Editing Cold fusion (section)

==Criticism==
Criticism of cold fusion claims generally take one of two forms: either pointing out the theoretical implausibility that fusion reactions have occurred in electrolysis setups or criticizing the excess heat measurements as being spurious, erroneous, or due to poor methodology or controls. There are several reasons why known fusion reactions are an unlikely explanation for the excess heat and associated cold fusion claims.<ref group="text" name="branching_and_gamma" />

===Repulsion forces===
Because nuclei are all positively charged, they strongly repel one another.{{sfn|ps=|Schaffer|1999|p=2}} Normally, in the absence of a catalyst such as a [[Muon-catalyzed fusion|muon]], very high [[Kinetic energy|kinetic energies]] are required to overcome this [[Coulomb's law|charged repulsion]].{{sfn|ps=|Schaffer|1999|p=1}}{{sfn|ps=|Morrison|1999|pp=3–5}} Extrapolating from known fusion rates, the rate for uncatalyzed fusion at room-temperature energy would be 50 orders of magnitude lower than needed to account for the reported excess heat.<ref>{{harvnb|Huizenga|1993|p=viii}} "''Enhancing the probability of a nuclear reaction by 50 orders of magnitude (...) via the chemical environment of a metallic lattice, contradicted the very foundation of nuclear science.''", {{harvnb|Goodstein|1994}}, {{harvnb|Scaramuzzi|2000|p=4}}</ref> In muon-catalyzed fusion there are more fusions because the presence of the muon causes deuterium nuclei to be 207 times closer than in ordinary deuterium gas.<ref>{{harvnb|Close|1992|pp=32, 54}}, {{harvnb|Huizenga|1993|p=112}}</ref> But deuterium nuclei inside a palladium lattice are further apart than in deuterium gas, and there should be fewer fusion reactions, not more.<ref name="distance">{{harvnb|US DOE|1989|pp=7–8, 33, 53–58 (appendix 4.A)}}, {{harvnb|Close|1992|pp=257–258}}, {{harvnb|Huizenga|1993|p=112}}, {{harvnb|Taubes|1993|pp=253–254}} quoting [[Howard Kent Birnbaum]] in the special cold fusion session of the 1989 spring meeting of the Materials Research Society, {{harvnb|Park|2000|pp=17–18, 122}}, {{harvnb|Simon|2002|p=50}} citing {{cite journal|mode=cs2  |author1=Koonin S.E. |author2=M Nauenberg |s2cid=4335882 |year= 1989 |title= Calculated Fusion Rates in Isotopic Hydrogen Molecules |journal= Nature |issue= 6227|pages= 690–692 |doi= 10.1038/339690a0 |bibcode = 1989Natur.339..690K |volume=339}}</ref>

Paneth and Peters in the 1920s already knew that palladium can absorb up to 900 times its own volume of hydrogen gas, storing it at several thousands of times the [[atmospheric pressure]].{{sfn|ps=|Close|1992|pp=19–20}} This led them to believe that they could increase the nuclear fusion rate by simply loading palladium rods with hydrogen gas.{{sfn|ps=|Close|1992|pp=19–20}} Tandberg then tried the same experiment but used electrolysis to make palladium absorb more deuterium and force the deuterium further together inside the rods, thus anticipating the main elements of Fleischmann and Pons' experiment.{{sfn|ps=|Close|1992|pp=19–20}}<ref name="similar_to_tandberg" /> They all hoped that pairs of hydrogen nuclei would fuse together to form helium, which at the time was needed in Germany to fill [[zeppelin]]s, but no evidence of helium or of increased fusion rate was ever found.{{sfn|ps=|Close|1992|pp=19–20}}

