Infrared divergence of the resonant Raman-Compton scattering

Abstract

The infrared divergence of the resonant Raman-Compton scattering has been studied in collisions of photons on atomic L electrons in the intermediate-momentum-transfer regime. Low-energy continua emitted by Zr atoms, excited, in the vicinity of the K edge, by the monochromatized x rays delivered by the LURE Synchrotron Radiation Facility, have been observed on very thin targets and compared with the theoretically predicted infrared divergence of the Raman scattering. The characteristic change in shape of these continua has been studied over a wide energy range below the Zr K edge.PACS numbers: 32.80. Cy, 32.30.Rj While the Raman scattering in molecules is a wellknown effect and a well-established technique, this process has only very recently be considered in the x-ray regime where inner-core excitations are involved. In such a case, where autoionizing levels are considered, this process exhibits a very different behavior, allowing the study of new effects through some yet unconsidered terms of the theory. In this process, schematically described in Fig. 1, an incoming photon hv\ is inelastically scattered by an atom, which is excited in the final state of the collision. When the intermediate (virtual) state V is close to a discrete (real) level, this process is resonant. When considering inner-core excitation, two decay processes of the virtual level may be taken into account: (a) The first is the well-known Raman scattering [ Fig. 1(a)] where the target atom is excited, and the incoming photon scattered at a lower energy. This process, in which a monoenergetic scattered line is emitted, has only quite recently been observed on an atomic discrete level. x This process is resonant on both sides of the discrete level; in the final state the atom is excited, with an L electron being promoted to an empty outermost level, (b) The second is the Raman-Compton scattering [ Fig. 1 (b)] where, in the decay channel, the available energy is shared between a photon and an electron (autoionizing level); continuum photon (and electron) energy spectra are then observed, (Is) ionization limit V hv r (ls)(np) hv. (2p)~ (np) hv~ hv. (2p) (a) Raman (b) Raman-Compton FIG. 1. Resonant Raman-Compton effect: (a) Raman scattering (inelastic scattering of a photon) and (b) RamanCompton scattering (the energy given to the atom is, in the final state, shared between an electron and a photon).whose maximum energy edges are equal to the total available energy («Av/-2^). This process is then asymmetrically resonant near the ionization energy level (the energy difference between the virtual level and the U ionization limit will be denoted by e), and in the final state the atom is ionized in the L shell.The virtual level decays by either (a) or (b). In the case of solid targets where the outermost excited electrons are not located in discrete energy states but in broad bands, these two processes cannot be experimentally separated and only complex continuum spectra are observed.In the example considered in Fig. 1, which is among the most typic...

Investigations on compton scattering: New directions

“…Although theory unambiguously predicts the infrared divergence, there are no convincing experimental observations. While some measurements were reported of the observed infared divergence (Spitale and Bloom, 1977;Basavaraju et al, 1987;Briand et al, 1989), they were later challenged by others Franck, 1989, 1990) or withdrawn, suggesting that the reported results were perhaps due to other phenomena such as bremsstrahlung following photoeffect. Manninen et al (1990) later observed an infrared rise, but concluded that it was due entirely to photoelectron bremmsstrahlung in the target.…”

Rayleigh, Compton and K-shell radiative resonant Raman scattering in 83Bi for 88.034keV γ-rays

“…The inclusion of C K stops the cross-sections from diverging as E in approaches B K . This behaviour has been clearly noticed in the measured KL radiative RRS distributions [10,25,26]. Taking this energy-dependence, the present measured cross-section can be used for a first-order estimate of RRS cross-sections at higher energies approaching B K = 90.526 keV.…”

Resonant Raman scattering of polarized and unpolarized x-ray radiation from Mg, Al, and Si

“…The excited atom can relax by means of a radiative (resonant Raman scattering) or a nonradiative process (the Auger resonant Raman effect [2]). According to the final state of the excited electron (i.e., into a discrete unoccupied bound state or into the continuous energy band above the Fermi level, in which the available energy is mutually shared in a continuous way among the electron and the scattered photon), the phenomenon has been distinguished by some authors as resonant Raman and resonant Raman-Compton scattering, respectively [3,4]. However, in many cases the discrete bound states merge into the continuum bands and/or when low-resolution spectrometers are used these two different scattering mechanisms cannot be separated.…”

“…Up until now several studies have been accomplished related to the systematic determination of the RRS cross sections for transition metals and rare-earth elements by means of synchrotron radiation, x-ray tubes coupled with crystal monochromators, and radioactive or proton-induced x-ray beams [3,4,[16][17][18][19][20][21][22][23][24][25][26]. Nevertheless, despite the important role played by low-Z elements such as Mg, Al, and Si in new materials (e.g., as impurities in silicon wafers) studies of these elements have been rather scarce.…”