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Mass-independent fractionation of even mercury isotopes

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Science Bulletin 2016年第2期61卷 116-124页

作者： Hongming Cai Jiubin Chen State Key Laboratory of Environmental Geochemistry Institute of Geochemistry Chinese Academy of Sciences Guiyang 550081 China University of Chinese Academy of Sciences Beijing 100049China

Practically all physical, chemical, and biologi- cal processes can induce mass-dependent fractionation of mercury （Hg） isotopes. A few special processes such as photochemical reduction of Hg（Ⅱ） and photochemical degradation of methylmercury （MeHg） can produce mass- independent fractionation （MIF） of odd Hg isotopes （odd- MIF）, which had been largely reported in variable natural samples and laboratory experiments, and was thought to be caused by either nuclear volume effect or magnetic isotope effect. Recently, intriguing MIF of even Hg isotopes （even- MIF） had been determined in natural samples mainly related to the atmosphere. Though photo-oxidation in the tropopause （inter-layer between the stratosphere and the troposphere） and neutron capture in space were thought to be the possible processes causing even-MIF, the exact mechanism triggering significant even Hg isotope anomaly is still unclear. Even-MIF could provide useful information about the atmospheric chemistry and related climate changes, and the biogeochemical cycle of Hg.

关键词： Mass-independent fractionation Evenmercury isotopes Processes producing even-MIF Mechanisms triggering even-MIF Self-shielding neutron capture

Examination of n-T_(9) conditions required by N=50,82,126 waiting points in r-process

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Communications in Theoretical Physics 2021年第10期73卷 147-157页

作者： Nguyen Duy Ly Nguyen Ngoc Duy Nguyen Kim Uyen Vinh N T Pham Faculty of Fundamental Sciences Vanlang UniversityHo Chi Minh City 700000Vietnam Department of Physics Sungkyunkwan UniversitySuwon 16419Republic of Korea Department of Physics Ho Chi Minh City University of EducationHo Chi Minh City 700000Vietnam

We examined the conditions of neutron density(n) and temperature(T9) required for the N = 50, 82,and 126 isotopes to be waiting points(WP) in the r-process. The nuclear mass based on experimental data presented in the AME2020 database(AME and AME ± Δ) and that predicted using FRDM,WS4, DZ10, and KTUY models were employed in our estimations. We found that the conditions required by the N = 50 WP significantly overlap with those required by the N = 82 ones, except for the WS4 model. In addition, the upper(or lower) bounds of the n-T9 conditions based on the models are different from each other due to the deviations in the two-neutron separation *** standard deviations in the nuclear mass of 108 isotopes in the three N = 50, 82, and 126 groups are about rms = 0.192 and 0.434 Me V for the pairs of KTUY-AME and WS4-KTUY models,respectively. We found that these mass uncertainties result in a large discrepancy in the nn-T_(9) conditions, leading to significant differences in the conditions for simultaneously appearing all the three peaks in the r-process abundance. The newly updated FRDM and WS4 calculations can give the overall conditions for the appearance of all the peaks but vice versa for their old versions in a previous study. The change in the final r-process isotopic abundance due to the mass uncertainty is from a few factors to three orders of magnitude. Therefore, accurate nuclear masses of the r-process key nuclei, especially for 76 Fe,81Cu,127Rh,132Cd,192Dy, and 197Tm, are highly recommended to be measured in radioactive-ion beam facilities for a better understanding of the r-process evolution.