This was also the belief of geologist Palmer, who convinced Steven Jones that the helium-3 occurring naturally in Earth perhaps came from fusion involving hydrogen isotopes inside catalysts like nickel and palladium.{{sfn|ps=|Close|1992|pp=63–64}} This led their team in 1986 to independently make the same experimental setup as Fleischmann and Pons (a palladium cathode submerged in heavy water, absorbing deuterium via electrolysis).{{sfn|ps=|Close|1992|pp=64–66}} Fleischmann and Pons had much the same belief,{{sfn|ps=|Close|1992|pp=32–33}} but they calculated the pressure to be of 10<sup>27</sup> [[Standard atmosphere (unit)|atmospheres]], when cold fusion experiments achieve a loading ratio of only one to one, which has only between 10,000 and 20,000 atmospheres.<ref group="text" name="pressure" /> [[John R. Huizenga]] says they had misinterpreted the [[Nernst equation]], leading them to believe that there was enough pressure to bring deuterons so close to each other that there would be spontaneous fusions.{{sfn|ps=|Huizenga|1993|pp=33, 47}}

===Lack of expected reaction products===
Conventional deuteron fusion is a two-step process,<ref group="text" name="branching_and_gamma" /> in which an unstable high-energy [[Reaction intermediate|intermediary]] is formed:
:[[deuterium|{{sup|2}}H]] + {{sup|2}}H → [[Alpha particle|{{sup|4}}He]][[Nuclear isomer|{{sup|*}}]] + 24 [[MeV]]
Experiments have shown only three decay pathways for this excited-state nucleus, with the [[Branching fraction|branching ratio]] showing the probability that any given intermediate follows a particular pathway.<ref group="text" name="branching_and_gamma"/> The products formed via these decay pathways are:
:{{sup|4}}He{{sup|*}} → [[neutron|n]] + [[Helium-3|{{sup|3}}He]] + 3.3 MeV ([[Branching fraction|ratio]]=50%)
:{{sup|4}}He{{sup|*}} → [[proton|p]] + [[Tritium|{{sup|3}}H]] + 4.0 MeV (ratio=50%)
:[[Isomeric transition|{{sup|4}}He{{sup|*}} → {{sup|4}}He]] + [[gamma particle|γ]] + 24 MeV (ratio=10{{sup|−6}})
Only about one in a million of the intermediaries take the third pathway, making its products very rare compared to the other paths.{{sfn|ps=|Schaffer|1999|p=2}} This result is consistent with the predictions of the [[Bohr model]].<ref group="text" name="consistent"/> If 1 watt (6.242 × 10{{sup|18}} eV/s){{refn|group="notes"|name=watt-ev|refn=1 W = 1 J/s ; 1 J = 6.242 × 10{{sup|18}} eV since 1 eV = 1.602 × 10{{sup|−19}} joule}} were produced from ~2.2575 × 10{{sup|11}} deuteron fusions per second, with the known branching ratios, the resulting neutrons and tritium ({{sup|3}}H) would be easily measured.{{sfn|ps=|Schaffer|1999|p=2}}{{sfn|ps=|Huizenga|1993|pp=7}} Some researchers reported detecting {{sup|4}}He but without the expected neutron or tritium production; such a result would require branching ratios strongly favouring the third pathway, with the actual rates of the first two pathways lower by at least five orders of magnitude than observations from other experiments, directly contradicting both theoretically predicted and observed branching probabilities.<ref group="text" name="branching_and_gamma" /> Those reports of {{sup|4}}He production did not include detection of [[gamma ray]]s, which would require the third pathway to have been changed somehow so that gamma rays are no longer emitted.<ref group="text" name="branching_and_gamma" />

