Neutron radiation
Neutron radiation is ionizing radiation, which consists of free neutrons ( kinetic energy with may different ).
Since neutrons are electrically neutral, the charges of the nuclei and the electrons have no influence into matter on their movement. Neutron radiation penetrates matter thus relatively easy. The ionizing effect arises indirectly, usually by engaging in atomic nuclei and their constituents (eg protons), which in turn act ionizing. Such collisions the neutrons of lower energy (slower) are.
The main effect of slow, especially thermal neutrons based on their ability to attach to atomic nuclei ( neutron capture ). Here, an isotope of that atom with increased by one mass number forms. Many of these isotopes are radioactive, so that also may occur long after neutron irradiation radiation. The free state of the neutron - and thus the neutron beams - ends in a material environment in a very short time, almost always in such a capture reaction; very few neutrons "experience" their radioactive decay.
Swell
Cosmic radiation is in the atmosphere or on the ground by interaction with molecules natural neutron radiation free. Due to the natural decay of atomic nuclei neutron radiation occurs rarely; placing them artificially ago with the help of neutron sources. In nuclear reactor neutrons are released during nuclear fission, as well as in nuclear fusion.
Another strong source of neutron bombs. They should kill with the help of neutron radiation people in the target area, but leave buildings and infrastructure relatively undamaged, so as to allow a re-use.
Use
In Materials Research Neutron beams are used to determine the atomic or molecular structure of solids ( neutron scattering). For monitoring the subcriticality of a nuclear reactor, the neutron radiation can be used such as a radium -beryllium neutron source. In the radiation therapy of malignant tumors was trying to kill cancer cells with neutron beams - but were quickly severe side effects in healthy tissue, which led to a shift away from the use of neutrons in radiation oncology.
Harmful effect on living organisms
The most harmful effect of fast neutrons in living tissue is the elastic scattering on hydrogen. It produces recoil protons, which in turn, and thus be harmful strongly ionizing in the tissue.
An indirect damage caused by thermal neutron radiation is due to the gamma radiation that occurs when the neutron capture on hydrogen.
The harmfulness of neutron radiation is also reflected in the high radiation weighting factors of the German Strahlenschutzverordung with values 5 to 20
In addition, rapid as well as thermal neutron radiation convert stable atomic nuclei by nuclear reactions in radioactive nuclei - the so-called activation.
Shielding
The shielding of neutron radiation is usually done with multiple processes (see also shielding (radiation) ): A moderator, such as water, paraffin or PVC, brakes fast free neutrons and converts part of the kinetic energy into heat. The thermal neutrons are then absorbed by, for example, cadmium or boron. The accompanying gamma radiation can finally be reduced by a layer of lead.