High precision mass measurements of the isomeric and ground states of 44V: improving constraints on the IMME parameters of the A=44, 0+ quintet
Abstract
The Isobaric Multiplet Mass Equation (IMME) has been successful at predicting the masses of isobaric analogue states in the same multiplet, while its coefficients are known to follow trends as functions of mass number. The Atomic Mass Evaluation 2016 [Chin. Phys. C 41, 030003 (2017)] 44V mass value results in an negative c coefficient for the IMME quadratic term. The b and c coefficients can provide constraints for construction of the isospin-nonconserving (INC) Hamiltonians for the pf shell. The excitation energy of the 0+, T=2 level in 44V is currently unknown and can be used to constrain the 44Cr mass. The aim of the experiment was to perform high-precision mass measurements to resolve the difference between 44V isomeric and ground states, to test the IMME, and to provide ingredients for identifying the 0+, T=2 state in 44V. High-precision Penning trap mass spectrometry was performed at LEBIT, to measure the cyclotron frequency ratios of [44g,mVO]+ versus [32SCO]+, a reference mass, to extract both the isomeric and ground state masses of 44V. The mass excess of the ground and isomeric states in 44V were measured to be -23\ 804.9(80) keV/c2 and -23\ 537.0(55) keV/c2. This yielded a new proton separation energy of Sp = 1\ 773(10) keV. The new mass values of 44V 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 verified with the IMME trend and agrees with the shell-model predictions using charge-dependent Hamiltonians. The mirror energy differences were determined between 44V and 44Sc, in line with isospin-symmetry. The new value of the proton separation energy determined will be important for the determination of the 0+, T=2 state in 44V and for prediction of the mass of 44Cr.