Coherent proton and deuteron states in neutron scattering
2008 (English)In: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. 77, no 6, 065301- p.Article in journal (Refereed) Published
Neutron Compton scattering has been used for a long time as a method to obtain information about proton momentum distributions in organic molecules, metal hydrides, etc. However, in a number of recent papers it has been shown that scattering on protons (and to some extent also on deuterons) shows intensities that are much smaller than expected when compared to those of the other constituents of the measured systems. This has raised the question if the Compton scattering process is fully understood (do, for instance, electron excitations take up part of the recoil energy and momentum?) and casts doubts on the reliability of the method for its original purpose. The present paper presents a detailed explanation for the intensity deficits in a number of studied systems without involving any participation of a third body in the scattering process. It is a development of an earlier proposed model, in which the intensity loss is caused by destructive interference in the waves representing the scattered neutron and the recoiling particle. These interferences appear when the scattering particles are indistinguishable (and therefore in a quantum superposition state) when seen by the neutron. It requires that the neutron coherence length (which is determined by the energy selection) is comparable to the internuclear distances. It is shown that the latter condition is at least partially fulfilled for two, three or four particles in the experiments and that it is likely that the necessary coherence remains over the very short duration (femtosecond (fs)) of the scattering process. Quantitative agreement is obtained for several proton and deuteron containing systems, including the observed dependence of the intensity deficit on scattering angle, which is explained in terms of the actual recoil energy as related to the proton- or deuteron-binding energy in the different systems. The question of available final states for the scattering system is discussed.
Place, publisher, year, edition, pages
2008. Vol. 77, no 6, 065301- p.
IdentifiersURN: urn:nbn:se:uu:diva-101149DOI: 10.1088/0031-8949/77/06/065301ISI: 000256544500014OAI: oai:DiVA.org:uu-101149DiVA: diva2:211984