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超重核的阿尔法衰变

第十四届核结构会议， 2012 年 4 月 11-16 ，湖州师范学院. 超重核的阿尔法衰变. 张鸿飞 兰州大学核科学与技术学院. Outline. 1 Introduction 2 The Method 3 Alpha decay process 4 Alpha decay of SHN 5 Summary. 1 Introduction.

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超重核的阿尔法衰变

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  1. 第十四届核结构会议，2012年4月11-16，湖州师范学院第十四届核结构会议，2012年4月11-16，湖州师范学院 超重核的阿尔法衰变 张鸿飞 兰州大学核科学与技术学院

  2. Outline 1 Introduction 2 The Method 3 Alpha decay process 4 Alpha decay of SHN 5 Summary

  3. 1 Introduction Alpha deacy is a typical quantum barrier tunneling problem, which was solved by WKB method several tens years ago. ( G.Gamow, Z.Phys.51 (1928)204; E.U. Condon and R.W.Gurney, Nature, 122 (1928) 439). The question how alpha particle emission from the mother nucleus is still open. The cluster-like theories suppose that alpha particle is preformed in the nucleus with a certain preformation factor, while the fission-like theories approaches consider that alpha particle is formed progressively during the very asymmetric fission of the parent nucleus. The experiment can not distinguish the two formation modes at this moment. (Royer and Zhang, PRC 77 (2008) 037602). Alpha decay is the main decay mode of the superheavy nuclei (SHN). The investigation of properties of these nuclei is extremely intriguing for exploring the position of the island of stability of the SHN, and understanding some new, unexpected features of nuclear structure.

  4. 2 The method (1) WKB approximation (2) Alpha decay potential barrier

  5. The generalized liquid drop model (GLDM) (Royer, JPG 26 (2000) 1149) Two improvements were made for the usual liquid drop model (1) Quasi-molecular shapes

  6. (2) Proximity energy The nuclear energy EN has been introduced to take into account the finite-range effects of the nucleon-nucleon force between the close surfaces . (Royer, NPA 444, (1985) 477) is surface parameter. The introduction of proximity force lowers the barrier of 7.3 MeV, and shift the peak 2.1 fm towards a more external position for 264Hs.

  7. 3 Alpha decay process There are two different decay modes for alpha decay in the market, cluster-like and fission-like modes. Cluster-like mode Fission-like mode The experimental investigation can not unambiguously distinguish these two decay modes up to now.

  8. In the framework of cluster-like mode(Zhang and Royer, PRC 77, (2008), 054318) (1) (2) (3) (4) The preformation factor P0 of an alpha cluster inside the mother nucleus can be extracted from Eq. (1).

  9. The penetration probability plays the most important role to determine the life-time of alpha decay. The preformation factor and assault frequency reflect the nuclear structure features of the mother nucleus.

  10. Clearly the closed shell structures play the key role for the preformation mechanism, and more the nucleon number is close to the magic nucleon numbers, the more the preformation of alpha cluster is difficult inside the mother nucleus. Zhang et al., PRC 80, (2009) 057301

  11. In the framework of fission-like mode(Wang,Zhang, Zuo and Li, CPL 27, (2010), 062103) log10v0

  12. An approach to deal with the assault frequencyZhang, Royer, Li, PRC 84 (2011) 027303 G is global quantum number.

  13. The alpha decay process is rather a radioactivity emission process of a cluster preformed on the surface of the nucleus but before the potential penetration.

  14. 4 Alpha decay properties of SHN Zhang, Gao, Wang, Li, Zhao, Royer, PRC, 85 (2012) 014325 To find out the reasonable alpha decay energy and the features of SHN. MMM results form Wang et al., PRC 81 (2010) 044322, PRC 82 (2010) 044304. Experimental data from Audi 2013. The RMS deviation with respect to 2149 measured nuclear masses Is 0.441 MeV ( the corresponding results with FRDM is 0.566 MeV). Another impressed improvement is the RMS deviation of 46 SHN is reduced 0.263 MeV ( 0.566 MeV for FRDM )

  15. One proton separation energies and alpha decay energies of 162 isotones and 184 isotones.

  16. Potential energy surface of 270Hs and 298114 by Constrained Relativistic Mean Field theory with the parameters NL3 The nucleus 270Hs is a double sub-magic nucleus and 298114 is a spherical double magic nucleus.

  17. Alpha decay life-times of Hs andZ=114 isotopes with WKB penetration probability, and the potential barrier is constructed by the GLDM. The calculated alpha decay half-live of 264Hs is 23.33 second with MMM Q, 15.14 second with experimental Q. For 298114, the calculated alpha decay half-live is 1537588.07 seconds ( about 18 days).

  18. 5 Summary • The alpha decay can be described by GLDM. • The alpha decay process is rather a preformed cluster emission mode. • 270Hs is a deformed double nucleus whose calculated alpha decay half-life is 23.33 seconds, and 298114 is a spherical double nucleus whose calculated alpha decay half-life is about 18 days. The spontaneous fission is another challenge for superheavy nuclei, which may be the main decay mode for nuclei far away from fission stability line.

  19. Thank you !

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