The recent interest in cold fusion was stimulated by reports from Utah scientists in March 1989 that fusion had occurred in experiments on the electrolysis of heavy water (D2O). Dr. Stanley Pons and Dr. Martin Fleischmann at the University of Utah claimed to measure a production of heat that could only be explained by a nuclear process. Dr. Steven Jones at Brigham Young University did not observe heat but claimed to observe neutron emission that would also indicate a nuclear process. The claims were particularly astounding given the simplicity of the equipment, just a pair of electrodes connected to a battery and immersed in a jar of D2O--equipment easily available in many laboratories.
This was not the first time fusion had been claimed to occur in electrolysis experiments, the earliest dating to the late 1920's in experiments that were later retracted, as discussed below. Nonetheless the implications of the Utah claims, if they were correct, and the ready availability of the required equipment, led scientists around the world to attempt to repeat the experiments within hours of the announcement. The Panel estimates that several tens of millions of dollars have been spent in the United States on cold fusion experiments. These experiments are discussed in the following sections.
To understand the initial excitement, and also the profound skepticism, that has surrounded cold fusion experiments, it is helpful to review the nature of the fusion process.
The excitement stems mainly from the claims of heat production by nuclear fusion in these experiments, and the implications of these claims on future energy supply. The attribution of heat production to fusion arises from the presence of deuterium, D, an isotope of hydrogen widely abundant in nature. The known fusion reactions in hydrogen isotopes are shown in Table 1.1.
|REACTION||Energy Release (MeV)||Reaction/sec per 1 W Output|
|D + D --> 3He + n||3.27||1.90x10l2|
|D + D --> T + p||4.03||1.54xl012|
|D + D --> 4He + gamma||23.85||2.61xl011|
|D + T --> 4He + n||17.59||3.53x1011|
|p + D --> 3He + gamma||5.49||1.13xl012|
|p + T --> 4He + gamma||19.81||3.14x1011|
All of these nuclear reactions produce millions of times more energy per reaction than do chemical reactions. A simple way to harness this energy would be an extremely important discovery.
Then why the skepticism?
First, while some researchers claim to confirm excess heat production, many report only negative results. The claims of excess heat are based upon rather difficult calorimetric measurements. Many laboratories do not find any heat production beyond that expected from normal water electrolysis, and the overall evidence in favor of excess heat production is not convincing (Section II).
The second reason for skepticism is the discrepancy between the claims of heat production and the failure to observe commensurate levels of fusion products, which should be by far the most sensitive signatures of fusion. Again referring to Table 1.1, we see that the only possible outcome of fusing two deuterium nuclei (each having 1 proton, 1 neutron) is the production of either tritium (T: 1 proton, 2 neutrons) or helium (2 protons, and either 1 neutron in He3 or 2 neutrons in He4). Moreover, the amount of heat produced and the amount of tritium or helium produced are strictly correlated by any of the currently understood fusion processes.
As is shown in Table 1.1, if 1 watt of heat production is observed (the maximum order of magnitude reported), then either tritium or helium must be produced at the same time at a rate of about 1012 atoms/second. In addition to tritium or helium, fusion in deuterium by the known reactions should also produce observable radiation in the form of a neutron, an energetic proton, or a gamma ray (see Table 1.1). These additional fusion products carry away most of the energy--millions of electron volts (MeV) of energy per particle. At such energies, the neutrons or gammas should escape and should be more readily observable than the heat. The proton should also be detectable directly or by its production of gamma rays.
The initial announcement by Pons and Fleischmann in March 1989 exhibited the discrepancy between heat and fusion products in sharp terms. Namely, the level of neutrons they claimed to observe was 109 times less than that required if their stated heat output were due to fusion.
The persistence of this major discrepancy in all subsequent experiments has led to various explanations as to how the observation of fusion products might be obscured. For example, some have suggested that in a solid the fusion energy is released directly as vibrations of the metal lattice, so that no hard radiations would be observed. In any case, this would not explain the absence of helium or tritium. Helium should be produced in about 50% of all reactions (see Table 1.1). Several electrodes from cold fusion experiments have been examined for helium, but at this writing, none has been reported. The amount of tritium directly observed in some experiments is much too small to account for observable heat. These data and their implications are discussed in Section III.
