Refractory Oxides with Tunable Porosity and Geometry as Versatile Fast-Release Solid Catchers for Rare Isotopes

The Department of Energy (DOE) seeks useful methods of generating intense beams of reaccelerated rare isotopes for the next-generation Facility for Rare Isotope Beams (FRIB), currently under construction at Michigan State University. Stopping high-energy, heavy-ion reaction products in fast-release solid catchers is an important method to be developed for realizing intense beams of short-lived isotopes of elemental or molecular species. Short-lived isotopes are expected to play a key role in unraveling the mysteries of nuclear physics, nuclear astrophysics, and fundamental interactions at low energies. General statement of how the problem is being addressed: This project will develop refractory, porous oxide monoliths as catchers, which retain open porosity after extended heating at high temperatures. The goal is to ensure that the oxide catcher retains open paths between grains for effusion of atoms or molecules from the catcher to the ion source in order to harvest unused rare isotope beams. Noble gases and reactive molecular species are targeted in these measurements. Simulations will be used as a predictive tool for the transient species of interest. What was done in Phase II: Phase II successfully established production methods to yttria-stabilized zirconia and hafnia disks (1–2 mm). The disks retained open, interconnected porosity (~50%) on the meso- to macro-scale upon heating to 1500 °C for up to 7-days and remained mechanically robust to handling. A very sensitive residual gas analyzer commissioned off-line showed excellent detection of 13CO molecules released from oxide nanopowder doped with 13C isotopic powder and on-line release of implanted 4He. What is planned for the Phase IIB project: More rigorous screening of candidate oxide catchers is planned in Phase IIB, to ensure sintering-free operation in isotope production conditions. On-line release studies will be conducted with light stable beams (4He, 13C) to downselect candidates for in-flight fragmentation reactions with 7Li and 18O to release 6He, and convert-and-release 16CO, both radioactive beams. Another goal is to adapt the porous oxide catcher technology for improved targetry in radioisotope production. Commercial applications and other benefits: Market need for these hot catcher materials exists in beam line facilities and FRIB for rare isotope production. Other potential markets include generation/delivery of radioisotopes to diagnostic and cancer therapy centers.