Secondary Neutron Yields Produced by Thick-Target Aluminum Interactions

In May 2015, neutron production from thick-target shielding experiments were conducted at the NASA Space Radiation Laboratory (NSRL) at Brookhaven National Laboratory (BNL). Secondary neutron yields produced by 0.4- and 1.0-AGeV iron ions impinging upon a 30 g/cm^2 aluminum target were measured with liquid scintillators at 10, 30, 45, 60, 80, and 135 degrees off the beam axis. Neutral and charged particle events in the liquid scintillators were first separated using thin plastic “veto” detectors. Neutron and gamma ray signal contributions in the neutral events were then separated with pulse shape discrimination. Finally, neutron energy spectra were produced using the time-of-flight technique. Experimental results will be compared with transport model calculations using codes such as MCNP and PHITS. Future experiments in 2016 and 2017 will include the use of a shadowbar system, front and back thick targets, and a variety of projectile species and energies. The shadowbar system will consist of two iron bars, one 1-meter long and the other 2-meters long, for use in a full background characterization, while the front and back targets are composed of high-density polyethylene or aluminum with thicknesses between 20 and 60 g/cm^2. Finally, proton, helium, carbon, silicon, and iron projectiles will be utilized at beam energies of 0.4, 0.75, 1.5, and 2.5 AGeV. This systematic study on secondary neutron production from a variety of thick targets by several high-energy ion species will be incorporated into the uncertainty analysis for NASA-developed transport codes. Ultimately, these measurements will help determine optimal shielding thicknesses for future space applications.