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Cold fusion is a controversial effect reported by some researchers to have been produced from nuclear reaction at conditions near room temperature and atmospheric pressure.

The first report of such an effect was published by Martin Fleischmann and Stanley Pons from the University of Utah in 1989. In their paper, they reported the observation of anomalous heating ("excess heat") of an electrolytic cell during electrolysis of heavy water. Lacking an explanation for the source of such heat, they proposed the hypothesis that the heat came from nuclear fusion of deuterium. The report of their results raised hopes of a cheap and abundant source of energy.

Cold fusion gained a reputation as a pathological science after other scientists failed to replicate the results. A review panel organized by the US Department of Energy (DOE) in 1989 did not find the evidence persuasive, and said that such "nuclear fusion at room temperature would be contrary to all understanding gained of nuclear reactions in the last half century" and "it would require the invention of an entirely new nuclear process."

Since then, other reports of anomalous heat production and anomalous tritium production have been reported in peer-reviewed journals and have been discussed at scientific conferences. Most scientists have met these reports with skepticism. In 2004 the US DOE organized another review panel (US DOE 2004) which—like the one in 1989—did not recommend a focused federally-funded program for low energy nuclear reactions. The 2004 panel identified basic research areas that could be helpful in resolving some of the controversies in the field. It stated that the field would benefit from the peer-review processes associated with proposal submission to agencies and paper submission to archival journals.

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.

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) 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."

Experimental reports

Excess heat

The excess power observed in some experiments is reported to be beyond that attributable to ordinary chemical or solid state sources; this excess power is attributed by proponents to nuclear fusion reactions.

The cold fusion researchers who presented their review document to the 2004 DoE panel said that "the hypothesis that the excess heat effect arises only as a consequence of errors in calorimetry was 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 (1.8 times input energy) 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. There are nearly 200 published reports of excess heat and other reviews by cold fusion researchers reach similar conclusions.

The 2004 DoE panel noted that significant progress has been made in the sophistication of calorimeters since 1989. Evaluations by the reviewers ranged from: 1) evidence for excess power is compelling, to 2) there is no convincing evidence that excess power is produced when integrated over the life of an experiment. The reviewers were split approximately evenly on this topic.

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 who presented 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 anomalies near the cathode surface in some experiments, evidence which introduce additional discrepancies between observations and conventional theory because of the increased Coulomb barrier, they said that it is generally accepted that these anomalies are not the ash associated with the primary excess heat effect. There are over 60 published reports of anomalous tritium production and other reviews by cold fusion researchers reach similar conclusions.

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. The evidence of D+D fusion was taken as convincing or somewhat convincing by some reviewers; for others the lack of consistency was an indication that the overall hypothesis was not justified. Contamination of apparatus or samples by air containing 4He was cited as one possible cause for false positive results in some measurements.

In 2007, the Space and Naval Warfare Systems Center San Diego 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 other pits are consistent with those obtained for alpha particles. They said that the experiment is reproducible.

Nuclear transmutations

In nuclear reactions, a chemical element may be transmuted into another. Nuclear transmutations have been reported in many cold fusion experiments since 1992. Transmutations in such experiments would be contrary to all understanding gained of nuclear reactions in the last half century; they would require the invention of an entirely new nuclear process. At the same time, the lack of a satisfactory explanation cannot be used to dismiss experimental evidence.

There are over 60 reports of nuclear transmutations. Tadahiko Mizuno was among the first to contribute a paper (Mizuno 2000 harvnb error: no target: CITEREFMizuno2000 (help)) and a book on the subject (Mizuno 1998). Dr. Miley, who also contributed to Inertial electrostatic confinement, wrote a review of these experiments. He reports that several dozen laboratories are studying these effects. Some experiments result in the creation of only a few elements, while others result in a wide variety of elements from the periodic table. Calcium, copper, zinc, and iron were the most commonly reported elements. Lanthanides were also found: this is significant since they are unlikely to enter as impurities. In addition, the isotopic ratios of the observed elements differ from their natural isotopic ratio or natural abundance. Many elements have multiple isotopes and the percentages of the different isotopes are constant on earth within one tenth of one percent. In general it requires gaseous diffusion, thermal diffusion, electromagnetic separation or other exotic processes of isotope separation or a nuclear reaction to change an element from its natural isotope ratio. The presence of an unnatural isotope ratio makes contamination an implausible explanation. Some experiments reported both transmutations and excess heat, but the correlation between the two effects has not been established. Radiations have also been reported. Miley also reviews possible theories to explain these observations.

