E1 and M1 transition strengths from two-quasiparticle structures in 168Er

Abstract

Lifetime measurements in 168Er were performed in the (n, γ) reaction using the generalized centroid-shift method with the following results: T 1 2 (JK π = 54 − at 1193.0 keV) = 0.70±0.07 ns and T 1 2 (JK π = 33 3 − at 1999.2 keV) = 0.44 −0.08 +0.12 ns . The size of some matrix elements of the ty 〈0 +| M 10 E |0 −〉(Δ K = 0) and 〈0 +| M 1−1 E|1 −〉(ΔK = 1) in 168Eris estimat The evolution of the strenghts of E1 transitions linking some negative-parity bands with the ground band in N = 100 isotones with varying spin and neutron number is considered. For K-forbidden transitions, ΔK = 0 admixtures in the E1 matrix elements are found to be dominant in 168Er and 170Yb, while in 174W ΔK = 1 admixtures become at least similarly important. In 168Er, K π = 2 γ + admixtures in the ground band appear responsible for up to 45% of the size of the E1 transition matrix elements. A surprisingly small mixing (∼0.01%) of the structure { 7 2 −[523]− 1 2 +[411]} p (K π = 3 3 − ) into the s 7 2 +[633]− 1 2 −[5]} n(K π = 3 1 − ) and vice versa is found to account for the measured B(M1 strenght of the band-head 33 3 − → 33 1 − transition.