Gated liquid scintillator detector for neutron time of flight measurements in a gas-puff Z-pinch experiment.

ABSTRACT

Detection of secondary D(t, n)4He neutrons produced when thin argon or krypton gas shells implode on a deuterium gas target is a very challenging task because the secondary neutron yield is a small fraction of the primary neutron yield and because the implosion is often accompanied by an intense hard X-ray burst. We built a large volume neutron time of flight (nTOF) detector using liquid scintillator (xylene solvent with small quantities of wavelength shifting PPO + bis-MSB fluors) in an attempt to increase the detection probability for secondary neutrons in our staged Z-pinch experiments at the 1 MA Zebra pulsed-power generator. Two fast, gated microchannel plate photomultiplier tubes detect the light created in 21 liters of liquid. The hard X-rays were successfully suppressed in the recorded nTOF traces, but we found no evidence of secondary neutrons. The signal quality from the primary D(d, n)3He neutrons was higher compared to the signal quality from a plastic scintillator nTOF, thus providing a more reliable estimate of the deuterium ion temperature at the pinch stagnation time. Cross-calibration with a silver activation detector enables standalone neutron yield measurement.