Further evidence for transmutation has come from an experiment made by Iwamura and associates, and published in 2002 in the Japanese Journal of Applied Physics. Instead of using electrolysis, they forced deuterium gas to permeate through a thin layer of caesium (also known as cesium) deposited on calcium oxide and palladium, while periodically analyzing the nature of the surface through X-ray photoelectron spectroscopy. As the deuterium gas permeated over a period of a week, the amount of caesium progressively decreased while the amount of praseodymium increased, so that caesium appeared to be transmuted into praseodymium. When caesium was replaced by strontium, it was transmuted into molybdenum with anomalous isotopic composition. In both cases this represents an addition of four deuterium nuclei to the original element. They have produced these results six times, and reproducibility was good. The energy released by these transmutations was too low to be observed as heat. No gamma rays were observed. When the calcium oxide was removed or when the deuterium gas was replaced by hydrogen in control experiments, no transmutation was observed. The authors analyzed, and then rejected, the possibility to explain these various observations by contaminations or migration of impurities from the palladium interior:

"Since the detected material, Pr, belongs to rare earth elements, it is difficult to assume that Pr accumulated on the Pd complex test pieces by an ordinary process. The purity of the used D2 gas is over 99.6% and most of the impurity is H2. The other impurities detected by a mass spectrometer are N2, D2O, O2, CO2 , CO and hydrocarbons; their amounts are all under 10 ppm. It is impossible for all of the distributed Pr in the Pd test piece to gather in the narrow surface area against the flow of D2 gas without the application of a specific force on Pr, because such a phenomenon breaks the law of thermodynamics. The third point is that the isotope ratio of produced elements is anomalous. In this paper, we show the isotopic anomaly of Mo. It provides evidence that the detected material, Mo, was produced by certain nuclear processes. If the Mo were a contaminant, such efficient isotope separations would not be possible. The last point is that the elements detected the D2 gas permeation vary depending on the given elements at the beginning of the experiments. It is very difficult to assume that the detected elements change depending on the given elements by external contamination. The above discussion strongly suggests the existence of low-energy nuclear transmutations induced by a simple method."

At the conclusion of their report, Iwamura et al. are cautious in presenting how such transmutations could be explained. Their conclusions are qualified by the reliance on several assumptions and by their model being presented as a hypothesis rather than an established theory. "If several assumptions are accepted, they (the results) are basically explained by the EINR model, which is one of the working hypotheses in the investigation of the nature of this phenomenon."

The experiment was replicated by researchers from Osaka University using Inductively Coupled Plasma Mass Spectrometry to analyze the nature of the surface (the Pd complex samples were provided by Iwamura). In later similar experiments by Iwamura, Barium 138 was transmuted to Samarium 150 and Barium 137 was transmuted into Samarium 149. The Barium 138 experiment used a natural isotope ratio of Barium. The Barium 137 experiment used a Barium 137 enriched isotope ratio. These transmutations represent an addition of six deuterium nuclei.

Szpak et al have also reported transmutations in electrolytic cells, and Bush and Eagleton have reported the appearance of radioactive isotopes with an average half-life of 3.8 days in electrolytic cells, an observation that is difficult to explain by contamination or migration.

