The heavy elements in the Universe are formed during the s- and r-processes mainly in AGB stars and supernovae, respectively. Simulation of s- and r-nucleosynthesis critically depends on the neutron capture and weak d...The heavy elements in the Universe are formed during the s- and r-processes mainly in AGB stars and supernovae, respectively. Simulation of s- and r-nucleosynthesis critically depends on the neutron capture and weak decay rates for all the nuclei on the reaction chain. The present work analyzes systematically the neutron capture rates (cross sections) for the s-process nuclei, including ～3000 rates on ～200 nuclei. The network calculations for the constant temperature s-process have been performed using the different data sets selected as the nuclear inputs to investigate the uncertainties in the predicted s-abundances. We show that the available cross sections of neutron capture on many s-process nuclei still carry large uncertainties, which lead to low accuracy in the determination of s-process isotope abundances. We analyze the neutron capture cross section data for the same unique isobar nucleus accorded by year from previous work. Such an analysis indicates that the s-process has been studied for more than fifty years and there exist two research stages around 1976 and 2002, respectively. The needs and opportunities for future experiments and theoretical tools are highlighted to remove the existing shortcomings in the neutron capture rates.展开更多
^(95)Zr(n,γ)^(96)Zr是稳定燃烧的恒星中合成^(96)Zr的唯一途径,对研究恒星演化和重元素合成具有重要的意义。由于^(95)Zr半衰期为64 d,直接测量^(95)Zr(n,γ)^(96)Zr截面极为困难,因此,本工作采用替代比率法间接测量^(95)Zr(n,γ)^(96...^(95)Zr(n,γ)^(96)Zr是稳定燃烧的恒星中合成^(96)Zr的唯一途径,对研究恒星演化和重元素合成具有重要的意义。由于^(95)Zr半衰期为64 d,直接测量^(95)Zr(n,γ)^(96)Zr截面极为困难,因此,本工作采用替代比率法间接测量^(95)Zr(n,γ)^(96)Zr截面。本工作测量了^(94)Zr(^(18)O,^(16)Oγ)^(96)Zr和^(90)Zr(^(18)O,^(16)Oγ)^(92)Zr反应,得到了复合核^(96)Zr*和^(90)Zr*衰变到γ道的几率比,并利用截面已知的^(91)Zr(n,γ)^(92)Zr截面乘以实验所测比率,得到了En=0～8 Me V能区的^(95)Zr(n,γ)^(96)Zr中子俘获截面。展开更多
中子辐射俘获反应在反应堆运行、核装置设计及核天体物理研究中起重要的作用.4πBaF_(2)探测装置有着高时间分辨能力、低中子灵敏度、高探测效率等优点,适合开展中子辐射俘获反应截面数据的测量.中国原子能科学研究院核数据重点实验室...中子辐射俘获反应在反应堆运行、核装置设计及核天体物理研究中起重要的作用.4πBaF_(2)探测装置有着高时间分辨能力、低中子灵敏度、高探测效率等优点,适合开展中子辐射俘获反应截面数据的测量.中国原子能科学研究院核数据重点实验室建立了伽马全吸收装置(Gamma total absorption facility,GTAF),该装置用28块六棱BaF_(2)晶体和12块五棱BaF_(2)晶体构成了外径25 cm,内径10 cm的球壳,覆盖了95.2%的立体角.利用GTAF在中国散裂中子源Back-n束线上,测量了197Au(n,γ)的反应截面数据.测量数据通过能量筛选、PSD方法、晶体多重性筛选进行了初步本底扣除,随后结合对^(nat)C及空样品的测量数据对本底进行了分析及扣除,获得了197Au俘获反应的产额,利用SAMMY程序拟合得到了^(197)Au在1—100 e V的共振能量、中子共振宽度和伽马共振宽度参数.实验测量结果与ENDF/B-VIII.0数据库符合良好,其共振参数存在一定差异,分析原因可能与GTAF能量分辨率、Back-n的中子能谱测量精度、以及实验本底扣除方法相关,这也是下一步工作的重点.展开更多
基金supported by the National Natural Science Foundation of China (Grant Nos. 11021504, 11175258, 11275068 and 11175001)the Major State Basic Research Development Program of China (Grant No.2013CB834406)
文摘The heavy elements in the Universe are formed during the s- and r-processes mainly in AGB stars and supernovae, respectively. Simulation of s- and r-nucleosynthesis critically depends on the neutron capture and weak decay rates for all the nuclei on the reaction chain. The present work analyzes systematically the neutron capture rates (cross sections) for the s-process nuclei, including ～3000 rates on ～200 nuclei. The network calculations for the constant temperature s-process have been performed using the different data sets selected as the nuclear inputs to investigate the uncertainties in the predicted s-abundances. We show that the available cross sections of neutron capture on many s-process nuclei still carry large uncertainties, which lead to low accuracy in the determination of s-process isotope abundances. We analyze the neutron capture cross section data for the same unique isobar nucleus accorded by year from previous work. Such an analysis indicates that the s-process has been studied for more than fifty years and there exist two research stages around 1976 and 2002, respectively. The needs and opportunities for future experiments and theoretical tools are highlighted to remove the existing shortcomings in the neutron capture rates.
文摘^(95)Zr(n,γ)^(96)Zr是稳定燃烧的恒星中合成^(96)Zr的唯一途径,对研究恒星演化和重元素合成具有重要的意义。由于^(95)Zr半衰期为64 d,直接测量^(95)Zr(n,γ)^(96)Zr截面极为困难,因此,本工作采用替代比率法间接测量^(95)Zr(n,γ)^(96)Zr截面。本工作测量了^(94)Zr(^(18)O,^(16)Oγ)^(96)Zr和^(90)Zr(^(18)O,^(16)Oγ)^(92)Zr反应,得到了复合核^(96)Zr*和^(90)Zr*衰变到γ道的几率比,并利用截面已知的^(91)Zr(n,γ)^(92)Zr截面乘以实验所测比率,得到了En=0～8 Me V能区的^(95)Zr(n,γ)^(96)Zr中子俘获截面。
文摘中子辐射俘获反应在反应堆运行、核装置设计及核天体物理研究中起重要的作用.4πBaF_(2)探测装置有着高时间分辨能力、低中子灵敏度、高探测效率等优点,适合开展中子辐射俘获反应截面数据的测量.中国原子能科学研究院核数据重点实验室建立了伽马全吸收装置(Gamma total absorption facility,GTAF),该装置用28块六棱BaF_(2)晶体和12块五棱BaF_(2)晶体构成了外径25 cm,内径10 cm的球壳,覆盖了95.2%的立体角.利用GTAF在中国散裂中子源Back-n束线上,测量了197Au(n,γ)的反应截面数据.测量数据通过能量筛选、PSD方法、晶体多重性筛选进行了初步本底扣除,随后结合对^(nat)C及空样品的测量数据对本底进行了分析及扣除,获得了197Au俘获反应的产额,利用SAMMY程序拟合得到了^(197)Au在1—100 e V的共振能量、中子共振宽度和伽马共振宽度参数.实验测量结果与ENDF/B-VIII.0数据库符合良好,其共振参数存在一定差异,分析原因可能与GTAF能量分辨率、Back-n的中子能谱测量精度、以及实验本底扣除方法相关,这也是下一步工作的重点.
