Spectroscopy of Low-lying States in $^{140}$Sm

Abstract

Electromagnetic transition strengths and spectroscopic quadrupole moments for 140 Sm were measured by means of multi-step Coulomb excitation with radioactive beam at the ISOLDE facility at CERN. A complementary experiment was performed at the Heavy Ion Laboratory in Warsaw to assign spins for non-yrast states using the angular correlation technique. Based on the new experimental data previous spin assignments need to be revised.

Lifetime measurement for the21+state inSm140and the onset of collectivity in neutron-deficient Sm isotopes

“…An experimental test of the γ -soft nature of the deformation in 140 Sm requires investigating higher-lying states beyond the 2 + 1 state, in particular nonyrast states. The Coulomb excitation data that were recently obtained [26,31] are expected to provide further information on the shape of 140 Sm and the onset of deformation in the neutron-deficient Sm isotopes.…”

“…The results complete the systematics of B(E2) values for neutron-deficient Sm isotopes below the N = 82 shell closure. The measurement of the lifetime of the 2 + 1 state is furthermore complementary to a recent Coulomb excitation experiment with radioactive 140 Sm beam [26,31] and can be used to constrain the Coulomb excitation analysis, improving the sensitivity to the spectroscopic quadrupole moment. Further insight into the evolution of nuclear shapes and collectivity can be expected to come from higher-lying yrast and nonyrast states and the electromagnetic matrix elements between them, which can be obtained from the Coulomb excitation data.…”

“…A surprisingly low-lying 0 + 2 state was reported at an excitation energy of only 990 keV [16], which could potentially hint to shape coexistence also near the ground state. However, a recent measurement of γ -γ angular correlations suggests that the original spin assignment of I π = 2 + for the state at 990 keV and the interpretation as the head of a γ -vibrational band is correct after all [26,27]. Because of the long lifetime of the 10 + states it is difficult to measure the much shorter lifetimes of the states below with Doppler-shift methods.…”

“…The resulting B(E2; 2 + 1 → 0 + 1 ) value extends the systematics towards the N = 82 shell closure and contributes to the understanding of how quadrupole collectivity evolves in this mass region. The lifetime measurement is complementary to a recent Coulomb excitation experiment with a radioactive 140 Sm beam [26,31]. A precise measurement of the lifetime of the 2 + 1 state can be used to constrain the Coulomb excitation analysis, as the Coulomb excitation probability for the 2 + 1 state depends both on the B(E2; 0 + 1 → 2 + 1 ) transition strength and the spectroscopic quadrupole moment Q s (2 + 1 ).…”

Revised spin values of the 991 keV and 1599 keV levels inSm140

“…A low-lying 0 + state as low as 991 keV excitation energy may be considered as an indication of shape coexistence also near the ground state. More information about the shape of 140 Sm near the ground state can be expected from a recent Coulomb excitation experiment [8] with the radioactive beam at the CERN on-line isotope mass separator ISOLDE [9]. However, the uncertainty in the spin assignment, in particular for the state at 991 keV, hampers the extraction of electromagnetic matrix elements from the Coulomb excitation * justyna.samorajczyk@gmail.com data and makes the results ambiguous.…”