Many of the superheavy elements discovered in the last few decades were produced by bombarding heavy-element targets with high-current beams of neutron-rich isotopes like 48Ca. We need ion beams of yet-more-massive neutron-rich elements to extend the periodic table further using similar methods. The Ion Source Group in Building 88 has been using the superconducting electron cyclotron resonance (ECR) ion source VENUS to develop 50Ti beams to address this need.
This method of superheavy element production imposes two primary demands of the ion source: high currents and efficient beam material use. The high currents are required for reasonable superheavy element production rates. The low natural abundances of these neutron-rich isotopes make them extremely expensive and so require efficient material-to-beam transfer. The Ion Source Group has been tasked with delivering a beam with over 150 e𝜇A of 50Ti, the heaviest natural isotope of titanium with 28 neutrons and an abundance of only 5.2%.
ECR ion sources can produce ion beams from any material that can be introduced into the plasma. For high-current metal ion beams, ovens are typically used to introduce atoms to the plasma in gaseous form. Resistive ovens have been successfully used in VENUS at lower temperatures, but high temperatures (over 2000 0C) are needed for Ti beam production. NSDs Dan Xie has been developing a new resistive oven design centered around a commercially available “boat.” In the last months, it has demonstrated days of its continuous, stable operation using natural titanium to produce currents in excess of 150 e𝜇A. The Ti consumption rate was less than 5 mg/hr, with further improvements expected through oven optimizations. These successes will realize the world’s most intense 50Ti beam for superheavy element production at the 88-Inch Cyclotron.