The Study Of High Excited States In¹¹B Nuclei

Since the usage of radioactive beam facilities in1980s, new phenomena, suchas halo and skin nuclei, disappearance of magic number predicted by shell mod-el, the emergency of new magic number, the inversion of energy level for groundstate, have extremely promoted the development of nuclear physics, resulting theformation of a new discipline–radioactive nuclear beam physics. Utilizing thelow and intermediate-high energy heavy ion beam, together with the heavy ionreactions serving as an artificial laboratory of nuclear physics available in terri-tory, could we investigate the extreme limited nuclei, such as the nuclei aroundproton or neutron drip-line that far away the-stability line, and also is pro-viding the most direct experimental evidence on understanding the fundamentalinteraction–nuclear force.The usage of radioactive beam facility and the development of technique onnuclear particle detection has made the availability of investigating both of thenuclear structure and key reactions in nuclear astrophysics, such as18Ne,22Mg,meanwhile extraordinarily advanced the nuclear astrophysics.Recent years, the exploration of cluster structure in low-lying excited statesin11B have been carried out theoretically and experimentally. The2+t clusterstructures were discovered and determined in succession for excited states at E=8.65MeV and12.65MeV. Only few knowledge, however, was obtained for thesestates, uncertainties of assignments of spin-parities, isospin components still existbecause of several single particle-decay channels are open at high excited statesthat well lie above the proton, neutron, particle separation energies. As one ofneutrino process nuclei in furthermore, the properties of energy levels in11B hasplay an important role in determining the results in calculations and the accuracyof nucleosynthesis path during the evolution of stellar which formed during thebig-bang explosion that predicted by nuclear astrophysics model. Experimental-ly, the excited states in11B was investigated by elastic-and inelastic-scatteringreaction of neutron, proton, triton, and particles on target nuclei, or by di- rect reactions, such as pick-up reactions (p,), stripped reactions (t, p),(d,p),(3He, p),(3He, d). The data for differential cross-section at excited statesaround single-particle separation energies were fitted by utilizing the shell model,optical model, and R-Matrix theories, an accordance of determinations of thesestates in resonance properties was obtained, except for several high excited s-tates. The precise measurements of high excited states could not only be helpfulfor the firm assignments of corresponding energy levels, but provide abundantexperimental information for the studying of nuclear structure with A=4n (nis non-zero integer) nuclei and make the validation of isospin physics in frontednuclear physics.In January,2012, we have performed the measurement of high energy levelsin11B with the combination of Thick-Target technique and Inverse Kinematicsresonance elastic scattering method(TTIK) at the Heavy Ion Research Facility(HIRFL) with Radioactive Ion Beam Line in Lanzhou (RIBLL). The secondarybeam10Be was generated by the RIBLL through the projectile fragmentationreaction of a59.62MeV18O primary beam provided by the Sector SeparationCyclotron(SSC) bombarding on a solid853.96mg/cm2-thick target of9Be. Theproduced10Be was transported and purified and finally reached the user terminaland incident on the41.85mg/cm2-thick polyethylene reaction target. Protonsthat emitted from the reactions of10Be+p�'11B*�'10Be+p was detected bythe silicon telescope arrays downstream from the target. The differential crosssection of the10Be+p resonance elastic scattering reaction was extracted bythe method of kinematics reconstruction, the resonance parameters of populat-ed excited states were determined from the R-Matrix fitting to the data. Thewidth of two of observed excited states located at E=14.55,16.18MeV bothwith isospin value of T=3/2are in accord with previous measurements withinuncertainty, but the assignments of their spin-parities are expected to be firmlydetermined by higher precise experiments because of the present poor statistic-s. The spin-parity of state located at E=14.74MeV is assigned to be3/2with a proton-decay partial width as large as830±145keV. A new、probableexisted state located at E13.46MeV was observed, which was fitted well withthe Breit-Wigner type single level formula and was considered to be probably an unnatural-parity state. It is revealed by the present measurement that Thick-Target Inverse Kinematics(TTIK) resonance elastic scattering method playing arole in studying the isospin properties of excited states in nuclei is an effectiveresearch approach.It should be emphasized here that the merits of Thick-Target Inverse Kine-matics resonance elastic scattering method shed light on the investigations of thenuclear structure, especially those reactions involving the weak-bound nuclei ofRIB with low intensities. The replacement of solid polyethylene target with pure,and continuation adjusted pressure gas target is a new technique that developswell recent years. Hopefully, experiments with inverse kinematics method withresonance elastic scattering reaction is expected to be carried out to preciselymeasure the properties of11B including the-rays decayed from the high excitedstates.