We report on a new lifetime measurement of the E_x=6792 keV state in 15O via the Doppler-shift attenuation method at the E=259 keV resonance in the reaction 14N(p,g)15O. This subthreshold state is of particular importance for the determination of the ground state astrophysical S factor of 14N(p,g)15O at stellar energies. The measurement technique has been significantly improved compared with previous work. The conclusion of a finite lifetime drawn there cannot be confirmed with the present data. In addition, the lifetime of the two states at E_x=5181 and 6172 keV have been measured with the same technique in order to verify the experimental method. We observe an attenuation factor F(tau)>0.98 for the E_x =6172 and 6792 keV states, respectively, corresponding to tau<0.77 fs. The attenuation factor for the E_x=5181 keV state results in F(tau)=0.78+/-0.02 corresponding to tau=8.4+/-1.0 fs in excellent agreement with literature.
Lifetime of 26S and a limit for its 2p decay energy
未知的同位素26 S,预计通过双质子(2 p)发射衰变,在理论上进行了研究,并在实验上进行了搜索。在相对论平均场(RMF)方法中检查了该核的结构。提出了一种在三体衰变计算中考虑多体结构的方法。RMF计算的结果被用来作为三集团衰变模型的输入,以研究该核可能的2 p衰变分支。在50.3A MeV ~(32)S束流的碎裂反应中进行了~(26)S的实验研究。没有观察到26 S或25 P(推测为26 S的质子不稳定子系统)的事件。根据获得的生产系统学,26 S的半衰期上限为T_{1/2} <79 ns was established from the time-of-flight through the fragment separator. Together with the theoretical lifetime estimates for two-proton decay this gives a decay energy limit of Q_{2p} >640 keV。发现25 P的类似限值为T_{1/2} <38 ns and Q_{p} >110 keV。在单质子发射是26 S衰变的主要分支的情况下,该核的极限Q_{2p} >230 keV。26 S可能存在于皮秒寿命范围内,对这种同位素的进一步研究有望用于飞行衰变技术。
Improved $S$-factor of the $^{13}$C(p,$γ$)$^{14}$N reaction at $E_{\mathrm{p}}\,=\,$330-740 keV and parameters of resonances at 448 keV and 551 keV
University of Edinburgh(爱丁堡大学);HUN-REN, Institute for Nuclear Research (HUN-REN Atomki)(匈牙利研究与创新网络核子研究所(HUN-REN Atomki));University of Surrey(萨里大学);University of Debrecen(德布勒森大学)
Hindered $ΔK=1$ Dipole Strength in octupole bands in $N=90$ $^{154}$Gd from Lifetime Measurements with $γ-γ$ fast timing technique
Variable Energy Cyclotron Centre(可变能量回旋加速器中心);Homi Bhabha National Institute(霍米·巴巴国家研究所);Institute of Modern Physics, Chinese Academy of Sciences(中国科学院近代物理研究所);Department of Physics, Hokkaido University(北海道大学物理学系);Nuclear Reaction Data Center, Hokkaido University(北海道大学核反应数据中心);Grand Accèlèrateur National d’Ions Lourds(重离子大型加速器)
First application of Markov Chain Monte Carlo-based Bayesian data analysis to the Doppler-Shift Attenuation Method
主要是由于$^{30}$ P $(p,γ)^{31}$ S反应的热核反应速率存在很大的不确定性,限制了我们对经典新星的理解,我们使用TRIUMF同位素分离器和加速器(ISAC-II)设施的多普勒频移寿命(DSL)设施对$^{31}$ S激发态进行了寿命测量。通过$^{3}$ He $(^{32}$ S $,α)^{31}$ S反应填充$^{31}$ S激发态。退激发$γ$射线被三叶草型高纯锗探测器探测到,与硅探测器望远镜探测到的$α$粒子重合。本文首次应用现代马尔可夫链蒙特卡罗贝叶斯方法对多普勒频移衰减法$γ$射线数据进行了线型分析。我们测定了$^{31}$ S的两个最低激发态的寿命。第一个实验上限上的四个高躺态的寿命已经得到。实验结果进行了比较,壳模型计算使用五个通用的$sd$壳哈密顿。$γ$射线起源于天体物理学上重要的$J^π=3/2^+$,260 keV $^{30}$ P $(p,γ)^{31}$ S共振的证据也被观察到,尽管对寿命的强烈限制需要更好的统计。
Rapid structural evolution of neutron-rich silicon isotopes toward N = 28
Facility for Rare Isotope Beams, Michigan State University(密歇根州立大学稀有同位素束设施);Department of Physics and Astronomy, Louisiana State University(路易斯安那州立大学物理与天文系);Department of Physics and Astronomy, Michigan State University(密歇根州立大学物理与天文系);Advanced Science Research Center, Japan Atomic Energy Agency(日本原子能机构先进科学研究中心);Center for Nuclear Study, University of Tokyo(东京大学核研究发展中心);Center for Computational Sciences, University of Tsukuba(筑波大学计算科学中心);Research Center for Nuclear Physics, Osaka University(大阪大学核物理研究中心);KU Leuven, Instituut voor Kern- en Stralingsfysica(荷语鲁汶大学核与辐射物理研究所)