Quadrupole moments of collective structures up to spin ∼65ℏ in 157Er and 158Er: A challenge for understanding triaxiality in nuclei

Diverse collective excitations in159Erup to high spin

“…The present experiment has also identified a band with a high moment of inertia, which is discussed in terms of a strongly deformed triaxial structure [20]. The lifetimes of states within similar structures in 157,158 Er [16] indicate discrepancies between the experimentally deduced and the predicted triaxial shape. The implications of this observation to 159 Er are discussed.…”

“…1 and has been assigned tentative spin values based on comparisons with CNS calculations [20]. Lifetime measurements on the bands in 157,158 Er [16] confirm that these bands are indeed strongly deformed. However, the experimentally extracted Q t values do not agree with the calculated favored triaxial minimum, which has positive gamma deformation.…”

“…In fact, a more deformed positive gamma or a negative-gamma deformation gives better agreement. These recent experimental results highlight a challenge for the understanding of the triaxial degree of freedom and suggest that other theoretical approaches may need to be explored [16]. Indeed, tilted cranking models suggest that the rotational axis can lie between the intermediate and short principal axes.…”

“…Moreover, rotational sequences have recently been identified that extend into the region of ultrahigh spin (> 60h) [15] and represent a re-emergence of collectivity beyond band termination in 158 Er. Comparison with results from cranked Nilsson-Strutinsky (CNS) calculations suggest that these collective rotational sequences are based on triaxial strongly deformed (TSD) shapes, although uncertainties persist as to the exact value of the gamma deformation [16]. A number of similar collective structures with characteristic high moments of inertia have now been observed in several neighboring nuclei [17][18][19][20][21].…”

High-spin terminating states in theN=88Ho155andRees1, Paul2, Simpson3 et al. 2015Phys. Rev. CSelf Cite6180View full textAdd to dashboardCite

“…The experimental states are compared with results from cranked Nilsson-Strutinsky calculations [9][10][11]. The behavior of 155 Ho at high spin is discussed in the context of other N = 88 isotones, and in particular 156 Er, where a new terminating state at I π = (46 + ) has been observed as part of a previous experiment [12][13][14].…”