Heavy-ion-induced production and physical preseparation of short-lived isotopes for chemistry experiments

Abstract

Physical separation of short-lived isotopes produced in heavy-ion-induced fusion reactions is a powerful and well-known method and often applied in investigations of the heaviest elements, called the transactinides ( Z ⩾ 104 ). By extracting these isotopes from a recoil separator, they can be made available for transport to setups located outside the heavily shielded irradiation position such as chemistry setups. This physical preseparation technique overcomes many limitations currently faced in the chemical investigation of transactinides. Here we describe the basic principle using relatively short-lived isotopes of the lighter group 4 elements zirconium (Zr) and hafnium (Hf) used as analogs of the lightest transactinide element, rutherfordium (Rf, element 104). The Zr and Hf isotopes were produced at the LBNL 88-Inch Cyclotron using a cocktail of 18O and 50Ti beams and the appropriate targets. Subsequently, the isotopes were physically separated in the Berkeley Gas-filled Separator (BGS) and guided to a Recoil Transfer Chamber (RTC) to transfer them to chemistry setups. The magnetic rigidities of the reaction products in low-pressure helium gas were measured and their identities determined with γ-spectroscopy. Using preseparated isotopes has the advantages of low background and beam plasma free environment for chemistry experiments. The new possibilities that open up for chemical investigations of transactinide elements are described. The method can readily be applied to homologous elements within other groups in the periodic table.