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The Synthesis of the Elements pp 527–598Cite as

A Process in Search of an Environment: The \(r\)-Process

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Part of the book series: Astrophysics and Space Science Library ((ASSL,volume 387))

Abstract

While the \(s\)-process can be described as a low neutron flux occurring over a long period of time, the \(r\)-process can be described as the opposite, namely, irradiation by a high neutron flux for a very short time. Hence, while the \(s\)-process could be described as a quiet, slow, hydrostatic evolution, the \(r\)-process is usually associated with the most violent phases in stellar life—the explosion that puts an end to the ‘normal’ life of the star. It seems that no in-between process exists, only the two extremes. Notwithstanding, problems with the explosion scenario have led astrophysicists to ponder on less violent circumstances where a milder variant of the \(r\)-process might take place. But whatever the situation, we are now looking for an extreme source of neutrons in an expanding environment. The adjective ‘extreme’ refers to the nuclear properties while the requirement of expansion refers to the astrophysical site, so that the synthesized isotopes can be ejected into space. Alpher, Bethe, and Gamow considered the Big Bang to be just such an explosive situation, but in this specific case we are supposedly immersed in the products.

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Notes

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    The actinide group includes the heaviest elements that terminate the periodic table. The group contains 14 chemical elements with atomic numbers from 90 to 103, thorium to lawrencium. Only thorium and uranium appear in nature in significant amounts. The other actinides are either man-made elements or decay products with very short decay times relative to the age of the Earth. All actinides are radioactive, with uranium and thorium having half-lives commensurate with the age of the Earth. More massive elements do not exist in nature, and when formed artificially, decay very quickly.

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    Giora Shaviv

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Shaviv, G. (2012). A Process in Search of an Environment: The \(r\)-Process. In: The Synthesis of the Elements. Astrophysics and Space Science Library, vol 387. Springer, Berlin, Heidelberg. https://doi.org/10.1007/978-3-642-28385-7_13

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