Target-projectile interactions

Experimentally, evidence for a target-projectile interaction can be gained from measuring the probability for formation of the products that populate the various exit channels. This information then serves as the basis for interpretation of the reaction mechanism through which a nuclear collision proceeds. It may also provide essential data for nuclear astrophysics, as described in Chap. 12 of Vol. 2, and for evaluating and implementing nuclear applications, discussed in Chaps. 38 and 39 of Vol. 4). 

Figure 15.6 Plot of the excitation energy of the completely fused species formed from a given target-projectile combination. Reactions are assumed to take place at the interaction barrier.

Ej is the orbital energy associated with the target wave function Here Vpg is an effective potential seen hy the active electron, which contains the screening effect produced by other electrons from the medium. For bare incident ions, the active-electron projectile interaction Vpg is just the Coulomb potential. However, in the case where the projectile carries electrons, we use a screened potential made up of the Coulomb part due to the projectile-nuclear charge and the static potential produced by the target electrons that screen the projectile-nuclear charge... 

The scattering of a proton with a He atom is at least a three-body problem involving the projectile-active-electron and the projectile-target-core interaction (the four-body problem is reduced to a three-body problem by application of the independent-electron frozen-core model). Therefore, the conversion from impact parameter to projectile-scattering angle should be done carefully. For incident energies above a few hundred eV/amu and for... 

If the projectile and target atoms interact like colliding billiard balls (elastic hard-spheres), the interatomic potential that represents this condition is called a hard-sphere potential. For a hard-sphere potential, the power-law cross-section parameter m in (4.19) is equal to 0. Derive the total cross-section, a (It), for a hard-sphere potential. 

As mentioned before, all terms are written down in App. B. Note that outside of the target, i. e. when the positions r, r, s, and s of the projectile particle are such that the target s particle densities vanish, only the terras A and B with their antisymmetric combinations survive. These terms exactly reproduce Eq. (122) except for the obvious change of sign of the projectile-target Coulomb interaction. 

These transmission coefficients are then the probability that the target-projectile collision will penetrate the interaction barrier and produce a nuclear reaction. Thus as i increases, decreases that is, - 1 corresponds to complete absorption and - 0 to pure elastic scattering. 

Double ionization can also take place following multiple projectile-electron interactions. The simplest of such processes is the one where the projectile interacts once with each of the target electrons, so that ffiey both escape. This is a two-step process with two projectile-electron interactions, and is, accordingly, denoted TS-2. 

The penetration velocities of projectiles interacting with explosives initiated by the projectile have been found to be much lower than the penetration velocities of inerts of the same density. Studies of projectile penetration dynamics in inert and reactive targets have been performed using the Eulerian reactive hydrodynamic code 2DE described in Appendix C. 

Theoretically, the asymptotic fonn of die solution for the electron wave fiinction is the same for low-energy projectiles as it is at high energy however, one must account for the protracted period of interaction between projectile and target at the intennediate stages of the process. The usual procedure is to separate the incident-electron wave fiinction into partial waves... 

Collision-induced dissociation (or decomposition), abbreviated CID. An ion/neutral process wherein the (fast) projectile ion is dissociated as a result of interaction with a target neutral species. This is brought about by conversion during the collision of part of the translational energy of the ion to internal energy in the ion. The term collisional-activated dissociation (or decomposition), abbreviated CAD, is also used. 

The problem used uniform cubical zones, 0.02 cm (5 projectile diameter) on a side, in the vicinity of the projectile/target interaction region. A total of 6,000,000 cells was used in the calculation, and the calculation required 100 CPU hours on a Cray/X-MP (416). 

A close analogy to the localized surface interaction can be found in the field of chemical kinetics, namely, in the spectator stripping mechanism (5, 6) of the gas reactions, as evidenced by the recent crossed-molecular-beams experiments. Here the projectile seems to meet with only a part of the target molecule (that one to be transferred), while the rest of the target behaves as a spectator, in a sense not taking part in the reaction. 

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