Proton-atom scattering

The peculiar behavior of H might be relevant to understand the hydrogen bond, which deforms the electronic cloud of the proton. On the other hand, it is surprising to discover an anomalous behavior for a closed-shell atom like He. However, it has been demonstrated in helium-atom-scattering that interactions between He atoms... 

Anti-protonic atoms. Recently neutron density distributions in a series of nuclei were deduced from anti-protonic atoms [30], The basic method determines the ratio of neutron and proton distributions at large differences by means of a measurement of the annihilation products which indicates whether the antiproton was captured on a neutron or a proton. In the analysis two assumptions are made. First a best fit value for the ratio I / of the imaginary parts of the free space pp and pn scattering lengths equal to unity is adopted. Secondly in order to reduce the density ratio at the annihilation side to a a ratio of rms radii a two-parameter Fermi distribution is assumed. The model dependence introduced by these assumptions is difficult to judge. Since a large number of nuclei have been measured one may argue that the value of Rj is fixed empirically. 

The goethite structure contains two types of O atoms designated as Oi and On (Fig. 2.4e). On the 0 site, the O atom is shared between octahedra of two different double chains, whereas the On atom is shared between octahedra in the same chain and is also linked to the proton. Neutron scattering has shown that the On-On distance is... 

In effect, the equation has been derived under the assumption of infinite nuclear mass. This is accurate enough for electron scattering, but for proton and atom scattering a coordinate transformation is needed, the details of which are given in Mott and Massey.26... 

X-rays are diffracted by the electrons on each atom. The scattering of the X-ray beam increases as the number of electrons, or equally, the atomic number (proton number), of the atom, Z, increases. Thus heavy metals such as lead, Pb, Z = 82, scatter X-rays far more strongly than light atoms such as carbon, C, Z = 6. Neighbouring atoms such as cobalt, Co, Z = 27, and nickel, Ni, Z = 28, scatter X-rays almost identically. The scattering power of an atom for a beam of X-rays is called the atomic scattering factor, /a. 

Rutherford proposed the nuclear model of the atom to account for the results of experiments in which alpha particles were scattered from metal foils. According to this model, the atom consists of a central core, or nucleus, around which the electrons exist. The nucleus has most of the mass of the atom and consists of protons (with a positive charge) and neutrons (with no charge). Each chemically distinct atom has a nucleus with a specific number of protons atomic number), and around the nucleus in the neutral atom are an equal number of electrons. The number of protons plus neutrons in a nucleus equals the mass number. Atoms whose nuclei have the same number of protons but different number of neutrons are called isotopes. 

F. -Linder, Energy loss studies of rotational and vibrational excitation in proton-molecule scattering, in "Electronic and Atomic Collisions. Invited Papers and Progress Reports", N. Oda and K. Takayanagi, eds., North-Holland, Amsterdam (1979), p. 535. 

Sir Ernest Rutherford (1871-1937 Nobel Prize for chemistry 1908, which as a physicist he puzzled over) was a brilliant experimentalist endowed with an equal genius of being able to interpret the results. He recognized three types of radiation (alpha, beta, and gamma). He used scattering experiments with alpha radiation, which consists of helium nuclei, to prove that the atom is almost empty. The diameter of the atomic nucleus is about 10 000 times smaller than the atom itself. Furthermore, he proved that atoms are not indivisible and that in addition to protons, there must also be neutrons present in their nucleus. With Niels Bohr he developed the core-shell model of the atom. 

Fig. 13. Measured channeling dips in the yield of elastically scattered 670 keV protons from the Si lattice (O) and the yield of the (p, a) nuclear reaction with UB atoms (A). The difference in the angular widths of the two dips is due to displacements of the boron atoms in B—H complexes from substitutional sites. From Marwick et al. (1987)...

Several types of ion-channeling experiments (see Chapter 9) also give useful information on atomic positions at impurities or impurity complexes. These include both scattering of channeled ions by atoms that disrupt the uniformity of a channel path and the production of nuclear reactions by collision of a channeled ion with an impurity nucleus (e.g., incident 3He colliding with dissolved 2H to give 4He plus a proton, which can be detected). Here again, one can study lattice positions of solute atoms and changes in populations of different sites. 

Finally in this section, we note that the use of perturbation theory, particularly for quasi-resonant charge transfer, has been developed by Battaglia, George and Lanaro They show that first-order perturbation theory is satisfactory for high-velocity atoms, with Eq lying outside the solid band, and they have examined in detail protons scattered from alkali-halide... 

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