Thermo-Mechanically Stable Tungsten Powders as Solid Catchers for the Fast Release of Stopped 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. This project will develop refractory tungsten powders as catchers, which retain open porosity after extended heating at high temperatures. The goal is to ensure that the tungsten 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. Alkalis, 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. Phase I demonstrated the feasibility of grain growth suppression in candidate W powders. Offline, ultrahigh vacuum heating of candidate powders showed very low outgassing rates compatible with on-line characterization. Modeling refractory carbides and sulfides to optimize the selective release of specific elements as molecular sidebands was successfully completed. A very sensitive residual gas analyzer commissioned off-line showed excellent sensitivity to detect 13CO molecules released from alumina nanopowder doped with 13C isotopic powder. More rigorous screening of candidate W catchers is planned in Phase II, to ensure sintering-free operation in isotope production conditions. On-line release studies will be conducted with light beams (4He, 7Li, 13C and 18O) followed by heavier beams (136Xe and 120Sn). Predictive simulations of release characteristics will be validated through on-line release profiles. Commercial applications and other benefits: The immediate market need for these hot catcher materials is the DOE and installations like FRIB that have powerful and unique techniques for rare isotope production. Potential other markets include porous metals, metal foams in thermal management applications and medical applications such as diagnostics and cancer therapy.