Chong Qi Dept. of Physics, KTH, Stockholm Deviations of alpha decay half-lives from the...
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![Page 1: Chong Qi Dept. of Physics, KTH, Stockholm Deviations of alpha decay half-lives from the Geiger-Nuttall law as a manifestation of nuclear structure effects.](https://reader034.fdocuments.us/reader034/viewer/2022050909/5697bff41a28abf838cbd0ed/html5/thumbnails/1.jpg)
Chong QiDept. of Physics, KTH, Stockholm
Deviations of alpha decay half-lives from the Geiger-Nuttall law
as a manifestation of nuclear structure effects
Swedish Nuclear Physics meeting16-17 November, 2010, Uppsala
Collaborators:R.J. Liotta, R. Wyss (KTH, Stockholm)A.N. Andreyev, M. Huyse, P. Van Duppen (KU Leuven, Belgium)
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Experimental status and the Geiger-Nuttall law of alpha decaysMicroscopic two-step description of alpha decay and generalization of the GN law; Clustering (formation) + Penetration
Abrupt change in alpha decay half-lives and alpha formation amplitudes;Explanation in term of pairing collectivity;Possible manifestation in other observables.
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1) Progress in experiments1) Progress in experiments
α radioactivity ~ 400 events observed in A > 150 nuclei;
A.N. Andreyev et al., Nature 405 430 (2000)
S.N.Liddick et al., Phys.Rev.Lett. 97, 082501 (2006)D.Seweryniak et al., Phys.Rev. C 73, 061301 (2006)
Decay of N~Z nuclei Fine structure
Alpha decay as a spectroscopic probe
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Theoretical understandingTheoretical 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
The Gamow theory does not carry structure information
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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).
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m→d +α
R is the distance between the center of mass of the cluster and daughter nucleus which divides the decay process into an internal region and complementary external region.
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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.
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C.Qi, F.R.Xu,R.J.Liotta,R.Wyss, PRL103, 072501 (2009), PRC80,044326 (2009)
On the logarithm scale the differences in the formation probabilities are usually small fluctuations along the straight lines predicted by the Geiger-Nuttall 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 ->BCS.
Generalization of the Geiger-Nuttall law:Universal decay law of alpha and cluster decays
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a division occurs between decays corresponding to N <126 and N >126;Sudden change at N = 126;The case that shows the most significant hindrancecorresponds to the α decay of the nucleus 210Po, one order of magnitude smaller than that of 212Po.
210Po
Discrepancy between experimental decay half-lives and UDL calculations->;Around the N=126 shell closure, UDL underestimate the half-lives by large factors.
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3) Theoretical explanation210Po vs 212Po (The later is the textbook example of alpha emitter )
3) Theoretical explanation210Po vs 212Po (The later is the textbook example of alpha emitter )
If we neglect the proton-neutron interaction
Two-body clustering
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210Pb
206Pb
Two-body clusteringTwo-body clusteringConfiguration mixing from higher lying orbits is important for clustering at the surface
r1=9fm
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R=r1=r2
Two-body clusteringTwo-body clustering
The two-body wave functions are indeed strongly enhanced at the nuclear surface;The enhancement is much weaker in 206Pb(gs) than that in 210Pb(gs)
Relatively small number of configurations in the hole-hole case;p1/2 dominance in 206Pb(gs);Radial wave functions of hole states less extended.
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Alpha formation amplitudeAlpha formation amplitude
Alpha particle is formed on the nuclear surface;The clustering induced by the pairing mode is inhibited if the configuration space does not allow a proper manifestation of the pairing collectivity.
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Odd-even staggering of binding energies and pairing correlation energies
Larger pairing energy => Enhanced two-particle clustering at the nuclear surface
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Previous explanations
Calculations underestimated the formation probability by several orders of magnitude due to the limited model space employed.Sn(206Po)>Sn(208Po)>Sn(210Po).
Reduced widths [similar to F(R)] of Po isotopes as a function of A
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The role played by proton-neutron correlation on alpha decays of N>>Z nuclei is marginal
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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)
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5) Next-step5) Next-step
Alpha decay of neutron-deficient nuclei and Z=82 shell closureA.N. Andreyev et al., to be published.
Suppression of alpha formation probabilities in neutron-deficient Po isotopes and limitation of the GN lawC. Qi et al., to be published
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5) Summary Alpha decay as a probe of nuclear structure.5) Summary Alpha decay as a probe of nuclear structure.
Microscopic studies of the alpha decay process and generalization of the GN law An abrupt change in alpha formation amplitudes is noted around the N=126 shell closure; Interpretation in term of pairing collectivity.Alpha decay as a probe of nuclear structure
Thank you!
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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.