Exploring uncharted territory (with a little help from your friends)

18 January 2018

12 months of meticulous planning and international collaboration have resulted in an outstanding result for the first experiments using the ISOLDE Solenoid Spectrometer (ISS) at CERN’s nuclear physics facility.


Animation of protons

Animation of protons ejected from the target (central red dot) and forced by the magnetic field to reach the detector array positioned along the beam axis.


The ISS was funded by STFC, with the main component, a superconducting solenoid magnet, being recycled from its original use in an MRI scanner in an Australian hospital. The advanced silicon detector array that will eventually form the heart of the spectrometer is under construction at the University of Liverpool, but UK researchers were keen to demonstrate the ISS’s potential before the CERN accelerator complex began its two-year maintenance and upgrade shutdown.

International collaboration is at the heart of fundamental physics, and the UK team, led by researchers from the University of Manchester worked closely with colleagues at Argonne National Laboratory on plans to borrow Argonne’s HELIOS silicon detector array and data acquisition system.

HELIOS is in regular use at Argonne, so the team had to find a window in Argonne’s experimental schedule to pack up the detector and ship it from Chicago to Geneva.

“It’s not just a question of changing the plugs,” says Argonne researcher, Ben Kay, “we spent 12 months of detailed planning to look at all the modifications that would be required to install our detector inside the magnet. It was really quite remarkable that there were no showstoppers or compromises.”

The UK-US team carried out two experiments to study previously unexplored isotopes at opposite ends of the mass scale. In reactions with a deuteron target, exotic beams of Magnesium-28 and Mercury-206 from HIE-ISOLDE picked up an extra neutron while the residual proton was detected by ISS, revealing the structure of the now heavier isotopes for the first time.

“These experiments were only possible because of the combination of the ISS and the ISOLDE beam - no other lab can deliver these radioactive beams with such intensity and energy,” says experiment lead, David Sharp (Manchester). “The quality of the beams provided by ISOLDE was better than we could have anticipated. To observe the states in these exotic nuclei so cleanly for the first time was really quite wonderful! The control room was packed!”

The team is now eagerly awaiting the completion of its own detector array and wondering what discoveries could be within reach when ISOLDE beams return in 2021.

Gif caption: Animation of protons ejected from the target (central red dot) and forced by the magnetic field to reach the detector array positioned along the beam axis.

Last updated: 25 February 2019

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