Three Axis instrument for Low Energy Spectrometry

Schematic side view (top) and horizontal cut (bottom) of the primary spectrometer and parts of the experimental zone

The H53 super-mirror (m=3) guide transports the neutrons from the horizontal cold source to the monochromator. The final 3m section (1) is interchangeable between a straight guide and an elliptically tapered, focusing, section.

A velocity selector (2) acts as broad band energy filter on the incoming neutron spectra for suppressing higher order contamination and lowering the general neutron background in the experimental zone. It is followed by the Virtual Source, a heavy slit with horizontal variable aperture (3).

The monochromator stage (4) consists of the three monochromators PG-002, Si-111 and Heusler (for polarization analysis) with the respective positioning mechanics. Due to the large transported divergence the neutron beam at this level has a section of ≈ 25 x 20 cm2, which is focused on the sample position in the following, respecting Rowland geometry for horizontal (monochromatic) focusing.

The entire shielding of the primary spectrometer is non-magnetic for avoiding attracting forces due to stray fields of magnets used on the sample table. It consists of sandwiches of poly-ethylene, Pb and B4C rubbers.