Cold fusion

The field of research and the name cold fusion began spectacularly in 1989 when chemists Stanley Pons of the University of Utah and Martin Fleischmann of the University of Southampton reported in a press conference that they had conducted low-cost experiments that led to the production of excess heat in an electrolytic cell in a manner that could only be produced by a nuclear process. The report of their results was widely publicized amidst worldwide excitement, briefly raising hopes that a cheap and abundant source of energy had been found. These and similar claims for unexpected nuclear reactions were not replicated with consistency by other laboratories. In 1989 and 1990, 20 groups at major U.S. laboratories, with 135 researchers, published papers describing attempted replications that failed. Consequently the interest of mainstream science has waned.

Two separate review panels organized by the United States Department of Energy, the first in 1989 and the second in 2004, concluded that not enough evidence for cold fusion existed for the federal government to finance further research. Both panels recommended 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. . ." This recommendation has not been implemented.

Many mainline scientists have since take the position that this is an example of either irreproducible science, or even pseudoscience.

Background

When a plasma is used to produce fusion between two deuterons, the process is called "plasma fusion" (or sometimes "hot fusion"). This reaction is known to emit neutrons and produce tritium in equal amounts. The established theory is that nuclear fusion reactions cannot be initiated without the input of significant energy because the charge barrier between nuclei, called the Coulomb barrier, cannot be overcome any other way. Cold fusion generated widespread publicity since it seemed defy these theoretical considerations and represented a potentially cheap and clean source of energy.

Reactions involving neutrons (or muons, or other neutral particles) can occur because these particles do not have a charge and can pass through the barrier. However, neutrons are not observed to form under conditions that produce the cold fusion reactions and they are not known to exist as free particles in ordinary materials.

Established theory holds that nuclear fusion reactions cannot be initiated without the input of significant energy because the charge barrier between nuclei, called the Coulomb barrier, cannot be overcome any other way. Cold fusion appears to defy this theory.

Experimental claims

Fleischmann and Pons, and others who have replicated their work, propose that nuclear reactions can be initiated without extra energy or application of neutrons by creating a special solid material: highly loaded palladium deuteride. That is, palladium which has absorbed nearly as many atoms of deuterium as the number of palladium atoms in the sample. This material is extremely difficult to produce. When fusion of deuterium takes place in this environment, they claim the main product is helium and heat, which are produced in the same ratio as they are with plasma fusion, and also tritium, neutrons, and mild radiation, which are detected at levels much lower than plasma fusion produces.

In addition, subsequent studies claim that more complex nuclear reactions can occur that are able to convert one element into another a process called transmutation for which the Coulomb barrier is even greater than between deuterium nuclei. Conventional theory can not explain such claims, and the observations have been difficult to reproduce, which is why the claims are controversial. In addition, some claims can be explained as being caused by error or unrecognized prosaic processes.

Continuing research

In spite of these objections, study of the effect has continued over the last 19 years. By September 1990, 92 groups from 10 countries reported successful replications. By the year 2000, over 200 groups had published replications in the peer-reviewed literature.

Evidence for a variety of nuclear processes has been presented including transmutation, fusion, and fission. For this reason, the terms "Low Energy Nuclear Reactions" (LENR), “Chemically Assisted Nuclear Reactions” (CANR), and "Condensed Matter Nuclear Science" (CMNS) are now used to describe work in this area of study. Many theories are being explored in order to identify a possible mechanism, although none have yet gained acceptance by conventional science. Many international conferences have been held and papers on the subject are regularly presented at American Physical Society, American Nuclear Society and American Chemical Society meetings in the US and at conferences in other countries. A website is available which provides most of the information on the subject. As a result, much more is known about the process than was available in 1989, when initial skepticism developed.

Excess heat production is an important characteristic of the effect and has created the most criticism. This is because calorimetry can be a difficult measurement and it is not well understood by many scientists. In addition, the original measurements, as well as a few other studies, were based on complex methods of isoperibolic calorimetry. Subsequently, evidence based on more readily understandable methods such as flow and Seebeck calorimetry have been published. For example, McKubre et al. at SRI spent millions of dollars developing a state of the art flow calorimeter (Fig. 1), which was used to study many samples that showed production of significant anomalous energy. Over 36 similar studies have observed the same general behavior as was reported by these workers. Of course, all of the positive results could be caused by various errors. This possibility has been explored in many papers, which have been reviewed and summarized by Storms. Although a few of the suggested errors might have affected a few studies, no error has been identified that can explain all of the positive results, especially those using well designed methods. At this time, it is safe to conclude that anomalous energy is produced, regardless of whether the source is nuclear reactions or something unknown to science. The magnitude of the heat release and the fact that no chemical fuel is consumed and no chemical ash produced rules out a chemical explanation.

