Phonon-mediated Nuclear Excitation Transfer

Abstract

Excitation transfer has long been of interest in biophysics, where electronic excitation is transferred from one location to another mediated by photon exchange. We are interested in the transfer of nuclear excitation mediated by phonon exchange, which according to our theoretical approach lies at the foundation of many anomalies in Condensed Matter Nuclear Science. The transfer of excitation from one site to another involves coupling to off-resonant intermediate states with either no excitation or double excitation; as such it is a quantum mechanical effect with no classical counterpart. The indirect coupling interaction can be determined from second-order perturbation theory for an electric dipole (E1) interaction, and the resulting interaction is weak due to destructive interference. We present results for resonant phonon-mediated excitation transfer based on the relativistic phonon-nuclear boost interaction identified recently. The analysis is extended to the more complicated case of magnetic dipole (M1) interactions, where fourth-order perturbation theory is needed for the interaction. We find severe destructive interference effects very much weaken the indirect interaction in both cases. Some improvement is possible due to loss; however, the improvement seems insufficient to account for the effects seen in excitation transfer experiments in our lab. To address this issue, we propose here that shifts in the off-resonant basis state energies could lead to much larger indirect interactions. The evaluation of shifts in the basis state energies is a major project, which requires the specification of the nucleon-nucleon interaction off of resonance, and the evaluation of off-resonant binding energies; these are projects to be addressed in the future. The transverse Breit interaction is given off of resonance. The resulting indirect interaction for excitation transfer is consistent with a delocalized transfer effect, and also with cooperative (Dicke) enhancements; we expect shifts in the basis state energies to lead to new models for up-conversion and down-conversion as well. Possible connections between the model and recent experimental results from excitation transfer experiments involving a ⁵⁷Co source on steel are discussed. We also consider incoherent excitation transfer, where the large excitation associated with the D₂/⁴ He transition is transferred to highly excited unstable states in the nuclei of the host lattice. While the mechanism was proposed many years ago to account for low-level emission of energetic alphas, there has subsequently been no clarification of mechanism associated with these experiments, which provides motivation for us to consider the possibility of confirming or rejecting the mechanism through a systematic study where the ejected particle energy is determined as a function of the nuclear mass of host lattice nuclei. The argument is extended to excitation transfer from the HD/³ He transition, where few MeV alpha emission may be a candidate explanation for the observations of Storms and Scanlan, and where proton emission from ⁶Li may be a candidate explanation for the 0.79MeV proton signal reported by Lipinski and Lipinski. Keywords: Excitation transfer; M1 transitions; Off-resonance states; Phonon-nuclear coupling; Theory