Ions leaving target foils at high velocity are highly ionized. The electronic configurations of such ions can produce enormous “hyperfine” magnetic fields at the nucleus, which can be used to probe the magnetic field generated by the constituents of the nucleus. The aim of this project is to measure and characterize the hyperfine fields of a variety of ions emerging from thin foils at a range of velocities. These data will test the theoretical models we are developing and form the basis for measurements of the magnetism of excited rare isotopes produced at several of the world’s leading radioactive beam laboratories, such as GANIL (France), ISOLDE-CERN (Switzerland) and NSCL (USA).
Measurements of free-ion hyperfine fields are made by initiating a nuclear reaction and letting the excited nuclei that are produced recoil out of the target into vacuum. The method is thus called ‘recoil in vacuum’ or RIV. Angular momentum conservation together with the hyperfine coupling causes the nuclear and electronic spins to undergo precession about the total. This precession is observed via changes in the intensity of the gamma-rays emitted by the nucleus. The figure shows the apparatus in the Heavy Ion Accelerator Facility that will be used for most of these measurements.
The project outcomes will include an improved understanding of free-ion hyperfine fields for applications to measurements of nuclear magnetism, particularly for our international experiments granted competitive beam-time at international radioactive beam facilities. Students will gain experience with radiation detectors, electronics, data acquisition, accelerator operations, and data analysis.