Study of the N=32 and N=34 Shell Gap for Ti and V by the First High-Precision Multireflection Time-of-Flight Mass Measurements at BigRIPS-SLOWRI

Abstract

<p>The atomic masses of 55Sc, 56;58Ti, and 56−59V have been determined using the high-precision<br>multireflection time-of-flight technique. The radioisotopes have been produced at RIKEN’s Radioactive<br>Isotope Beam Factory (RIBF) and delivered to the novel designed gas cell and multireflection system,<br>which has been recently commissioned downstream of the ZeroDegree spectrometer following the<br>BigRIPS separator. For 56;58Ti and 56−59V, the mass uncertainties have been reduced down to the order of 10 keV, shedding new light on the N ¼ 34 shell effect in Ti and V isotopes by the first high-precision mass measurements of the critical species 58Ti and 59V. With the new precision achieved, we reveal the<br>nonexistence of the N ¼ 34 empirical two-neutron shell gaps for Ti and V, and the enhanced energy gap<br>above the occupied νp3=2 orbit is identified as a feature unique to Ca. We perform new Monte Carlo shell<br>model calculations including the νd5=2 and νg9=2 orbits and compare the results with conventional shell<br>model calculations, which exclude the νg9=2 and the νd5=2 orbits. The comparison indicates that the shell<br>gap reduction in Ti is related to a partial occupation of the higher orbitals for the outer two valence neutrons at N ¼ 34.<br></p>