Evaluation of the 1077 keV γ-ray emission probability from ~(68)Ga decay

68Ga decays to the excited states of68Zn through the electron capture decay mode. New recommended values for the emission probability of 1077 keV γ-ray given by the ENSDF and DDEP databases all use data from absolute measurements. In 2011, JIANG Li-Yang deduced a new value for 1077 keV γ-ray emission probability by measuring the69Ga(n,2n)68Ga reaction cross section. The new value is about 20% lower than values obtained from previous absolute measurements and evaluations. In this paper, the discrepancies among the measurements and evaluations are analyzed carefully and the new values are re-recommended. Our recommended value for the emission probability of 1077 keV γ-ray is(2.72±0.16)%.     

Evaluation of the 1077 keV γ-ray emission probability from 6SGa decay

6SGa decays to the excited states of aSzn through the electron capture decay mode. New recommended values for the emission probability of 1077 keV γ-ray given by the ENSDF and DDEP databases all use data from absolute measurements. In 2011, JIANG Li-Yang deduced a new value for 1077 keV γ-ray emission probability by measuring the 69Ga（n,2n） 6SGa reaction cross section. The new value is about 20% lower than values obtained from previous absolute measurements and evaluations. In this paper, the discrepancies among the measurements and evaluations are analyzed carefully and the new values are re-recommended. Our recommended value for the emission probability of 1077 keV γ-ray is （2.72±0.16）%.     

（n,2n）反应实验研究中的中子准直器设计

用3He球形4中子探测器，通过直接反应法可以对核素的（n,2n）反应截面进行测量。在此类实验中，要求对中子束进行很好的准直。好的准直器设计要求能够提高样品处的中子注量率的均匀性，同时保证中子束流边缘处的下降幅度，能够降低低能中子所占份额。本工作采用FLUKA和MCNPX对圆柱形准直器、单锥形准直器及三种不同斜率的双锥形准直器对中子注量率的均匀性和低能中子所占份额进行了对比研究，结果表明，低斜率的双锥形准直器可以满足实验对这两方面的要求。同时，在有样品和无样品两种条件下，对探测系统经由这五种不同准直器准直后的中子束流的响应做了对比，结果显示，经过低斜率的双锥形准直器准直的中子束流，探测系统在有样品时表现为较高的计数率，在无样品时表现为较低的本底。除此之外，对准直器出口处的斜率对准直效果的影响也做了比较。最终中子准直器选用为这种低斜率的双锥形准直器，材料选用为紫铜、不锈钢、聚乙烯和铅。准直孔开口处直径为2.64 cm，长度为137 cm，经准直后样品处的中子束斑直径为3.2 cm。     

Cross-section measurement for the ~(93)Nb(n,2n)~(92g)Nb reaction at the neutron energy of 14.6 MeV by the AMS method

The cross-section for the~(93)Nb(n,2n)~(92g)Nb reaction has been measured at the neutron energy of 14.6 Me V using neutron activation and accelerator mass spectrometry(AMS)determination of the long-lived product nuclide~(92g)Nb.The neutron energy was generated from the D+T neutron source at the China Institute of Atomic Energy(CIAE).The neutron flux was monitored by measuring the activity of~(92m)Nb produced in the competing reaction channel of~(93)Nb(n,2n)~(92m)Nb.At the neutron energy of 14.6 MeV,the~(93)Nb(n,2n)~(92g)Nb reaction cross-section of(736±220)mb was obtained for the first time.