Configurations and decay hindrances of high- K states in Hf180

Abstract

Multi-quasiparticle high-K states, several of which are isomeric, were observed in 180 Hf with the Gammasphere array. Lifetimes in the ns -µs range were determined using centroid-shift and decay measurements within a µs coincidence time window. The configurations of high-K states involve two and four quasiparticles, with states up to K π =(18 − ) established. High-K excitations are found to be progressively more favored with increasing excitation energy. The K quantum number is quite robust up to the highest spins observed, as evidenced by the large values of the reduced hindrance for isomeric decays. Rotational bands built on three high-K states are identified, and the measured branching ratios in these sequences enable the assignment of underlying configurations. Multiquasiparticle calculations using the Lipkin-Nogami approach for pairing, with blocking included, reproduce the observed high-K energies quite well.

Microscopic description of rotation: from ground states to the extremes of ultra-high spin

“…However, the pairing strength is different in even-even and oddmass nuclei in the CSM+PNC approach [13]; this is a well known deficiency of the cranked shell model (see, for example, Ref. [16]). In contrast, the same pairing strength is used in even-even and odd-mass nuclei in the CRHB+LN approach and, according to Ref.…”

Isomers in Tl203 and core excitations built on a five-nucleon-hole structure

“…This procedure has been used to assign multipolarity to transitions with relatively low energy (≈100-400 keV), which may have significant conversion coefficients. Further details of the above data analysis methods are described elsewhere [8,11,[23][24][25]. It may be noted that Tl x rays are not clearly visible in the spectra since Pb absorbers were placed on the Ge-detector modules to prevent triggering on x rays primarily from the excitation of the Au target.…”

Isomers in 203Tl and core excitations built on a five-nucleon-hole structure

“…To determine the half-life of the µs isomer, several three-dimensional histograms spanning suitable time intervals within the 800 µs beam-off period were created. Further details of data analysis methods are described elsewhere [17][18][19]. 203 Tl up to medium spin and excitation energy of E x ≈ 3 MeV had been identified earlier through the 204 Hg(d,3n) reaction with an incident deuteron energy of ≈ 25 MeV [9], and projectile fragmentation using a 1 GeV/nucleon 238 U beam on a thick 9 Be target [12].…”