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

•Alpha decay systematics and microscopic description;•Abrupt change in alpha formation amplitudes;•Explanation and possible manifestation in other observables.

1)Introduction: Progress in experiments1)Introduction: Progress in experimentsα radioactivity ~ 400 events observed in A > 150 nuclei;

Heavy-cluster decays 11 events observed in trans-lead nuclei223Ra(14C), Rose and Jones, Nature 307, 245 (1984);

Proton decay more than 40 events observed in the rare-earth region.

New decay modesDi-proton decayNeutron decay12C cluster decayα decay of N≈Z nuclei

1)Introduction: Theoretical understanding1)Introduction: Theoretical understandingThe 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)⋯⋯⋯⋯

2) Microscopic description of alpha decay2) Microscopic description of alpha decay

Shell ModelH.J. Mang, PR 119,1069 (1960); I. Tonozuka, A. Arima, NPA 323, 45 (1979).BCS approachHJ Mang and JO Rasmussen, Mat. Fys. Medd. Dan. Vid. Selsk. (1962)DS Delion, A. Insolia and RJ Liotta, PRC46, 884(1992).

m d

R is the distance between the center of mass of the cluster and daughter nucleus

Alpha formation amplitudeAlpha 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.

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.

210Po

a division occurs between decays corresponding to N <126 and N >126;Sudden change in α-decay systematics at N = 126;The case that shows the most significant hindrancecorresponds to the α decay of the nucleus 210Po.

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 )

210Pb

206Pb

Two-body clusteringTwo-body clustering

The importance of configuration mixing

R=r1=r2

Two-body clusteringTwo-body clustering

Alpha formation amplitudeAlpha 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.

Delta-function approximationDelta-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.

4) Possible manifestation in other observables cross sections of (p,t) reactions on Pb isotopes

4) Possible manifestation in other observables cross sections of (p,t) reactions on Pb isotopes

M. Takahashi, PRC27,1454(1983)

5) Summary Alpha decay as a probe of nuclear structure.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)

谢 谢 !Thank you!

Evaluation of deformation effects•

θ1. Effective approach:

2. Froman approach:

The transimission matrix

Ka=c