Nuclear inelastic spectrum

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). 

All these techniques are referred to as nuclear resonance scattering (NRS) of synchrotron radiation they include a wide spectrum of experimental techniques, such as nuclear forward scattering (NFS), nuclear inelastic scattering (NIS), nuclear... 

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).

Fig. 9.34 Monitoring of inelastic excitations by nuclear resonant scattering. The sidebands of the excitation probability densities for phonon creation, S(E), and for annihilation, S —E), are related by the Boltzmann factor, i.e., S(—E) = S E) tTvp —Elk T). This imbalance, known as detailed balance, is an intrinsic feature of each NIS spectrum and allows the determination of the temperature T at which the spectrum was recorded...

Fig. 1. (Top) y-Ray energy spectrum of the reaction 19F(p,ay)160 measured by a 3-inch Nal detector. Proton energy is 2.7 MeV, sample material is fluorapatite. (Middle) y-Ray energy spectrum for the same reaction acquired by a high purity germanium detector. The sample is meteoritic material. Low energy lines from several other nuclear reactions can be identified. (Bottom) Low-energy y-ray spectrum from 19F(p,p y)19F inelastic scattering recorded with a thin Ge(Li) detector. Reproduced with permission from Grambole and Noll [59],...

Nuclear interactions between the neutron and the nucleus giving most of the elastic scattering and the inelastic scattering from the phonon contributions. The phonon contribution will consists of a number of terms the normal one-phonon, two-phonon (multiphonon) contribution from the coherent part of the cross section, and the density-of-states of the total phonon spectrum as seen by the incoherent cross section. Naturally, the ratio of these two contributions will depend on the relative coherent and incoherent cross sections. 

Fig. 29. The low-temperature spectrum of EuNi P as function of momentum transfer ( j i30meV). The hatched area is due to the nuclear incoherent elastic scattering and inelastic phonon scattering. (From Holland-Moritz et al. 1989a.)...

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