| The level structures of 119Sn and 76As have been studied via in-beam spectroscopy.We first introduced the level structures and shape coexistence of the semimagic nucleus 119Sn,and then introduced the first observation of the high spin state of the odd-odd nucleus 76As in the A～80 mass region.Sn isotopes near the magic number of proton Z=50 play an important role in the study of low-energy nuclear structure.Their low energy states can be well reproduced by using shell model-calculations.Recently,experiments have found that some nuclei of Sn isotopes exhibit coexistence of spherical and prolate shapes.The spherical state is considered to be dominated by neutron quasiparticle excitation.The deformed structure is thought to be excited by the protons in the shell of Z=50,and the valence nucleons is coupled to the two-particle two-hole intrusion state.The coexistence of spherical and deformed collective bands has been systematically observed in even-even nuclei 106-118Sn and odd-A nuclei 109-117Sn.Whether the heavier Sn isotopes still have the shape coexistence phenomen-on is an open question.The high spin state of atomic nucleus 119Sn near the stability line is difficult to population through conventional fusion evaporation reactions,excited states in 119Sn were populated in the incompete fusion 7Li+116Cd reaction via the(7Li,1p3n),(7Li,1d2n),and(7Li,1t1n)channels.A 7Li beam of 42MeV was provided by the HI-13 Tandem Accelerator at the China Institute of Atomic Energy in Beijing(CIAE).The target was self-supporting 116Cd with a thickness of 2.5mg/cm2.The γ rays of the product nuclei were detected with an array consisting of nine Compton-suppressed HPGe detectors and two low-energy photon spectrometer(LEPS)detectors.The detectors were calibrated for both energy and efficiency using 152Eu and 133Ba sources placed at the target position.A total of approximately 1.2 ×108 γ-γ coincidence events were accumulated during the experiment.A total of 8 new transitions were discovered in this experiment,and the multipolarity of the transitions was determined by extracting the ADO values of gamma rays;A new energy level sequence is found.Through the systematics comparison of its experimental characteristics and the theoretical calculation of the adiabatic and configuration-fixed three-axis relativistic mean field method,it is shown that this energy level sequence in 119Sn is a prolate shape deformation band,thus extending the experimental observation of the deformation collective band of Sn isotope chain to the mass number of 119.Since the discovery of the first 80Br chiral atomic nucleus in 2011,the study of the chiral atomic nucleus in the A～80 mass region has aroused great interest of researchers.Several candidate atomic nuclei have been discovered in this nuclear region,forming a "chiral atomic island".How large is this chiral atomic island,and where is its boundary?In addition,does this lightest chiral atomic island exhibit any special properties?This requires us to further study the nuclear structure of the 80 nuclear region.The excited state of odd-odd nucleus 76As in the A～80 mass region was populated by the fusion evaporation reaction of 74Ge(4He,1p1n)76As.The experiment was performed in the iThemba National Laboratory of South Africa.The beam was provided by the separated sector cyclotron(SSC)accelerator,the beam energies are 58.6MeV and 62.6MeV,the thickness of the target is 2.85mg/cm2,the thickness of the carbon backing is 10.7mg/cm2,and the y rays were detected by AFRODITE(African Omniposition Detector for Innovative Technologies and Experiments)detection array,including 8 Clover detectors and 2 low-energy photon detectors(LEP).Totally 3×109 y-y coincidence events were obtained from this experiment.After data analysis,a total of 28 new energy levels,42 new transitions and 5 rotational bands were found,and the configuration of two positive parity rotational bands were suggested as πg9/2?vg9/2,the three negative parity bands configuretions were suggested as πf5/2?vg9/2,πp3/2?vg9/2 and πg9/2?v(p3/2/f5/2),respectively.The pair of positive parity bands were interpreted as chiral doublet bands by studying their experimental energy spectra,S(Ⅰ),and electromagne-tic transition probability ratios.By systematically comparing the energy level splitting values of candidate chiral bands in the 80 mass region,it was found that the energy level splitting of the 76As double band is the smallest,indicating that 76As is likely to be the most stable chiral geometrically discovered atomic nucleus in the A～80 mass region. |
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