Nuclear reaction

Nuclear reactions are the transformations of the kernels in their interaction with elementary particles ' -quanta or each other. The nuclear reaction takes place with the release of energy (if formed the nucleus has a greater binding energy on the particle) and the energy absorption (if the reaction products have a lower binding energy on the particle than the original nucleus). Nuclear reactions occurring with the release of energy, called organizing exoergic, with energy absorption are called endogenerating. Due to the energy of particles in the nucleus (see atomic Nucleus) in nuclear reactions allocated energy around 106 times more than during chemical reactions. Endogenerating reactions are carried out, if the energy of the bombarding particle more threshold energy E. for this type of reaction. The likelihood of this reaction is characterized by a cross-section of a s - probability of turning one core as a result of this nuclear reactions under the influence of one particle incident on 1 sm2 target surface, and is numerically equal to the cross-section of the kernel, σ measured either in square centimetres or Barnov, equal to 10-24 cm2 (a true cross section of the kernel is PG and in quantity equal to 10-24 cm2). Another characteristic of nuclear reactions is the output of the W is the ratio of the number of acts of this nuclear reaction among caught on target particles. Nuclear reactions are well described by a model compound nucleus, according to which they proceed in two stages: first, the particle is caught by the kernel and is formed excited intermediate, or compound, the kernel. For the time longer than time needed for passage of the particles through the core of the bombarding particle due to the large number of collisions (more 106) transfers its energy to all the particles of the kernel, so it is fairly even distribution of its individual nucleons (core temperature rises). If as a result of fluctuations of the energy of one of the nucleons will be at some point more of its energy ties, the nucleon will leave the kernel. For example, the reaction of N147 (n, p) C146 first formed an integral kernel N147, which then decays with the emission of a proton. The correctness of this concept is confirmed by the fact that the angular and energy distribution of emitted particles is determined only by the properties of the compound nucleus, and also that the type and probability of decay of the given compound nucleus does not depend on the ways of its formation in the bombing of different particles. For example, a compound nucleus Br82 always breaks down in the following ways: Br82 → Br82+'; Se81+p; As78+α; Br80+2n, regardless of the means of obtaining it. The core represents a quantum-mechanical system consisting of nucleons, which, like the atom, can be in the States with a certain energy. These energy levels are defined by the collective motion of nucleons (see atomic Nucleus). With increasing excitation energy of nuclei Eb energy levels E, and their width G is increasing, and the distance between neighboring levels decrease and the role of individual levels of the compound nucleus affects only at low excitation energies Eb in light nuclei.
At low energies of the particles, the wave properties play a significant role in the interaction with the nucleus, the phenomenon of resonance (similar to the resonance absorption of light), implying a sharp increase σ for values matching with any level of the compound nucleus (see Neutron, Neutron). Most clearly, all the patterns nuclear reactions are observed in the interaction with neutrons, as Coulomb barrier prevents the penetration of them in the kernel. For Eb resonance energies there are extreme highs to narrow intervals neutron energy. With increasing E levels of the compound nucleus overlap and resonant absorption of particles is missing, because the interaction of particles is caused in this case by all levels of the kernel; wave properties of particles stop to play a role. In this case σ differs little from the geometrical cross section of the kernel πr2. If Eb in the capture of particles smaller than the binding energy of nucleons in the nucleus Ecb, then there is only the reaction of the radiation capture with the emission V-ray (n, V), (p, V). At high energies, plays an essential role of competition of certain types of decay of the compound nucleus. Thus all (F) for certain types of disintegration has smooth highs.
When nuclear reactions with charged particles, R, d, alpha, t and other essential role is played by the Coulomb barrier, which increases with Z nuclei and charge particles.
When bombarded by neutrons are formed, as a rule, beta-active kernel due to excess in them neutrons (see Radioactivity), except reaction (h, a) and (n, 2n). Under bombardment by proton are formed β+-active nuclei.
Most of isotopes for medical research purposes is produced by neutron irradiation by the reaction (n, V). Reaction with a particles similar to the reactions under the influence of protons. When reactions (alpha, n) are formed β+-active nuclei, when reactions (alpha, p) stable kernel. Outputs for reactions with a particles smaller than for reactions with protons. All other laws for σ from E remain qualitatively the same as for R. Nuclear reactions with dataname have a number of essential features. From the reactions with dataname d receive large amounts of radioactive isotopes: Na24, P32, J131, Br82, Cu -64 , etc. as alpha-particles easier to expedite than p, and these reactions have more outputs. Reactions coming under the influence of V-ray, called photonuclear; they are observed only when the ' energy-quantum more to the energy of particles in the nucleus, and are used to determine these energies. Studied reactions with tritons - tritium nuclei type (t, a) and (t, n) on light nuclei. The thermonuclear reaction of the specified type occur in the explosion of the hydrogen bomb.
In recent years carried out a nuclear reactions under the influence of multiply charged ions. For example, Li6 (Li6, a) Within10; 12 (12, a) Ne20. At the bombardment of nuclei of multiply charged ions are observed reaction to the transfer of neutron: Mg24 (N14, N13) Mg25 and others At high energies bombarding particles (>100 MeV) is consistent emission (evaporation) of nucleons and light particles d, a, t with energy 10-15 MeV from highly excited nucleus and the nucleus disintegration into separate parts, consisting of a few nucleons (the formation of stars). At very high energies (about 1000 MeV) there is a complete breakdown of the kernel on a separate nucleons. With increasing energy of 100 MeV and above the wavelength of the nucleon X becomes smaller than the diameter of the nucleon, and therefore there is interaction projectiles with separate nucleons of the nucleus, resulting in the kernel becomes partially transparent and full σ becomes smaller geometric. The splitting of nuclei into separate fragments can be difficult to identify them. The processes of fission of nuclei by high-energy particles play a significant role in cosmic rays. At ultra-high energies nuclear reactions proceed with the formation of new particles: mesons and hyperons, antiprotons, antineutrons, and others, formed at interaction of projectiles with separate nucleons.