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Cold fusion is nuclear fusion that supposedly may occur at conditions near room temperature and atmospheric pressure. Early announcements raised hopes of a cheap source of electricity or fuel, but as yet, no reproducible results have gained scientific consensus as to the existence of the phenomenon.

The idea was brought into public consciousness by an announcement made in 1989 by the chemists Stanley Pons and Martin Fleischmann at the University of Utah that they had generated excess heat that they believed at the time could only be explained by the occurrence of a nuclear reaction. Their apparatus was relatively simple: a pair of electrodes immersed in heavy water. Early attempts to replicate the effect were unsuccessful after which cold fusion gained a reputation as an example of pathological science.

More than 490 reports in peer-reviewed journals have suggested unexplained phenomenon from cold fusion experiments, including nearly 200 published reports of anomalous heat, and over 60 of anomalous tritium production. While many such reports have appeared in non-mainstream publications, many have also been been published in peer-reviewed journals.

The United States Department of Energy convened a panel to investigate their claims in 1989. This and a second panel in 2004 found the claims of cold fusion to be no more convincing than they had been 15 years previous, and not convincing enough to justify a federally-funded program, but identified a number of basic science research areas that could be helpful in resolving some of the controversies in the field. Also in 2004, a review report by Physics Today described most scientists as deeply skeptical, while noting "the existence of a small and devoted coterie of researchers who continue to investigate the alleged effect."

Ongoing controversy

The 1989 DOE panel said that it was not possible to state categorically that cold fusion has been convincingly either proved or disproved,. In the 2004 panel, two-thirds of the reviewers did not feel the evidence was conclusive for low energy nuclear reactions, one found the evidence convincing, and the remainder indicated they were somewhat convinced. The nearly unanimous opinion of the reviewers in the 2004 review was that funding agencies should entertain individual, well-designed proposals for experiments that address specific scientific issues relevant to the question of whether or not there is anomalous energy production in Pd/D systems, or whether or not D-D fusion reactions occur at energies on the order of a few eV. These proposals should meet accepted scientific standards, and undergo the rigors of peer review. No reviewer recommended a focused federally funded program for low energy nuclear reactions. Popular science journal Physics Today, which had been skeptical of the outcome in advance of the review, interpreted the report as a "chilly encore" for cold fusion.

The skepticism towards cold fusion results from three issues: the lack of consistently reproducible results, the absence of nuclear products in quantities consistent with the excess heat, and the lack of a mainstream theoretical mechanism.

Reproducibility of the result

The cold fusion researchers who presented their review document to the 2004 DoE panel on cold fusion said that the observation of excess heat has been reproduced, that it can be reproduced at will under the proper conditions, and that many of the reasons for failure to reproduce it have been discovered. Despite the assertions of these researchers, most reviewers stated that the effects are not repeatable.

In 1989, the DoE panel noted that "Even a single short but valid cold fusion period would be revolutionary. As a result, it is difficult convincingly to resolve all cold fusion claims since, for example, any good experiment that fails to find cold fusion can be discounted as merely not working for unknown reasons."

Nuclear products

If the excess heat were generated by the fusion of 2 deuterium nuclei, the most probable outcome would be the generation of either a tritium nucleus and a proton, or a He and a neutron. The level of neutrons, tritium and He actually observed in Fleischmann-Pons experiment have been well below the level expected in view of the heat generated, implying that these fusion reactions cannot explain it. If the excess heat were generated by the fusion of 2 deuterium nuclei into He, a reaction which is normally extremely rare, gamma rays and helium would be generated. In 1989, insufficient levels of helium and gamma rays have been observed to explain the excess heat.

The cold fusion researchers who presented their report to the 2004 DoE panel said that, since then, three independent studies have shown that the rate of helium production measured in the gas stream varies linearly with excess power.

Theoretical mechanisms

Another issue is that current theories describing conventional "hot" nuclear fusion cannot explain how a cold fusion reaction could occur at relatively low temperatures, and that there is currently no accepted theory to explain cold fusion. The 1989 DoE panel noted that "Nuclear fusion at room temperature, of the type discussed in this report, would be contrary to all understanding gained of nuclear reactions in the last half century; it would require the invention of an entirely new nuclear process", but it also recognized that "the failure of a theory to account for cold fusion can be discounted on the grounds that the correct explanation and theory has not been provided", that is, the lack of a satisfactory explanation could not be used to dismiss experimental evidence.

