Lifetime Measurement Of Candidate Chiral Doublet Bands In The Odd-odd Nucleus ⁸⁰Br

Chiral symmetry is a widespread symmetry in nature.The chiral symmetry of nuclei was first proposed in 1997 by S.Frauendorf and Jie Meng.Although it is later than the proposal of the chirality symmetry in molecules and the ba-sic particles,this theory has opened a new field of a nucleus research,and has become a hot topic.They pointed out that the triaxial nucleus shows the chiral symmetry when its rotating.A pair of nearly degenerate 0△ I=1 bands based on the same configurations can be observed in experiment.Besides,the pair of near degeneracy bands with chiral nuclei should also have the following characteristic-s:The S（I）（S（I）＝[E（I）-E（I-1）]/2I）values of the pair of near degeneracy bands should possess a smooth dependence with spin.There should be very similar B（M1）and B（E2）transition strengthes between the chiral partner states.The B（M1）/B（E2）ratios staggering as a function of spin.The spin alignments be-tween the doublet bands should be very similar.The interband B（E2）transitions disappear in the chiral region.Among them,the similar electromagnetic tran-sition probability value is an important criterion.However,because the B（M1）and B（E2）are related to level lifetime,this makes it a physical quantity difficult to extract from experiment.At 2011,odd-odd nucleus ⁸⁰Br was proposed as a chiral nucleus by Shouyu Wang.It is also the first chiral nucleus in the A～80 region.However,there is also a lack of the most direct evidence,that is,the similar values of B（M1）and B（E2）.Current work focuses on the lifetime measurement of the high spin states,and thus obtains the B（M1）and B（E2）values,in order to provide the evidence for the existence of the chiral doublet bands in⁸⁰Br.The experiment was performed in the MP tandem accelerator of the Max-Planck-Institut fur Kernphysik Heidelberg,Germany.Excited states in⁸⁰Br were populated using the 76Ge（7Li,4n）reaction at a beam energy of 35 MeV.In the experiment about 1.4×109 coincidence events of fold 2 or higher were Geasured.Emitted γ rays were measured with six EUROBALL CLUSTER detectors po-sitioned at±40°,±90°,and ± 140 ° relative to the beam direction.In this work,the data from the detectors located in ±40° and ± 140° degrees are used for lifetime extractions,and the data from all detectors are used to extract the transition intensities.Based on the analysis of data,this paper shows the lifetime of levels from 9+ to 12+ in chiral doublet bands and the transition intensities of the⁸⁰Br.According to these results,we obtained electromagnetic transition probability of the levels from 9+ to 12+ in chiral doublet bands.We compare these experimental values with the results of the particle rotor model calculations.It shows that these two bands have the same electromagnetic transition probability values with controllable error range.So we suggest the⁸⁰Br is a chiral nucleus.