s-process

physics

Also known as: slow neutron capture, slow neutron process, slow process(Show More)

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July 13, 2026

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The s-process, or slow neutron capture, is a key mechanism in astrophysics responsible for creating heavier chemical elements. This process occurs when atomic nuclei capture neutrons at a relatively slow rate. If a nucleus captures a neutron and becomes unstable, it undergoes beta decay (converting a neutron into a proton) before it can capture another neutron. This allows for the gradual buildup of heavier elements, particularly those with more protons.

The s-process is believed to happen during the stable phases of stellar evolution. In contrast, the r-process (rapid neutron capture) occurs in more explosive stellar events. Together, these neutron capture processes help explain the observed abundances of elements heavier than iron in the universe.1

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chemical element
Neutron capture
…capture; and the s -process, slow neutron capture. If neutrons are added to a stable nucleus, it is not long before the product nucleus becomes unstable and the neutron is converted into a proton. Outside a nucleus, a neutron decays into a proton and an electron by a process called…
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…capture; and the s -process, slow neutron capture. If neutrons are added to a stable nucleus, it is not long before the product nucleus becomes unstable and the neutron is converted into a proton. Outside a nucleus, a neutron decays into a proton and an electron by a process called…
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star
Evolution of high-mass stars
…first such process, called the slow, or s-, process, the flux of neutrons is low. A nucleus captures a neutron and leisurely emits a beta particle; its nuclear charge then increases by one.
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…first such process, called the slow, or s-, process, the flux of neutrons is low. A nucleus captures a neutron and leisurely emits a beta particle; its nuclear charge then increases by one.
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transuranium element
Synthesis of transuranium elements
…to the slow-neutron capture, or s-process, described above). Underground detonations of nuclear explosive devices during the late 1960s resulted in the production of significant quantities of einsteinium and fermium isotopes, which were separated from rock debris by mining techniques and chemical processing. Again, the heaviest isotope found was that of…
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…to the slow-neutron capture, or s-process, described above). Underground detonations of nuclear explosive devices during the late 1960s resulted in the production of significant quantities of einsteinium and fermium isotopes, which were separated from rock debris by mining techniques and chemical processing. Again, the heaviest isotope found was that of…
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