Advances in precision, resolution, and separation techniques with radioactive, highly charged ions for Penning trap mass measurements

摘要

Highly charged ions (HCI) have recently been introduced to the mass spectrometry of short-lived nuclides with Penning traps. In comparison to singly charged ions, HCI enable a gain in achievable experimental precision by a factor identical to the charge state q. When combined with advanced excitation methods such as a Ramsey scheme, this technique has the potential to improve the precision by 1-2 orders of magnitude over the conventionally achieved precision. At the TITAN facility at TRIUMF - to date unique in this approach for measurements of rare isotopes - HCI are formed in an electron beam ion trap (EBIT). This fulfils the requirement of fast and efficient charge breeding that is imperative for online produced nuclides. So far, HCI of rare isotopes with half-lives as short as 65 ms or charge states up to q = 22+ have been successfully used for mass measurements. In addition, HCI offer novel opportunities in the suppression of contaminating isobars, typically a major problem when exploring the nuclear mass surface ever closer to the drip-lines. Particularly, charge breeding to electronic shell closures results in a distinction of different isobars in their corresponding charge state and consequently allows for separation independently of isobaric mass differences. Finally, HCI serve as a tool for increased resolution, valuable in the study of low-lying isomers. This was demonstrated at TITAN with the mass doublet ~(78m78)Rb which requires a resolving power of R ≈ 6.5 × 10~5.