Cold fusion observations are contrary to the conventional physics of nuclear fusion in several ways :

• The average density of deuterium atoms in the palladium rod seems vastly insufficient to force pairs of nuclei close enough for fusion to occur according to mechanisms known to mainstream theories. The average distance is approximately 0.17 nanometers, a distance at which the attractive strong nuclear force cannot overcome the Coulomb repulsion. Deuterium atoms are closer together in D₂ gas molecules, which do not exhibit fusion.
• There is no known mechanism that would release fusion energy as heat instead of radiation within the relatively small metal lattice. The direct conversion of fusion energy into heat is not possible because of energy and momentum conservation and the laws of special relativity.

Cold fusion researchers have proposed various speculative theories (for a full review, see Storms 2007 harvnb error: multiple targets (2×): CITEREFStorms2007 (help)) to explain the reported observations, but none has received mainstream acceptance. Also, because the reported processes may not technically be fusion, the DOE calls it "low energy nuclear reaction."

Ongoing controversy

Since the initial excitement over Fleishman and Pons, the reality of the existence of cold fusion has been supported by a few researchers who have tried to reproduce excess energy production in electrolytic cells. Most scientists are dismissive of these efforts, but the researchers have managed to gain some attention in recent years and in 2006 sessions of both the American Chemical Society and the American Physical Society were devoted to low-energy nuclear reactions. Still, skepticism about the existence of cold fusion is the default position of most scientists. Two issues are cited as being problematic: the lack of consistently reproduceable results and the lack of a theoretical mechanism.

Reproducibility of the result

The cold fusion researchers presenting their review document to the 2004 DoE panel on cold fusion said that the observation of excess heat has been reproduced, that it can be reproduced at will under the proper conditions, and that many of the reasons for failure to reproduce it have been discovered. Despite the assertions of these researchers, most reviewers stated that the effects are not repeatable.

In 1989, the DoE panel said: "Even a single short but valid cold fusion period would be revolutionary. As a result, it is difficult convincingly to resolve all cold fusion claims since, for example, any good experiment that fails to find cold fusion can be discounted as merely not working for unknown reasons."

Theoretical mechanisms

Cold fusion's most significant problem in the eyes of many scientists is that current theories describing conventional "hot" nuclear fusion cannot explain how a cold fusion reaction could occur at relatively low temperatures, and that there is currently no accepted theory to explain cold fusion. The 1989 DoE panel said: "Nuclear fusion at room temperature, of the type discussed in this report, would be contrary to all understanding gained of nuclear reactions in the last half century; it would require the invention of an entirely new nuclear process", but it also recognized that the lack of a satisfactory explanation cannot be used to dismiss experimental evidence.

Cold fusion observations are contrary to the conventional physics of nuclear fusion in several ways :

• Nuclear reaction in general: The average density of atoms in the palladium rod seems vastly insufficient to force pairs of nuclei close enough for fusion to occur according to mechanisms known to mainstream theories. The average distance is approximately 0.17 nanometers, a distance at which the attractive strong nuclear force cannot overcome the Coulomb repulsion. Actually, deuterium atoms are closer together in D2 gas molecules, which do not exhibit fusion.

• Deuterium fusion products: if the excess heat were generated by the fusion of 2 deuterium atoms, the most probable outcome would be the generation of either a tritium atom and a proton, or a He and a neutron. The level of neutrons, tritium and He actually observed in Fleischmann-Pons experiment have been well below the level expected in view of the heat generated, implying that these fusion reactions cannot explain it. If the excess heat were generated by the hot fusion of 2 deuterium atoms into He, a reaction which is normally extremely rare, gamma rays and helium would be generated. Again, insufficient levels of helium and gamma rays have been observed to explain the excess heat.