Excess heat by electrolysis experiments

The Fleischmann and Pons experiment

In their original set-up, Fleischmann and Pons used a Dewar flask (a double-walled vacuum flask) for the electrolysis, so that heat conduction would be minimal on the side and the bottom of the cell (only 5 % of the heat loss in this experiment). The cell flask was then submerged in a bath maintained at constant temperature to eliminate the effect of external heat sources. They used an open cell, thus allowing the gaseous deuterium and oxygen resulting from the electrolysis reaction to leave the cell (with some heat too). It was necessary to replenish the cell with heavy water at regular intervals. The authors said that, since the cell was tall and narrow, the bubbling action of the gas kept the electrolyte well mixed and of a uniform temperature. The efficacy of this stirring method and thus the validity of the temperature measurements would later be disputed. Special attention was paid to the purity of the palladium cathode and electrolyte to prevent the build-up of material on its surface, especially after long periods of operation.

The cell was also instrumented with a thermistor to measure the temperature of the electrolyte, and an electrical heater to generate pulses of heat and calibrate the heat loss due to the gas outlet. After calibration, it was possible to compute the heat generated by the reaction.

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 rose suddenly to about 50 °C without changes in the input power, for durations of 2 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.

The Faraday-efficiency effect

Lacking any other plausible explanation, the anomalous excess heat produced during such electrolysis was attributed by Pons and Fleischmann to cold nuclear fusion. It was discovered that, in some circumstances, such excess heat can be the product of conventional chemistry, i.e. internal recombination of hydrogen and oxygen. Such recombination leads to a reduction in the Faraday efficiency of the electrolysis. The Faraday-efficiency effect is the observation of apparent excess heat due to a reduction in the Faraday efficiency.

A group of investigators led by Zvi Shkedi, built in 1991-1993 several well-insulated cells and calorimeters which included the capability to measure the actual Faraday efficiency in real time during the experiments. The cells were of the light-water type; with a fine-wire nickel cathode; a platinum anode; and K₂CO₃ electrolyte. A total of 64 experiments were performed in which the actual Faraday efficiency was measured. The results were analyzed twice; once with the popular assumption that the Faraday efficiency is 100%, and, again, taking into account the measured Faraday efficiency in each experiment. The average Faraday efficiency measured in these experiments was 78%. The first analysis, assuming a Faraday efficiency of 100%, yielded an average apparent excess heat of 21% of input power. The second analysis, taking into account the measured Faraday efficiency, yielded an actual excess heat of 0.13% +/- 0.48%. In other words, when the actual Faraday efficiency was measured and taken into account, the energy balance of the cells was zero, with no excess heat. The investigators concluded their publication with the following word of caution: "All reports claiming the observation of excess heat should be accompanied by simultaneous measurements of the actual Faraday efficiency." Jones et al. confirmed the Shkedi et al. findings with the same conclusion: "Faradaic efficiencies less than 100% during electrolysis of water can account for reports of excess heat in 'cold fusion' cells."

Edmund Storms observed that " values attributed to Jones et al. gives a good example of biased reasoning. They measured the recombination fraction at very low currents, where is high, and used these values to dismiss all measurements using open cells, without acknowledging that most successful studies used much higher currents or closed cells where this correction is unnecessary."

Fleischmann did measure Faraday efficiency in his experiments: it was better than 99%. Fritz Will, former president of the Electrochemical Society, noted in his review of Jones' paper that " fraction of O₂ recombining with H₂ decreases significantly with increasing current density. On the basis of their results at low current densities, a group of researchers recently concluded that H₂ + O₂ recombination is the source for the "excess heat' reported by other groups and attributed by some to 'cold fusion'. However, reported excess heat values, ranging from a low of 23% at 14 mA/cm to a high of 3700% at 6 mA/cm, are much larger than can be explained by recombination. Whatever the explanation for the large amounts of excess heat reported by various groups, H₂ + O₂ recombination must be rejected as a tenable explanation."

