Everything about Neutron Scattering totally explained
The term
"Neutron Scattering" encompasses all scientific techniques whereby the deflection of
neutron radiation is used as a scientific probe. Neutrons readily interact with atomic nuclei and magnetic fields from unpaired electrons, making a useful probe of both structure and magnetic order. Neutron Scattering falls into two basic categories - elastic and inelastic. Elastic scattering is when a neutron interacts with a nucleus or electronic magnetic field but doesn't leave it in an excited state, meaning the emitted neutron has the same energy as the injected neutron. Scattering processes that involve an energetic excitation or relaxation by the neutron are inelastic: the injected neutron's energy is used or increased to create an excitation or by absorbing the excess energy from a relaxation, and consequently the emitted neutron's energy is reduced or increased respectively.
For several good reasons,
moderated neutrons provide an ideal tool for the study of almost all forms of
condensed matter. Firstly, they're readily produced at a nuclear
research reactor or a
spallation source. Normally in such processes neutrons are however produced with much higher energies than are needed. Therefore
moderators are generally used which slow the neutrons down and therefore produce wavelengths that are comparable to the atomic spacing in solids and liquids, and kinetic energies that are comparable to those of dynamic processes in materials. Moderators can be made from
Aluminium and filled with liquid
hydrogen (for very long wavelength neutrons) or liquid
methane (for shorter wavelength neutrons). Fluxes of 10
7/s - 10
8/s are not atypical in most neutron sources from any given moderator.
The neutrons cause pronounced
interference and
energy transfer effects in scattering experiments. Unlike an
x-ray photon with a similar wavelength, which interacts with the
electron cloud surrounding the
nucleus, neutrons interact with the nucleus itself. Because the neutron is an electrically neutral particle, it's deeply penetrating, and is therefore more able to probe the bulk material. Consequently, it enables the use of a wide range of sample environments that are difficult to use with
synchrotron x-ray sources. It also has the advantage that the cross sections for interaction don't increase with atomic number as they do with radiation from a synchrotron x-ray source. Thus neutrons can be used to analyse materials with low atomic numbers like proteins and surfactants. This can be done at synchrotron sources but very high intensities are needed which may cause the structures to change. Moreover, the nucleus provides a very short range, isotropic potential varying randomly from
isotope to isotope, making it possible to tune the nuclear scattering contrast to suit the experiment:
The neutron has an additional advantage over the x-ray photon in the study of condensed matter. It readily interacts with internal
magnetic fields in the sample. In fact, the strength of the magnetic scattering signal is often very similar to that of the nuclear scattering signal in many materials, which allows the simultaneous exploration of both nuclear and magnetic structure. Because the neutron scattering amplitude can be measured in absolute units, both the structural and magnetic properties as measured by neutrons can be compared quantitatively with the results of other characterisation techniques.
Further Information
Get more info on 'Neutron Scattering'.
|
External Link Exchanges
Do you know how hard it is to get a link from a large encyclopaedia? Well we're different and will prove it. To get a link from us just add the following HTML to your site on a relevant page:
<a href="http://neutron_scattering.totallyexplained.com">Neutron scattering Totally Explained</a>
Then simply click through this link from your web page. Our crawlers will verify your link, extract the title of your web page and instantly add a link back to it. If you like you can remove the words Totally Explained and embed the link in article text.
As long as your link remains in place, we'll keep our link to you right here. Please play fair - our crawlers are watching. Your site must be closely related to this one's topic. Any kind of spamming, dubious practises or removing the link will result in your link from us being dropped and, potentially, your whole site being banned. |