The known rate of the decay process together with the inter-atomic spacing in a [[metallic crystal]] makes heat transfer of the 24 MeV excess energy into the host metal lattice prior to the intermediary's decay inexplicable by conventional understandings of [[momentum]] and energy transfer,<ref>{{harvnb|Scaramuzzi|2000|p=4}}, {{harvnb|Goodstein|1994}}, {{harvnb|Huizenga|1993|pp=207–208, 218}}</ref> and even then there would be measurable levels of radiation.<ref>{{harvnb|Close|1992|pp=308–309}} "Some radiation would emerge, either electrons ejected from atoms or X-rays as the atoms are disturbed, but none were seen."</ref> Also, experiments indicate that the ratios of deuterium fusion remain constant at different energies.<ref name="Huizenga_chemical_environment">{{harvnb|Close|1992|pp=268}}, {{harvnb|Huizenga|1993|pp=112–113}}</ref> In general, pressure and chemical environment cause only small changes to fusion ratios.<ref name="Huizenga_chemical_environment" /> An early explanation invoked the [[Oppenheimer–Phillips process]] at low energies, but its magnitude was too small to explain the altered ratios.{{sfn|ps=|Huizenga|1993|pp=75–76, 113}}

===Setup of experiments===
Cold fusion setups utilize an input power source (to ostensibly provide [[activation energy]]), a [[platinum group]] [[electrode]], a deuterium or hydrogen source, a [[calorimeter]], and, at times, detectors to look for byproducts such as helium or neutrons. Critics have variously taken issue with each of these aspects and have asserted that there has not yet been a consistent reproduction of claimed cold fusion results in either energy output or byproducts. Some cold fusion researchers who claim that they can consistently measure an excess heat effect have argued that the apparent lack of reproducibility might be attributable to a lack of quality control in the electrode metal or the amount of hydrogen or deuterium loaded in the system. Critics have further taken issue with what they describe as mistakes or errors of interpretation that cold fusion researchers have made in calorimetry analyses and energy budgets.{{citation needed|date=March 2021}}

====Reproducibility====
In 1989, after Fleischmann and Pons had made their claims, many research groups tried to reproduce the Fleischmann-Pons experiment, without success. A few other research groups, however, reported successful reproductions of cold fusion during this time. In July 1989, an Indian group from the [[Bhabha Atomic Research Centre]] ([[P. K. Iyengar]] and M. Srinivasan) and in October 1989, [[John Bockris]]' group from [[Texas A&M University]] reported on the creation of tritium. In December 1990, professor [[Richard Oriani]] of the [[University of Minnesota]] reported excess heat.{{sfn|ps=|Taubes|1993|pp=364–365}}

Groups that did report successes found that some of their cells were producing the effect, while other cells that were built exactly the same and used the same materials were not.{{sfn|ps=|Platt|1998}} Researchers who continued to work on the topic have claimed over the years that many successful replications had been made, but still had problems getting reliable replications.{{sfn|ps=|Simon|2002|pp=145–148}} [[Reproducibility]] is one of the main principles of the scientific method, and its lack led most physicists to believe that the few positive reports could be attributed to experimental error.{{sfn|ps=|Platt|1998}}<ref group="text" name="reger"/> The DOE 2004 report said among its conclusions and recommendations:

{{blockquote|text=Ordinarily, new scientific discoveries are claimed to be consistent and reproducible; as a result, if the experiments are not complicated, the discovery can usually be confirmed or disproved in a few months. The claims of cold fusion, however, are unusual in that even the strongest proponents of cold fusion assert that the experiments, for unknown reasons, are not consistent and reproducible at the present time. (...) Internal inconsistencies and lack of predictability and reproducibility remain serious concerns. (...) The Panel recommends that the cold fusion research efforts in the area of heat production focus primarily on confirming or disproving reports of excess heat.{{sfn|ps=|US DOE|2004}}}}

====Loading ratio====
[[File:Gas-ColdFusionCell-SRI-Intl-McKubre.jpg|thumb|upright|Michael McKubre working on deuterium gas-based cold fusion cell used by [[SRI International]]]]

