Synthesis of the neonuclide thorium-207 from the Institute of Modern Physics, Chinese Academy of Sciences

Recently, Gan Zaiguo’s team and collaborators at the Institute of Modern Physics of the Chinese Academy of Sciences synthesized the neonuclide thorium-207 and discovered the parity effect of the decay energy of the nuclear region a with a proton number greater than 82 and a neutron number less than 126 (Z>82, N<126), which was published in the form of a letter in the form of a letter in May 19 in the Physical Review C.

The Institute of Modern Physics of the Chinese Academy of Sciences, in collaboration with researchers from Sun Yat-sen University, Lanzhou University, Guangxi Normal University, Institute of Theoretical Physics of the Chinese Academy of Sciences, Tongji University, and the Russian Institute of Nuclear Research, successfully synthesized the neonucleus thorium-207 by fusing and evaporating reaction 36Ar+176Hf on the inflatable recoil nuclear spectrometer of the Lanzhou Heavy Ion Accelerator, and measured its a-particle energy and half-life of 8167(21)keV and 9.7(+46.6-4.4) ms, respectively. The synthesized thorium-207 is the 34th nuclide synthesized by modern physics.

The study also discovered and explained the novel phenomenon of the parity effect of a decay energy. Through systematic analysis of new and existing data, the researchers found that in the Z>82, N<126 nuclear regions, both isotopes and homonynous a decay energy showed regular parity oscillations with oscillation amplitudes of 20-160 keV. This finding contradicts the belief that a decay energy does not have a parity effect, usually based on the Bethe-Weizsäcker formula.

According to Gan Zaiguo, in order to explore the formation mechanism of the a decay energy parity effect, the researchers used the relativistic Hartree-Fock-Bogoliubov model (RHFB) and the large-scale shell model (LSSM) to theoretically analyze the nuclei in the Z>82, N<126 nuclear regions.

RhFB model calculations show that the parity effect of the a decay energy comes from the blocking effect on the associated and unpaired nucleons. In addition to the energy, the pair correlation affects the parity oscillation of the decay energy through nucleon scattering. The LSSM model results show that the parity effect of a decay energy is caused by a configuration mixture containing special orbitals. It is worth noting that neither nucleon scattering in the RHFB model nor configuration mixing in the LSSM model is beyond the theoretical framework of the mean field and is not included in the classical Bethe-Weizsäcker formula.

“This work not only synthesizes the neonuclide thorium-207, but also reveals the reasons why a decay can exhibit parity effects, which requires further improvement of the nuclear mass formula.” Gan Zaiguo said.

Image 1.png

Two-dimensional diagram of the triple-associated chain ER-a1-a2 of the 36Ar+176Hf reaction product. The abscissa and ordinate coordinates represent the a-particle energy of the parent and daughter nuclei, respectively. (Photo: Yang Huabin)

Image 2.png

a parity effect of decay energy. (a) The decay of a neutron Po-U isotope ground state to ground state can change with the number of neutrons. (b) A decay extracted using the three-point formula can oscillate along the parity of isotopic chains. (c) Amplitude distribution of isotope parity oscillations. (d) The decay of a part of the neutron prime ground state to the ground state can change with the number of neutrons. (e) a decay can oscillate along the parity of the same neutron prime chain. (f) Distribution of odd and even oscillation amplitudes with neutron elements. (Photo: Yang Huabin)

This work has been supported by the National Key Research and Development Program, the Strategic Pilot Science and Technology Project of the Chinese Academy of Sciences, the National Natural Science Foundation of China and other projects. (Source: China Science Daily, Liu Ruinan, Gan Xiao)

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