Determination of the stellar reaction rate for 12C（α,γ）16O： using a new expression with the reaction mechanism

The astrophysical reaction rate of 12C(α, γ)16O plays a key role in massive star evolution. However, this reaction rate and its uncertainties have not been well determined yet, especially at T9=0.2. The existing results even disagree with each other to a certain extent. In this paper, the E1, E2 and total (E1+E2) 12C(α, γ)16O reaction rates are calculated in the temperature range from T9=0.3 to 2 according to all the available cross section data. A new analytic expression of the 12 C(α, γ)16 O reaction rate is brought forward based on the reaction mechanism. In this expression, each part embodies the underlying physics of the reaction. Unlike previous works, some physical parameters are chosen from experimental results directly, instead of all the parameters obtained from fitting. These parameters in the new expression, with their 3σ fit errors, are obtained from fit to our calculated reaction rate from T9=0.3 to 2. Using the fit results, the analytic expression of 12C(α, γ)16O reaction rate is extrapolated down to T9=0.05 based on the underlying physics. The 12C(α, γ)16 O reaction rate at T9=0.2 is (8.78 ± 1.52) × 1015 cm3s-1mol-1. Some comparisons and discussions about our new 12 C(α, γ)16 O reaction rate are presented, and the contributions of the reaction rate correspond to the different part of reaction mechanism are given. The agreements of the reaction rate below T9=2 between our results and previous works indicate that our results are reliable, and they could be included in the astrophysical reaction rate network. Furthermore, we believe our method to investigate the 12C(α, γ)16O reaction rate is reasonable, and this method can also be employed to study the reaction rate of other astrophysical reactions. Finally, a new constraint of the supernovae production factor of some isotopes are illustrated according to our 12C(α, γ)16O reaction rates.     

Density effect of the neutron halo nucleus induced reactions in intermediate energy heavy ion collisions

Using an isospin-dependent quantum molecular dynamics (IQMD) model, we study the 15C induced reactions from 30-120 MeV/nucleon systematically. Here the valence neutron of 15C is assigned at both 1d5/2 and 2s1/2 states respectively in order to study the density effect of reaction mechanism. It is believed that the existent neutron halo structure at the 2s1/2 state of 15C will affect the light particle emission evidently. In our calculation, the different density distributions of 15C at two states are calculated by relativistic mean field (RMF) model and introduced in the initiation of IQMD model, respectively. It is found that some observables such as emission fragmentation multiplicity, emission neutron/proton ratio and emission neutrons’ kinetic energy spectrum are sensitive to the initial density distribution.     

用修正的擦碎模型研究碎裂反应的同位素分布

对统计擦碎模型(SAA)的计算方法进行修正和优化,并引入参数化的介质中核子-核子碰撞截面和核物质密度分布弥散度,可很好符合从中能到高能下碎裂反应产生同位素分布的实验截面,并能计算和拟合远离峰位、很低截面的同位素分布.     

Proton Halo or Skin in the Excited States of Light Nuclei

Properties of nuclei 13,15,N and 9B are investigated in the relativistic mean-field theory with NLz and NL3 force parameters.The calculated binding energies are very close to the experimental ones.The calculations show that the first excited state (1p1/2) in 9B,the first excited state (2s1/2)in 13 N and the second excited state(2s1/2) in 15N are weakly bound .In particular,for 13N and 15N,the proton density distributions in the two above excited states have a long tail and the rms radii of the last proton are greatly larger compared with their respective matter radii.It is predicted that a proton halo exists in the first excited state of 13N and in the second excited state of 15N,respectively.It also indicates that the first excited state in 9B is a proton skin state.     

Photons from a Chemically Equilibrating Quark-Gluon Plasma at Finite Baryon Density

We study hard photon production in a chemically equilibrating quark-gluon plasma at finite baryon density based on the Juttner distribution of partons of the system. We find that the photon yield is a strongly increasing function of the initial quark chemical potential.     

质子滴线附近的β缓发质子衰变

简要回顾了实验小组在过去8年中获得的实验结果, 即采用氦喷嘴快速带传输系统 +“p-γ”符合方法, 在稀土区质子滴线附近首次观测了9种新核素的β缓发质子衰变, 在A=90核区的N=Z线附近获得了5种核素的β缓发质子衰变的新数据. 并把这14种核素的半衰期, 自旋宇称, 形变以及生成反应截面的实验值与流行的核模型理论预言进行了系统地对比讨论. 从中看出:(1)⁸⁵Mo, ⁹²Rh以及“等待点”核⁸⁹Ru和⁹³Pd半衰期的实验值比近期Moller等人的宏观-微观理论预言值[At. Data Nucl Data Tables, 66, 131(1997)]长5—10倍, 因而明显地影响天体rp过程生成的核素丰度;(2)实验指认的质子滴线核¹⁴²Ho和¹²⁸Pm的自旋宇称与流行理论预言不符, 但用Woods-Saxon-Strutinsky方法可以计算得到相符的位能面;(3)实验估计的9种稀土核的生成截面比通用的Alice和HIVAP程序的计算值要小1—2个数量级.     

朗之万方程模拟核裂变碎片的同位旋标度

使用结合朗之万方程和统计分支的组合模型模拟¹¹²Sn+¹¹²Sn和¹¹⁶Sn+¹¹⁶Sn两个同位旋相关的反应系统, 通过高斯分布采样的方式得到了核裂变的碎片分布, 将两系统碎片的同位素和同中子异位素的分布相比, 发现存在同位旋标度律现象. 同时提取了同位旋标度系数, 发现同位旋标度系数是和碎片分布宽度相关的, 并且同能量、单位质量的粘滞系数也有很强的依赖关系.     

Photon Production in a Chemically Equilibrating Quark-Gluon Plasma at Finite Baryon Density： Complete Leading Order Results

We investigate hard photon production of the near-collinear bremsstrahlung and a new process called the inelastic pair annihilation, fully including the LPM effect, in a chemically equilibrating quark-gluon plasma at finite baryon density, and find that the effect of the system evolution on the photon production and large contribution of the bremsstrahlung make the total photon yield of the two processes as a strongly increasing function of the initial quark chemical potential.     

中能区86Kr+197Au反应中的能量耗散、π介子阈下产生和流角

用扩展BUU模型计算了中能区⁸⁶Kr+¹⁹⁷Au重系统的能量耗散、π介子阈下产生和流角,定量地拟合了43MeV/u ⁸⁶Kr+¹⁹⁷Au实验的能量耗散和类弹碎片核电荷数的关系及类弹类靶碎片核电荷数的关联.     

中子分布弥散度对反应总截面的影响

在引入库仑场修正的Glauber模型基础上,区分入射弹核和靶核中的中子、质子,并考虑有限力程相互作用,发展了一个计算核反应总截面的微观修正模型.如果引入一个核内中子分布弥散度随中子分离能的变化关系,则能较好地解释奇异核(如⁸He,¹¹Li,¹¹Be)反应总截面的反常增加.同时,该修正模型还能在低能到高能的范围内较好地拟会稳定核的反应总截面.