(M1+E2) decay rate in Ar2+ ions measured at a heavy-ion storage ring

The radiative lifetime of the 3s(2)3p(4) S-1(0) level in Ar2+ ions has been measured by time-resolved observation of the magnetic dipole (M1) transition to the ns(2) np(4) P-3(1) level, on ions circulating in a heavy-ion storage ring. The result of 145 +/- 5 ms compares well with various theoretical predictions, but is significantly more accurate and more precise than earlier measurements