Improved isochronous mass spectrometry with tune measurement

In conventional isochronous mass spectrometry (IMS) performed at a storage ring, the precision of mass measurement for short-lived nuclei depends on the precise determination of the revolution times (<em>T</em>s) of stored ions. However, the resolution of <em>T</em> inevitably deteriorates due to the magnetic rigidity spread of the ions, resulting in limited mass resolving power. In this work, we measure the betatron tune <em>Q</em> (the number of betatron oscillations within a single revolution) of the ions, and construct a correlation between <em>T</em> and <em>Q</em>. From this correlation, the <em>T</em> are transformed corresponding to a fixed <em>Q</em> with higher resolution. Using the transformed <em>T</em>s, we re-determine the masses of ⁶³Ge, ⁶⁵As, ⁶⁷Se, and ⁷¹Kr, which agree well with the mass values measured by the newly developed IMS (<em>Bρ</em>-IMS). We also study the systematics of Coulomb displacement energies (CDEs) and find that the anomalous staggering in CDEs is removed using the new mass values. This method of <em>T</em> transformation is very useful for the conventional IMS equipped with a single time-of-flight detector.