First measurements of the absolute neutron spectrum using the Magnetic Recoil Spectrometer (MRS) at OMEGA

A new type of neutron spectrometer, called a Magnetic Recoil Spectrometer (MRS) has been built and activated at OMEGA, and currently being developed at the National Ignition Facility (NIF), for measurements of the absolute neutron spectrum in the range 6 to 30 MeV, from which ¿R, Ti and yield can be determined. From the down-scattered neutrons in the range 6- 0 MeV, a ¿R can be inferred. From the tertiary spectrum (>20 MeV), a second determination of the ¿R can be inferred for high-yield implosions, which can be compared directly to the down-scattered neutron inferred ¿R. Having such self-consistency check could prove immensely important for NIF fizzles that are on the threshold to ignite. In addition, absolute yield and a highly resolved 14-MeV primary neutron spectrum can be measured. This allows for measurements of Ti and, possibly more interestingly, non-thermal features, deviations from a single temperature and the effect of alpha-particle heating that might give an insight into the nature of a failed ignition-capsule implosions. In this talk, the results from the first measurements of the absolute spectrum of the down-scattered and primary neutrons at OMEGA will be presented.