Nuclear elastic scattering

Many processes can occur when a neutron strikes an atom. Neutrons carry no charge and their interaction with electrons is negligible, but when an incident neutron comes close enough to the very small atomic nucleus to transfer some kinetic energy to the nucleus as a whole, the nucleus moves but has no internal excitation. This process is called nuclear elastic scattering and may be visualized as billiard balls colliding. The energy of nuclear motion eventually dissipates as heat. 

Fig. 49. Background-corrected spectra of TmTe at 300K obtained with = 3.65meV as a function of energy, but presented in a scale linear in time-of-flight. The upper frame shows the spectra at ambient pressure in the pressure cell, and the lower frame the one at 28kbar. The solid line represents the best fit, the dashed line is the magnetic component, whereas the hatched area is due to nuclear elastic scattering. (From Walter et al. 1992.)...

Amundsen, 1981, Measurement of Sr K-shell ionization probability across the nuclear elastic-scattering resonance at 5060 keV, Phys. Rev. A, 24 1218. 

Because the cross-sections for nuclear reaction are usually lower than the cross-sections for elastic scattering of projectiles used in RBS or in elastic recoil detection analysis (ERDA), higher currents must be used to obtain comparably high intensity in... 

Nuclear absorption of incident X-rays (from the synchrotron beam) occurs elastically, provided their energy, y, coincides precisely with the energy of the nuclear transition, Eq, of the Mossbauer isotope (elastic or zero-phonon peak at = E m Fig. 9.34). Nuclear absorption may also proceed inelasticaUy, by creation or annihilation of a phonon. This process causes inelastic sidebands in the energy spectrum around the central elastic peak (Fig. 9.34) and is termed nuclear inelastic scattering (NIS). 

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)...

The shape resonances have been described by Feshbach in elastic scattering cross-section for the processes of neutron capture and nuclear fission [7] in the cloudy crystal ball model of nuclear reactions. These scattering theory is dealing with configuration interaction in multi-channel processes involving states with different spatial locations. Therefore these resonances can be called also Feshbach shape resonances. These resonances are a clear well established manifestation of the non locality of quantum mechanics and appear in many fields of physics and chemistry [8,192] such as the molecular association and dissociation processes. 

Megaelectron volt (MeV) ion beam techniques offer a number of non-destructive analysis methods that allow to measure depth profiles of elemental concentrations in material surfaces. Elements are identified by elastic scattering, by specific nuclear reaction products or by emission of characteristic X-rays. With nuclear microprobes raster images of the material composition at the surface can be obtained. Particle-induced gamma-ray emission (PIGE) is especially suited for fluorine detection down to the ppm concentration level. 

Neutron elastic scattering is one of the most powerful tools in the determination of the magnetic structure of an ordered material. At the onset of magnetic order additional reflections on the nuclear pattern are created, due to interactions between the electrons of the nuclei. The variation of the intensity of these magnetic reflections with temperature yields the ordering temperature as well as the spontaneous magnetization of the sublattices and thus the critical exponent /5. 

Fig. 15. Basic equipment for measuring a nuclear inelastic scattering spectrum. Detector 1 measures the intensity of the incoherent nuclear forward scattering, which proceeds both elastically and inelas-tically detector 2 measures only the intensity of the coherent nuclear forward scattering, which proceeds elastically. Figure according to Ruffer and Chumakov (224).

Reflection high-energy RHEED composition. The momentum transfer in backscattering collisions between nuclei is used to identify the nuclear masses in the sample, and the smaller, gradual momentum loss of the incident nucleus through electron-nucleus interactions provides depth-profile information. Monoenergetic electrons of 1 -20keV are elastically scattered from a Atomic structure... 

Different types of interaction are distinguished, as illustrated in Fig. 8.23. (The spherical form is a simplification which is only applicable for nuclei with nuclear spin / = 0.) On path 1 the nuclei are not touching each other elastic scattering and Coulomb excitation are expected. On path 2 the nuclei are coming into contact with each other and nuclear forces become effective inelastic scattering and transfer reactions... 

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