アイテム詳細

要旨

Excited or short-lived nuclei often decay by emitting alpha particles that are assumed to be preformed inside the nucleus and confined in the nuclear potential well. In this picture, α decay refers to the tunneling of the alpha particle through the potential barrier. In this thesis we investigate for the first time how strong laser fields can assist the tunneling of the alpha particle and thus influence the nuclear decay. Generally speaking, laser-assisted α decay can be described as laser-assisted tunneling of a quasistationary state, i.e, a slowly decaying state. Our theoretical treatment is developed starting from the complex trajectory formulation of the wellknown strong-field approximation used to describe laser-induced ionization. We extend this formulation and develop a method to treat the decay of quasistationary states. The effect of both static and optical and x-ray monochromatic fields on the lifetimes and α-particle emission spectra are investigated for a number of α-emitting nuclei. We find that even at strong intensities, the laser-induced acceleration of the α decay is negligible, ranging from a relative modification in the decay rate of 10−3 for static fields of electric field strengths of 1015 V/m, to 10−8 for strong optical fields with intensities of 1022 W/cm2, and to 10−6 for strong x-ray fields with laser intensities around 1024 W/cm2. However, the effect of the external field is visible in the spectrum of emitted α particles, leading in the case of optical fields even to rescattering phenomena for intensities approaching 6 × 1022 W/cm2. The dynamics of the alpha particle in laser fields of intensities below the rescattering limit is investigated.