There’s no substitute for using the right tool for the job at hand. Using low-energy radiation sources simply isn’t suitable for certain tasks: equipment used in cancer treatment requires a strong, monochromatic source of radiation to produce hard X-rays. Other similar radiation sources find applications in nuclear waste processing. To design devices that steadily emit a specific type of radiation, physicists use a special kind of crystal, referred to as a crystalline undulator. In a recent study published inEPJ D, a team has demonstrated the ability to control radiation emissions from a particle travelling through such a device. Tobias Wistisen from Aarhus University, Denmark, and colleagues have shown how to manipulate the emitted radiation by selecting a combination of incoming particle charge and energy, oscillation amplitude and period of the undulator’s crystalline lattice.