Lifetime measurements of first excited states in 16,18C

TL;DR

This study measures the lifetimes of the first 2+ excited states in 16C and 18C isotopes, revealing hindered transition strengths and resolving previous discrepancies through improved experimental techniques.

Contribution

The paper provides new lifetime measurements of 16C and 18C, clarifies previous inconsistencies, and demonstrates persistent transition hindrance in these isotopes.

Findings

Measured 18C lifetime as 18.9 ps with improved accuracy.

Re-measured 16C lifetime as 18.0 ps, resolving earlier discrepancies.

Found transition hindrance persists in 18C, similar to 16C.

Abstract

The electric quadrupole transition from the first 2+ state to the ground 0+ state in 18C was studied through lifetime measurement by an upgraded recoil shadow method applied to inelastically scattered radioactive 18C nuclei. The measured mean lifetime is 18.9 +/- 0.9 (stat) +/- 4.4 (syst) ps, corresponding to a B(E2;2+ -> 0+) value of 4.3 +/- 0.2 +/- 1.0 e2fm4, or about 1.5 Weisskopf units. The mean lifetime of the first 2+ state in 16C was remeasured to be 18.0 +/- 1.6 +/- 4.7 ps, about four times shorter than the value reported previously. The discrepancy between the two results was resolved by incorporating the gamma-ray angular distribution measured in this work into the previous measurement. These transition strengths are hindered compared to the empirical transition strengths, indicating that the anomalous hindrance observed in 16C persists in 18C.