Neutron capture

Neutronenanlagerung (name in astrophysics ) or neutron (name in nuclear physics and nuclear engineering ) is a nuclear reaction in which a neutron is absorbed by an atomic nucleus without causing particles are released to ground; the binding energy obtained is dispensed rather than gamma radiation. After his formula notation - see below for examples - this type of reaction is also called n -gamma reaction.

Since the neutron is in contrast to the proton carries no electric charge, and is therefore not rejected by the atomic nucleus, it can easily approach him with less kinetic energy. The Neutronenanlagerung runs in stars from the s-or r-process. She plays in the cosmic nucleosynthesis an important role, because it explains the origin of the elements with mass numbers greater than 56, so the atoms that are heavier than iron atoms. This can not be formed by thermonuclear reactions, that is, by nuclear fusion in stars.

The vast majority are in a normal environment released on Earth neutrons after they become thermally trapped cores in this way. Technically, the neutron capture in suitable materials important for the control of nuclear reactors, and the shielding against neutron radiation, see neutron absorber.

The picture shows a nuclear chart with color coding of the cross section for neutron capture ( neutron capture ). Highlighted by double lines are the magic numbers of protons and neutrons; you can see that this cross section, however, is usually small, far from magic numbers large in such magic nuclei.

Neutron at small neutron flux

Is not too high neutron flux, such as neutron irradiation in a nuclear reactor, a neutron is captured by the atomic nucleus in each case. The mass number ( number of nucleons in the nucleus ) results in an increased first example is the formation upon irradiation of natural gold, 197Au, the gold isotope 198Au in a highly excited state by emission of a γ - quantum decays very rapidly to the ground state of 198Au. In formula notation:

Or in short:

The gold isotope 198Au is a β - emitter, so its nucleus decays by emitting an electron and an electron anti-neutrinos to the mercury isotope 198Hg.

The above-mentioned s- process in the interior of stars running in essentially the same.

Neutron with a large neutron flux

When r-process inside the star, the neutron flux density is so high that the atomic nucleus between the neutron captures "no time" for the beta decay has, ie, the average time interval between neutron captures is short compared to the half-life of beta decay. The mass number is thereby greatly without the atomic number increases. Only then decompose the resulting highly unstable nuclides by each of several successive β - decays to stable or slightly unstable, so long-lived nuclides with correspondingly higher atomic numbers.