Abstract
Precise measurements of the lifetimes of the first excited 2+ states in the stable even-A Sn isotopes 112–124Sn have been performed using the Doppler shift attenuation technique. For the isotopes 112Sn, 114Sn and 116Sn the E2 transition strengths deduced from the measured lifetimes are in disagreement with the previously reported values and indicate a shallow minimum at N=66. The observed deviation from a maximum at mid-shell is attributed to the obstructive effect of the s1/2 neutron orbital in generating collectivity when near the Fermi level.
Highlights
Precise measurements of the lifetimes of the first excited 2+ states in the stable even-A Sn isotopes 112−124Sn have been performed using the Doppler shift attenuation technique
Scheme, which supplies an exact solution to the simple pairing Hamiltonian for one single j-shell. It predicts a constant excitation energy for the first excited 2+ state and a parabolic behavior with the maximum value at midshell of the transition probabilities to these first-excited 2+ states, B(E2; 0+g.s. → 2+1 ) (in the following abbreviated as B(E2)), as a function of the number of particles in this j-shell [4]
The energy of the first excited 2+ state is near constant across the entire major N = 50 − 82 neutron shell and at least in its upper half the B(E2) values decrease with increasing neutron number from the mid-shell nucleus 116Sn toward the N = 82 shell closure following a smooth parabolic behavior as described by seniority truncated large scale shell model calculations [5, 6, 7]
Summary
Precise measurements of the lifetimes of the first excited 2+ states in the stable even-A Sn isotopes 112−124Sn have been performed using the Doppler shift attenuation technique. Besides the lifetime measurement we were aiming to determine the magnetic moments of the 2+1 states using the transient field technique (the magnetic moment results will be presented elsewhere [15]); the beam particles impinged on multilayer targets consisting of 0.67 mg/cm2 (0.66 mg/cm2 in the 122Sn run) natural C, 10.8 (10.9) mg/cm2 natural Gd, 1.0 (1.0) mg/cm2 Ta and a 4.86 (5.23) mg/cm2 Cu layer.
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