig. 4
Extrapolated to thermal energies with the same screening and a deuteron density of 1.2 times ten to the twenty-first per cubic centimetre, the deuteron-deuteron fusion rate at room temperature would exceed ten million events per second per cubic centimetre; the lithium-plus-deuteron rate would be vanishingly small by comparison.Companion ICCF8 report, Section 4, closing paragraphs
The way in
https://doi.org/10.1143/ptps.154.365How to cite it
Jirohta Kasagi (2004) Low-Energy Nuclear Reactions in Metals doi:10.1143/ptps.154.365