Finally, physicists have a way to ‘see’ inside short-lived nuclei Premium

Physicists have developed a femtoscope that can probe the structure of short-lived atomic nuclei using electron scattering. A set-up reported in a new study at RIKEN produced caesium-137 ions, moved them to a system SCRIT that organises the ions as a target, and then smashed electrons into them. The resulting interference patterns were recorded by a magnetic spectrometer.

Around 150 years ago, three scientists named Ernest Rutherford, Hans Geiger, and Ernest Marsden exposed a thin gold foil to radiation. Based on how the rays were deflected by atoms in the foil, they figured out that every atom has a dense centre where its mass and positive charge are concentrated.

Seventy years ago, Robert Hofstadter led a team that bombarded electrons at thin foils. The higher energy of the electrons allowed them to ‘probe’ the nucleus. Based on these interactions, the team understood how charges and magnetic fields were arranged inside a nucleus.

In each case, physicists were able to ‘see’ inside stable atoms, and then inside their nuclei, by using other particles.

Now, researchers in the RIKEN Nishina Center for Accelerator-Based Science, in Japan, have taken a big leap forward in this tradition – by demonstrating a set-up that can use electron scattering to ‘see’ inside unstable nuclei, including those that don’t occur naturally.

The previous experiments used thin foils that were easy to hold. The new one is more sophisticated, using an apparatus to hold the nuclei of caesium-137 atoms as well as make sure electrons could interact with them, using a system called SCRIT. The wait for this advancement is why a similar study couldn’t be conducted before.

The results were published in the journal Physical Review Letters on August 30.

First, the researchers accelerated electrons in a particle accelerator to energise them, and then smashed them into a block of uranium carbide. This produced a stream of caesium-137 ions (atoms stripped of electrons). This isotope of caesium has a half-life of around 30 years.