Low Energy Target Irradiation at LERF Theresa Benyo and Larry Forsley NASA Glenn Research Center March 17, 2017

Goal Expand the capabilities of the LERF to below 5 MV kinetic energy Determine the effect of low (below 3 MV) kinetic energy gamma rays on beryllium and deuterated metals Resolve electron screening thresholds in a stationary laboratory center of mass

Objective Study the gamma/electron irradiation effects on deuterated metals. Past research involved accelerated deuteron beams relative to the laboratory frame center of mass. Focus of this study explores a stationary laboratory frame center of mass for the deuteron while increasing the electron density and energy to investigate the effect of electron screening. In order to cleanly observe the effect, this study proposes to start from below the photo-dissociation thresholds of beryllium and deuterium then move up in energy.

NASA and Jefferson Labs Collaboration Inter-agency agreement in place to: Investigate turning down the e-beam to below 3MV kinetic energy Implement hardware modifications to accommodate the lower energy beam Design and install necessary hardware to allow specimen exposure to photon/electron flux in desired energy range. Develop method/protocol to measure beam energy, end-point, spread, current, and frequency Irradiate several materials

Reproduce Conditions of Previous Experiments Can the beam kinetic energy be tuned down from the nominal 5-10 MV to the desired 1.5-3 MV range? Can the beam stably produce a minimum flux of 176 μA/mm2 at these lower beam kinetic energies? Can the machine operate at the desired > 250 Hz operating frequency and equivalent flux on target? If necessary, is the beam spatial size and energy dispersion compatible with blocking higher kinetic energy electrons?

Diagram of LERF and NASA Test Location Dipole Magnets 150 MV Accelerator Tube

NASA and DOE (Jefferson Labs) Collaboration Phase 1 Beam propagation code for LINAC settings at low MV (1.5 to 3 MV) Determine a solution to achieving electron beam kinetic energies running from 1.5-3MV if the computer model determines that it is possible. Determine and report to NASA the anticipated beam properties: End point energy and spread/accuracy of end point energy (desired to within 1%) Anticipated average current level for each of the energies of interest Determine the operating pulse rate/frequency at each of the lower beam energies Electron beam spot size Characterize dipole magnets to determine current settings for lower energy range. Phase 2 Complete hardware modifications for injector portion of the LERF according to the beam reconfiguration design to meet the needed electron beam energy and current. Install necessary hardware to allow exposure of sample to either electron beam (titanium window) or photon beam (tungsten/copper braking target) Run the accelerator at various kinetic energies < 3MV and expose various materials to the electron or photon beam. Measure activation of the materials and neutron/charged particle emissions as a function of exposed kinetic energies to journal level accuracy Jointly publish paper and submit to peer review journal

Modeling, Materials, and Measurements MCNP (Los Alamos Monte Carlo nuclear particle modeling): Activation cross-sections: (𝛾,n), (𝛾,p) (n,n’), (n,p), (p,n) Low Z, Nuclear Active materials: 2H1, 6Li3, 7Li3, 9Be4 High Z, Witness Materials: Mo, Hf, Er, etc. High Z, Screened deuteron sources ErD2.8, HfD2, etc. Post-Experiment Diagnostics: HPGe (𝛾 spectroscopy) Liquid Scintillator (𝛼,𝛽 spectroscopy) Solid State Nuclear Track Detectors (n) Real time measurements: BubbleTech neutron counters High RF/EMI and 𝛾 Environment: makes real-time electronic readout difficult We need assistance in neutron and proton readout in this environment! JANIS Cross-Section Tables Mo-99/ Tc99m Gamma Spectroscopy - NASA LINAC Exp: HfD2, Mo

Summary NASA and Dept of Energy collaboration to enhance the operating capability of the LERF If successful, will operate the LERF at various kinetic energies from 1.5-3 MV with beryllium and various deuterated metals as the targets. Advance understanding of electron screening in deuterated materials