Particle accelerators do more than just particle physics research. Suzie Sö’t take long for the destructive power of these rays to be turned to medicinal benefit. X-rays kill cancer cells through ionization. By stripping electrons from water molecules, the X-ray photons leave a highly chemically reactive wake. The reactive water molecules bind to, and destroy, DNA. But X-ray beams don’t differentiate between healthy and cancerous cells, so their destructive force is hard to localize to the problem zones alone. One option is to use protons, rather than X-ray photons. Particle accelerators can take protons from inside a Hydrogen atom, form them into high energy beams and more specifically target a tumour. However, instead of passing through the body like X-ray photons, the protons stop at the tumour, thanks to a phenomenon called the ‘Bragg peak’. By tuning the energy of a proton beam, the dose can be much more carefully controlled. This video is supported by the Science and Technology Facilities Council. Watch the rest in this series here: https://www.youtube.com/playlist?list=PLbnrZHfNEDZx0mVe9wGxg5kyKdofRJJ7m The Ri is on Twitter: http://twitter.com/ri_science and Facebook: http://www.facebook.com/royalinstitution and Tumblr: http://ri-science.tumblr.com/ Our editorial policy: http://www.rigb.org/home/editorial-policy Subscribe for the latest science videos: http://bit.ly/RiNewsletter