Fission-Fusion: A new reaction mechanism for nuclear astrophysics based on laser-ion acceleration

We propose to produce neutron-rich nuclei in the range of the astrophysical r-process around the waiting point N = 126 by fissioning a dense laser-accelerated thorium ion bunch in a thorium target (covered by a CH2 layer), where the light fission fragments of the beam fuse with the light fission fragments of the target. Via the 'hole-boring' mode of laser Radiation Pressure Acceleration using a high-intensity, short pulse laser, very efficiently bunches of 232Th with solid-state density can be generated from a Th target and a deuterated CD2 foil, both forming the production target assembly. Laser-accelerated Th ions with about 7 MeV/u will pass through a thin CH2 layer placed in front of a thicker second Th foil (both forming the reaction target) closely behind the production target and disintegrate into light and heavy fission fragments. In addition, light ions (d,C) from the CD2 layer of the production target will be accelerated as well, inducing the fission process of 232Th also in the second Th layer. The laser-accelerated ion bunches with solid-state density, which are about 1014 times more dense than classically accelerated ion bunches, allow for a high probability that generated fission products can fuse again. The high ion beam density may lead to a strong collective modification of the stopping power, leading to significant range and thus yield enhancement. Using a high-intensity laser as envisaged for the ELI-Nuclear Physics project in Bucharest (ELI-NP), order-of-magnitude estimates promise a fusion yield of about 103 ions per laser pulse in the mass range of A = 180-190, thus enabling to approach the r-process waiting point at N = 126.