History

Early work

Cold fusion revolves around the idea that palladium or titanium might catalyze fusion stemmed from the special ability of these metals to absorb large quantities of hydrogen, including its deuterium isotope, the hope being that the deuterium atoms would be close enough together to induce fusion at ordinary temperatures. The special ability of palladium to absorb hydrogen was recognized as early as the nineteenth century by Thomas Graham. In the late nineteen-twenties, two German scientists, F. Paneth and K. Peters, reported the transformation of hydrogen into helium by spontaneous nuclear catalysis when hydrogen was adsorbed by finely divided palladium at room temperature. These authors later acknowledged that the helium they measured was due to background from the air.

In 1927, Swedish scientist J. Tandberg stated that he had fused hydrogen into helium in an electrolytic cell with palladium electrodes. On the basis of his work he applied for a Swedish patent for "a method to produce helium and useful reaction energy." After deuterium was discovered in 1932, Tandberg continued his experiments with heavy water. Due to Paneth and Peters' retraction, Tandberg's patent application was eventually denied.

The term "cold fusion" was coined by Dr Paul Palmer of Brigham Young University in 1986 in an investigation of "geo-fusion," or the possible existence of fusion in a planetary core.

Pre-announcement and announcement

In the 1960s, Fleischmann and his research team began investigating the possibility that chemical means could influence nuclear processes. Simple quantum mechanical calculations indicate that such effects should be negligibly small, but Fleischmann started to explore whether collective effects, that would require quantum electrodynamics to calculate, might be significant. By 1983, Fleischmann had experimental evidence leading him to believe that condensed phase systems developed coherent structures up to 10m in size.

In 1988, Fleischmann and Pons applied to the United States Department of Energy for funding towards a larger series of experiments. Up to this point they had been funding their experiments using a small device built with $100,000 out-of-pocket.

The grant proposal was turned over for peer review, including Steven E. Jones of Brigham Young University. Jones had worked on muon-catalyzed fusion for some time, and had written an article on the topic entitled Cold Nuclear Fusion that had been published in Scientific American in July 1987. Similar to Fleischmann and Pons, Jones claimed that he detected fusion but with a more modest claim, but it was discredited because the rates were far too low to be commercially practical.

Both Fleischmann and Pons`, and Jones research teams met on occasion in Utah to discuss sharing research and techniques. During this time, Fleischmann and Pons described their experiments as generating considerable "excess energy", in the sense that it could not be explained by chemical reactions alone. This could bear significant commercial value and would be protected by patent protection. Jones, however, was measuring neutron flux, which was not of commercial interest. In order to avoid problems in the future, the teams apparently agreed to simultaneously publish their results, although their accounts of their March 6 meeting differ.

In mid-March, both research teams were ready to publish their findings, and Fleischmann and Jones had agreed to meet at an airport on March 24 to send their papers to Nature via FedEx. Fleischmann and Pons, however, broke their apparent agreement, submitting their paper to the Journal of Electroanalytical Chemistry on March 11, and disclosing their work via a press conference on March 23.

Jones, upset, faxed in his paper to Nature after the press announcement was made.

Post-announcement

The press initially reported on the experiments widely, and due to the surmised beneficial commercial applications of the Utah experiments, "scores of laboratories in the United States and abroad" attempted to repeat the experiments.

On April 10, 1989, Fleischmann and Pons, who later suggested pressure from patent attorneys, published a rushed "preliminary note" in the Journal of Electroanalytical Chemistry. This paper notably contained a gamma peak without its corresponding Compton edge, a discrepancy that triggered accusations of fraud. Their earlier paper was followed up a year later in July 1990, when a much longer paper, going into details of calorimetry but abandoning mention of any nuclear measurements, was published in the same journal.

Also occurring on April 10, a team at Texas A&M University published their results of excess heat, followed up by a team at the Georgia Institute of Technology in regards to neutron production. Both results were widely reported on in the press, although both Texas A&M and Georgia Institute of Technology withdrew their results for lack of evidence. For the next six weeks, additional competing claims, counterclaims and suggested explanations kept the topic of Cold Fusion paramount, and led some journalists refer to the situation as "fusion confusion."

