On January 27^th, at the Maison des Amis Montagnards in Geneva, friends, colleagues from CERN, and numerous ISOLDE users said the last goodbye to Bruce Marsh, who has been one of the main innovators of the laser ion sources at ISOLDE that have contributed to the many scientific successes of the facility. Bruce passed away on December 30^th in a climbing accident, at the age of 43.

Organisationally, Bruce has been part of the STI Group, previously in the Engineering (EN) and now in the Accelerator System (SY) Department. However, from his first day at CERN, his activities have been intimately linked to our Department and the science of the ISOLDE facility.

Bruce’s adventure with CERN started in September 2002, when he became a CERN ‘user’ sent by the University of Manchester to spend part of his doctoral thesis [1] at ISOLDE to contribute to the developments of the radioactive-ion laser ion source (RILIS). After the thesis, in 2007, Bruce joined CERN full time as Senior Fellow in the RILIS team and shortly after became CERN staff in the same team. In 2022, he became the leader of Laser Ion Sources and Injector section, thus expanding his responsibilities to include CLIC and AWAKE facilities, and the gamma-factory project, to which he made many highly-valued contributions.

RILIS was a real game-changer for ISOLDE, as it was the first laser-based system to provide ionised unstable nuclei which over the coming years has been copied in facilities around the world. RILIS provided many new beams [2] for ISOLDE researchers. It also opened the possibility to study nuclear ground-state properties (magnetic dipole moments, electric quadrupole moments, spins, and charge radii) of many of the laser-ionised isotopes via the technique of in-source laser ionisation spectroscopy. These measurements were performed in close collaboration between the RILIS team and the ISOLDE nuclear-decay spectroscopy ‘users’. These two facets of RILIS have paved the way for many important studies in nuclear-structure physics and in other fields and have led to numerous highly-cited publications, close to 150 of which have been co-authored by Bruce (and cited close to 3000 times).

One of the first and notable examples is the laser ionisation and in-source spectroscopy of polonium [3-7], which has no stable isotopes and thus required for identification the use of alpha or gamma detectors that were provided by the WINDMILL decay-spectroscopy setup. The first polonium beam time brings back many memories. On the last shift, a thunderstorm took the power down at all of CERN, but Bruce with the PhD student who worked with WINDMILL managed to bring the whole ISOLDE back to life within two hours. Unfortunately, their joy didn’t last long because when they called the PSB to ask for protons to ISOLDE they learnt that the proton beam will be back only after their last scheduled shift. That beam time also coincided with the time of a famous polonium poisoning of a spy in London, thus bringing some unexpected attention to ISOLDE. The project was probably one of the longer-running experiments at ISOLDE: with runs in 2007, 2009, 2012, before being finally concluded in 2022.

A more recent example of Bruce’s contribution to the excellence of ISOLDE physics programme is provided by the in-source laser spectroscopy of mercury isotopes, which addressed the question of nuclear-shape ‘staggering’, opened 45 years earlier at ISOLDE [8]. Bruce led the studies, from the moment of conceiving the idea, to co-developing the laser scheme, through to writing the proposal, making the production checks, running the experiments, analysing the data, and finally writing the manuscript. The results were published in Nature Physics [9], with Bruce as the corresponding author. The study contributed substantially to the understanding of shape coexistence [10] in atomic nuclei, with the strong shape staggering observed uniquely in the mercury chain, illustrating the competition between single-particle and collective degrees of freedom at play in atomic nuclei. Bruce developed the technique of in-source laser spectroscopy to its perfection with respect to sensitivity, which made studies possible on short-lived radioactive isotopes that were produced with minute quantities. Colleagues also remember his positive and constructive attention for all partners in the collaboration.

Bruce Marsh with one of the RILIS lasers.

In addition, the above developments for mercury beams [11], an efficient ionisation scheme and high resolution allowing to ionise selectively the nuclear ground state or isomer, enabled more high-impact experiments with mercury beams. Nucleon transfer on ²⁰⁶Hg accelerated at HIE-ISOLDE [12] was one of the first experiments using the ISOLDE Solenoidal Spectrometer (ISS) [13-14]. Another experiment, which included Coulomb excitation on an isomerically-pure beam of ¹⁸⁵Hg, was performed at the MINIBALL setup in 2023 [15]. 

