Lifetime measurement of the ³⁹Ca 11/2- state and E2 transition strengths of mirror nuclei near N=Z

Assuming perfect isospin symmetry, the E2 transition matrix elements of isobaric multiplets are expected to follow a linear trend as a function of isospin projection. However, measurements of the 2+→0+ transition in the A=38 triplet of Ca, K, and Ar show a deviation from this trend with an enhanced transition in ³⁸Ca with respect to its mirror ³⁸Ar. By studying an analogue transition in ³⁹Ca we can ascertain if this enhancement persists in neighboring nuclei or if ³⁸Ca is anomalous. A recoil-distance method (RDM) lifetime measurement of the ³⁹Ca (11/2-) state was conducted at the NSCL utilizing a ⁴²Sc secondary beam, the TRIPLEX plunger, GRETINA, and the S800 spectrograph. Our data on the ³⁹Ca (11/2-)→7/2- transition provides a useful reference for the 2+→0+ transition in ³⁸Ca, assuming that the ³⁹Ca states are formed by the f7/2 neutron coupled to the ³⁸Ca core. A preliminary analysis of the lifetime measurement will be presented and a possible enhancement in the ³⁹Ca E2 strength will be discussed via a comparison to a simple core shell calculation with various effective charges.