Laser-Triggered Nuclear Reactions

Abstract

Nearly 30 ago, laser physicists dreamed of the laser as a particle accelerator [1]. With the acceleration of electrons, protons, and ions up to energies of several tens of MeV by the interaction of an intense laser pulse with matter, this dream has become reality within the last ten years. Today, highly intense laser systems drive microscopic accelerators. Nuclear reactions are induced by the accelerated particles. This article intends to outline the unique properties of laser-based particle and bremsstrahlung sources, and the diversity of new ideas that arise from the combination of lasers and nuclear physics.Triggering nuclear reactions by a laser is done indirectly by accelerating electrons to relativistic velocities during the interaction of a very intense laser pulse with a laser-generated plasma. These electrons give rise to the generation of energetic bremsstrahlung, when they are stopped in a target of high atomic number. They can as well be used to accelerate protons or heavier ions to several tens of MeV. Those bremsstrahlung photons, protons, and ions with energies in the typical range of the nuclear giant dipole resonances of about a few to several tens of MeV may then induce nuclear reactions, such as fission, the emission of photoneutrons, or proton-induced emission of nucleons. To induce one of these reactions, a certain energy threshold -the activation energy of the reaction -must be exceeded.Since the first demonstration experiments, nuclear reactions were used for the spectral characterization of laser-accelerated electrons and protons as well as bremsstrahlung [2,3,4,5]. A whole series of classical known nuclear reactions has been shown to be feasible with lasers, such as photo-induced fission [6,7], proton-and ion-induced reactions [5,8,9], or deuterium fusion [10,11,12,13,14]. Recently the cross section of the (γ,n)-reaction of 129 I was measured in laser-based experiments [15,16,17]. This last step from the pure observation of nuclear reactions to the measurement of nuclear parameters is of importance regarding the small size of