Athena: A Unique Radiation Environment Platform At The National Ignition Facility

This paper describes the ATHENA platform, an energy tuning assembly, which was developed to spectrally shape the National Ignition Facility (NIF) deuterium-tritium fusion neutron source to a thermonuclear (fusion) plus prompt fission neutron spectrum with a capability to act as a short-pulse neutron source. This unique, otherwise inaccessible radiation environment complements existing experimental facilities and capabilities. The flexible ATHENA irradiation positions were modeled using an ensemble of Monte Carlo simulations with stochastic sampling of the nuclear cross-sections to characterize the radiation environments and uncertainty for the platform. Validation of the internal neutron spectrum produced from fielding ATHENA at NIF occurred through neutron flux unfolding with 20 measured activation products. The STAYSL unfolded neutron flux resulted in a reduced chi(2) value of 1.4 with a larger contribution from Ti-46(n,2n) reaction channel. The total ionizing dose was measured to be 515 +/- 7.9% rad(TLD-400), whereas the modeled values indicated a lower value of 290 +/- 4.6% rad(TLD-400). The NIF experiment demonstrated that ATHENA is capable of producing a thermonuclear and prompt fission neutron spectrum with a 50 nanosecond pulse width and a 1-MeV equivalent neutron fluence of 3.6 x 10(12) n/cm(2) with strong radial uniformity over the sample volume. Example case studies of ATHENA for integral experiments and microelectronic device responses are also presented.