Helmholtz Zentrum Berlin


hzbNEAT • The Path of the Neutron

What NEAT sees best

authored a year ago:

NEAT gets sun glasses: the polarisation option

Many sun glass manufacturers promote their products by mentioning polarisation. Those products are supposed to reduce reflections. They are able to do so by filtering cross-polarised photons which occur when light is reflected on glossy surfaces. But what do these sun glasses and the NEAT upgrade have in common?

The NEAT scientists also want to make use of polarisation. But neutrons don’t have any polarisation, do they? The polarisation of photons is determined by the orientation of their electric field. Of course, neutrons lack of such an electric field but they own another interesting property: the spin. The spin is a quantum mechanical property. It can be measured separatly in each dimension of space (often described as x-, y- and z-coordinates) and will either be up or down but nothing in between. Ramil and his colleagues now want to use this behaviour to investigate their materials. So they will put an analyser (in fact, a filter for specific spin orientations) just behind the sample. This analyser is a very special kind of helium. We know that helium reacts with neutrons (this is crucial to detect them). But the scientists are able to prepare the helium to let it pass neutrons of a specific spin orientation in one dimension. This is achieved by using the spin of the helium and quantum mechanical selection rules. Eventually, the analyser is doing the same job as the polarised sun glasses.

Neutron scattering is the standard procedure to investigate magnetic properties and the spin plays an important role in these magnetic landscapes; “a three-dimensional mapping of scattered polarised neutrons” as Ramil described it. By adding spin analyses to the toolbox, the NEAT can recover even more secrets from the depth of the materials because it provides additional information of the interaction of neutrons and matter.