Studying the world’s rarest substance in the hope of improving cancer treatment

Astatine is an element that can be used to treat cancer, but is very hard to study. Researchers from the University of Gothenburg and CERN will now work together, using pioneering methods in an attempt to map astatine.

The radioactive element astatine is the world’s rarest substance. It occurs in very small quantities in nature, since it quickly decays into other substances – its half-life is just seven hours. However, the short half-life and the fact that it decays by emitting an alpha particle make it suitable for treating cancer.

SINCE ASTATINE IS so rare in nature, researchers must first create it in order to study it. And to have time to study it. CERN researcher Sebastian Rothe is one of those who has succeeded in doing so. He has managed to measure the amount of energy required in order to create a positive astatine ion, known as the ionisation potential. He met Dag Hanstorp, a professor of physics at the University of Gothenburg who researches negative ions, at an international conference. They decided to work together to study negative astatine ions.

SEBASTIAN IS SPENDING a few weeks visiting Gothenburg, to ensure – as he puts it – that “everything is going to plan”. The plan involves obtaining access during the year to ISOLDE, a facility at CERN where every imaginable element can be created via core reactions, in order to produce and study negatively charged astatine ions.
“We hope to be able to carry out an initial test at CERN in July,” he says.

SINCE IT IS NOT possible to test the experiment in Gothenburg using the unstable substance, the research team is using the closely related element iodine instead. Like astatine, iodine is a halogen and has similar properties. In order to study atoms and molecules, light is used in atomic physics. Laser light, to be precise, which – in contrast to white light – consists of a single colour from the light spectrum. By setting the exact wavelength in the lab, researchers can see which wavelength is required in order to get an electron to accept light and jump up a shell. The light that has been sent in is thereby changed, giving a new colour.
“Which colours are absorbed?” asks Dag. “What light is required? By using lasers, we can find out various things about atoms and molecules.”

THIS IS THE MOST sensitive method of measurement available for studying negative ions. Researchers can use light to find out more about a particular substance, and they can also track the substance since the behaviour of many substances is already known. By combining theoretical physics and experiments, they can then build up models for the appearance of atoms. Negative ions – Professor Hanstorp’s specialist area – are atoms or molecules with an extra electron.
“Negative ions are particularly hard to model, as the electrons must share the attraction from the core. For example, the two electrons in the negative hydrogen ion must, to a certain extent, be on opposite

FACTS

The alpha particle is a helium core that is emitted on radioactive decay of certain heavy atom cores. Alpha radiation – the radiation that consists of alpha particles – can cause biological damage and is therefore used to kill cancer cells.

Astatine is used in targeted alpha therapy (TAT), whereby cancer patients are treated with alpha particle radiating nuclides. The method is already being used in clinical studies, including at Sahlgrenska University Hospital in Gothenburg, where women with ovarian cancer can be treated.