Experimental evidence of a variant neutron spectrum from the T(T,2n)alpha reaction at center-of-mass energies in the range of 16-50 keV

Full calculations of six-nucleon reactions with a three-body final state have been elusive and a long-standing issue. We present neutron spectra from the T(t,2n)alpha (TT) reaction measured in inertial confinement fusion experiments at the OMEGA laser facility at ion temperatures from 4 to 18 keV, corresponding to center-of-mass energies (Ec.m.) from 16 to 50 keV. A clear difference in the shape of the TT-neutron spectrum is observed between the two Ec.m., with the 5He ground state resonant peak at 8.6 MeV being significantly stronger at the higher than at the lower energy. The data provides the first conclusive evidence of a variant TT-neutron spectrum in this Ec.m. range. In contrast to earlier available data, this indicates a reaction mechanism that must involve resonances and/or higher angular momenta than L=0. This finding provides an important experimental constraint on theoretical efforts that explore this and complementary six-nucleon systems, such as the solar 3He(3He,2p)alpha reaction.