(image: the DRAGON experiment in TRIUMF’s Isotope Separator and Accelerator (ISAC-1) facility)
In Fall 2021, teams working on DRAGON (the Detector of Recoils And Gammas of Nuclear Reactions) marked a celebratory occasion for the twenty-year anniversary of the experiment’s commissioning, acknowledging a key milestone for the long-standing TRIUMF community of nuclear physicists, engineers, technicians, and students.
The DRAGON experiment has been a mainstay in TRIUMF’s scientific portfolio since 2001, measuring the majority of the world’s radiative capture reactions with rare isotope beams so far and, in the process, making a number of first-in-the-world measurements.
DRAGON uses beams of rare isotopes, targets, and a suite of highly sensitive detectors to study certain nuclear reactions that occur in stars, called ‘radiative capture’ reactions, to try and better understand how (and how quickly) different elements are produced in explosive stellar environments. This information is vital for helping us understand the lives of stars, the manner in which elements are formed, and how the proportions of matter we see in the universe came to be.
(image: members of the DRAGON team in 2017, including 2017 FYSRE Award winner Gaurav Tenkila)
Teams with DRAGON accomplish this by bombarding specialized targets made of hydrogen or helium (the two lightest elements, which fuel nuclear reactions within the fiery atmospheres of stars) with rare isotope beams. The interactions between hydrogen or helium and the rare isotope beam are the same star-bound reactions that we know can produce a suite of heavier elements up to iron. Then, the reaction products (called ‘recoils’) are filtered out as they travel down a 20-metre electromagnetic device, finally being detected and counted at the end.
Enter(ed) the DRAGON
Following nearly a decade of proposals, planning, construction, and assembly, the final elements of the DRAGON gas target and electromagnetic separator were installed late in the summer of 2001.
Then, over three hectic days from September 15th to 17th, the DRAGON team worked to finalize its commissioning and prove that separator worked as designed.
Using a beam of neon ions, the teams navigated the desired species from the reaction, gamma rays and heavy ion products, while rejecting unreacted ions from the isotope beam, which outnumbers the gammas and heavy ions by 10 orders of magnitude.
"Progress was made in the fog of battle,” said David Hutcheon, TRIUMF researcher emeritus and the principal designer of the DRAGON device. “Those final days called on a number of the accelerator staff and DRAGON group alike. Everyone in our team summoned a tremendous amount of resolve, intense focus, and ingenuity to overcome a variety of technical issues.”
Finally, the nuclear recoils were detected in coincidence with the gamma rays from the reaction.
(image: DRAGON’s gamma-ray detection array)
In the twenty years since, teams with DRAGON have established a prolific track record of precise measurements for a variety of reactions and elements. These data have been critical for a variety of areas of research in physics, astronomy, and beyond, including analyses of nova explosions and resolving theoretical models for how stars form and burn.
“DRAGON truly represents the pinnacle of decades of research into recoil separator devices and radiative capture reactions,” said Chris Ruiz, Head of the Nuclear Physics Department and DRAGON group lead. “Like much of the research conducted at TRIUMF, our science with DRAGON has benefited immensely from the unique confluence of world-leading expertise and infrastructure convened here on-site. Due to its design and its place within the ISAC isotope beam paradigm where intense, high quality rare isotope beams make these reactions possible at stellar energies, DRAGON has enjoyed little competition.”
(image: a sticker from the early days of DRAGON)
Over the years DRAGON has made several key measurements towards the understanding of stellar behavior and nucleosynthesis. For example, the measurement of the fusion of radioactive 21-sodium with hydrogen to make 22-magnesium was able to explain why orbiting gamma-ray observatories had not yet identified long-lived radioactive 22-sodium via its characteristic decay line in the remnants of classical nova explosions: the fusion was more powerful than previously thought, leading to less 22-sodium being formed.
Similarly, the measurement of 26-aluminium fusion with hydrogen (to make 27-silicon) explained just how much of the visible 26-aluminium, seen all over the galaxy via its characteristic decay line, could be produced by classical nova explosions. A more recent measurement of the fusion of 19-neon with hydrogen helped to tie observations from ground-based telescopes and the Hubble Space Telescope of the element fluorine in a classical nova remnant, to the latest computer simulations of those objects.
DRAGON remains one of the foremost devices of its kind in the world; it has inspired designs for radiative capture-recoil separator experiments at other facilities, including the SECAR device at FRIB. However, due to its exceptionally high performance and unique high-intensity rare isotope beams (including those forthcoming from TRIUMF’s Advanced Rare Isotope Laboratory, ARIEL), DRAGON will continue making competitive world class measurements for decades to come. Congratulations to the DRAGON team for the years of hard work and dedication.
*Editor’s note: TRIUMF would like to acknowledge the recent passing of Shawn Bishop, who was an integral member of the early DRAGON team. This story is dedicated to the memories of Shawn and John M. D'Auria, DRAGON pioneers and fondly-remembered friends of many in the TRIUMF community*
For more information:
- Dive into DRAGON with this 360 video
- How particle accelerators work
- Learn more about ARIEL and the future of TRIUMF science
- Recap ISAC and ARIEL science with the TRIUMF History Minute: ISAC & ARIEL