Dr. P. K. Iyengar's Website

PREFACE TO COLD FUSION

Energy production in the Universe is mostly based on nuclear reactions especially fusion reactions of light element nuclei. Energy production in the Sun on the basis of fusion of hydrogen, its isotopes and elements up to carbon have been well theorized by now. It is natural to expect that there will be a large variety of nuclear reactions which will lead to the product of nuclear energy. In fact there is a whole gamut of fusion reactions in astrophysics which suggest various combinations of nuclear interactions and modes of decay for energy production.

The collapse of binary stars and the transformation of neutron stars into black holes are the ultimate phases of stellar evolution and production of fusion energy therefrom. Even before the discovery of the neutron, scientists had predicted and even tried to prove that nuclear energy could be generated through fusion of hydrogen nuclei (protons). It was however only after detailed accelerator based research in nuclear physics, that the cross sections and Q values for these reactions became available. This enabled many conjectures to be made. Some of the candidate reactions considered for the generation of fusion energy are: (p+p), (p+d), (d+d), (d+t) etc. The familiarity of scientists with accelerator based nuclear reactions, however, led them to believe that fusion reactions can take place only on the basis of overcoming the potential barrier caused by the electrostatic interaction. This demands that the particles have considerable relative velocity and from the analogy of what is happening in the Sun, thermonuclear fusion was considered as the most appropriate technique for releasing fusion energy on a large scale. We are all aware of the many experimental attempts that have been made over the last, four decades to obtain conditions appropriate for thermonuclear fusion. The principle of confinement of these hot plasmas by means of complex magnetic fields in special configurations was invented in the early fifties. Of these the Tokamak has been a major success and has almost reached the stage of breakeven in energy production. However, the large size and the expensive equipment needed to attain even this breakeven stage have raised doubts about its commercial viability. The technique of generating temperatures of 100 million degrees using the principle of inertial confinement was first demonstrated in a thermonuclear bomb. The same principle has been borrowed and adapted in making fusion reactions possible in small pellets using lasers, electron beams and heavy ion beams. However even this approach of releasing nuclear energy through a series of fusion micro-explosions has not lived up to its early expectations as the power and energy of the driver beams for obtaining the requisite pellet energy gain became uncomfortably high. Small and more elegant methods are therefore being attempted. Techniques such as Z-pinches, combined magnetic and inertial confinement schemes etc are under experimentation. As an interim measure it has meanwhile been suggested that fusion devices may be employed as a source of neutrons for producing fissile fuel for use in fission reactors. Thus in quest of establishing the best method of producing fusion energy there has been considerable innovations and cross fertilization of new ideas during the last couple of decades. However new ideas are always welcome and must be tried out.

Cold fusion which we are discussing here is one such innovation which on the face of it looks so simple that it seems too good to be true. It has generated considerable speculation on the processes which cause fusion in the solid state at room temperatures. The basic problem is essentially to bring together ions of hydrogen isotopes at distances of a few Fermis so that fusion takes place. It is worth recalling here previous attempts to bring together hydrogen nuclei todistances at which the spontaneous fusioning rate would increase considerably. The most effective method has been the replacement of the orbital electron of a molecular hydrogen ion by a μmeson or muon as it is called. Because of its heavier mass, the muon is able to squeeze the nuclei into a more compact molecule and cause a fusion reaction. Besides, the muon is found to have an additional advantage, because of its longer life time (2 μs), freed after a fusion reaction, it is able to catalyze more fusions. Almost 200 catalyzed fusions per muon have been experimentally observed in (d-t) mixtures to date. It is some of the same scientists who were concerned with the physics of muon catalyzed fusion who have now reported cold fusion in aattice of palladium.

