Nuclear transmutation

See also transmutation of species and transubstantiation.

Transmutation is the conversion of one object into another. Transmutation of chemical elements occurs through nuclear reactions. This is called nuclear transmutation. Natural transmutation is when radioactive elements spontaneously decay over a long period of time and transform into other more stable elements. Artificial transmutation occurs in machinery that has enough energy to cause changes in nuclear structure of the elements.The machines that can cause artificial transmutation include the particle accelerator and tokamak reactor.

Photoneutron Process

Transmutation of the elements can occur naturally or artificially by the photoneutron process. A Gamma ray (high-energy photon) with an energy greater than the neutron binding force can eject a neutron from a stable nucleus to cause transmutation to another element. A 6.8 Mev Gamma ray can eject a neutron from the nucleus of Mercury isotope 198. The resulting Mercury isotope 197 is radio-active (half-life 2.7 days), decaying into Gold isotope 197. Mercury isotope 198 is 10% of naturally obtained Mercury. The Spallation Neutron Source nearly completed at Oak Ridge National Laboratory will cause transmutation of Mercury to Gold and other precious metals below Gold in atomic mass.[[1]]

Origin

The term dates back to the search for the philosopher's stone. It was applied consciously to modern physics first by Frederick Soddy when he, along with Ernest Rutherford, discovered that radioactive thorium was converting itself into radium in 1901. At the moment of realization, Soddy later recalled, he shouted out: "Rutherford, this is transmutation!" Rutherford snapped back, "For Christ's sake, Soddy, don't call it transmutation. They'll have our heads off as alchemists."

Overview

Transmutation of transuranium elements (actinides) such as the isotopes of plutonium, neptunium, americium, and curium has the potential to help solve the problems posed by the management of radioactive waste, by reducing the proportion of long-lived isotopes it contains. When irradiated with neutrons in a nuclear reactor, these isotopes can be made to undergo nuclear fission, destroying the original actinide isotope and producing a spectrum of radioactive and nonradioactive fission products.

Reactor types

For instance, plutonium can be reprocessed into MOX fuels and transmuted in standard reactors. The heavier elements could be transmuted in fast reactors, but probably more effectively in a subcritical reactor[2] which is sometimes known as an energy amplifier and which was devised by Carlo Rubbia.

Reasoning behind transmutation

Isotopes of plutonium and other actinides tend to be long-lived with half-lives of many thousands of years, whereas radioactive fission products tend to be shorter-lived (most with half-lives of 30 years or less). From a waste management viewpoint, transmutation of actinides eliminates a very long-term radioactive hazard and replaces it with a much shorter-term one.

It is important to understand that the threat posed by a radioisotope is influenced by many factors including the chemical and biological properties of the element. For instance cesium has a relatively short biological halflife (1 to 4 months) while strontium and radium has a very long biological half-life. As a result strontium-90 and radium are much more able to cause harm then cesium-137 when a given activity is ingested.

Many of the actinides are very radiotoxic because they have long biological half-lives and are alpha emitters. In transmutation the intention is to convert the actinides into fission products. The fission products are very radioactive, but the majority of the activity will decay away within a short time. The most worrying shortlived fission products are isotopes such as iodine-131, but it is hoped that by good design of the nuclear fuel and transmutation plant that this fission product can be isolated from man and his environment and allowed to decay. In the medium term the most important fission products are strontium-90 and cesium-137; both have a half life of about 30 years. The cesium-137 is responsible for the majority of the external gamma dose experienced by workers in nuclear reprocessing plants and at this time (2005) to workers at the Chernobyl site. When these medium lived isotopes have decayed the remaining isotopes will pose a much smaller threat.

Accelerated radioactive decay

• Accelerated radioactive decay using intense magnetic fields

Various scientists have proposed bombarding spent fuel with electromagnetic rays to accelerate the decay process. This is different than transmutation, although some concepts use spallation (as does transmutation). Gamma rays have been suggested very effective, but gamma rays are very difficult to produce and may need to be precisely tuned to the target actinide or fission product.

In 2006, Professor Howard R Reiss, former departmental head for nuclear physics in the United States Navy, has proposed using high-intensity radio waves (in the AM band). He believes his method can increase the decay rate 10 times, and he intends to organize experiments to prove this. [3]

In stars

Gold is actually created by supernovae, which however transmute a lot of it into lead - a much easier process. Gold is valuable, precisely because it is a rather rare product. The alchemical belief in transmutation was based on a thoroughly wrong understanding of the underlying processes. Lavoisier first identified the chemical elements and Dalton restored the Greek notion of atoms to explain chemical processes. The disintegration of atoms is a distinct process involving much greater energies.

