The Investigation Of Resonant Levels For Neutron Capture Reactions Of ⁵⁸Ni,⁶¹Ni In Weak S-Process

In the nuclear astrophysics,how to produce heavy elements has been one of the most important issues today.In stars,about half of the elements from Fe to U are produced in the s process,among which the elements from Fe to Zr are mainly synthesized by the weak s process occurring above 8 solar masses.In the nucleosynthesis of weak s process,the content of ⁵⁸Ni is very rich.Like ⁶²Ni,it is a seed nuclide in the nucleosynthesis path,so it presents a unique bottleneck effect on the nucleosynthesis of weak s process.However,⁶²Ni is usually overestimated compared to the observational data of solar system elements in model calculations.Among them,the captured radiation data is extremely limited,and the measurement accuracy is insufficient.The spin-parity assignment of high excited state energy levels is also controversial,which limits the calculation accuracy of s process and r process in the star model.In this project,we used the multi-channel multi-level AZURE complex core R-matrix program to calculate and analyze the ⁵⁸Ni?n,??⁵⁹Ni reaction of P.Zugec in2014,the ⁵⁸Ni?n,p?⁵⁸Co reaction of J.Konijn in 1963,the ⁵⁸Ni?n,??⁵⁵Fe reaction of V.V.Ketlerov in 1997 and A.Fessler in 1999,the ⁶¹Ni?n,??⁶²Ni reaction of A.Ernst in1970.The main conclusions are as follows:?1?Four new suggested energy levels and parity values of ⁵⁹Ni were obtained for the analysis of ⁵⁸Ni?n,??⁵⁹Ni reaction channels:E_x=9009.2 keV?1/2^-??9021.7 keV?3/2^-??9023.9 keV?3/2⁺??9061.2 keV?1/2⁺?;?2?Through the analysis of ⁵⁸Ni?n,p?⁵⁸Co reaction,the spin-parity of E_x=11.3553MeV?1/2⁺?and 11.4393 MeV?3/2⁺?was identified for the first time.Optimized the spin-parity values of E_x=11.6411 MeV?3/2⁺?and 11.9066 MeV?3/2⁺?resonance energy levels,supplementing almost all existing reports of E_x=11-13 MeV at ⁵⁹Ni spin-parity value of energy levels in the excitation energy range;?3?By fitting the reaction of ⁵⁸Ni?n,??⁵⁵Fe,our work identified the spin-parity of excitation energy at E_x=13.4812 MeV?3/2⁺??13.4977 MeV?3/2⁺??13.7246 MeV?3/2⁺??14.4662 MeV?3/2^-??16.3516 MeV?3/2^-??17.4831 MeV?3/2^-??19.8673 MeV?3/2⁺??23.1014MeV?3/2^-?at the first time.?4?Based on the ⁶²Ni level parameters obtained by the reaction of ⁶¹Ni?n,??⁶²Ni measured by S.Kopecky et al.in 2006 and fitted by the multilevel REFIT program,a multi-channel multi-level R-matrix fitting was performed on the measurement data of ⁶¹Ni?n,??⁶²Ni by A.Ernst et al.in 1970.By calculating and comparing thec² values,the three proposed new energy levels and parity indicators are E_x=10628.1 keV?1^-??10631.6 keV?1^-??10668.5 keV?1⁺?respectively.The other two new energy levels are E_x=10636.3 keV and 10685.8 keV.Due to the experimental error of these two energy levels,the most likely values of spin-parity are 1⁺and 2⁺respectively,but the possibility of spin-parity values such as1^-,2^-and 1⁺,1^-and 2^-cannot be ruled out accordingly.The identification of new energy level parameters in this work not only enriches the understanding of nuclear structure information,but also affects the nuclear reaction rate and abundance of Cu and above elements in the nuclear synthesis path in s process.Providing a new possible explanation for further understanding the excessive calculation of abundance of ⁶²Ni and ^63,65Cu elements in star models.New higher resolution measurement is higly required for further confirmation for the above mentioned assignments of level parameters.