ISOLDE historic photos
ISOLDE historic photos (Image: CERN)

It turns out no one knows what the DE at the end of CERN’s ISOLDE facility stands for. “Damned expensive?” chuckles Björn Jonson, who has just charmed me with his experiences of serving on the Nobel committee, as I sit in awe opposite him in the CERN canteen.

ISOLDE celebrates 50 years of physics on 16 October 2017. On this day, half a century ago, the first beams were run through the ISOLDE experiment, and CERN's longest running experimental facility began its life. To document this achievement, we've made a short documentary series. Watch the first part, on the experiment's history here.(Video: Christoph Madsen/CERN)

The first four letters of CERN’s longest-running experiment site, ISOLDE, which celebrates 50 years of physics today, stand for Isotope mass Separator On-Line. As one of the first students to work on the project, I assumed that Jonson could reveal the truth about the last two letters of the acronym but, when pushed, he teases: “or it might stand for Danish Engineering, which is, of course, the best.”

Jonson joined ISOLDE in 1967, when the facility had yet to become a facility and was still just a single experiment. But ISOLDE’s extraordinary history began 17 years earlier, when two physicists in Copenhagen, Otto Kofoed-Hansen and Karl-Ove Nielson, had an idea.

nuclear spectroscopy,ISOLDE,SC

Björn Jonson started working at ISOLDE in 1967 as a fellow. Three years later he got a staff position and moved his wife and three daughters to Switzerland from Sweden in his brand new Volvo. This picture was taken five years later, in 1975, just before he became leader of the ISOLDE facility. Jonson is sitting at the console setting up surface barrier detectors for the study of a beta-decay particle emission. Winfried Grüter stands on the right.

(Image: CERN)

The pair wanted to learn more about the atoms that make up every piece of matter in our Universe, by studying the properties of the nucleus at their centre. They wanted to study a type of radioactive decay that some of these nuclei undergo, called Beta decay, but their own equipment was unable to separate out the interesting nuclei from the others fast enough.

In 1960, a proposal was made to use CERN’s Synchrocyclotron (the SC) accelerator to produce a high-intensity proton beam that could be directed into specially developed targets to yield lots of different atomic fragments. Different devices could then be used to ionise, extract and separate these different nuclei according to their mass, forming a low-energy beam that could then be delivered to various experimental stations. Thus, the idea of “ISOLDE”, the Isotope Separator On-Line DEvice was born.

Curious legacy

Each year, ISOLDE scientists use the facility to push the boundaries of the nuclear chart. By discovering and expanding what we know about ever more exotic nuclei, they are answering fundamental questions about our world, while also helping society by applying this knowledge to real life.


Helge Ravn (right) was put in charge by the then Director-General, Carlo Rubbia, of moving the ISOLDE facility from the SC to the new PSB.(Image: CERN)

Although CERN’s name is the European Organization for Nuclear Research, it’s now better known for collliding high-energy beams of protons to produce and study sub-atomic particles, like the Higgs boson. But despite the trend across the rest of the Laboratory towards particle physics, at ISOLDE the focus has remained on nuclear physics, where a low-energy proton beam (of 1.4 GeV) isused to produce and study exotic radioactive nuclei.

“Curie was an inspiration, she drew so many women into a career of nuclear physics and chemistry that now ISOLDE has one of the best ratios of female scientists”
– Helge Ravn, Technical Group Leader from 1971 to 2000

“What we do at ISOLDE is directly in line with what Madame Curie did,” says Helge Ravn. As a student in CERN’s nuclear chemistry group before the ISOLDE experiment was built, his fascination with the subject shines through. “Curie was an inspiration, she drew so many women into a career of nuclear physics and chemistry that now ISOLDE has one of the best ratios of female scientists. It’s pioneering diversity at CERN and in science,” explains Ravn.

ISOLDE,Experiments and Tracks

In 1991, the Synchrocyclotron was shut down, and ISOLDE had to move to a new location and be connected to the new Proton Synchrotron Booster in order to continue. The new facility was built (you can see the work here) in record time, to prevent disruption to the physics community as much as possible. (Image: CERN)

The research undertaken, originally by Marie Curie and now continued by the scientists at ISOLDE, is not just helping to redress the gender balance but also contributing to treating cancer with radiation, teaching us about the stars, and even helping to make computers faster.

Narrow escape

Despite ISOLDE’s reputation and achievements, it almost came to a sudden death, when the decision was finally made to shut down the ageing, analogue SC, which, having been abandoned by other experiments long before, was only supporting the ISOLDE facility.

Photowalk 2015

Fifty years on, the experimental hall at ISOLDE is unrecognisable. (Image: Samuele Evolvi/CERN)

“Less than two years later, we had beam and could run again. It was an amazing feat that could only be achieved thanks to the infrastructure and competences at CERN. There’s nowhere else like ISOLDE,” smiles Jonson, echoing the sentiments of virtually every scientist I’ve met who works there.

ISOLDE was relocated and now beams are provided by the Proton Synchrotron Booster and ISOLDE’s physics was able to continue. The humble 1960s experiment grew and grew, and fifty years later the facility now provies beam for roughly 50 experiments per year, supported by more than 500 scientists.


This is the first part of a series celebrating 50 years of ISOLDE physics. You can continue reading the series here.