He Resonance in the TT Neutron Spectrum*

An understanding of the TT neutron spectrum is necessary for accurate modeling of neutron spectra as well as for analysis of experimental data from ICF implosions. The ⁵He resonance is an important component of the TT spectrum. Available OMEGA data suitable to study the ⁵He state include neutron time-of-flight spectra collected at three different ion temperatures. ¹ These data are used in a multi-step least-squares analysis that models the resonance line shape for the individual reaction branches involved in TT fusion including ⁵He (ground state) + n and ⁵He* (first excited state) + n. This analysis reveals a first excited state at ~2 MeV (Ref. 2) in ⁵He. The shape of the ⁵He resonance changes with ion temperature as expected and the width of each state is used to determine its lifetime.

 ¹ M. Gatu Johnson et al., “First Experimental Evidence of a Variant Neutron Spectrum from the T(T,2n)α Reaction at Center-of-Mass Energies in the Range of 16–50 keV,” submitted to Physical Review Letters.

² C. Wong, J. D. Anderson, and J. W. McClure, Nucl. Phys. 71, 106 (1965).