No particle accelerator in the world is strong enough to create a usable beam of uranium ions. But that will change next month, when Japan switches on a huge facility of connected accelerators, to produce the world's most powerful beams of heavy radioactive isotopes.

Radioisotopes are forms of elements that are unstable because they contain either more or fewer neutrons than usual, and so undergo radioactive decay. Nuclear physicists are studying rare short-lived isotopes to understand their properties and how they are formed. The RIKEN research institute in Saitama, Japan, already has accelerators that can create the world's strongest radioisotope beams, but even these are only powerful enough to produce usable beams for the lighter elements.

Scientists will be able to study nuclear isotopes that exist only in the hottest stars.

But next month, RIKEN will switch on a major upgrade. The ¥44-billion (US$378 million) Radioactive Isotope Beam Factory will add two more ring cyclotrons and the world's first superconducting ring cyclotron to the existing linear accelerator and ring cyclotron. It will then be able to accelerate beams of any element up to uranium at 70% of the speed of light. The accelerated beams are smashed into a target such as beryllium to knock out neutrons and protons and create the desired radioisotopes.

The facility should open a new realm of astrophysics. “With this new facility, scientists at RIKEN have the opportunity to study nuclear isotopes that exist only in the hottest stars of the Universe,” says John Schiffer, a senior scientist at the Argonne National Laboratory in Chicago, Illinois.

As well as exploring the formation of uranium, RIKEN plans to measure the properties of various very short-lived nuclei, as well as looking for 'magic numbers' of neutrons and protons that allow heavy nuclei to be surprisingly stable. These experiments will start from next year, with full operation scheduled for 2011. The facility makes Japan the world leader in the field, says Ysushige Yano, director of the RIKEN Nishina centre for accelerator-based science, adding that Japan's other big physics facilities have just been upgrades of US and European versions. “But this time it is different,” he boasts. “This time, Japanese scientists are leading the way.”

Rivals aim not to let Japan savour its victory for long. A US plan for a superconducting linear accelerator called the Rare Isotope Accelerator has stalled, at a proposed cost of $1 billion. But France is expected to complete construction of its new radioisotope facilities, including experiments, by around 2012 and Germany by 2014. “In five or six years, Japan may lose the number one position,” says Sydney Gales, director of the French heavy-ion accelerator GANIL in Caen.