| Symmetry and its breaking are of great importance in nuclear physics,such as chiral,reflection,and pseudospin symmetries.In 1997,Frauendorf and Meng pointed out that rotating triaxial nucleus may exhibit chiral geometry.The ideal chiral geometry in nuclei entails the angular momentum vectors of the valence proton,valance neutron,and core are mutually perpendicular to each other,thereby forming either a left-or a right-handed system.The experimental signal of the chiral symmetry breaking in nuclei is the observation of chiral doublet bands,which are a pair of nearly degenerate ΔI=1 bands with the same parity.So far,candidate chiral doublet bands have been reported experimentally in the A≈80,100,130,and 190 mass regions of the nuclear chart.In the A≈80 mass region,80Br,78Br,82Br,84Rb,81Kr,76Br and 74As have been reported as candidate chiral nuclei.The first part of the thesis is the observation of candidate chiral doublet bands in 84Rb.High-spin states in 84Rb have been studied using the 76Ge(11B,3n)reaction at a beam energy of 36 MeV.A pair of nearly degenerate positiveparity doublet bands have been extended.A total of 9 new transitions and one new level are added to the level scheme.According to the experimental properties,the positive-parity doublet bands have been interpreted as candidate chiral doublet bands.This interpretation is supported by the triaxial relativistic meanfield theory and the triaxial particle-rotor model calculations.The systematic comparison of the candidate chiral bands in the A≈80 mass region are also discussed.This work is the first observation of candidate chiral doublet bands in Z=37 Rb isotopes and extends the boundaries of the chiral nuclei in the A ≈80 mass region.The second part of the thesis is the performance and upgrade of the CsIbowl ancillary light charged particle detector array.For several decades,high resolution γ-ray spectroscopy research with large HPGe detector arrays played a cornerstone role in nuclear structure studies.Recently,nuclear research is gradually advancing towards high energy,high angular momentum,and high isospin,which means that the cross section of interested channel is gradually reduced.Therefore,auxiliary detection arrays are often needed to select reaction channels and reduce background interference.Nuclear structure study at high spins of neutron-deficient nuclei,populated in weak exit channels of heavy-ion fusion evaporation reactions,is difficult as there is strong γ-ray background from nuclei populated through strong accompanying exit channels.The conventional technique of coincidence γ-ray spectroscopy is difficult to follow for weak channels in the absence of any reaction channel selection device.A light charged particle detector array,named the CsI-bowl,has been developed as an ancillary detector to provide the selection of exit channels for in-beam γ-ray spectroscopy experiments.It consists of 64 CsI(Tl)detectors,which were packed to a tea-bowl structure.The scintillation light is collected by photodiodes that provide high quantum efficiency and minimal mass.The design,construction,PID resolution,and performances of exit channel selection of the CsI-bowl array are described.In the source tests,the best values of the FOM=3.3 and 12.1 can be obtained to identify α-particles and γ-rays using the charge comparison method for CsI-PD and CsI-APD detectors,respectively.The CsI-bowl array provided the good PID resolution for α-particles and protons in the 58Ni(19F,xpyn)fusion-evaporation reaction and the exit channels of interested can be selected.An upgrade version of CsI-bowl,named CsI-ball,has been under construction.The scintillation light will be collected by avalanche photodiode or silicon photomultiplier to further improve the PID capabilities. |
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