On April 12, Pons received a standing ovation from about 7,000 chemists at the semi-annual meeting of the American Chemical Society. The University of Utah asked Congress to provide $25 million to pursue the research, and Pons was scheduled to meet with representatives of President Bush early May.

One month later, on May 1, the American Physical Society held a session on cold fusion, reported a string of failed experiments. A second session began the next day with other negative reports, and eight of the nine leading speakers stated that they ruled the initial Utah claim as dead. Dr. Steven E. Koonin of Caltech called the Utah report a result of "the incompetence and delusion of Pons and Fleischmann." Dr. Douglas R. O. Morrison, a physicist representing CERN, called the entire episode an example of pathological science.

By the end of May, much of the media attention had faded due to not only to the competing results and counterclaims, but also to the limited attention span of modern media. While the research efforts cooled significantly, similar cold fusion projects continued around the world.

In July, the first successful replication of the excess heat was completed by Richard Oriani, a professor of physical chemistry at the University of Minnesota. The results were published in his paper, "Calorimetric Measurements of Excess Power Output During the Cathodic Charging of Deuterium Into Palladium," in Fusion Technology. Nature published papers critical of cold fusion in July and November.

In November, a special panel formed by the Energy Research Advisory Board, under a charge of the United States Department of Energy, reported the result of their investigation into cold fusion. The scientists in the panel found the evidence for cold fusion to be unconvincing. Nevertheless, the panel was "sympathetic toward modest support for carefully focused and cooperative experiments within the present funding system." As 1989 wore on, cold fusion was considered by mainstream scientists to be self-deception, experimental error and even fraud, and was held out as a prime example of pseudoscience. The United States Patent and Trademark Office has rejected most patent applications related to cold fusion since then.

In 1991, Dr. Eugene Mallove stated that the negative report issued by MIT's Plasma Fusion Center in 1989, which was highly influential in the controversy, was fraudulent because data was shifted without explanation, and as a consequence, this action obscured a possible positive excess heat result at MIT. In protest of MIT's failure to discuss and acknowledge the significance of this data shift, Mallove resigned from his post of chief science author at the MIT news office on June 7, 1991. He maintained that the data shift was biased to support the conventional belief in the non-existence of the cold fusion effect as well as to protect the financial interests of the plasma fusion center's research in hot fusion.

Nobel Laureate Julian Schwinger also stated in 1991 that he had experienced "the pressure for conformity in editor's rejection of submitted papers, based on venomous criticism of anonymous reviewers," and that "the replacement of impartial reviewing by censorship will be the death of science." He resigned as Member and Fellow of the American Physical Society, in protest of its peer review practice on cold fusion.

In 1992, General Electric challenged the Fleischmann-Pons 1990 report in the Journal of Electroanalytical Chemistry, stating that the claims of excess heat had been overstated. The challenge concluded that the Fleischmann and Pons cell generated 40% excess heat, more than ten times larger than the initial error estimate. Despite the apparent confirmation, Fleischmann and Pons replied to General Electric and published a rebuttal in the same journal.

Moving beyond the initial controversy

In the 1990s, there was little cold fusion research in the United States, and much of the research during this time occurred in Europe and Asia. Fleischmann and Pons relocated their laboratory to France under a grant from the Toyota Motor Corporation, and later sued La Repubblica, an Italian newspaper and a journalist for their suggestion that cold fusion was a scientific fraud. They lost the libel case in an Italian court. In 1996, they announced in Nature that they would appeal the court's decision, but never did.

By 1991, 92 groups of researchers from 10 different countries had reported excess heat, tritium, neutrons or other nuclear effects. Over 3,000 cold fusion papers have been published including about 1,000 in peer-reviewed journals (see indices in further reading, below). In March 1995, Dr. Edmund Storms compiled a list of 21 published papers reporting excess heat and articles have been published in peer reviewed journals such as Naturwissenschaften, European Physical Journal A, European Physical Journal C, Journal of Solid State Phenomena, Physical Review A, Journal of Electroanalytical Chemistry, Japanese Journal of Applied Physics, and Journal of Fusion Energy (see indices in further reading, below).

