In the present research, we used the 17Ne beam at 30.8 MeV/u to bombard the 43mg/cm2 12C target and measured the angular correlations between the fragments and emitted proton. In the break-up reaction of 17Ne, one-proton knockout would result in an unstable nu-cleus 16F, which would further decay by the proton emission. The measured angular correlation between the 16F momentum and the relative momentum of its decay products was compared with theoretical calculations and indicated that the valence proton in 17Ne has the most probability to be situated in the s1/2 orbital with a small admixture of the d5/2 orbital. The present results suggest that 17Ne has a halo structure.
Four high-purity germanium 4-fold segmented Clover detectors have been applied in the experiment of neutron-rich nucleus 21N. The performance of those four Clovers have been tested with radioactive sources and in-beam experiments, and the main results including energy resolution, peak-to-total ratios, the variation of the hit pattern distribution in different crystals of one Clover detector with the energy of γ ray, and absolute full energy peak detection effciency curve, were presented.
Knockout reaction experiment was carried out by using the 6He beams at 61.2 MeV/u impinging on a CH2 target. The α core fragments at forward angles were detected in coincidence with the recoiled protons at larger angles. From this exclusive meas urement the valence nucleon knockout mechanism and the core knockout mechanism can be distinguished by the relation be tween the polar angles of the core fragments and the recoiled protons, respectively. It is demonstrated that the core knockout mechanism may result in some strong contamination to the real invariant mass spectrum.
Lü LinHui1, YE YanLin1, JIANG DongXing1, HUA Hui1, ZHENG Tao1, LI ZhiHuan1, GE YuCheng1, LI XiangQing1, LOU JianLing1, CAO ZhongXin1, SONG YuShou1, XIAO Jun1, LI QiTe1, QIAO Rui1, YOU HaiBo1, CHEN RuiJiu1, XU HuShan2, WANG JianSong2, GUO ZhongYan2, ZHANG XueYing2, LI Chen2, HU ZhengGuo2, CHEN RuoFu2, WANG Meng2, XU ZhiGuo2, YUE Ke2, TANG Bin2, ZANG YongDong2, ZHANG XueHeng2, YAO XiangWu2, CHEN JinDa2 & BAI Zhen2 1 School of Physics and State Key Laboratory of Nuclear Physics and Technology, Peking University, Beijing 100871, China
The Halo and cluster structure at the ground state of unstable nuclei are among the most exciting phenomena of current nuclear physics. Probing these structures requires a careful selection of reaction tools. In the past twenty years, knockout reactions have been used intensively to investigate spectroscopically the structure of unstable nuclei. In this report we have illustrated the latest development of the knockout reaction tool and have emphasized the recoiled proton tagging method. A quantitative criteria is developed to evaluate the quasi-free feature of the knockout process. The newly discovered 'towing mode' reaction tool is also outlined and its applicability at transit energies is discussed.
We have tested and analyzed the properties of two-dimensional Position-Sensitive-silicon-Detector (PSD) with new integrated preamplifiers. The test demonstrates that the best position resolution for 5.5 MeV α particles is 1.7 mm (FWHM), and the best energy resolution is 2.1%, which are notably better than the previously reported results. A scaling formula is introduced to make the absolute position calibration.
The direct proton capture and resonance proton capture properties of stellar reactions 22Mg(p,γ)23Al and 26Si(p,γ)27P are studied by employing a mean-field potential obtained from the Skyrme-Hartree-Fock(SHF) model.Calculations with the SHF potential reproduce well the loosely-bound structure of the ground states as well as the widths of the resonant states in these nuclei.With the obtained potential we estimate the reaction rates of direct proton capture and resonance proton capture to nuclei 23Al and 27P.The effect of the 27P loosely-bound structure on the S factor of the direct proton capture is also discussed.
The β-decays of neutron-rich carbon,nitrogen and fluorine isotopes have been sys-tematically studied using the OXBASH shell Model.In the psd,spsd and spsdpf model space,we use the W BP interaction to calculate the half-lives and neutron emission probabilities of neutron-rich carbon and nitrogen isotopes,respectively.With the USD (W) and CW interactions,we calculate the half-lives and neutron emission probabilities of neutron-rich fluorine isotope in the sd model space,respectively.The calculated half-lives and neutron emission probabilities repro-duce recent experimental data very well.It seems to show that the particles of the neutron-rich carbon and nitrogen isotopes are mainly excited in the spsd space.The β-decay of 21N to the neutron bound states in 21O is mostly the first forbidden transition which makes the neutron emission probability increase.The theoretical calculation of β-decay of 25F to 25Ne with CW interaction shows that CW interaction is better than USD interaction.
Total Routhian Surface (TRS) calculations have been performed for even-even nuclei along proton drip line to study nuclear ground-state deformations, as well as the odd proton nuclei Ho and Tm isotopes. The drip line nuclei show the expected shape transition with the shell e?ects. Ground-state shape changes from prolate to oblate at 143Ho and 145Tm in these two isotopes, which is due to the γ instability around N =76.
High-spin states in 157yb have been populated in the 144Sm(16O, 3n)157yb fusion-evaporation reaction at a beam energy of 85 MeV, and two rotational bands have been established for the first time. Within the framework of the triaxial particle-rotor model, the energy spectra and single-particle configurations of 157yb are investigated. The calculated energy spectra agree well with the experimental data. The newly observed vf7/2 band, and the previously known vi13/2 band in 157yb, are also discussed by means of Total-Routhian-Surface methods. The structural characters observed in 157Yb provide evidence for the shape coexistence of three distinct shapes: prolate, triaxial and oblate. At higher spins, both the vf7/2 band and the vi13/2 band in 157yb undergo a shape evolution with sizable alignments occurring.
