When the X-ray beam
is turned on, X-rays hit the crystal. A pattern of spots
is made on the screen at the other side. The pattern
shows where the X-rays hit particles inside the crystal.
This is called a diffraction pattern. Some spots are
darker than others. Very complicated mathematics called
Fourier transformation is done using a computer to change
the spot pattern into a picture showing how the particles
in the crystal are arranged. A father and son team,
both called William Bragg, invented X-ray crystallography
in 1912 (to tell them apart, their second names are
used – the father was called William Henry and the son
William Lawrence). At the time, all the calculations
were done by hand – so not surprisingly they won a Nobel
prize in 1915 for their hard work. The method has been
used to solve the structures of many important molecules.
In the 1950s Francis Crick and James Watson used pictures
of DNA taken by Rosalind Franklin to solve the DNA structure.
Dorothy Hodgkin worked out the structures of the antibiotic
penicillin (in 1946), vitamin B12 (in 1956) and insulin
(in 1969), winning a Nobel prize in 1964. Now, crystallographers
work on molecules the inventors had not even heard of!