The generation of excess heat has been reported by (among others):

• Michael McKubre, director of the Energy Research Center at SRI International,
• G. Preparata (ENEA (Italy))
• Richard A. Oriani (University of Minnesota, in December 1990),
• Robert A. Huggins (at Stanford University in March 1990),
• Y. Arata (Osaka University, Japan),
• T. Mizuno (Hokkaido University, Japan),
• T. Ohmori (Japan),

The most common experimental set-ups are the electrolytic (electrolysis) cell and the gas (glow) discharge cell, but many other set-ups have been used. Electrolysis is popular because it was the original experiment and is the more commonly known way of conducting the cold fusion experiment; gas discharge is often used because it is believed to be the set-up that provides an experimenter a better chance at replication of the excess heat results.

Researchers share their results at the International Conference on Cold Fusion, recently renamed International Conference on Condensed Matter Nuclear Science. The conference is held every 12 to 18 months in various countries around the world, and is hosted by The International Society for Condensed Matter Nuclear Science, a scientific organization that was founded as a professional society to support research efforts and to communicate experimental results. A few periodicals emerged in the 1990s that covered developments in cold fusion and related new energy sciences (Fusion Facts, Cold Fusion Magazine, Infinite Energy Magazine, New Energy Times).

Between 1992 and 1997, Japan's Ministry of International Trade and Industry sponsored a "New Hydrogen Energy Program" of $20 million to research cold fusion. Announcing the end of the program, Dr. Hideo Ikegami stated in 1997 "We couldn't achieve what was first claimed in terms of cold fusion." He added, "We can't find any reason to propose more money for the coming year or for the future."

In 1994, Dr. David Goodstein described cold fusion as "a pariah field, cast out by the scientific establishment. Between and respectable science there is virtually no communication at all. Cold fusion papers are almost never published in refereed scientific journals, with the result that those works don't receive the normal critical scrutiny that science requires. On the other hand, because the Cold-Fusioners see themselves as a community under siege, there is little internal criticism. Experiments and theories tend to be accepted at face value, for fear of providing even more fuel for external critics, if anyone outside the group was bothering to listen. In these circumstances, crackpots flourish, making matters worse for those who believe that there is serious science going on here.

Cold fusion advocates said that cold fusion is suppressed, and that skeptics suffer from "pathological disbelief". They said that there is virtually no possibility for funding in cold fusion in the United States, and no possibility of getting published. They said that people in universities refuse to work on it because they would be ridiculed by their colleagues.

In February 2002, a laboratory within the United States Navy released a report that came to the conclusion that the cold fusion phenomenon was in fact real and deserved an official funding source for research. Navy researchers have published more than 40 papers on cold fusion.

In 2004, the United States Department of Energy (USDOE) decided to take another look at cold fusion to determine if their policies towards cold fusion should be altered due to new experimental evidence. They set up a panel on cold fusion.

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.

Notes

• α. References to publications are listed in Storms 2007, pp. 52–61, 79–81 and in Hagelstein et al. 2004, pp. 25–29, to include Arata & Zhang 1998, Iwamura, Sakano & Itoh 2002, Mizuno et al. 2000 harvnb error: no target: CITEREFMizunoOhmoriAkimotoTakahashi2000 (help), Miles et al. 1993 and Bush et al. 1991 harvnb error: no target: CITEREFBushLangowskiMilesOstrom1991 (help). 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.

