When x-rays ‘shine’ through a crystal and are ‘photographed’ on the other side they leave a pattern which contains information on the crystal structure not dissimilar to how a shadow contains information on what exactly it was that blocked the light.
However, for various reasons, deciphering the crystal structure from the x-ray pattern is a difficult task (although made easier in recent years as computing power increases) that requires a great deal of physics and mathematics to solve.
One tool in the solution is a mathematical formula called the Patterson Function. At 11am this coming Tuesday – Halloween in America – I will be giving/taking my oral exam and my topic is “Patterson Methods and Crystal Structure Determination”. I will present a 45 minute talk on the Patterson Function and it’s various uses in crystallography, and will be quizzed on the topic by a comittee of three faculty members. I’m not particularly concerned – I have spent about 2 months preparing – but since some of the mathematics is tricky I hope certain questions may not be asked!