Lifetime measurement of the 167.1 keV state in Ar41

The Advanced-Time-Delayed method was used to measure lifetimes of the states in Ar-41 populated in the beta decay of Cl-41. The nuclei Cl-41 were produced at ISOLDE by 1.4-GeV proton bombardment of a thick UCx target and mass-separated as molecular ions, XeCl+. Our measured half-life of the 167.1-keV state, T-1/2=315(15) ps, is significantly lower than the previously measured value of 410(30) ps. We have also determined T-1/2=260(80) ps and T-1/2 <= 46 ps for the 515.9- and 1867.7-keV states, respectively. These are the shortest lifetimes measured so far with the ultrafast timing method using the new LaBr3(Ce) crystals for gamma-ray detection.