The New NG-7

The new NG-7 will be a straight 50 mm x 120 mm guide, similar to the previous version.  However, the upstream guide components will be coated with m = 2 supermirror rather than ⁵⁸Ni, which will provide a factor of 2+ improvement in data rate for all instruments on the guide.

The new NG-7 will support 5 instruments, the \(\alpha\)-\(\gamma\) high accuracy neutron fluence instrument, 2 neutron interferometry instruments, the PHADES test station, and a 30 m SANS instrument. We plan to have these instruments begin to return to scientific operation around late 2026, starting with the 30 m SANS.  The relocation of \(\alpha\)-\(\gamma\) (formerly located on NG-6), will increase the data rate on that instrument by a factor of 3, and will facilitate upgrade paths for both that instrument and the NG-6 Cold Neutron Imaging Station.   \(\alpha\)-\(\gamma\)  will occupy the space previously held by NG7 horizontal sample reflectometer, which was recently decommissioned after an exceptionally productive 30+ year run.  The NCNR will maintain horizontal surface reflectometry capabilities by running the MAGIk instrument in “Horizontal Sample Mode.” 

Alpha-Gamma 2.0

The \(\alpha\)-\(\gamma\) instrument relies on a totally absorbing neutron detector and has been used to measure the absolute neutron fluence of a cold, monoenergetic neutron beam to a precision that is five times better than the previous state of the art.  In conjunction with a weakly absorbing neutron detector known as the flux monitor, it is used to measure the neutron fluence in a beam-based measurement of the neutron lifetime, in precise measurements of key neutron absorption cross sections (notably in Li, B, and ²³⁵U(n,f)), and as part of an effort to recalibrate the US national radioactive neutron source NBS-1.

Building on the success with this program and considering the continuing need for neutron metrology with even smaller uncertainties, a design for a new pair of instruments is underway (version 2.0). The new devices are depicted in the figure below.  They are considerably larger than the current instrument in order to accommodate a larger neutron beam.  In addition, they feature a larger number of gamma-ray and solid-state detectors in order to increase solid angle while simultaneously reducing certain geometry-based systematic errors.  Finally, several features are incorporated to simplify and render safer the routine operation of these delicate devices.  This is important for our eventual goal of operating these devices as a service for interested outside users.