1. Chong Qi ( 亓冲 ) Dept. of Physics, KTH, Stockholm Abrupt changes in alpha decay systematics as a manifestation of collective nuclear modes 赤峰学院 全国核结构大会 2010 年 07 月 24 日－ 30 日 赤峰学院 全国核结构大会 2010 年 07 月 24 日－ 30 日 Alpha decay systematics and microscopic description; Abrupt change in alpha formation amplitudes; Explanation and possible manifestation in other observables.

2. 1)Introduction: Progress in experiments  α radioactivity ~ 400 events observed in A > 150 nuclei;  Heavy-cluster decays 11 events observed in trans-lead nuclei 223 Ra( 14 C), Rose and Jones, Nature 307, 245 (1984);  Proton decay more than 40 events observed in the rare-earth region.  New decay modes  Di-proton decay  Neutron decay  12 C cluster decay  α decay of N≈Z nuclei

3. 1)Introduction: Theoretical understanding The Geiger-Nuttall law of alpha decays H. Geiger and J. M. Nuttall, Philos. Mag. 22, 613 (1911).  Schematically: quantum tunneling interpretation by Gamow in 1928 J. Dong et al, PRC81, 064309 (2010); D.Ni, Z.Ren, PRC81, 064318 (2010); H.F. Zhang et al, PRC80, 057301 (2009); J.Pei, F.R. Xu, PLB650, 224 (2008) ⋯⋯⋯⋯

4. 2) Microscopic description of alpha decay Shell Model H.J. Mang, PR 119,1069 (1960); I. Tonozuka, A. Arima, NPA 323, 45 (1979). BCS approach HJ Mang and JO Rasmussen, Mat. Fys. Medd. Dan. Vid. Selsk. (1962) DS Delion, A. Insolia and RJ Liotta, PRC46, 884(1992). R is the distance between the center of mass of the cluster and daughter nucleus

5. Alpha formation amplitude CQ et al, Phys.Rev.C80,044326 (2009); 81,064319 (2010). R should be large enough that the nuclear interaction is negligible, i.e., at the nuclear surface.

6. C.Qi, F.R.Xu,R.J.Liotta,R.Wyss, PRL103, 072501 (2009), PRC80,044326 (2009)  On the logarithm scale of the Geiger-Nuttall law the differences in the formation probabilities are usually small fluctuations along the straight lines predicted by that law;  The smooth trend is a consequence of the smooth transition in the nuclear structure that is often found when going from a nucleus to its neighboring nuclei.

7. 210 Po   a division occurs between decays corresponding to N 126;  Sudden change in α-decay systematics at N = 126;  The case that shows the most significant hindrance corresponds to the α decay of the nucleus 210 Po.

8. 3) Theoretical explanation: 210Po vs 212Po (The later is the textbook example of alpha emitter ) 3) Theoretical explanation: 210Po vs 212Po (The later is the textbook example of alpha emitter )

9. 210 Pb 206 Pb Two-body clustering The importance of configuration mixing

10. R=r 1 =r 2 Two-body clustering

11. Alpha formation amplitude The clustering induced by the pairing mode is inhibited if the configuration space does not allow a proper manifestation of the pairing collectivity.

12. Delta-function approximation The clustering induced by the pairing mode is inhibited if the configuration space does not allow a proper manifestation of the pairing collectivity.

13. 4) Possible manifestation in other observables cross sections of (p,t) reactions on Pb isotopes M. Takahashi, PRC27,1454(1983)

14. 5) Summary Alpha decay as a probe of nuclear structure.  An abrupt change in alpha decay systematics is noted;  It is explained as a sudden hindrance of the clustering of the nucleons that eventually form the α particle.  Further investigations systemical calculations, shell effects, alpha decays of superheavy nuclei Collaborators: Furong Xu (Beijing) R.J. Liotta, R. Wyss (KTH, Stockholm, Sweden) D.S. Delion (Bucharest) A.N. Andreyev, M. Huyse, P. Van Duppen (KU Leuven)

15. 谢 谢 ! Thank you!

16. Evaluation of deformation effects θ 1. Effective approach: 2. Froman approach: The transimission matrix Ka=c