© Image: SRI, Inc.
Figure 1. Labyrinth (L and M) Calorimeter and Cell developed by McKubre et al. at SRI. The entire calorimeter is contained in a vacuum Dewar to isolate it from the surroundings. Water flows into the inner region after its temperature is measured where it enters. After passing by and completely covering the wall of the electrolytic cell, it exits through a mixing tube, designed to insure that the measured temperature represents the average. Gas in the cell makes contact with a catalyst to insure all of the O₂ and D₂ is returned to the cell as D₂O. Loss or gain of gas is measured external to the cell. The D/Pd ratio of the Pd cathode is measured using its resistivity, which is determined using the 4 probe method. Heating wire is wrapped around the electrolytic cell to maintain constant temperature and to allow calibration. The device was demonstrated to be accurate and stable to better than ±50 mW.

To show that the source of the energy is a nuclear reaction, it is necessary to show that the amount of energy is related to the amount of a nuclear product. Until the work of Miles et al. various unexpected nuclear products had been detected, but never in sufficient amounts. Miles et al. showed that the helium was generated when anomalous heat was measured and that the relationship between the two measurements was consistent with the amount of energy known to result from a d-d fusion reaction. Since then, five other studies have observed the same relationship. Some of the detected helium could have resulted from helium known to be in normal air. It is unlikely that the heat and helium measurements were wrong by just the right amount every time the measurements were made. When helium leaks into a cell with air, it is found in much larger amounts than Miles and others observed, and it leaks in along with other gases that were not present in the sample. Thus, heat and helium appear to be correlated, but the nuclear process producing helium is still to be determined.

Nuclear products other than helium are detected in much smaller quantities. Early in the history, great effort was made to detect neutrons, an expected nuclear product from the d-d fusion reaction. Except for occasional bursts, the emission rate was found to be near the limit of detection or completely absent. This fact was used to reject the initial claim. It is now believed that the few observed neutrons are caused by a secondary nuclear reaction, possibly having nothing to do with the helium producing reaction. Tritium is another expected product of d-d fusion, which was sought. Again, tritium was detected but only in small amounts that were inconsistent with expectations. Nevertheless, the amount of tritium detected could not be explained by any prosaic process after all of the possibilities had been completely explored. The source of tritium is still unknown although it clearly results from a nuclear reaction that is initiated within the apparatus. Various nuclear products normally associated with d-d fusion also have been detected as energetic emissions, but at very low rates. Clearly, unusual nuclear processes are occurring in material where none should be found. Cold fusion researchers feel that this fact alone, regardless of the explanation, requires serious attention.

Finally, the presence of heavy elements having unnatural isotopic ratios and in unexpected large amounts are detected under some conditions. These are the so called transmutation products. Work in Japan has opened an entirely new aspect to the phenomenon by showing that impurity elements in palladium, through which D₂ is caused to pass, are converted to heavier elements to which 2D, 4D or 6D have been added. The claims have been replicated in Japan.

Although initial observations were made using an electrolytic cell in which the active material was palladium and the source of fuel was D₂O, many other methods are now claimed to produce the same kind of nuclear reactions. In addition, the active material can be several other materials besides palladium, all of which need to have a unique structure and generally are present with nanosized dimensions.

Explanations for the phenomena

Many theories are being explored, a few examples of which are:

1. Reduction of the Coulomb barrier by electrons being concentrated between the nuclei;
2. Conversion of deuterium into a wave structure that ignores the Coulomb barrier,
3. Creation or release of neutrons within the structure, which add to nuclei that are present,
4. Creation of clusters of deuterons that interact as units,
5. Involvement of phonons to concentrate energy at the reaction site and carry away the released energy.
6. Models showing that the Coulomb barrier is not as high as previously thought if certain conditions are present.

All of these mechanisms are only possible because a regular lattice of atoms and electrons is available and because the normally applied large energy does not hide these subtle processes. Models based on experience using high energy and/or a plasma, in which this regular array of atoms is not present, are not applicable.

A clean, cheap source of energy?

If the claims are real, regardless of their explanation, what are the potential consequences to society? Like plasma fusion -- which is produced in a Tokamak reactor such as the upcoming ITER -- cold fusion is also proposed to produce energy from the fusion reaction. Unlike plasma fusion, cold fusion produces only helium without a significant amount of radioactive products. The main source of energy proposed for plasma and cold fusion is deuterium, which is present in all water.

The hopes of nuclear fusion as an energy source are fueled by the fact that enough deuterium is available on earth to produce energy at present rates for billions of years. The cost of refining deuterium from water is far cheaper per unit of energy than for chemical, wind or solar energy. While plasma fusion requires huge installations to be practical the attraction of cold fusion is that it could be practical on a small scale. By 1990, cold fusion cathodes produced temperature and power density equal to a fission reactor core, and power levels up to 100 W, so if the reaction can controlled and generated on demand, it seems likely that it can be used as a practical source of energy. If it can be made to work, mankind could expect to produce pollution-free, low cost power without the risk posed by radioactive products, far into the future.