A third reason for skepticism is that cold fusion should not be possible based on established theory. Nuclear fusion reactions have been studied for many years and their potential as a vast source of energy was well understood from the outset. It was also understood that net energy production from fusion should
The importance of high temperature arises as follows. For fusion to occur, two deuterium nuclei must come very close together. Because of their positive charge, nuclei repel each other, whereby they normally are separated by about 0.1 nanometer, much too far apart for fusion to occur. However, at very high temperatures, the atoms move with enough speed to overcome the mutual repulsion of their nuclei and therefore they do undergo close collisions. They approach more closely the higher the temperature until finally, at millions of degrees centigrade, fusion reactions begin to occur at a rapid rate.
While it is possible to observe fusion reactions in the laboratory by accelerating deuterium nuclei to equivalent speeds in a particle accelerator, this cannot produce net power because the accelerated nuclei will preferentially slow down by colliding in cold matter rather than undergoing fusion. Thus, it has been thought that the way to create useful fusion energy is to recreate on earth the high temperatures found in stars. A major effort toward this goal has been underway for three decades.
The idea that palladium or titanium might catalyze fusion stems from the special ability of these metals to absorb large quantities of hydrogen (or deuterium), the hope being that deuterium atoms would be close enough together to induce fusion at ordinary temperatures. The special ability of palladium to absorb hydrogen was recognized in the nineteenth century. 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 is absorbed 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 claimed 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 D2O. Due to Paneth and Peters' retraction, Tandberg's patent application was denied eventually [PAN].
In fact, even though palladium can store large amounts of deuterium, the deuterium atoms are still much too far apart for fusion to occur in normal theories. Actually, deuterium atoms are closer together in D2 gas molecules, which do not exhibit fusion. The closest deuterium-deuterium distance between deuterons in palladium is approximately 1.7x10-1 nanometers. This distance is large compared to the bond distance in D2 gas molecules of 0.74x10-1 nanometers (Section IV).
The discrepancy between actual atomic spacings versus what is required for fusion to occur is not a small matter. The spacing requirement is mitigated by the quantum mechanical phenomenon of tunneling whereby nuclei at greater nominal separation may sometimes exist at very small separations, albeit very rarely. Even so, theoretical calculations indicate that a separation distance 1/10 normal
atomic spacings would be required to obtain a measurable fusion rate for palladium saturated with deuterium at a density roughly like that of the solid palladium. However, as ordinary experience shows, compressing solid matter 10-fold in length--a 1000-fold reduction in volume--would require enormous pressures. The effective "pressure" binding atoms in metals is orders of magnitude weaker (see Section IV).
These theoretical considerations apply both to the claims of excess heat and also to the more modest claims, first from Brigham Young University, that neutrons near background levels had been observed in D2O electrolysis experiments, and later in pressurized D2 gas experiments. These latter claims concerning neutrons correspond to only 0.1 neutron per second, 1012 times less than would be needed to explain measurable heat. On the other hand, even such a slow rate of neutron production is at least 1040 times theoretical expectations (see Section III).
Finally, we note that the Panel has not considered the well established and reproducible process of muon catalysis, itself sometimes called cold fusion. The muon, first discovered in cosmic rays in the 1940's, is an elementary particle with a mass 207 times that of an electron. In muon catalysis, the heavy, negatively-charged muon acts like a heavy electron in binding deuteron pairs at close enough spacing for fusion to occur. As presently understood, muon catalysis will not produce net energy in competition with the power required to produce the muons (too few reactions before the muon sticks to a helium nucleus made in the process).
The calorimetric measurements of heat are discussed in Section II. The claims of observations of fusion products are discussed in Section III. Materials properties relevant to palladium and other metals used in cold fusion experiments are discussed in Section IV. Conclusions and recommendations are given in Section V.