We can't see cells, bacteria, and molecules with the naked eye because the wavelength of visible light is relatively large compared with these objects. Some basic principles: light moves like a wave, and so it only catches objects that fall within the path of the wave. If an object is smaller than the length between of one wave then it gets lost.
X-ray photons and neutrons both have very short wavelengths, so they will scatter off very small objects, like molecules. The angles at which the light scatters are very small – hence the name 'small angle scattering' (SAS); so scientists need powerful machines capable of both producing intense , well collimated forms of light and measuring very small changes in the direction of that light.
The angles may be small, but SAS experiments can uncover huge amounts of information. From determining the shape and density of molecules in a sample, to exploring the behaviour and chemical composition of materials, SAS can reveal a whole lot.
But that’s not all; it’s the samples SAS can study that make it really cool. The technique works well on ‘disordered systems’, where the arrangement of atoms is random. Other techniques involve freezing or modifying samples so that the atoms line up in an ordered way, but SAS doesn’t need much order to produce information.
This makes it very quick and easy to use – SAS doesn’t require much in the way of sample preparation. It also means that it can be used to study some really interesting samples. Liquids, gels, and all sorts of other gooey stuff can all be studied with the technique. From mud to rubber, SAS allows scientists to get stuck in to all sorts of messy samples and still garner valuable structural information.
And if you weren’t yet convinced, SAS has some other really interesting properties. It's usually non-destructive, so samples remain intact. It’s also a great all-rounder; useful in many fields, from archaeology to nanotechnology. And although it produces quite low-resolution images of the samples it targets, SAS can pick up more at once, so it’s perfect for macromolecules or big complex systems. For what it offers in convenience, breadth, and unique insight, there’s no doubt about it: SAS is pretty darn cool.