Induced radioactivity

Activation as is known in physics, the conversion into a stable unstable, radioactive materials ( radionuclides ) by irradiation. Activation is always a sequence of nuclear reactions. In principle, any type of nuclear reaction can leave radioactive products.

Neutron radiation

Thermal neutrons

Practically important is mainly neutron activation. This includes the capture of a thermal neutron is generally understood, because most nuclides have this large cross sections. The neutron activation in a research reactor or by means of a neutron source is an important, highly sensitive detection method for trace elements. It is also used for the production of radionuclides, for example for medical purposes.

In many cases, for example in structural materials of nuclear reactors, by neutron activation is an undesirable effect. It is also possible that large particle by activating radioactive substances generated in the bottom, which can then be transported to the ground under certain circumstances.

Fast neutrons

The activation of a fast neutron nuclear reactions is based on the type (n, p) or (n, alpha), at a very high neutron energy (from about 10 MeV) and (n, 2n). It is sometimes used as a method of analysis for elements in which the thermal neutron capture results in no measurable good radionuclide.

As an undesirable effect on the material of future fusion reactors, they will cause the majority of the radioactivity of these plants.

Photon radiation

Gamma radiation and bremsstrahlung can have an activating effect by nuclear photoeffect. This occurs depending on the element from a gamma energy of about 2 MeV; In this case, a neutron, or proton is ejected from the core, which then in turn triggers other nuclear reactions. In aqueous media this is especially true for the deuterium ( heavy water ), which is of course always included; Moreover, the available water is used as moderator and slows down the particles from the ' thermal ' energy at which then enter the subsequent reactions. However, it is used in industrial irradiation facilities as isotope 60Co radiation source that emits the decay two gamma quanta with a mean energy of 1.25 MeV. This energy is not sufficient to enable existing elements in typically food; However, there are a few isotopes which hardly occur in foods (eg indium), low threshold energy but also a very small cross section (activation probability), so this theoretical activation in practice is hardly measurable.

When high-energy particle (eg electrons) triggers in heavy material bremsstrahlung, this can also cause the nuclear photo effect. Therefore, for example in the food irradiation with electron beam the maximum energy required by law (see Codex Alimentarius).

Uploaded Teilchenstrahlungen

Charged particle beams such as alpha and beta radiation (from radioactive decay ) as well as accelerated electrons release their energy in matter piecemeal in successive shocks to the electrons of the atomic shell from and reach only a fraction of cases ever an atomic nucleus. However, there are at sufficiently high particle an indirect effect: the particles may produce bremsstrahlung under braking, which can cause might photoeffect by nuclear activation.

The activation effect of particle radiation is generally insignificant compared to the direct harmful effects that come into existence by the power transmitted to the material or tissue impact energy. The absorbed energy is converted to a small part directly into heat, but for the most part consumed by ionization; hence the name ' ionizing radiation '. With the ions to be particularly chemically reactive components ( atoms or molecules ) is then carried out chemical reactions, which may cause adverse effects or desired.

Nuclear fission

Nuclear fission also lead to radioactive products, but is usually not referred to as activation.