• Conversion to heat: there is no known mechanism that would release fusion energy as heat instead of radiation within the relatively small metal lattice. Robert F. Heeter said that the direct conversion of fusion energy into heat is not possible because of energy and momentum conservation and the laws of special relativity.

Cold fusion advocates have proposed various speculative theories to explain the reported observations. Such ideas run counter to mainstream physical theories and associated observational evidence.

Experimental reports

Measurement of excess heat

The cold fusion researchers presenting their review document to the 2004 DoE panel on cold fusion said that the possibility of calorimetric errors has been carefully considered, studied, tested and ultimately rejected. They said that over 50 experiments conducted by SRI International showed excess power well above the accuracy of measurement. Arata and Zhang said they observed excess heat power averaging 80 watts over 12 days. The researchers also said that the amount of energy reported in some of the experiments appeared to be too great compared to the small mass of the material in the cell for it to be stored by any chemical process. They said that their control experiments using light water never showed excess heat.

When asked about the evidence for power that cannot be attributed to an ordinary chemical or solid state source, the 2004 DoE panel was evenly split. Many of the reviewers noted that poor experiment design, documentation, background control and other similar issues hampered the understanding and interpretation of the results presented to the DoE panel. The reviewers who did not find the production of excess power convincing said that excess power in the short term is not the same as net energy production over the entire time of an experiment, that all possible chemical and solid state causes of excess heat had not been investigated and eliminated as an explanation, that the magnitude of the effect had not increased after over a decade of work, and that production over a period of time is a few percent of the external power applied and hence calibration and systematic effects could account for the purported effect.

Nuclear products

The cold fusion researchers presenting their review document to the 2004 DoE panel on cold fusion said that there are insufficient chemical reaction products to account for the excess heat by several orders of magnitude. They said that three independent studies have shown that the rate of helium production measured in the gas stream varies linearly with excess power. Extensive precautions were taken to ensure that the samples were not contaminated by helium from the earth's atmosphere (5.2 ppm). Bursts of excess energy were time-correlated with bursts of He in the gas stream. However, the amount of helium in the gas stream was about half of what would be expected for a heat source of the type D + D -> He. Searches for neutrons and other energetic emissions commensurate with excess heat have uniformly produced null results. Although there appears to be evidence of transmutations and isotope shifts near the cathode surface in some experiments, they said that it is generally accepted that these anomalies are not the ash associated with the primary excess heat effect.

For a nuclear reaction to be proposed as the source of energy, it is necessary to show that the amount of energy is related to the amount of nuclear products. When asked about evidence of low energy nuclear reactions, twelve of the eighteen members of the 2004 DoE panel did not feel that there was any conclusive evidence, five found the evidence "somewhat convincing" and one was entirely convinced.

In 2007, Pamela Mosier-Bos and her team reported their observation of pits in CR-39 detectors during D/Pd codeposition experiments in the European Physical Journal. They said that those pits have features consistent with those observed for nuclear generated tracks, that the Pd cathode is the source of those pits, that they are not due to contamination or chemical reactions. They attributed some pits to knock-ons due to neutrons, and said that others are consistent with those obtained for α particles.

Other kinds of fusion

Some other kinds of fusion may be termed "cold" in some sense but are separate from the cold fusion controversy. "Cold" may be taken in the sense that no part of the reaction is actually hot (except for the reaction products), or that the energies required are low and the bulk of the material is at a relatively low temperature. Some other kinds of fusion are "hot", involving reactions which create macroscopic regions of very high temperature and pressure.

Locally cold fusion

• Muon-catalyzed fusion is a well-established and reproducible fusion process which occurs at low temperatures. It has been studied in detail by Steven Jones in the early 1980s. Because of the energy required to create muons, it is not able to produce net energy.

Generally cold, locally hot fusion

• In cluster impact fusion, microscopic droplets of heavy water (on the order of 100-1000 molecules) are accelerated to collide with a target, so that their temperature at impact reaches at most 10 kelvin, 10,000 times smaller than the temperature required for hot fusion. In 1989, Friedlander and his coworkers observed 10 more fusion events than expected with standard fusion theory. Recent research () suggests that the calculation of effective temperature may have failed to account for certain molecular effects which raise the effective collision temperature, so that this is a microscopic form of hot fusion.

