This reaction mechanism allows us to populate regions that are not accessible by the more commonly used fusion-evaporation, fission or fragmentation reaction mechanisms. Multi-nucleon transfer reactions offer significantly higher cross-section in the N = 126 region south-east from ²⁰⁸Pb which is critical to our understanding of the last abundance peak in the r-process, but it is also extremely competitive in many other regions of the chart of nuclides.

Multi-nucleon transfer reactions have not been used extensively in the past to produce radioactive species mainly because the reactions are peripheral in nature and the associated kinematics result in the recoils being emitted at large angles which makes them difficult to collect efficiently in a separator. The N = 126 factory overcomes this difficulty by using the large RF gas catcher technology we have developed for CARIBU to collect these recoils, cool them, and form a low-emittance low-energy beam. This beam contains all species produced by the reaction and is then pre-separated in a magnetic separator with mass resolution of roughly 1 part per 1000, accumulated in an RF buncher, and then passes through a multi-reflection time-of-flight (MR-TOF) system which provides a resolution of roughly 1 part per 100,000 and hence essentially pure beams to a small low-energy area. The whole process, from production to beam delivery on the target station ​‚takes less than 100 ms. The N = 126 facililty is designed to operate with up to 10 puA of primary beam, typically 136Xe for neutron-rich isotope production, on various targets. The system is designed for the gas catcher to collect the target-like recoils from the reaction so that changing the target changes the region over which the production occurs; for example, the main reaction to reach the N = 126 region is ¹³⁶Xe on ¹⁹⁸Pt or ²⁰⁸Pb. A view of the N = 126 system is shown below.

The N = 126 factory will start operating in 2022 and will be initially limited to 10% of the design power until the operating parameters have been well established. The expected mass-separated yields over the chart of nuclides at 10% of full power are shown in the figure below.

For more information, please contact Guy Savard at savard@​anl.​gov .