Using Rutherford backscattering spectroscopy to characterize targets used for nuclear reaction cross section measurements performed with laser-accelerated ions*

A project is underway to develop a platform for measuring low energy nuclear reaction cross sections using light ion beams accelerated from the rear side of targets illuminated with an ultra-intense laser. These ions, accelerated via the target-normal sheath acceleration (TNSA) mechanism, strike a nuclear production target placed behind the laser-illuminated target. The reaction products are collected, and their activity is measured to determine the nuclear cross section. We report on a set of experiments designed to characterize the nuclear production targets. These targets consist of lithium deposited on a substrate and coated with a thin metal film in a deposition chamber. The thin metal film must be thick enough to prevent the lithium from reacting with air during handling but thin enough to allow the projectile TNSA ions to pass through. The thickness of the metal overcoat has been measured using Rutherford backscattering spectroscopy (RBS) at the SUNY Geneseo 1.7 MV Pelletron accelerator.  In RBS, an MeV proton or alpha particle beam strikes the target at normal incidence and the energy spectrum of the backscattered ions is measured with a silicon detector.  The elemental composition of the target and its thickness can be inferred from the resulting spectrum.