Nuclear transmutation

History

The term transmutation dates back to the search for the alchemy, it was believed that such transformations could be accomplished in table-top experiments.

It was first consciously applied to modern physics by 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."

Some researchers have said they have found evidence of transmutation of elements in biological processes (see Kervran) but these theories are regarded as pseudoscience by virtually all modern scientists.

Naturally occurring gold is actually created in supernovae, which ironically transmute some gold into lead — a much easier process. Gold is valuable precisely because of its rarity. The alchemical belief in transmutation was based on a thoroughly wrong understanding of the underlying processes. atoms to explain chemical processes. The disintegration of atoms is a distinct process involving much greater energies.

In stars

Main article: Nucleosynthesis

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, 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 of carbon on this basis.

Gold

Nuclear experiments have successfully transmuted lead into gold, but the expense far exceeds any gain[1]. It would be easier to convert gold into lead via beta decay by leaving gold in a nuclear reactor for a long period of time.

¹⁹⁷Pb (halflife 1.4x10¹⁷ years)

Transmutation of nuclear wastes

Overview

Transmutation of fission products.

Reactor types

For instance, plutonium can be reprocessed into neutron sources have also been proposed as well suited [3] [4].

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 cesium-137 when a given activity is ingested.

Many of the actinides are very radiotoxic because they have long biological half-lives and are 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.

Long-lived fission products

Some radioactive fission products can be converted into shorter-lived radioisotopes by transmutation. Transmutation of all fission products with halflife greater than one year is studied in [5], with varying results.

Cs-137, with halflives of about 30 years, are the largest radiation emitters in used nuclear fuel on a scale of decades to a few hundreds of years, and are not easily transmuted because they have low neutron absorption cross sections. Instead, they should simply be stored until they decay. Given that this length of storage is necessary, the fission products with shorter halflives can also be stored until they decay.

The next longer-lived fission product is samarium. Given the smaller quantities and its low-energy radioactivity, Sm-151 is less dangerous than Sr-90 and Cs-137 and can also be left to decay.

Finally, there are only 7 long-lived fission products. They have much longer halflives in the range 211,000 years to 16 million years. Two of them, reprocessed uranium remaining as waste. [6]

Of the remaining 5 long-lived fission products, Cs-135, are produced in larger quantities, but also not highly mobile in the environment. They are also mixed with larger quantities of other isotopes of the same element.