At a time when the world is searching for cheaper and cleaner forms of energy, much effort has been invested in alternative forms such as wind turbines and solar cells. However, as is well understood, harvesting these forms of energy does not provide a continuously reliable source of energy – the wind does not always blow, and the Sun does not always shine! Are there other abundant sources of clean energy found in nature that could be utilised for practical application? The answer to this question is yes – and this is where the story of nuclear fusion comes in.
Nuclear fusion is the process whereby two atomic nuclei can be fused together – overcoming the strong electrostatic repulsive forces (Coulomb barrier) between them – to produce a heavier atomic element and in the process release large amounts of energy. For instance, two deuterium (an isotope of hydrogen) nuclei can fuse together to form tritium (another isotope of hydrogen), a proton and release energy. Such reactions occur in the Sun. Very high temperatures are normally required for this type of reaction to occur – the Sun at its core has a temperature of around 15 million degrees Celsius. Much research has been performed over the last 60 years to reproduce the conditions in the Sun and trigger fusion reactions. Consider, for example, the Joint European Torus (JET) project based at the United Kingdom Atomic Energy Authority Culham Centre for Fusion Energy, Oxfordshire, UK. Although fusion reactions have been achieved, the break-even point of releasing as much fusion energy as the input energy necessary to instigate such reactions has not yet been established. Conventional fusion research is expensive – to date, around $50 billion has been spent on fusion reseach worldwide.
Since the fuel for fusion (deuterium) is commonly found in water, an abundant (and continually available) source of power is waiting to be exploited once the practical problems of fusion technology can be resolved. The yield of energy would be huge – a kilogram of deuterium would deliver around a million times more energy than that harvested from a kilogram of coal or oil. In addition, there would be no harmful radiation products.
Against this backdrop, an announcement made by University of Utah electrochemists Stanley Pons and Martin Fleischmann almost thirty years ago , on 23 March 1989, shocked the scientific world – the nuclear fusion processes that occur at the temperature of the Sun could be replicated at room temperature. Their apparatus was a relatively simple electrolytic cell comprising a heavy water electrolyte (the source of deuterons) and a palladium cathode. They found that excessive heat was produced, which could not be explained in terms of chemical reactions, and there was evidence of neutrons emitted – suggesting nuclear fusion. The finding was dubbed ‘cold fusion’.
Not surprisingly, the scientific establishment (especially physicists) were highly sceptical of the findings. Immediately, experiments were performed by laboratories around the world in order to reproduce the results. The results were mainly negative or inconclusive. Part of the problem was that many of the details of the original experimental setup and procedures were not disclosed by Pons and Fleischmann – probably as a result of a desire on the part of the University of Utah to file for patent rights. Hence, it was difficult to reproduce the conditions. For instance, it is now known that a certain threshold for the so-called loading effect (establishing the correct ratio of deuterium-palladium mix in the host metallic lattice) must be reached before any nuclear effect can be initiated. Overnight, ‘cold fusion’ became an object of derision. Universities discouraged any further reasearch into the pheneomenon, and academic journals would not publish any work on the subject. As a result, further research went largely underground, performed by a mix of enthusiasts and academics (consisting of many retired professors) in simple makeshift laboratories housed in home basements and garages around the world.
Fast forward to the present day, and the evidence from a great deal of research from the underground community is that reactions with nuclear signatures do indeed occur in electrolysis machines at room temperature. However, the effect is difficult to reproduce; some, as yet unidentified, conditions must be met in terms of the lattice properties and structure of the host cathode material (e.g. palladium). There are many scientific sources of information documenting these findings such as Cold Fusion Now.
Some conventional nuclear reactions involving D-D (deuteron-deuteron) interactions are described below:
D + D -> He4 + γ + 23.9MeV (<0.01)
D + D -> T + p + 4.03MeV (0.5)
D + D -> He3 + n + 3.27MeV (0.5)
The possible nuclear particle products are helium (He4), tritium (T), protons (p), neutrons (n) and helium-3 (He3). Energy releases are defined in mega electron-volts (MeV), and the probability of the reaction shown in parentheses – for instance, the probability of the second reaction is 50%.
These nuclear products, together with excess energy release, have been detected in ‘cold fusion’ experiments suggesting that nuclear reactions are indeed occurring. However, the amounts of nuclear particles emitted are not in line with that expected with ‘hot’ fusion. For instance, the major observation appears to be the least probable one for conventional fusion – i.e. the D-D reaction that creates helium4 and a gamma ray of 23.8MeV. Instead of a gamma ray emission, the energy associated with the ‘hot’ fusion gamma ray appears to be released as extra phonon energy within the lattice. Various mechanisms have been proposed to explain how the fusion process might occur at room temperature, some invoking novel lattice conditions that allow for the drastic reduction of the Coulomb barrier in order that fusion occur. Other theories suggest the creation of neutrons from electron-proton interactions which are subsequently absorbed into nuclei (without the need to overcome Coulombic repulsion) to produce the chain of observed nuclear products. There is a growing consensus that the existence of special environments within the lattice act as triggers – for instance, closed cracks, voids or other deformations. A good summary of evidence and theoretical models may be found here.
As alluded to earlier, it is difficult to replicate results. For instance, with palladium as the cathode material, lattice deuterium build up can be susceptible to the formation of cracks on initial exposure to deuterium. These then act as pathways for it to escape if they end at the lattice surface, and the necessary build up of deuterons within the host lattice does not occur. This would hint that perhaps the crystalline structure, defects and composition of impurities within the lattice play a crucial role.
However, it is clear that the last thirty years has yielded much valuable work on ‘cold fusion’ – or Low Energy Nuclear Reactions (LENR), as it is now commonly referred to. In fact, due to the consistency of positive results many governmental institutions, such as NASA, have been quietly working on their own research programs in recent times. In the private sector companies such as Brilluoin Energy in California are now taking the technology seriously, with a view to taking a practical solution to market.
Mastering ‘cold fusion’ has not been easy – the conditions under which it occurs are subtle. One lesson to be learned is that the disciplines of condensed matter and nuclear physics need to work more closely together – perhaps establishing a new sub discipline entitled Solid State Nuclear Reactions. More progress could have been made if the science community had not been so dismissive of the subject in the early days. In his book The Science Delusion, biologist Rupert Sheldrake describes how contemporary science easily dismisses ideas that do not fit in with current paradigms – thus stifling scientific and technological progress. In view of recent developments, it would make sense for the scientific community to promote LENR by way of more money for research. Then, ‘hot’ and ‘cold’ fusion research could be carried out on a more equitable basis. If the latter proves to become more viable and cheaper, we could then wind down the effort on the former. We could then embark on a road that encourages the technological development of a relatively inexpensive, safe and user-friendly source of energy.