• In sonoluminescence, acoustic shock waves create temporary bubbles that collapse shortly after creation, producing very high temperatures and pressures. In 2002, Rusi P. Taleyarkhan explored the possibility that bubble fusion occurs in those collapsing bubbles. If this is the case, it is because the temperature and pressure are sufficiently high to produce hot fusion.

• The Farnsworth-Hirsch Fusor is a tabletop device in which fusion occurs. This fusion comes from high effective temperatures produced by electrostatic acceleration of ions. The device can be built inexpensively, but it too is unable to produce a net power output.

• Antimatter-catalyzed fusion uses small amounts of antimatter to trigger a tiny fusion explosion. This has been studied primarily in the context of making nuclear pulse propulsion feasible.

Several of these systems are "nonequilibrium systems", in which very high temperatures and pressures are produced in a relatively small region adjacent to material of much lower temperature. In his doctoral thesis for Massachusetts Institute of Technology, Todd Rider did a theoretical study of all non-equilibrium fusion systems. He demonstrated that all such systems will leak energy at a rapid rate due to Bremsstrahlung, radiation produced when electrons in the plasma hit other electrons or ions at a cooler temperature and suddenly decelerate. The problem is not as pronounced in a hot plasma because the range of temperatures, and thus the magnitude of the deceleration, is much lower.

Hot fusion

• "Standard" fusion, in which the fuel reaches tremendous temperature and pressure inside a fusion reactor, nuclear weapon, or star.

References

1. Electrochemist Dr. Dieter Britz, who has remained neutral on the question of whether cold fusion exists, has compiled a cold fusion bibliography which includes 479 published scientific journal articles marked "res+" indicating positive research results.
2. ^ Storms, Edmund (2007). The Science of Low Energy Nuclear Reaction. Singapore: World Scientific Publishing. pp. pp 52-61 and pp 79-81. ISBN 9789812706201. {{cite book}}: |pages= has extra text (help) Cite error: The named reference "Storms" was defined multiple times with different content (see the help page).
3. Cited in 2004 DoE review:
   Y. Arata and Y-C Zhang, "Anomalous difference between reaction energies generated within D₂0-cell and H₂0 Cell", Jpn. J. Appl. Phys 37, L1274 (1998)
   Iwamura, Y., M. Sakano, and T. Itoh, "Elemental Analysis of Pd Complexes: Effects of D₂ Gas Permeation". Jpn. J. Appl. Phys. A, 2002. 41: p. 4642.
   Other:
   Mizuno, T., et al., "Production of Heat During Plasma Electrolysis in Liquid," Japanese Journal of Applied Physics, Vol. 39 p. 6055, (2000)
   M.H. Miles et al., "Correlation of excess power and helium production during D₂O and H₂0 electrolysis using Palladium cathodes]", J. Electroanal. Chem. 346 (1993) 99
   B.F. Bush et al, "Helium production during the electrolysis of D₂0 in cold fusion", J. Electroanal. Chem. 346 (1993) 99
4. Broad, W.J. "Team Visits Fusion Lab But Divides on Claims" The New York Times, June 6, 1989
5. Physics Today, "Cold fusion gets chilly encore", Jan 2005
6. See the 2004 DOE report
7. ^ Feder, T. "DOE Warms to Cold Fusion", Physics Today, April 2004, pp 27
8. ^ US DOE 1989, p. 36 harvnb error: no target: DOE1989 (help).
9. US DOE 2004, p. 5 harvnb error: no target: DOE2004r (help).
10. [http://www.physicstoday.org/vol-58/iss-1/p31a.html Cold Fusion Gets Chilly Encore, Physics Today, Jan 2005
11. US DOE 1989, pp. 6–8 harvnb error: no target: DOE1989 (help).
12. Hagelstein et al. 2004, p. 14 harvnb error: no target: DOE2004 (help).
13. US DOE 2004, p. 3 harvnb error: no target: DOE2004r (help).
14. US DOE 1989, pp. 5–6 harvnb error: no target: DOE1989 (help).
15. Hagelstein et al. 2004, p. 8 harvnb error: no target: DOE2004 (help).
16. Close 1991, p. ? harvnb error: no target: CITEREFClose1991 (help).
17. Huizenga 1992, p. ? harvnb error: no target: CITEREFHuizenga1992 (help).
18. US DOE 1989, p. 37 harvnb error: no target: DOE1989 (help).
19. US DOE 1989, pp. 6–7 harvnb error: no target: DOE1989 (help).
20. Goodstein 1994, p. 528 harvnb error: no target: CITEREFGoodstein1994 (help).
21. Kee 1999, p. 5 harvnb error: no target: CITEREFKee1999 (help).
22. US DOE 2004, p. 1 harvnb error: no target: DOE2004r (help).
23. Energy Research Advisory Board of the United States Department of Energy, "Report on Cold fusion research", November 1989
24. Close, F., "Too Hot to Handle. The Race for Cold Fusion." 1992, New York: Penguin, paperback.
25. Huizenga, J.R., "Cold Fusion: The Scientific Fiasco of the Century". second ed. 1993, New York: Oxford University Press.
26. "Cold fusion research : A Report of the Energy Research Advisory Board to the United States Department of Energy". 1989. Retrieved 2007-11-21. the failure of a theory to account for cold fusion can be discounted on the grounds that the correct explanation and theory has not been provided
27. Cite error: The named reference Goodstein was invoked but never defined (see the help page).
28. Kee B., "What is the current scientific thinking on cold fusion? Is there any possible validity to this phenomenon?", Scientific American, Ask the Experts, October 21, 1999, p. 5
29. See the review document submitted to the 2004 DoE panel on cold fusion by the researchers
30. See the Report of the Review of Low Energy Nuclear Reactions by the 2004 DOE panel on cold fusion
31. Presented by Mosier-Boss, Szpak and Gordon at the APS meeting in March 2007 ( slide 7) Cited by Krivit, New Energy Times, March 16, 2007
32. See the review document submitted to the 2004 DoE panel on cold fusion by the researchers
33. See the Report of the Review of Low Energy Nuclear Reactions by the 2004 DOE panel on cold fusion
34. Mosier-Boss et al, "Use of CR-39 in Pd/D co-deposition experiments", Eur. Phys. J. Appl. Phys. 40, 293-303 (2007)