Genuine scientific transmutation is nicely described in Ken Croswell's book The Alchemy of the Heavens. He summarised the process as:

Burbidge, Burbidge, Fowler, Hoyle

Took the stars and made them toil:

Carbon, copper, gold, and lead

Formed in stars, is what they said

This summarises Synthesis of the Elements in Stars (Reviews of Modern Physics, vol. 29, Issue 4, pp. 547–650), by William Alfred Fowler. E. Margaret Burbidge, Geoffrey Burbidge, and Fred Hoyle, which was published in 1957. The paper explained how the abundances of essentially all but the lightest chemical elements could be explained by the process of nucleosynthesis in stars. Hoyle correctly predicted a previously unknown energy level for carbon on this basis.

Cold fusion

Cold fusion is a process in which various researchers claim that nuclear reactions can occur when hydrogen isotopes are forced into lattice positions in some metals. Most experiments have used the (electrolytic cell) to force deuterium into palladium. Cold fusion received an extremely bad press in 1989 because the excess heat which was the only evidence at the time was difficult to reproduce. Also many physicists refused to accept heat alone as proof of a reaction and argued that the reaction products had to be the same as in hot fusion. However experiments continued to the present and heat, tritium, helium, and transmuted elements have been found.

Nuclear transmutations have been reported in cold fusion experiments since 1992. . Tadahiko Mizuno, George Miley, and Yasuhiro Iwamura and their associates are prominent transmutation experimenters. However many other experimenters have also seen transmutation evidence in their experiments. In Mizuno’s experiments trace amounts of many kinds of elements appeared on palladium cathodes after electrolysis that produced excess heat. In a particular experiment the elements found were C, O, Cl, Si, Ca, Ti, Cr, Mn, Fe, Co, Ni, Cu, Zn, Mo, Pd, Sn, Pt, Hg, Pb, As, Ga, Sb, Te, I, Hf, Re, Ir, Br, Xe. Some of these elements existed as impurities in the cathode (palladium) , anode (platinum), or electrolyte (lithium hydroxide). However some like zinc and xenon did not. Large differences from natural isotropic ratios were seen for Cr, Cu, Zn, Xe, Pd, and Pt. In general it requires gaseous diffusion, thermal diffusion, electromagnetic separation or other exotic processes of isotope separation or a nuclear reaction to change an element from its natural isotope ratio. Thus an unnatural isotope ratio makes contamination an implausible explanation.

Miley wrote a review of many experiments where transmutation occurred. He reported that transmuted element masses were higher than the maximum possible impurity masses in some experiments. Calcium, copper, zinc, and iron were the most common reported elements. Rare earth elements were found which is important because rare earth elements are unlikely to be impurities.

So far the clearest evidence for transmutation has come from Iwamura and associates. An important experiment was published in 2002 in the Japanese Journal of Applied Physics which is one of the top physics journals in Japan. In this experiment a thin film of palladium was deposited on top of alternating thin layers of palladium and calcium oxide on top of bulk palladium to form a gas membrane. In one case a thin layer of cesium was deposited on top of the the membrane. In another case a thin layer of strontium was deposited on the top of the membrane. Deuterium gas was placed on the cesium or strontium side of the membrane and a vacuum chamber was on the bulk palladium side. The gas was allowed to permeate for from 2 days to a week when the deuterium gas chamber was evacuated and X-ray photoelectron spectroscopy tests were conducted to measure transmutations. Then the deuterium gas was replaced to continue the test. Thus the rate of transmutation was measured against time. It was found that the cesium was converted to praseodymium and the strontium was converted to molybdenum. These transmutations represent an addition of 4 protons and 4 neutrons to the original element. This experiment was conducted in a Mitsubishi Heavy Industries clean room. The Iwamura experiment was replicated by experimenters from Osaka University.In later similar experiments by Iwamura Barium 138 was transmuted to Samarium 150 and Barium 137 was transmuted into Samarium 149. The Barium 138 experiment used a natural isotope ratio of Barium. The Barium 137 experiment used a Barium 137 enriched isotope ratio. The transmutations represent an addition of 6 protons and 6 neutrons. It seems like an enormous Coulomb barrier was over come in these experiments. However attempts to find a theory are being made by Takahashi and others

Alchemy

In alchemy, it is believed that such transformations can be accomplished in table-top experiments, but this is not accepted science. Some researchers say they have found evidence of transmutation of elements in biological processes (see Kervran).

Modern nuclear experiments have successfully transmuted lead into gold. The great expense of the procedure, however, far exceeds any financial gain[4]. In many ways it would be easier to convert gold into lead by nuclear means. By leaving gold in a high flux nuclear reactor for a long time then some lead could be generated.

^{197Au + n --> 198Au (half life 2.7 days) --> 198Hg + n --> 199Hg + n --> 200Hg --> + n --> 201Hg --> + n --> 202Hg + n --> + n --> 203Hg (half life 47 days) --> 203Tl + n --> + n --> 204Tl (half life 3.8 years) --> 204Pb (half life 1.4 x 1017 years)}