High Intensity Laser Driven Photo-Proton Reactions

High energy gamma rays, produced via ultra intense laser-gas interactions have been used to induce photo-proton reactions in various materials. The Jena multi-terawatt, (I=5x10''19 W/cm''2, 80 fs) table-top laser is focused into a He gas jet (10''19 cm''-3), generating a relativistic plasma channel, while the stability of the channel formation is monitored with a 2ω probe beam. Electrons in the relativistic channel are accelerated to energies of ∼5-40MeV and have a quasi exponential energy profile with temperatures of the order of 10 MeV. the electrons are incident on a primary converter target (tantalum) og high proton number (z), thus generating high energy Bremsstrahlung photons, which can induce (γ, n) and (γ, p) reactions in a secondary target. Specifically, secondary targets of various z (magnesium, titanium, zinc and molybdenum) have been investigated, to compare the ratios of (γ, p) and (γ, n) reactions as a function of z. Photonuclear data describing the interaction of photons with atomic nuclei are of great importance for a variety of applications, such as radiation shielding, radiotherapy and possible transmutation studies. While the majority of work carrie out using both conventional nuclear techniques and laser plasma produced photons has looked at photo-neutron reactions, it has been highlighted that the charged particle emission is as important, especially in the low z range, where the threshold energies and cross sections may be very similar. (Author)