Neutron Diagnostics on MegaJoule Neutron Imager for Radiography

Neutron diagnostics are used to support the development of a neutron imager and deuterium-based neutron source at the Lawrence Livermore National Laboratory MegaJOuLe Neutron Imaging Radiography (MJOLNIR)
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Dense Plasma Focus (DPF) experiment. The MJOLNIR DPF produces z-pinch like plasma column that generates short (~10s of ns), high-yield (several 10
¹¹
) neutron pulse. Neutrons originate from a combination of thermonuclear and beam-target fusion interactions, leading to a forward directed neutron source. Additionally, electron beams formed during the z-pinch produce bremsstrahlung radiation. The neutron yield is measured with beryllium, yttrium, and bromide activation. Plastic scintillators coupled with photomultiplier tubes or photo diodes with well-characterized delay times and resolutions measure the neutron and x-ray radiation signal emitted from the DPF as a function of time. These detectors are placed at different distances and angles to characterize the anisotropic x-ray and neutron emissions from the DPF. The neutron energy can be inferred from the time difference between the arrival time of x-ray and neutron signals, assuming the x-rays and neutrons are emitted in the same event. As device parameters such as pressure, voltage, and dopant gas composition are varied changes in the source characteristics are observed.