Bruce’s curious mind, friendly personality, devotion to make RILIS work, even at most impossible times of the day and week, brought him appreciation and friendship of the whole ISOLDE scientific community. His uniqueness was also illustrated by the fact that he broke the stereotypes of a British person: he didn’t like football, he was late to some work events and to most private ones, and he didn’t like tea with milk. In addition, he was the main character in many surreal and mostly entertaining stories, linked very often to his love of climbing and cakes. These were told and retold multiple times over the last 20 years over coffee, but also at many nuclear physics conferences and workshops. Despite such adventures, away from work and at scientific events, Bruce was the most reliable colleague one could imagine in terms of maintaining the capabilities of the ISOLDE facility and its scientific output.

In addition to collaborating closely with many ISOLDE users, Bruce was also a much valued supervisor and mentor to a team of doctoral students and CERN fellows, several of whom are now CERN staff in the SY department. He has been also the coordinator of an EU Innovative Training Network LISA devoted to the laser ionisation and spectroscopy of actinide elements. The network trained over a dozen doctoral students, with some being since recently also CERN fellows.

The ISOLDE community will also remember Bruce for his strong feeling of justice. He would never be afraid to speak up when he felt for example that a colleague’s conduct was not right, when a student was given hard time by their supervisor, or when an administrative procedure had caused a flaw. His courage to draw attention to such issues triggered changes that brought wider justice beyond the individuals for whom he had spoken up.

Bruce will be deeply missed by the whole ISOLDE community.

Further Reading

[1] B. A. Marsh, PhD thesis, CERN-THESIS-2007-143

[2] ISOLDE isotope production database, including RILIS elements : https://isoyields2.web.cern.ch/

[3] T. E. Cocolios, B. A. Marsh, et al., Resonant laser ionization of polonium at RILIS-ISOLDE for the study of ground- and isomer-state properties, Nucl. Instrum. Meth. B 266 (2008) 4403–4406

[4] T. E. Cocolios et al., Early onset of ground-state deformation in the neutron-deficient polonium isotopes, Phys. Rev. Lett. 106 (2011) 052503

[5] M.D. Seliverstov, Charge radii of odd-A Po-191-211 isotopes, Phys. Lett. B 719 (2013), 362

[6] M.D. Seliverstov et al., Electromagnetic moments of odd-A Po193–203,211 isotopes, Phys. Rev. C 89 (2014) 3, 034323

[7] D. Fink et al., In-Source Laser Spectroscopy with the Laser Ion Source and Trap: First Direct Study of the Ground-State Properties of 217,219Po, Phys. Rev. X 5 (2015) 1, 011018.

[8] J. Bonn et al., Sudden change in the nuclear charge distribution of very light mercury isotopes. Phys. Lett. B 38, 308 (1972)

[9] B.A. Marsh, B. A. et al. Characterization of the shape-staggering effect in mercury nuclei. Nat. Phys. 14, 1163 (2018).

[10] A.N. Andreyev  et al., A triplet of differently shaped spin-zero states in the atomic nucleus 186Pb. Nature 405, 430 (2000)

[11] Day Goodacre, T. et al. Blurring the boundaries between ion sources: The application of the RILIS inside a FEBIAD type ion source at ISOLDE. Nucl. Instrum. Meth. B 376, 39 (2016).

[12] V.I. Mishin, V.N. Fedoseyev, H.-J. Kluge et al., Chemically selective laser ion-source for the CERN-ISOLDE on-line mass separator facility, Nucl. Instrum. Meth. B 73 (1993) 550-560

[13] Tang, T. L. et al. First Exploration of Neutron Shell Structure Below Lead and Beyond N=126. Phys. Rev. Lett. 124, 062502 (2020).

[14] https://ep-news.web.cern.ch/content/isoldes-solenoidal-spectrometer-iss-new-tool-studying-exotic-nuclei

[15] https://ep-news.web.cern.ch/content/investigating-exotic-structures-exotic-nuclei-miniball