计算平均中子辐照量新公式的验证  

Test and Verification for Calculating Formula of Mean Neutron Exposure

作　　者：张凤华[1,2] 崔文元[2] 张波[2] 

机构地区：[1]沧州师范学院物理与电子信息系,河北沧州061001 [2]河北师范大学物理科学与信息工程学院,河北石家庄050016

出　　处：《河北师范大学学报（自然科学版）》2010年第5期549-554,共6页Journal of Hebei Normal University：Natural Science

基　　金：国家自然科学基金(10973006);河北省自然科学基金(A2009000251);河北省高校百名优秀创新人才支持计划基金;河北师范大学校内重点基金

摘　　要：最近的研究结果指出,低质量AGB(asymptotic giant branch)星辐射s-过程核合成模型氦壳层核合成区域的中子辐照量分布,同以前的对流核合成模型一样仍然非常接近指数分布;但是每个脉冲的中子辐照量Δτ和平均中子辐照量τ0之间的关系却不再是τ0=-Δτ/lnr,而近似为τ0=-Δτ/ln{q[1.002 0+0.660 2(r-q)+4.612 5(r-q)2-10.896 2(r-q)3+13.913 8(r-q)4]}(r为重叠因子,q为13C壳层占氦壳层的质量比例).利用文献对26颗Ba星以及太阳系s-过程元素观测丰度恒星模型核合成数值计算的拟合结果,以及经典模型的拟合结果,对新关系式进行了检验.结果表明,该关系式对其中的19颗Ba星以及太阳系都是适用的,对于另外7颗Ba星,关系式的失效可从模型参量数值的选择以及2种拟合机制的差异性等方面得到解释.研究结果证明了新关系式的可靠性.Recent results suggest that the distribution of neutron exposures in the He-shell nucleosynthesis regions in the model of radiative s-process nucleosynthesis for low-mass AGB（Asymptotic Giant Branch） stars,is approximately exponential,which is like those of the previous convective s-process scenarios.However,the relation between the neutron exposure Δτ of each pulse and the mean neutron exposure τ0 can not be represented by τ0=Δτ/ln r,which should be approximately τ0 =Δτ/ln{q[1.002 0＋0.660 2（r-q）＋4.612 5（rq）^2-10.896 2（r-q）^3＋13.913 8（r-q）^4]}（r is the overlap factor,q is the mass ratio of the 13 C shell to the He shell）.A further test for the reliability of the new formula is given,using the published results of s-process numerical calculations and the classical model by simulating the s-element abundance distributions for 26 Ba stars and the solar system.The results show that the new formula is suited for 19 Ba stars and the solar system.For the other 7 Ba stars,the invalidity of the new formula can be explained by the choice of value for model parameters and the differences between the two fitting mechanism.The results demonstrate that the new formula is reliable.

关 键 词：平均中子辐照量 AGB星 s-过程核合成 

分 类 号：P148[天文地球—天体物理]