Prof. Dietrich Habs (Sektion Physik der Ludwig-Maximilians-Universitaet Muechen), Introducing the Fission-Fusion Reaction Process: Using a Laser-Accelerated Th Beam to produce Neutron-Rich Nuclei towards the N=126 Waiting Point of the r Process

Wednesday 30 Jun 2010, 11:00 → 12:00 Europe/Bucharest

We propose to produce neutron-rich nuclei in the range of the astrophysical r process (the rapid neutron-capture process) around the waiting point N = 126 by fissioning a dense laser-accelerated thorium ion bunch thorium target (covered by a thin carbon layer), where the light fission fragments of the beam fuse with the light fission fragments of the target. Via laser Radiation Pressure Acceleration (RPA) using a high-intensity, short pulse laser, very efficiently bunches of solid state density of 232Th can be generated from a first thin (ca. 150 nm) Th production target spot, placed on a CH2 backing (ca. 0.003 mm). Laser accelerated Th ions with about 7 MeV/u will pass through a thin carbon layer placed in front of a thicker second Th foil closely behind the first target and desintegrate into light and heavy fission fragments. In addition light ions (p,C) from the CH2 backing of the first Th target will be accelerated as well, inducing the fission process of 232Th also in the second Th target. The laser-accelerated ion bunches with solid state density, which are about 1015 times more dense than classically accelerated ion bunches, allow for a high probability that generated fission products can fuse again when the fragments from the thorium beam strike the second Th reaction target. In contrast to classical radioactive beam facilities, where intense but low-density radioactive beams of one ion species are merged with stable targets, the novel fission-fusion process draws on the fusion between neutron-rich, short-lived, light fission fragments both from beam and target. Moreover, the high ion beam density may lead to a strong collective modification of the stopping power in the target by 'snowplough-like' removal of target electrons, leading to significant range enhancement, thus allowing to use rather thick targets. Using a high-intensity laser with 300 J and 15 fs pulse length (20 PW), as e.g. envisaged for the ELI-Nuclear Physics project in Bucharest (ELI-NP), order-of-magnitude estimates promise a fusion yield of about 106 ions per laser pulse in the mass range of A = 180-190, thus enabling to approach the r-process waiting point at N=126. First studies on ion acceleration, collective modifications of the stopping behaviour and the production of neutron-rich nuclei can also be performed at the up-coming new laser facility CALA (Center for Advanced Laser Applications) in Garching [ http://arxiv.org/abs/1007.1251v1 ]