High-precision mass measurements of the isomeric and ground states of $^{44}$V : Improving constraints on the isobaric multiplet mass equation parameters of the A=44 , 0$^+$ quintet
Résumé
Background: The quadratic isobaric multiplet mass equation (IMME) has been very successful at predicting the masses of isobaric analog states in the same multiplet, while its coefficients are known to follow specific trends as functions of mass number. The Atomic Mass Evaluation 2016 [Chin. Phys. C 41, 030003 (2017)]1674-113710.1088/1674-1137/41/3/030003 V44 mass value results in an anomalous negative c coefficient for the IMME quadratic term; a consequence of large uncertainty and an unresolved isomeric state. The b and c coefficients can provide useful constraints for construction of the isospin-nonconserving Hamiltonians for the pf shell. In addition, the excitation energy of the 0+,T=2 level in V44 is currently unknown. This state can be used to constrain the mass of the more exotic Cr44. Purpose: The aim of the experimental campaign was to perform high-precision mass measurements to resolve the difference between V44 isomeric and ground states, to test the IMME using the new ground state mass value and to provide necessary ingredients for the future identification of the 0+, T=2 state in V44. Method: High-precision Penning trap mass spectrometry was performed at LEBIT, located at the National Superconducting Cyclotron Laboratory, to measure the cyclotron frequency ratios of [VO44g,m]+ versus [SCO32]+, a well-known reference mass, to extract both the isomeric and ground state masses of V44. Results: The mass excess of the ground and isomeric states in V44 were measured to be −23804.9(80) keV/c2 and −23537.0(55) keV/c2, respectively. This yielded a new proton separation energy of Sp=1773(10) keV. Conclusion: The new values of the ground state and isomeric state masses of V44 have been used to deduce the IMME b and c coefficients of the lowest 2+ and 6+ triplets in A=44. The 2+c coefficient is now verified with the IMME trend for lowest multiplets and is in good agreement with the shell-model predictions using charge-dependent Hamiltonians. The mirror energy differences were determined between V44 and Sc44, in line with isospin-symmetry for this multiplet. The new value of the proton separation energy determined, to an uncertainty of 10 keV, will be important for the determination of the 0+, T=2 state in V44 and, consequently, for prediction of the mass excess of Cr44.