8. The cross section for Photodisintegration Reaction.

Photodisintegration Reaction - the absorption of gamma-ray photons by atomic nuclei and the accompanying ejection of protons p, neutrons n, or heavier particles from the nuclei. The (γ, p) and (γ, n) photonuclear reactions have been studied the most; other reactions, such as (γ, d), (γ, pn), and (γ, t) are also known. For a proton or a neutron, which are called nucleons, to be ejected from an atomic nucleus, the gamma-ray photon energy ℰ_γ must exceed the binding energy of the nucleon in the nucleus. The total cross section for all possible photonuclear reactions is called the gamma-ray absorption cross section for a nucleus. For all except very light nuclei, the cross section σ_γ is small at high and low gamma-ray energies but has a high broad maximum, which is called a giant resonance (Figure 1), at some intermediate energy. As the mass number A of the nucleus increases, the position of the giant resonance decreases monotonically from 20–25 million electron volts (MeV) in light nuclei to 13 MeV in Figure 1. A giant resonance heavy nuclei. The relation between the energy ℰ_m that corresponds to the resonance peak and A is described by the equation ℰ_m = 34A^–1/6. The term “photonuclear reactions” is sometimes applied to processes in which the absorption of high-energy gamma rays—that is, photons with energies of ~ 1.5 × 10⁸ eV—by nuclei or individual nucleons results in the production of pions or other elementary particles. Examples of such reactions include γ + p → n + π^– and γ + p → p + π⁰.

17. Nuclear reactions under the high energy electron. Electrons can experience elastic and inelastic scattering on nuclei. If the electron energy is sufficient, the processes are knocking protons from the nucleus (e, p) . The interaction between electrons and muons with nuclei is electromagnetic in nature. This allows the use of muons to detect the charge distribution in the nucleus , information about utlovyh point probably different transitions , the spin excitations. Interaction of muons with nuclei occurs cherezzahvat muon orbit muonic atom . Muon capture preceded by inhibition in substance and muon capture a distant orbit. This forms a muonic atom . In nuclear reactions induced by nucleons , whose energy is greater than the threshold meson production possible emission of mesons , which can also cause nuclear reactions and participate in the development of the intranuclear cascade . Most studied nuclear reactions on μ- mesons . Many nuclear reactions induced by pions , similar to the corresponding nuclear reactions induced by nucleons , for example, inelastic scattering , charge and knocking , etc. However, there are other nuclear reactions involving pions , which have no analogues in nucleon-nucleus interactions. These include the double charge exchange reaction of pions and nuclear reaction pion absorption . The study of these nuclear reactions allows us to investigate the correlation of nucleons in the nucleus. In the interaction of pions (p-), kaons ( K ) and antiprotons (p ~ ) with the Coulomb field of the nucleus of an atom and place their capture so-called education . exotic (Androna) atoms , and then the absorption core. Study of X-ray spectra of hadronic atoms provides information about how the distribution of charge density in the core and on the properties themselves negatively charged particles that have replaced the electron in an atom , Head-on collisions of massive nuclei at ultra- relativistic energies ( > 5 GeV / nucleon), create a new form of matter - quark-gluon plasma . This phase transition is feasible at an energy density GeV/fm3^3 , which can be reached at 17 GeV / nucleon.