稳定线附近Ir同位素三轴形变及形状演化研究

High excited states of 189,190Ir nuclei near stability will be populated by incomplete fusion reaction induced by the weakly bound nucleus 9Be on 187Re. By detecting the alpha particle in coincidence with the de-excited gamma ray, high-spin states of 189,190Ir can be firmly identified. To obtain the reduced transition probabilities B(E2) and B(M1) of the excited states, the lifetime of excited states will be measured by means of Doppler-shift attenuation method (DSAM). This project aims at the two main goals: i) search for the possibility of chiral bands in 190Ir nucleus, the results could provide a strong evidence for nuclear triaxiality in mass A=190 region, and ii) search for multi-quasiparticle high-K isomeric states in 189Ir, the structure of which is of particular interest in investigating the static and dynamic effects on quantum number K of nuclei due to the triaxial degree of freedom. The comparison of theoretical calculation and experimental result will enable us to investigate the shape and shape evolution for iridium isotopes near A=190 region.

利用弱束缚核非完全熔合反应187Re(9Be,alpha-Xn)布居稳定线附近核189,190Ir的高激发态，通过alpha-gamma-gamma符合技术建立其高自旋能级纲图。采用多普勒位移衰减法(DSAM)测定189,190Ir的能级寿命，提取B(E2)及B(M1)值。着重在190Ir核中寻找手征双重带，获取A=190核区三轴形变存在的强有力实验证据；在189Ir核中寻找高K多准粒子组态及同核异能态，研究gamma形变自由度对K量子数的影响；最后，通过理论计算与实验比较，深入了解Ir同位素形变及其演化规律。

我们利用了弱束缚核的非完全熔合反应186W(7Li,xn)，在日本大阪大学加速器上开展了189,190Ir的高自旋态首轮实验研究，更新并扩展了189Ir的能级结构，通过衰变信息证实了实验中产生并布居了190Ir的高激发态，同时，本次实验首次建立了丰中子核189Os的高自旋态能级结构。为了进一步提高实验的统计量，我们申请了中国原子能院的束流，第二轮实验计划于2022年3月份进行。