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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 Scientist
  • Matt Devlin
  • (505) 665-0421
  • Instrument Assistant
  • Hye Young Lee
  • (505) 665-7252

Target 4 Flight Path 15L (Chi-Nu)

The Chi-Nu experimental area is centered 22.50 meters from the spallation target. It has two arrays of neutron detectors which are not usually used concurrently. 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 (Fig. 1).

Chi Nu Detector

Fig. 1 – The array of 54 neutron detectors using liquid scintillators now in construction.

For lower energy neutrons, below about 1 MeV, an array of 20 6Li-glass detectors is used (Fig. 2)

Chi Nu Detector

Fig. 2. – Partial array of 6Li-glass detectors looking at a fission chamber.

The 90-meter station is used primarily for neutron detector development and calibration, both for high energy neutrons with beam and for fission-spectrum neutrons with a 252Cf spontaneous fission neutron source. With beam, the long flight path is ideal for developing detectors for neutrons with energies above 10 MeV. Beams up to about 10 cm or as small as 2 mm in diameter are routinely used. The 252Cf source, with approximately 5E5 fissions per second is in a standard Oak Ridge fission ion chamber that can produce a fast (1ns) start pulse for time-of-flight experiments (Fig. 3). Effects of neutron scattering in the room are now well understood through Monte Carlo simulations.

Chi Nu Detector

Fig. 3. – 252Cf fission source used to calibrate and characterize detectors. (top panel) Fast signal from the fission chamber; (bottom panel) 252Cf fission source set up in the 90-meter station for calibrating a neutron detector.