Ion beam analysis of lithium targets used to measure laser-driven nuclear reaction cross sections*

A project is underway to develop a platform for measuring light ion nuclear reaction cross sections at the Laboratory for Laser Energetics (LLE) using beams of particles produced by the target normal sheath acceleration (TNSA) mechanism. This technique could enable the measurement of nuclear reaction cross sections that are not accessible with conventional accelerators. One reaction currently under investigation to test the feasibility of this technique is the 7Li(d,p)8Li reaction. The deuteron beam, produced by TNSA, is incident on a lithium target producing the radioactive isotope 8Li with a half life of 840 ms. Counting the resulting activity of the 8Li produced in this process allows the reaction cross section to be determined.  A set of lithium targets has been produced at Houghton University by depositing a thin film (~2 um) of lithium onto a stainless steel substrate.  These targets have been studied using ion beam analysis (IBA) performed at the 1.7 MV Pelletron accelerator laboratory at SUNY Geneseo.  A proton beam from the accelerator is incident on the target and the energy spectrum of the backscattered particles is measured using a silicon detector.  We have used both Rutherford backscattering spectroscopy (RBS) and nuclear reaction analysis (NRA) to determine the thickness and composition of the lithium layer in these targets.  The detection of energetic alpha particles produced via the 7Li(p,α) reaction is used to provide additional information regarding the thickness of the lithium layer on these targets.