References

1. Fleischmann & Pons 1989, p. 301.
2. Browne 1989, para. 1.
3. ^ Browne 1989, para. 29.
4. ^ US DOE 1989, p. 37.
5. Van Noorden 2007, para. 2.
6. cf. Chubb et al. 2006.
7. Feder 2005
8. ^ US DOE 1989, p. 36.
9. US DOE 2004, p. 5.
10. US DOE 1989, pp. 6–8.
11. Hagelstein et al. 2004, p. 14.
12. US DOE 2004, p. 3.
13. US DOE 1989, pp. 5–6.
14. Hagelstein et al. 2004, p. 8.
15. Close 1991, p. ?.
16. Huizenga 1992, p. ?.
17. US DOE 1989, pp. 6–7.
18. Goodstein 1994, p. 528.
19. Kee 1999, p. 5.
20. US DOE 2004, p. 1.
21. US DOE 2004, p. 3.
22. Hagelstein et al. 2004, p. 1.
23. Storms 2007, pp. 52–61.
24. ^ Biberian 2007, p. ?.
25. ^ Hubler 2007, p. ?.
26. US DOE 2004, p. ??.
27. Mosier-Boss, Szpak & Gordon 2007, slide 7
    reported in Krivit 2007, p. 2.
28. Hagelstein et al. 2004, p. 7.
29. Szpak et al. 2005, p. 2.
30. Iwamura, Sakano & Itoh 2002, p. 4647.
31. Storms 2007, p. 79-81.
32. US DOE 2004, p. ??.
33. Mosier-Boss et al. 2007, p. ?.
34. Storms 2007, p. 93-95.
35. Prow 2001.
36. Miley & Shrestha 2003 harvnb error: no target: CITEREFMileyShrestha2003 (help)
37. Miley & Shrestha 2003, p. ? harvnb error: no target: CITEREFMileyShrestha2003 (help).
38. Iwamura, Sakano & Itoh 2002, pp. 4642–4650.
39. Iwamura, Sakano & Itoh 2002, p. 4648-4649.
40. Iwamura, Sakano & Itoh 2002, p. ??.
41. Higashiyama et al. 2003, p. 1 harvnb error: no target: CITEREFHigashiyamaSakanoMiyamaruTakahashi2003 (help)
42. Iwamura 2004, p. 1 harvnb error: no target: CITEREFIwamura2004 (help).
43. Szpak et al. 2005, p. ??.
44. Bush & Eagleton 1994, p. 334.
45. Browne M. "Physicists Debunk Claim Of a New Kind of Fusion", New York Times, May 3, 1989
46. Shkedi et al. 1995, pp. 1720–1731.
47. Shkedi 1996, p. 133.
48. Shkedi et al. 1995, p. ??.
49. Jones et al. 1995, p. 1.
50. Storms 2007, p. 195.
51. Fleischmann et al. 1990, p. 301.
52. Will 1997, p. 177.
53. ^ Crease & Samios 1989, p. V1.
54. ^ US DOE 1989, p. 7.
55. Kowalski 2004, II.A2.
56. Fleischmann 2003, p. 1 harvnb error: no target: CITEREFFleischmann2003 (help).
57. Evans 1982, p. ??.
58. ^ Fleischmann 2003, p. 3 harvnb error: no target: CITEREFFleischmann2003 (help).
59. Kowalski 2004, V.
60. ^ Browne 1989.
61. ^ Krivit 2005.
62. Tate 1989, p. 1.
63. Platt 1989.
64. Bowen 1989.
65. Oriani et al. 1990, pp. 652–662.
66. Gai et al. 1989, pp. 29–34.
67. Williams et a. 1989, pp. 375–384.
68. Mallove 1999, p. ??.
69. Schwinger 1991, p. ??.
70. Wilson 1992, p. 1.
71. Beaudette 2002, pp. 188, 357–360.
72. Mallove 1991, p. 246-248.
73. Pollack 1997, p. C4.
74. Goodstein 1994, p. ??.
75. Josephson 2004, p. ??.
76. Feder 2004, p. 27.
77. Rusbringer 2005
78. Szpak & Mosier-Boss 2002a
79. Szpak & Mosier-Boss 2002b
80. Kim et al. 1992, pp. 373–376.

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Further reading

• 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 on the subject of cold nuclear fusion.