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The Fundamental Neutron Physics Beamline is the 13th beamline at the Spallation Neutron Source (SNS) in Oak Ridge, TN.

Upstream of the choppers, a monochronomater, once installed, will be used to select 8.9A neutrons for the UCN beamline (13A), while the rest of the neutrons (that aren't stopped by the choppers) will proceed down the cold neutron guide to 13B. NPDGamma will be installed on the cold beamline (13B).



The FNPB (13b) has housing to potentially hold 4 choppers at 5.5m, 7.5m, 9m, and 10.5m. Current plans are to install 2 during the August 2008 shutdown (done - at 5.5m and 7.5m).

The choppers are first subjected to 72 hours of testing (running at 60Hz as well as frequencies slighter smaller and larger, as TVA doesn't consistently supply electricity at 60Hz).

The choppers can be seen here while undergoing tests in the chopper lab.


A monochromator will be installed to select 8.9A neutrons for the nEDM experiment.

Secondary Shutter

The secondary shutter was installed in early 2008.

Neutron Flux

The Flux on the FnPB was measured several times and with different detectors, due to initial inconsistencies and strange behavior at anything but low power.

Most Recent Status Update(September 9th, 2008)

For more (old and new) beamline pictures, check Beamline Images.

IRR -- September 5th, 2008

  • Minimal prestarts, mostly paperwork and additional shielding
    • Hope is to finish the prestarts by Sep 10th, get permission to open primary shutter by end of the day on Sep 11th.
    • Current plan (September 10th) - Open the Shutter at noon on September 12th.

The beamline is currently under vacuum.

Sept. 5 2008

Recent Tasks and pictures:

  • Chopper installation - complete (see: pictures)
  • Labyrinth walls - done
  • Beam stop (see: pictures)
  • 6Li Plate - done
  • In shield cabling - done
  • PPS installation - done
  • Roof Blocks (check out the molds)
  • Secondary Shutter - to be tested again with the actual control computer - done and works!
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