Kπ=8−isomers andKπ=2

Abstract

Isomers have been populated in 246 Cm and 252 No with quantum numbers K π = 8 − , which decay through K π = 2 − rotational bands built on octupole vibrational states. For N = 150 isotones with (even) atomic number Z = 94-102, the K π = 8 − and 2 − states have remarkably stable energies, indicating neutron excitations. An exception is a singular minimum in the 2 − energy at Z = 98, due to the additional role of proton configurations. The nearly constant energies, in isotones spanning an 18% increase in Coulomb energy near the Coulomb limit, provide a test for theory. The two-quasiparticle K π = 8 − energies are described with single-particle energies given by the Woods-Saxon potential and the K π = 2 − vibrational energies by quasiparticle random-phase approximation calculations. Ramifications for self-consistent mean-field theory are discussed.

Investigation of high-Kstates in252No

“…The deformed shell gaps indicated by the experiments are N = 152 and Z = 100 [1]. The present neutron and proton level schemes at equilibrium deformation differ from those in previous publications [9,16,48,49].…”

“…This assignment was made by analogy with other N = 150 isotones. In fact, K π = 8 − isomers have been found in 244 Pu [16,17], 246 Cm [16,18], 248 Cf [19], and 250 Fm [20]. Very similar level schemes are observed in 246 Cm and 250 Fm, where the I π = 8 − isomer decays into the ground-state rotational bands via an intermediate excited band.…”

“…The presence of side bands with spin and parity 2 − seems to be a common feature in N = 150 isotones (e.g., 252 No, 250 Fm [20], 248 Cf [19], and 246 Cm [16,18]). The similar and low excitation energy (E x ∼ 1 MeV) of the K π = 2 − bandhead level suggests a collective character (namely, octupole correlations).…”

“…The decay of 254 No was recently revisited by Herzberg et al [13] and by Tandel et al [14], where a second isomer was found. In the nucleus 252 No, a new K isomer with a half-life of 110 ± 10 ms at an excitation energy of 1254 keV was discovered at SHIP (GSI, Darmstadt) [15] and confirmed at FMA (Argonne National Laboratory) [16], both experiments using decay spectroscopy techniques.…”

“…On the other hand, both HFB models predict the two-quasiproton states at higher excitation energies (i.e., E x ∼ 2000 keV). In contrast, the macroscopic-microscopic Woods-Saxon calculations predict K π = 8 − isomers at ∼1 MeV for both two-quasineutron and two-quasiproton configurations [2,16,20]. Recent random phase approximation (RPA) calculations predict a two-neutron quasiparticle state at 1300 keV [24].…”