关键词： neutron capture r-process nuclear mass isotopic abundance precise mass measurement

The complex momentum representation approach and its application to low‑lying resonances in 17 O and^(29,31)F

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Nuclear Science and Techniques 2023年第1期34卷 43-50页

作者： Si‑Zhe Xu Shi‑Sheng Zhang Xiao‑Qian Jiang Michael Scott Smith School of Physics Beihang UniversityBeijing 100191China Physics Division Oak Ridge National LaboratoryOak RidgeTN 37831‑6354USA

Approaches for predicting low-lying resonances,uniformly treating bound,and resonant levels have been a long-standing goal in nuclear ***,we explored the viability of the complex momentum representation(CMR)approach coupled with new *** focus on predicting the energy of the low-lying 2p_(3∕2)resonance in 17 O,which is critical for s-process nucleosynthesis and missing in previous theoretical *** a Woods-Saxon potential based on the Koning-Delaroche optical model and constrained by the experimental one-neutron separation energy,we successfully predicted the resonant energy of this level for the first *** predictions of the bound levels and 1d_(3∕2)resonance agree well with the measurement ***,we utilize this approach to study the near-threshold resonances that play a role when forming a two-neutron halo in^(29,31)*** found that the CMR-based predictions of the bound-level energies and unbound 1f7∕2 level agree well with the results obtained using the scattering phase shift ***,we successfully found a solution for the 2p_(3∕2)resonance with energy just above the threshold,which is decisive for halo formation.

关键词： neutron capture Low-lying resonance Complex momentum representation Resonance energy

Quenching ofγ0 transition results from 2p-1h doorway mechanism by p-wave neutron excitation

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Chinese Physics C 2020年第10期44卷 68-73页

作者： Tao-Feng Wang Xiao-Ting Yang T.Katabuchi Zi-Ming Li Zhi-Bo Xu G.N.Kim T.I.Ro Ying-Lu Han Li-Hua Zhu M.Igashira School of Physics Beihang UniversityBeijing 100191China Beijing Advanced Innovation Center for Big Data-based Precision Medicine Beihang UniversityBeijing 100191China Department of Physics Kyungpook National UniversityDaegu 702-701Korea Department of Physics Dong-A UniversityBusan 604-714Korea China Institute of Atomic Energy Beijing 102413China Research Laboratory for Nuclear Reactors Tokyo Institute of TechnologyTokyo 152-8550Japan Chongqing Jianan Instrument Co. LTDChongqing 400060China

The ratio ofγtransition-intensities from the initial capture state to low-lying states may represent the model-independentγ-strength function,which reflects the effects of different neutron-capture reaction *** extraordinary quenching of theγ0 transition from the p-wave neutron radiative capture in 57Fe is observed,for the first time,from the pronounced enhancement of theγ-strength function ratios fγ1/fγ0 and fγ2/fγ*** 2p-1h doorway excitation leads to suppression of theγ0 transition to the ground state and the enhancement of theγ1 andγ2 transitions to the first and second excited states,*** fp sub-shells supply the exact number of spaces required for the 2p-1h configuration,which features the neutron capture mechanism in the vicinity of A=55.

关键词： neutron capture nuclear decay nuclear structure

Calculation of astrophysical reaction rate of ^(82)Ge(n,γ)^(83)Ge

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Chinese Physics C 2009年第S1期33卷 79-81页

作者：王勉陈永寿李志宏柳卫平舒能川 China Institute of Atomic Energy

The neutron capture reaction on a neutron-rich near closed-shell nucleus 82Ge may play an important role in the r-process following the fallout from nuclear statistical equilibrium in core-collapse supernovae. By carrying out a DWBA analysis for the experimental angular distribution of 82Ge(d, p)83Ge reaction we obtain the single particle spectroscopic factors, S2,5/2 and S0,1/2 for the ground and first excited states of 83Ge=82Gen, respectively. And then these spectroscopic factors are used to calculate the direct capture cross sections for the 82Ge(n, γ)83Ge reaction at energies of astrophysical interest. The optical potential for neutron scattering on unstable nucleus 82Ge is not known experimentally. We employed a real folding potential which was calculated by using the proper 82Ge density distribution and an effective nucleon-nucleon force DDM3Y. The neutron capture reactions on neutron-rich closed-shell nuclei are expected to be dominated by the direct capture to bound states. We will show that the direct capture rates on these nuclei are sensitive to the structure of the low-lying states.

关键词： neutron capture spectroscopic factor astrophysical reaction rate