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UBC Theses and Dissertations

First mass measurements of highly charged, short-lived nuclides in a Penning trap and the mass of 74Rb Ettenauer, Stephan


To date, Vud of the Cabibbo-Kobayashi-Maskawa quark mixing matrix is most precisely determined from superallowed 0⁺ → 0⁺ nuclear β-decays. In addition to half-life, Branching Ratio, and transition energy (called Q_EC-value) of a superallowed decay, theoretical corrections have to be considered to extract Vud. Among those, the isospin symmetry breaking corrections, δC , show discrepancies between different theoretical models, which are critical to be resolved. ⁷⁴Rb has the largest δC of all 13 superallowed β-emitters used to obtain Vud and would carry particular weight to discriminate between models were it not limited by the uncertainty in the Q_EC-value. However, ⁷⁴Rb’s half-life of 65 ms has previously posed a real challenge to the experimental precision in its Q_EC -value, which is best determined by direct mass measurements in Penning traps. In this work, Penning trap mass measurements of short-lived nuclides have been performed for the first time with highly-charged ions, using the TITAN facility. Compared to singly-charged ions, this provides an improvement in experimental precision that scales with the charge state q. Neutron-deficient Rb-isotopes have been prepared in an electron beam ion trap to q = 8 − 12+ prior to the mass measurements. In combination with a Ramsey scheme, this opens the door to unrivalled precision with gains of 1-2 orders of magnitude. The method is particularly suited for short-lived nuclides such as ⁷⁴Rb and its mass has been determined. In the realm of fundamental symmetries studied in low-energy nuclear systems such as in ⁷⁴Rb, the precision achieved by highly-charged ions is essential. For mass measurements motivated by nuclear structure or nuclear astrophysics, where the present experimental precision is already sufficient, this novel technique significantly reduces the measurement time and thus allows one to map the nuclear mass landscape more broadly. In the exploration towards the limits of nuclear existence where experimental efforts typically face shorter half-lives and lower production yields of radioisotopes, the same precision can be achieved by compensating for both challenges with the higher charge state. Finally, highly-charged ions provide opportunities for an unprecedented resolving power to identify low-lying nuclear isomers. This potential has firstly been demonstrated with ⁷⁸,⁷⁸mRbq⁼⁸⁺.

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