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Weapons Neutron Research Flight Paths

The Weapons Neutron Research Facility (WNR) provides neutron and proton beams, and detector arrays for basic, applied, industrial, and defense-related research.


  • LANSCE Weapons Physics Group Leader (acting)
  • Paul Koehler
  • (505) 606-0743

Overview of Flight Paths

Each flight path’s name identifies the target and the direction of the flight path (FP) with respect to the proton beam. For example, 4FP15R is a FP (flight path) that starts at Target 4 and is 15 degrees to the right (15R) of the incoming proton beam. The beams are transmitted at three different vertical levels: Target 4, Target 2, and Lujan Center (Target 1).

flight paths diagram

The layout of the flight paths at the LANSCE neutron sources.

flight paths diagram

A schematic drawing of the Target-2 and Target-4 flight paths.

The flight paths and the major research program that are on each flight path are briefly described below, and described in more detail by clicking on the individual flight path.

Target 4 Flight Paths

For the Target 4 flight paths, the neutron spectrum depends on the angle of the flight path with respect to the proton beam.

flight paths diagram

The calculated neutron spectra for various flight paths at Target 4.

As seen in this plot, the most forward angle flight paths at 15 degrees have the most intensity at high energy and somewhat lower intensity at lower neutron energy. The more backward angle flight paths at 90 degrees have significantly lower intensity at high energy and more intensity at lower energies. The flight paths at 30 and 60 degrees fit between those extremes. The shape of the neutron spectrum at the different flight path angles must be considered when choosing a flight path for a particular experiment.

  • 4FP90L is the location of the Time Projection Chamber (TPC) that is used to measure fission cross sections to high precision.
  • 4FP30L has two experimental stations. The first station (ICE House) is approximately 20 m from the production target and is used by industry, universities, and other national laboratories to measure neutron-induced failures in semiconductor devices.
  • 4FP15L is unique among the WNR flight paths in that it has two experimental locations available at distances of 22 and 90 meters from the spallation target. It is primarily used for the Chi-Nu experiments at 22 meters and neutron detector development and calibration at 90 meters.
  • 4FP15R is being used to study few-body nuclear physics. The current experiment involves measuring the n-p capture cross section, which is important for understanding big bang nucleosynthesis.
  • 4FP30R or ICE II, is primarily used by industry, universities, and other national laboratories to measure neutron-induced failures in semiconductor devices.
  • 4FP60R is the location of the GEANIE spectrometer which consists of 26 Compton-suppressed, high-resolution germanium γ-ray detectors at a distance of 20-m. The GEANIE instrument is used to address issues of nuclear structure, spectroscopy, and cross-section measurements for both stockpile stewardship, nuclear technology, and basic science.

Target 2 (Blue Room)

  • Target 2 is used for proton beam irradiation experiments. Beam is available directly from the linac or from the proton storage ring (PSR). Present and past experiments include:
  • A Lead Slowing-Down Spectrometer (LSDS) for measuring cross sections with ultra-small samples.
  • PSR pulse-on-demand beam to study the shock induced by the incident beam on a liquid-mercury target for the ORNL Spallation Neutron Source (SNS).
  • Pulsed beam experiments to simulate intense neutron environments for semiconductor certification.
  • Proton irradiation of detectors and component testing for the Large Hadron Collider at CERN.

Lujan Center Flight Paths

  • FP5 is a general purpose flight path that is currently being used for low-energy fission cross sections and neutron radiography. It has two detector areas: one at approximately 10 m in ER-1 and the second at a distance of 60 m that is reached from the Target 4 yard.
  • FP14 is the location of the Detector for Advanced Neutron Capture Experiments (DANCE). It consists of a 4-π array of BaF2 scintillators. It was designed for neutron capture measurements on sub-milligram and radioactive samples. These measurements support radchem measurements for Defense Programs, cross section measurements for the Advanced Fuel Cycle Initiative, and basic nuclear astrophysics.
  • FP12 is currently used by the SPIDER spectrometer to measure fission fragment yields. FP12 has a neutron guide which can be used for fundamental neutron physics experiments such as developing a new ultra-cold neutron source using solid oxygen.