Study of Organic Scintillators for Neutron Imaging

Summary form only given. The possibility of obtaining gated images of a burning inertial confinement fusion (ICF) target with low background signals have renewed interest in neutron imaging as an ICF diagnostic. Using neutron time of flight (nTOF) techniques combined with a coded aperture, the burning core (hot spot) of the target can be imaged recording the 14 MeV neutrons, while the down-scattered, 10 to 6 MeV neutrons, yield an image of the surrounding cold fuel. The diagnostic's effectiveness in recording a useful image depends on the choice of scintillator. The optimal scintillator should have a prompt response that is fast enough to follow the width of the 14.1 MeV neutron peak, a fast and thorough decay to reduce the induced background or "afterglow" in the down-scattered images, and high sensitivity throughout the energy range of interest. The available data usually is restricted to the prompt response time, and includes only a portion of the scintillation decay. Six commercially available organic scintillators (plastic and liquid) have been studied as candidates for use in a neutron imaging diagnostic prototype under development at LLNL. The scintillator light emission decay spectra have been recorded for 14.1 and 2.5 MeV neutrons both in 100 and 1000 ns windows. Additional spectra were recorded using band pass filters in a search for fast components of the emitted light. The absolute photon gain (photons/interaction) of the samples has been computed at both energies. Results will be presented for several commercially available candidate scintillators.