The interactions of alpha particles with nuclei

Abstract

The principal types of interactions of cy particles with nuclei up to an energy of 200 MeV are reviewed, together with the theories used to understand their mechanisms. Elastic scattering is described by the optical model and this may be extended to include inelastic scattering by means of the coupled-channels formalism. The cy particle may break up as it encounters the nuclear field and the fragments may or may not be captured by the nucleus. It is also possible for pick-up and stripping reactions to occur, as well as fragmentation. If the cy particle, or one or more of its fragments, is captured by the nucleus it initiates a cascade of interactions leading to an equilibrated system that subsequently decays by statistical evaporation. During the course of this cascade pre-equilibrium particles can be emitted. Theories of these processes are described and these enable a quantitative understanding of the reactions to be attained.

Nuclear Gamma-Ray De-Excitation Lines and Continuum From Accelerated-Particle Interactions in Solar Flares

“…Projectile energy (MeV nucleon -1 ) Stockhorst et al 1982Gadioli et al 1984 α + 93 Nb → 90 Nb + 3n + "α" 0 20 40 60 1 10 100 1000 Gadioli et al 1986Michel & Brinkman 1980 α + 59 Co → 57 Co + 2n + "α" for the alpha-inelastic reactions with 24 Mg and 28 Si producing the strong lines at 1.369 and 1.778 MeV are shown along with the measurements at low α-projectile energies. We have adopted the following rule for establishing line production cross sections in alpha-inelastic reactions: "At those energies where they are available (typically at energies 10 MeV nucleon −1 where the α particle is unbroken producing the first peak of the cross section) laboratory measurements are used.…”

“…But at high energies, the α particle can be broken, yielding several possible exit channels for the projectile: (α, pt), (α, dpn), (α, 3 He n), (α, 2d), and (α, 2p 2n). This type of reaction is referred to as inelastic breakup (Gadioli & Hodgson 1986). Above the threshold energies for these new reactions, the reaction is no longer two-body even though the target nucleus is unchanged (other than being excited).…”

“…This pattern has been seen in measured cross sections of spallation reactions of the type (α, xn yp) where x, y > 2 when the measurement is for the residual nucleus, independent of the identity of the other nucleons (as in the measurement of the production of radioactive nuclei). One example is the reaction α + 59 Co → 57 Co + 2n + "α," whose measured cross section is shown in Figure 2(a) (from Gadioli & Hodgson 1986). Here, "α" refers to all of the possible combinations of two protons and two neutrons.…”

“…Another example is the reaction α + 93 Nb → 90 Nb + 3n + "α," whose cross section is shown in Figure 2(b) (from Gadioli et al 1984). There are many such examples, and in their review of α-particle interactions, Gadioli & Hodgson (1986) indeed considered this pattern to be a general rule for such reactions: "The excitation functions of alpha reactions show structure with an initial peak, a valley, and a second rise to a flat plateau. The first peak and the valley correspond to α-particle emission, mainly by evaporation in the peak and by preequilibrium emission in the valley.…”

Optical model analysis of90, 92, 94, 96Zr+4He elastic scattering at 35.4 MeV

“…From an extensive study of the elastic scattering of alpha particles from nuclei, it has been demonstrated that the alpha particles are sensitive probes particularly to explore the nuclear surface [1]. As alpha particles are T=0 projectiles, it is of interest to employ them to study their elastic scattering from a number of isotopes of a given element and to understand the nature of the interaction in terms of the isotopic composition and the nuclear structure.…”