Cold fusion/Electrolytic cell fusion
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In the original work, a constant current was applied to the cell continuously for many weeks, and heavy water was added as necessary. For most of the time, the power input to the cell was equal to the power that went out of the cell within measuring accuracy, and the cell temperature was stable at around 30 °C. But then, at some point (and in some of the experiments), the temperature reportedly rose suddenly to about 50 °C without changes in the input power, for durations of two days or more. The generated power was calculated to be about 20 times the input power during the power bursts. Eventually the power bursts in any one cell would no longer occur, and the cell was turned off.
Pons and Fleischmann also initially reported that a cell was generating 2.45 MeV neutrons at a rate three times the natural background rate. There was, however, no equipment directly measuring neutron energies, and this report was based on a mistaken inference from a gamma-ray spectrum, and the neutron findings were retracted. The most spectacular result they reported was that in one cell the most of the electrode melted and part of it vaporized, destroying the cell and the fume hood enclosing it.
In March, 2004, the U.S. Department of Energy (DOE) decided to review all previous research of cold fusion in order to see whether further research was warranted by any new results. The review document (PDF file) submitted to the DOE by the group of scientists who had requested a new review process states that "The experimental evidence for anomalies in metal deuterides, including excess heat and nuclear emissions, suggests the existence of new physical effects". It recognizes indirect evidence in support of the D + D → 4He + 23.8 MeV (heat) reaction, although the measurement of 4He quantity is imprecise.
Others have pointed out that helium and excess heat do not confirm that specific reaction, that there are other conceivable nuclear reactions with deuterium as fuel and producing helium as the ash; one theory is that special conditions in the metal lattice cause, at or near the surface, the arrangement of two deuterium molecules such that the four deuterons are in a symmetric tetrahedral arrangement, and one physicist, Takahashi, has calculated and published that if this configuration is created, it will rapidly collapse into a (very small) Bose-Einstein condensate, then fuse and form a single atom of Beryllium-8, which is very unstable and which will rapidly decay into two helium atoms plus 47.6 MeV of energy, and some of the problems asserted with the d+d hypothesis disappear, most notably that there is no predicted neutron or gamma radiation from that reaction, and the problem of a reaction requiring two particles or photons as a product for conservation of momentum. However, there still remain unsolved problems; Takahashi predicts that the Be-8 nucleus will radiate much or most of its energy of excitation as a series of photon emissions, which would be absorbed by the lattice, but still, when Be-8 decays from the ground state, the energy of the helium nuclei will be approx 90 MeV each, and there should be some secondary effects from this, notably Bremmstrahlung radiation. A recent paper by Hagelstein proposed an upper limit of 10 KeV for radiation produced by the reactions in palladium deuteride.
Storms (2007) has said that no theory has so far succeeded in accounting for all the observed effects without assuming some unknown process, and no theory has successfully made predictions of new behavior subsequently proven by experiment. However, it must be said that Preparata predicted, early on, that helium would be found, before it was actually found.
While the measurement of 4He is difficult, it has been done with sufficient accuracy and with careful attention to the possibility of leakage, and correlation of excess energy with helium has been calculated by Storms to be at 25 +/- 5 MeV, reviewing a series of studies.
Huizenga, in Cold fusion, scientific fiasco of the century, 1993 edition, noting the report of helium correlated with excess heat by Miles et al, wrote, "If it were true that 4He was produced from room-temperature fusion in amounts nearly commensurate with excess heat, one of the great puzzles of cold fusion would have been solved! However, as is the case with so many cold fusion claims, this one is unsubstantiated and conflicts with other well-established experimental findings."
Huizenga then proposes the same previous theoretical objections as the "well-established experimental findings," not any findings that excess heat in cold fusion experiments is not correlated with helium. He asserts that if helium is produced, it "must be accompanied by large intensities (in fact, lethal doses) of the associated 23.8 MeV gamma ray," and he asserts that if this gamma ray is not observed, one cannot "be sure that the 4He is produced by fusion and is not an experimental artifact." However, this point depends upon an assumption that if there is fusion, it must be the same reaction as hot d-d fusion, which only (rarely) branches to helium production, and which is then always accompanied by that gamma ray. A possible theory that would explain helium production without gammas is given above, and there are other theories; researchers in the field are leaning, as of 2010, toward acceptance that there is some kind of cluster fusion taking place, with another theoretical paper being published by Kim in Naturwissenschaften, 2009, that also proposes the formation of Bose-Einstein condensates as a possible explanation.