From the point of view of understanding the physics behind cold fusion, one needs to discuss the lattice structure and its rearrangement when hydrogen is absorbed in palladium, titanium or other alloys used for the storage of hydrogen. It is the fact that enormous (quantities of hydrogen can be stored in these materials at densities comparable to or higher than that of liquid hydrogen that first gave a clue that perhaps the internucleax distances can be brought down in such lattices. Many attempts have been made by theorists to evaluate the fusioning rate in such lattices. Some of these are based on an extension of the well known theory for muon catalyzed fusion, wherein both the internuclear distances and the height of the potential barrier are varied. Both will have the effect of increasing the fusion rate from 10-64 per second/per ion pair in heavy water to something of the order of 10-23 per second per ion pair which is required in order to explain the experimentally observed neutron production rate in cold fusion experiments. Whether it ispossible to have such drastic changes in the fusion probability, which is essentially dictated by quantum mechanics considerations, is a matter of intense debate and discussion.

I would like to invite your attention to a novel application of the principles of quantum mechanics to such a problem. Several years ago Rand McNally had speculated on the feasibility of the occurrence of nuclear reactions at room temperature and was perhaps the first person to coin the phrase "cold fusion" as early as in 1983. To quote his own words "The problem of neutron transfer in solid media is no longer an elementary binary collision process involving Coulomb barriers and brief collision times but rather one in which the nuclei are continuously in each other's proximity. Since 135Xe has a slow neutron capture radius approaching that of the inter atomic distance the nuclear barrier would perhaps be grossly reduced. Thus it is remotely possible that some combination of natural processes may permit barrier penetration to occur much more readily and a nuclear reaction to ensue". He also proposed the term "de Broglie interaction length" to emphasize the fact that the de Broglie wave length of particles with small kinetic energy is very long. The importance of the de Broglie interaction length can be seen in the extraordinarily high cross section for absorption of slow neutrons by certain nuclei. It is therefore of interest to know what the de Broglie interaction length of a deuteron with very small energy is in a palladium lattice. Further,what happens to the charge distribution of such a deuteron extended in space and the effects of its polarization are too speculative. If the charge distribution has dimensions of the order of a de Broglie interaction length, then the potential barrier due to Coulomb interaction may perhaps become much smaller. If so then fusion should be much more probable at very low temperatures.

From the experimental point of view, the proof of cold fusion must come from a demonstration of the production of neutrons, He3, He4, tritium, gamma rays and other end products of nuclear transmutation reactions. Unfortunately experiments performed so far have used very small electrodes and small cells, and there have not been sufficiently large sized experiments which can give unqualified proof of the number of neutrons or radioactivity produced from this process. Our attempts in different groups at Trombay have however all shown reliable data on neutron and tritium production. These are described in the various papers included in this compilation. It is interesting that fusion reactions also take place when deuterium ions are introduced into a metallic lattice by simply absorbing deuterium gas into titanium or palladium. The group at Frascati in Italy first succeeded in producing neutrons by this method. It is not our expectation that cold fusion will become an energy source tomorrow or the day after. After all even in 1939 when neutron induced fission in uranium was discovered, it took several years to find out how to set up a fission chain reaction and release fission energy in a large scale. Without detailed measurements of the number of neutrons produced in fission by the Columbia University  group and the invention by Fermi of the heterogeneous neutron multiplying system, the nuclear reactor would not have become a reality. Similarly one has to explore and understand the basic mechanisms of fusion in a lattice and determine how this could be used either to produce energy directly or to produce neutrons and tritium in a sustained manner. It is too early to predict the time frame in which this will happen but for those of us familiar with the historical evolution of nuclear technology, one can foresee how it can change our perspective drastically. It is therefore necessary for us to involve ourselves deeply into understanding the mysteries of this new phenomenon. The source of such energy, namely deuterium, is ordinary water which is available in plenty and the technology to separate and concentrate deuterium from water is by now well established in our country. I would therefore end this Preface by quoting from what Dr. Homi Bhabha said at the first International Conference on Peaceful Uses of Atomic Energy in 1955. He predicted that "in a couple of decades from now fusion energy will become possible and that will ensure energy production for man's needs as long as there is sea water on this earth". It is therefore a historical occasion for us to renew our efforts in research and development in an area so vital for human prosperity. I hope this report will stimulate the interest of scientists and engineers from various disciplines in this centre to channelise their efforts in such a way that we lead in this emerging technology.

This Preface is an edited version of the Inaugural talk delivered by Dr. P.K. Iyengar, Director, BARC at the one day meeting on 'Cold Fusion' held at Trombay on 18th May 1989.