An alpha particle is a small but heavy fragment of an atomic nucleus. It doesn't travel far, but it hits hard: it leaves a dense trail of damage, like a bullet piercing a target. That's why alpha radiation is used in medicine to precisely destroy cancer cells. But how a cell responds to such a hit depends on the particle's energy, how many arrive and how quickly, and where they land. Previously, studying this was difficult: particles quickly lose energy in air, and controlling them was poor.

The new setup solves this problem. The alpha source is placed in a vacuum chamber, where there's nothing to collide with along the way. The distance from the source to the target can be varied from 57 to 381 mm, which allows the particle flux to be changed by a factor of 100. The energy can be attenuated by placing absorbing layers in the path, from zero to 4.6 MeV. The target is mounted on a movable stage that follows a programmed path: you can draw a stripe, a grid, or any shape with particles. The exposure time is controlled by a shutter with an accuracy of 0.3 seconds.

Such precision opens the way to systematic experiments. You can vary the energy independently, the delivery rate independently, and the irradiation pattern independently. This is important for improving targeted alpha therapy, where radioactive atoms are delivered directly to the tumor. And for radiation protection: we will better understand which doses and regimes are safe and which are not.