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About Target 4 Flight Path 15L (Chi-Nu)

This flight path is primarily used for the Chi-Nu experiments at 22 meters and neutron detector development and calibration at 90 meters.


  • Instrument Science
  • Keegan Kelly
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  • Instrument Assistant
  • Matt Devlin
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Target 4 Flight Path 15L (Chi-Nu)

The Chi-Nu experimental area is centered 21.50 m from the spallation target. It has two arrays of neutron detectors which alternately can be placed in the cave around a target, and are used to detect neutrons produced at the Chi-Nu target position. These arrays are used primarily for detecting prompt fission neutrons or neutrons from elastic or inelastic scattering. For produced neutrons above about 500 keV, an array of up to 54 liquid scintillation neutron detectors is used. For neutrons from 10 keV to about 2 MeV, an array of 22 Li-glass detectors is used. Fig. 1 has a picture of both arrays, with the liquid scintillator array around the target position.

In order to minimize room return of neutrons to detectors near the target position, the 22 m cave has a “false-floor,” such that the concrete floor is 2 m below the false floor, and the cave walls are also well removed from the target position. The effects of neutron scattering in the experimental equipment and the room are now well understood through Monte Carlo simulations.

Chi-Nu photo

Fig. 1 – The array of 54 neutron detectors using liquid scintillators (foreground around the target position), and a parallel-plate avalanche counter in the target position for detecting fission events. The array of Li-glass detectors is behind and above the other detectors, in storage on top of the beamline shielding.

The 90-meter station is used primarily for neutron detector development and calibration, both for high energy neutrons with beam. The long flight path is ideal for developing detectors for neutrons with energies above 10 MeV, for which the resolution in time-of-flight, and hence incident neutron energy, is improved with the long flightpath. Beams up to about 10 cm or as small as 2 mm in diameter are routinely used.