Single-Shock Platform for Activation Studies with a Prompt Source of Fast Neutrons

Laura Hopkins (15-ERD-046)

Project Description

Implosion of targets at the National Ignition Facility at Lawrence Livermore allows access to previously inaccessible regions of high density and temperature phases coupled with high neutron fluences (neutrons per unit area received by a surface). These new regimes can provide a wealth of information on high-energy-density physics and the neutron activation of atomic species. High-atomic-number species, such as xenon, are of particular interest because of their use in post-detonation nuclear forensics and global atmospheric monitoring. The goal of this project is to design and qualify a platform geared specifically to study the neutron activation of radioisotopes at the National Ignition Facility. The initial platform qualification will occur with isotopes of xenon selected to potentially provide the first experimental measurement of electron-mediated nuclear and plasma interactions. The subsequent shot series will measure xenon neutron-activation ratios in two different implosion regimes where the neutron yield is dominated by shock production or where both shock and compression contribute.

A successful outcome of this project will include an assessment of nuclear–plasma interaction effects in a high-energy-density plasma formed by imploding a laser target, as well as a comparison between neutron production in a shock-dominated system with a shock and a compression system. Furthermore, activation of atmospheric xenon by a source of prompt, fast neutrons will be measured, and the resulting isotopic species ratios will be quantified and compared with previous research, with a goal of reducing uncertainties introduced by previously utilized measurement techniques. This project is also anticipated to qualify and characterize a new species-activation platform for future expanded studies at the National Ignition Facility. At the conclusion of this project, we anticipate that a high-atomic-number, doped indirect-drive platform with the necessary diagnostics will be well characterized for follow-on experiments utilizing alternate high-atomic-number species undertaken by programmatic research efforts.

Mission Relevance

This research addresses the challenge of experimentally observing nuclear–plasma interactions, which can cause significant changes in high-energy-density plasmas found in nuclear weapons tests and astrophysical settings. This will be accomplished using a novel neutron-activation target platform for the National Ignition Facility to induce these interactions on highly excited nuclear states during implosion. The effort is directly aligned with Livermore's strategic focus area in stockpile stewardship science, which requires new approaches for probing nuclear–plasma interactions to better understand boost physics in weapons.

FY16 Accomplishments and Results

To advance nuclear–plasma interaction effects studies, xenon activation studies, and xenon spectroscopy studies in FY16, we (1) were awarded two dedicated National Ignition Facility shot days through a competitive proposal process; (2) fielded a new gas-cell diagnostic on three ride-along shot opportunities (see figure); (3) collected xenon activation data from each ride-along, which provided a baseline for the new diagnostic functionality as well as initial data sets for xenon activation studies; (4) hired and trained a new postdoctoral researcher; (5) made progress on simulation capabilities of nuclear–plasma interaction effects and on xenon spectroscopic output using two radiation-hydrodynamics codes coupled with two atomic physics codes; and (6) used these simulations to produce expected experimental signatures.

Spectrum of gamma rays emitted in the decay of excited meta-stable and unstable ground states produced by the activation of natural xenon (rev. sci. instrum. 87, 11d825 [2016]). activation was accomplished by utilizing the new national ignition facility gas-cell diagnostic, shown (inset) installed on a diagnostic instrument manipulator ready for target chamber installation.
Spectrum of gamma rays emitted in the decay of excited meta-stable and unstable ground states produced by the activation of natural xenon (Rev. Sci. Instrum. 87, 11D825 [2016]). Activation was accomplished by utilizing the new National Ignition Facility gas-cell diagnostic, shown (inset) installed on a diagnostic instrument manipulator ready for target chamber installation.

Publications and Presentations

  • Bleuel, D. L., et al., Method for detection of nuclear–plasma interactions in a 134Xe-doped exploding pusher at the National Ignition Facility. (2015). LLNL-JRNL-674268.
  • Ratkiewicz, A., et al., A new gas cell diagnostic for the National Ignition Facility. High Temperature Plasma Diagnostics Conference, Madison, WI, June 5–9, 2016. LLNL-ABS-684256.
  • Ratkiewicz, A., et al., “A recoverable gas-cell diagnostic for the National Ignition Facility.” Rev. Sci. Instrum. 87, 11D825 (2016). LLNL-JRNL-695435.
  • Ratkieweicz, A., et al, Experimental measurement at the NIF of electron-mediated nuclear plasma Interactions. NIF/JLF Users' Group Meeting, Livermore, CA, Jan. 31–Feb. 3, 2016. LLNL-PRES-681817.