See also

• Alchemy
• Transmutation
• Pathological science
• Protoscience

Further information

Books

• Close, Frank E..Too Hot to Handle: The Race for Cold Fusion. Princeton, N.J. : Princeton University Press, 1991. ISBN 0-691-08591-9; ISBN 0-14-015926-6.
• Huizenga, John R. Cold Fusion: The Scientific Fiasco of the Century. Rochester, N.Y.: University of Rochester Press, 1992. ISBN 1-878822-07-1; ISBN 0-19-855817-1.
• Kozima, Hideo. The Science of the Cold Fusion phenomenon, Elsevier Science, 2006. ISBN 0-08-045110-1.
• Mallove, Eugene. Fire from Ice: Searching for the Truth Behind the Cold Fusion Furor. John Wiley & Sons, Inc., 1991. ISBN 0-471-53139-1.
• Park, Robert L. Voodoo Science: The Road from Foolishness to Fraud. New York: Oxford University Press, 2000. ISBN 0-19-513515-6.
• Storms, Edmund. Science of Low Energy Nuclear Reaction: A Comprehensive Compilation of Evidence and Explanations. World Scientific Publishing Company, 2007 ISBN 9-8127062-0-8.
• Taubes, Gary. Bad Science: The Short Life and Weird Times of Cold Fusion. New York, N.Y. : Random House, 1993. ISBN 0-394-58456-2.

External links

• 1989 Energy Research Advisory Board, "Conclusions and recommendations"
• U.S. DoE 2004 Cold Fusion Review - U.S. Department of Energy review of 15 years of cold fusion experiments
• Recent papers on cold fusion listed on New Energy Times
• Some selected articles on cold fusion
• Britz's cold nuclear fusion bibliography: An extensive overview and review of almost all available publications about cold nuclear fusion.

• Pseudoscience