Shape coexistence inAu187

Abstract

The level structure of odd-proton '" Au was studied using the " Yb{' F,4n) reaction. Gammagamrna coincidence, angular distributions and y-y-time measurements were used to establish the energies, spins, parities, and lifetimes for the states in the decay scheme of '"Au. Both prolate and oblate structures have been established. The prolate bands are built on the~h9/2 (o, =+~) and thẽ i &3/2 (cx=~) particle states. An oblate, strongly coupled band built on a 90+10 ns isomeric state is reported for the first time. A second oblate structure built on the A»/~p roton-hole state was established to much higher spin than before. The backbend present in the~i »/2 band has been interpreted as the alignment of a pair of h9/p protons.

Evidence for shape coexistence in186Pt

“…The band 2 in 184pt shows a crossing with an alignment gain of A i~4 h due to i13/2 quasineutrons [4]. In 186pt the (vi~3/2) 2 crossing is absent in the prolate (+,0)o and (-, 1)2 bands as well as in all bands of lS5Ir [19] and 187Au [20].…”

“…This is further supported by the fact that no crossing is observed in the lrh9/2 bands in 18Sir and 187Au. Consid- [20] ering blocking this can only be understood if the crossing in the (+, 0)o band of ls6pt is due to the (7~h9/2) 2 configuration. This conclusion is confirmed by the observation of a crossing in the rci13/2 band of lSVAu at he)=0.24 MeV with an alignment gain of A i ~ 6 h. A rotational alignment of a h 9/2 quasiproton pair is only expected for a prolate nuclear shape.…”

“…A configuration assignment for the (+, 0)o band after the crossing can be obtained from blocking arguments considering the backbending behaviour of bands in the neighbouring nuclei 185pt [3], 18Sir [19] and 18VAu [20] as shown in Fig. 4b.…”

Triaxial deformation and nuclear shape transition in192Au

“…In the present work this sequence was expanded up to I π = 29 − with the level energy of 5708.2 keV. An I π = 20 + isomer (T 1/2 = 5.4 (3) ns, E i = 2153 keV with respect to the 11 − isomer) was established previously [21]. Spin and parity values were assigned to this state in accordance with the systematics of similar structures in the neighboring nuclei, e.g., the 20 + state in 190 Au is an isomer (T 1/2 = 6.9(1) ns E i =2172 keV with respect to the 11 − isomer) [21].…”

“…The lighter isotopes are prolate deformed. By adding more and more neutrons, the shape becomes oblate with the quadrupole deformation parameter β 2 [1] taking values β 2 ≤ 0.15 [2][3][4]. A prolate-oblate shape change has been discussed for these nuclei [5][6][7][8][9][10][11].…”