The work of Miles has since been confirmed by other studies by multiple research groups, but has not attracted much attention outside of the community of those studying cold fusion. The mention of heat/helium in the 2004 DoE report was marred by an error made by the anonymous reviewer, who, in the summary, reported evidence of correlation incorrectly, distorting it in a manner that made what has been a clear correlation, in the experimental reports, into an anticorrelation, appearing to be mere chance and thus very possibly artifact from helium measurement errors. There is no report in the literature, where helium was sought at the same time as excess heat was measured, where helium was found but not excess heat, whereas in every experiment with palladium deuteride, when excess heat was found, so was helium, in roughly the right quantity to be "consistent with" 23.8 MeV, allowing for experimental error. (It is not considered proven that the exact ratio is 23.8 MeV, and there are other proposed reactions that would lead to excess heat and helium at different ratios that might be within range. All of them are nuclear reactions, there being no known way to produce helium without a nuclear reaction of some kind.)
Hence, within the field, that the fuel for this reaction is deuterium and that the ash is helium, and that either fusion or something equivalent is happening, is no longer controversial, and criticism published under peer review of this position has disappeared, since at least 2004 or earlier, whereas papers making this as an assumption are increasingly being published under peer review, and in mainstream journals (such as Naturwissenschaften) or books with mainstream publishers.
The reproducibility of the result was an early issue in cold fusion research, and it was difficult to design experiments which were fully reproducible by following a clear recipe, and, without that, many were understandably skeptical. In 1989 and 1990, other groups, with little specific information having been published yet, attempted to reproduce the Fleischmann-Pons work, taking only a few weeks, whereas it had taken the original researchers five years to come to the point that they saw 15% of their cells produce excess heat. There were serious difficulties with the solid palladium material, and later researchers were able to better characterize these, and, in addition, other experimental approaches came to be adopted, such as co-deposition or gas-loading under pressure, all leading to, according to a 2007 Chinese review, many groups reporting 100% reproducibility.
Some of the early experiments that were considered negative replications did show small amounts of excess heat, later analysis has shown, but because this was well below the levels of heat reported by Pons and Fleischmann, they were considered negative results. Some of them measured helium, and did not find helium at significant levels. From the point of view of heat/helium importance, this confirms the later findings of correlation, these being, effectively, rough control experiments showing that if not enough excess heat is found to predict measurable helium, measurable helium is also not found.
Further, in 2008, Pamela Mosier-Boss, et all, with the U.S. Navy SPAWAR group in San Diego, California, published, in Naturwissenschaften, a report of finding energetic neutrons, in co-deposition cells, that received wide attention. Many previous reports had found radiation from these cells using a similar technique, Solid State Nuclear Track detectors, so the finding of radiation was not new. However, neutrons were a kind of Holy Grail to researchers looking for evidence of fusion, but previous reports had found levels of neutrons, using electronic detectors, which were barely above background, often coming in bursts, which might be attributed to cosmic rays. The low levels of neutrons were even used as evidence against fusion since, it was argued, fusion would have produced far higher levels of neutrons. However, the authors of the SPAWAR paper do not attribute the neutrons to the primary reaction, but to possible secondary reactions, and they cite the Takahashi Be-8 theory mentioned above as a possible primary reaction. Neutrons are a sign of nuclear reactions, generally, only rarely being produced by radioactive decay. The neutron levels found in that Naturwissenschaften report were approximately ten times background, as shown by control SSNTDs. Later published work, using a gold underlying cathode, show far higher levels of apparent neutron-caused tracks.
Many nuclear and particle physicists, in particular, remain highly skeptical, as can be seen by blog posts and occasional comments in replies to media inquiries.
Source: w:Cold_fusion#Current_understanding_of_physics and writing by Wikiversity participants, sources to be added.
Discussion
See Talk:Electrolytic cell fusion
- Do you think study of cold fusion leads to meaningful results in physics?
- Do you think it is likely that cold fusion will ever provide a useful source of energy?
- Additional topics for study:
- What role have news stories played in the ability of researchers to obtain funding for cold fusion?
- Which governments support cold fusion research?