Observation/confirmation of hindered E2 strength in ~(18)C/~(16)C

摘要

We have measured the lifetime of the first excited 2~+ state in ~(18)C using an upgraded recoil shadow method to determine the electric quadrupole transition. The measured mean lifetime is 18.9 ± 0.9 (stat)±4.4 (syst) ps, corresponding to B(E2; 2~+_1 → 0~+_(gs)) = 4.3±0.2±1.0 e2 fm4, or about 1.5 Weisskopf units. The mean lifetime of the first 2+ state in 16C was remeasured to be 18.3 ± 1.4 ± 4.8 ps, about four times shorter than the value reported previously. The discrepancy is explained by incorporating the γ-ray angular distribution obtained in this work into the previous measurement. The observed transition strengths in 16,18C are hindered compared to the empirical values, indicating that the anomalous E2 strength observed in 16C persists in 18C.