Cold fusion researchers ([[Michael McKubre|McKubre]] since 1994,{{sfn|ps=|Simon|2002|pp=145–148}} [[Italian National Agency for New Technologies, Energy and Sustainable Economic Development|ENEA]] in 2011<ref name=ENEA_Magazin/>) have speculated that a cell that is loaded with a deuterium/palladium ratio lower than 100% (or 1:1) will not produce excess heat.{{sfn|ps=|Simon|2002|pp=145–148}} Since most of the negative replications from 1989 to 1990 did not report their ratios, this has been proposed as an explanation for failed reproducibility.{{sfn|ps=|Simon|2002|pp=145–148}} This loading ratio is hard to obtain, and some batches of palladium never reach it because the pressure causes cracks in the palladium, allowing the deuterium to escape.{{sfn|ps=|Simon|2002|pp=145–148}} Fleischmann and Pons never disclosed the deuterium/palladium ratio achieved in their cells;{{sfn|ps=|Huizenga|1993|p=82}} {{As of|2002|lc=y}} there were no longer any batches of the palladium used by Fleischmann and Pons because the supplier changed the manufacturing process,{{sfn|ps=|Simon|2002|pp=145–148}} and researchers still had problems finding batches of palladium that achieved heat production reliably.{{sfn|ps=|Simon|2002|pp=145–148}}

====Misinterpretation of data====
Some research groups initially reported that they had replicated the Fleischmann and Pons results but later retracted their reports and offered an alternative explanation for their original positive results. A group at [[Georgia Institute of Technology|Georgia Tech]] found problems with their neutron detector, and Texas A&M discovered bad wiring in their thermometers.{{sfn|ps=|Bird|1998|pp=261–262}} These retractions, combined with negative results from some famous laboratories,{{sfn|ps=|Browne|1989}} led most scientists to conclude, as early as 1989, that no positive result should be attributed to cold fusion.{{sfn|ps=|Bird|1998|pp=261–262}}{{sfn|ps=|Saeta|1999|loc= (pages 5–6; "Response"; Heeter, Robert F.)}}

====Calorimetry errors====
The calculation of excess heat in electrochemical cells involves certain assumptions.<ref>{{harvnb|Biberian|2007}} "Input power is calculated by multiplying current and voltage, and output power is deduced from the measurement of the temperature of the cell and that of the bath"</ref> Errors in these assumptions have been offered as non-nuclear explanations for excess heat.

One assumption made by Fleischmann and Pons is that the efficiency of electrolysis is nearly 100%, meaning nearly all the electricity applied to the cell resulted in electrolysis of water, with negligible [[Joule heating|resistive heating]] and substantially all the electrolysis product leaving the cell unchanged.{{sfn|ps=|Fleischmann|Pons|Anderson|Li|1990}} This assumption gives the amount of energy expended converting liquid D<sub>2</sub>O into gaseous D<sub>2</sub> and O<sub>2</sub>.{{sfn|ps=|Fleischmann|Pons|Anderson|Li|1990|loc=Appendix}} The efficiency of electrolysis is less than one if hydrogen and oxygen recombine to a significant extent within the calorimeter. Several researchers have described potential mechanisms by which this process could occur and thereby account for excess heat in electrolysis experiments.{{sfn|ps=|Shkedi|McDonald|Breen|Maguire|1995}}{{sfn|ps=|Jones|Hansen|Jones|Shelton|1995|p=1}}{{sfn|ps=|Shanahan|2002}}

Another assumption is that heat loss from the calorimeter maintains the same relationship with measured temperature as found when calibrating the calorimeter.{{sfn|ps=|Fleischmann|Pons|Anderson|Li|1990}} This assumption ceases to be accurate if the temperature distribution within the cell becomes significantly altered from the condition under which calibration measurements were made.<ref>{{harvnb|Biberian|2007}} "Almost all the heat is dissipated by radiation and follows the temperature fourth power law. The cell is calibrated ..."</ref> This can happen, for example, if fluid circulation within the cell becomes significantly altered.{{sfn|ps=|Browne|1989|loc=para. 16}}{{sfn|ps=|Wilson|Bray|Kosky|Vakil|1992}} Recombination of hydrogen and oxygen within the calorimeter would also alter the heat distribution and invalidate the calibration.{{sfn|ps=|Shanahan|2002}}{{sfn|ps=|Shanahan|2005}}{{sfn|ps=|Shanahan|2006}}