Test-tube fusion experiment repeated

时间:2019-03-04 01:06:01166网络整理admin

By NINA HALL and JONATHAN BEARD AN AMERICAN nuclear physicist confirmed last week the recent claims of two chemists that by electrolysing heavy water in a simple cell at room temperature they achieved nuclear fusion. However, Steven Jones of Brigham Young University in Utah warned that his group’s experiments produced only extremely small amounts of energy – in fact, 13 orders of magnitude lower than that claimed by the chemists. Stanley Pons from the University of Utah and Martin Fleischmann from the University of Southampton astounded journalists and annoyed scientists when, two weeks ago, they announced at a press conference that they had achieved ‘fusion in a test tube’ at room temperature. Physicists have spent hundreds of millions of pounds trying to produce a safe form of nuclear energy by mimicking the process that makes the Sun shine. This involves fusing isotopes of hydrogen, deuterium (one proton, and one neutron) and of tritium (one proton and two neutrons) at 100 million Degree C to give helium-4 and an energy-carrying neutron. The chemists electrolysed heavy water using a platinum anode and a palladium cathode. The electrical current split the heavy water into oxygen anions and deuterium cations (deuterons), which flooded into pores in the palladium cathode. Metals such as palladium are well known for absorbing hydrogen. Sometimes they store it. In the case of deuterium, however, it seems that the deuterons were forced together so closely that they fused. Scientists have treated the chemists’ results with caution. Pons and Fleischmann claim that the experiment produced several times more energy, in the form of heat, than it consumed in the form of electricity. Pons and Fleischmann had also failed to detect any neutrons directly. Jones had tried to retain a dignified silence after Pons and Fleischmann gave their results to the press before they had been published in a refereed paper. But he found himself surrounded by hundreds of academics, students and journalists when he gave a colloquium at Columbia University in New York last Friday. When pressed to say whether what he calls ‘piezonuclear fusion’ could become a practical source of energy, Jones estimated that it would take ’20 years to never. If you own an oil well, don’t go out and sell it.’ Jones, who has already established his reputation in another kind of cold fusion involving exotic particles called muons (see Box opposite), has been working on piezonuclear fusion since 1986, with support from the US Department of Energy. He has spent the past three years repeating his experiments and designing a sufficiently sensitive detector to measure the handful of neutrons that his experiment produces. Jones’s apparatus consists of a glass beaker, with an anode of gold foil and a cathode made of various metals – he tried a dozen or so. The experiment typically lasts about eight hours. Unlike Pons and Fleischmann, Jones has managed to measure the energies of neutrons emitted in his cell. According to Jones, the fusion process produces only 200 neutrons an hour, so he needed an extremely sensitive detector. To shield the neutron counter from background radiation, Jones surrounded the cell with stacks of cardboard boxes labelled ‘$20’ and containing 2500 copper pennies. The neutron spectrum showed a bulge at 2.5 megaelectronvolts – the signature of deuterium-deuterium fusion. Jones stressed that his apparatus did not produce any gamma-rays and that the heat produced was much too small to measure. According to Jones, one critical piece missing from the current breakthroughs in work on cold fusion is a ‘theoretical framework’. He says: ‘We have a Cinderella but no shoe. In this way, it is similar to the work on high-temperature superconductivity.’ Last Friday, as Jones spoke in New York, Fleischmann presented his results to a packed audience of physicists on the other side of the Atlantic, at the European Laboratory for Particle Physics, CERN, in Geneva. But he spoke only after Carlo Rubbia, the director of CERN, ordered out all the journalists. Fleischmann reported on his calculations, in which the measured rise in temperature showed that the palladium electrode yielded 20 watts per cubic centimetre at the highest electrical currents applied. This, Fleischmann said, is a higher yield than any conceivable chemical process can produce. So it must involve a nuclear reaction. The fusion of two deuterons can go two ways. They can either form a tritium nucleus and a proton, or a helium nucleus and a neutron. The easiest product to detect is tritium because it is radioactive. In the second process, the neutrons emitted have a characteristic energy, which is what Jones measured. Fleischmann and Pons have tried to look for tritium and neutrons. They have some evidence from rays emitted from the water bath surrounding the electrolytic cell. Neutrons can be captured by protons in water to form deuterium nuclei – a process that emits gamma-rays with an energy of 2.2 megaelectronvolts. Fleischmann and Pons apparently detected gamma-rays of this energy, but there is no indication that they came from the cell itself. In addition, the chemists measured the radioactivity of tritium. But the levels appear to be far lower than what you would expect from fusion between deuterons, say physicists at CERN. Fleischmann is anxious for other scientists to repeat his experiments. He is particularly keen for researchers to check the heat measurements and calculations. Another useful exercise, he says, would be to carry out the experiment with ordinary water, which behaves chemically like the heavy version. Fleischmann said that he and Pons did not carry out this reaction because it would have ruined their electrodes, which are very expensive to make. Such experiments could confirm that a nuclear reaction is indeed taking place. Whatever the true nature of the reaction, something very strange is going on. The conditions inside the palladium electrode are certainly unusual. For example, although there are plenty of electrons inside the metallic crystal lattice of the palladium, the deuterons do not form atoms and then molecules of deuterium. This deuterium would eventually escape from the electrode as a gas which usually happens in electrolysis. Instead, the deuterons continue to fill the metal lattice, packing tightly enough to produce a compression equivalent to a pressure of 10**27 atmospheres. Jones has already published a paper which derives a relationship between the fusion rate and the increase in the density of deuterium molecules. One kilogram of deuterium at a pressure sufficient to achieve a density of 66 grams per cubic centimetre, which corresponds to an average separation between deuterons that is half that in a normal molecule of deuterium, will produce one fusion per minute. The results from Jones, Fleischmann and Pons will activate physicists and chemists on both the experimental and theoretical fronts (see ‘Japanese mimic cold fusion’). It is not yet clear why the two groups of researchers have obtained different results. Only detailed and accurate measurements will show what is really going on. It is the theoretical implications of the bizarre reactions that are intriguing physicists and chemists alike. But at least one theoretical physicist, Johann Rafelski, a theoretician at the University of Arizona in Tucson, says that he can explain the rates of fusion observed by Jones . Even if piezonuclear fusion never becomes a practical proposition,