Neutron Guides

Guides are used to transport the neutrons from the moderator to most of the instrument where the experiment is carried out. The guides are tubes made in a way to totally reflect as many neutrons as possible much like how an optical fiber would transport a beam of light.

In contrast to optical fibers, neutron guides are however often coated with a clever combination of layers of nickel and other materials in order to totally reflect as many neutrons as possible. The layers in the coating are stacked in a way to increase the grazing angle for which the neutrons will be totally transmitted. Nevertheless, the angle of total reflection is usually below a degree (except for very low-energy neutrons) which means that even in guides, many neutrons are lost which have larger incoming angles than a fraction of a degree when they hit the guide wall.

A schematic view of an elliptical neutron guide. The illustration shows that the guide can be from 1 to 100 meters long and that the width between the guides is approximately 3 cm. Blue arrows show an example of the grazing angle for which the neutrons will be totally transmitted.

Figure. A schematic view of an elliptical neutron guide.