Speaker
Dr
Christian BECK
(IPHC & Universite de Strasbourg)
Description
A great deal of research work has been performed in the field of alpha clustering since the pioneering discovery, by Bromley and his collaborators half a century ago, of molecular resonances in the excitation functions for 12C+12C scattering [1]. Our knowledge of this field of nuclear molecular physics has increased considerably [2] and nuclear clustering remains one of the most fruitful domains of nuclear physics [3-7], facing some of the greatest challenges and opportunities in the years ahead.
The question whether quasi-molecular resonances always represent true cluster states in the compound systems, or whether they may also simply reflect scattering states in the ion-ion potential is still unresolved [1-3]. In many cases, these resonant structures have been associated with strongly-deformed shapes and with clustering phenomena, predicted from the Nilsson-Strutinsky approach, the cranked alpha-cluster model, or other mean-field calculations (see for instance last chapter of [4] and references therein). Of particular interest is the relationship between superdeformation (SD) and nuclear molecules, since nuclear shapes with major-to-minor axis ratios of 2:1 have the typical ellipsoidal elongation (with quadrupole deformation parameter beta ~0.6) for light nuclei. Furthermore, the structure of possible octupole-unstable 3:1 nuclear shapes (with beta ~1.0) - hyperdeformation (HD) - for actinide nuclei has also been widely discussed in terms of clustering phenomena. Typical examples of the possible link between quasi-molecular bands and extremely deformed (SD/HD)shapes have been widely discussed in the literature for N=Z nuclei such as 28Si [8], 32S [9], 36Ar [10-12], 40Ca [13] and 48Cr [14,15].
Large quadrupole deformations and alpha-clustering in light N = Z nuclei are known to be general phenomena at low excitation energy. For high angular momenta and higher excitation energies, very elongated shapes are expected to occur in alpha-like nuclei for A(CN)= 20-60. In fact, highly deformed shapes and SD rotational bands have been recently discovered in several such N = Z nuclei, in particular, 36Ar using gamma-ray spectroscopy techniques [16,17]. Extremely deformed rotational bands in 36Ar are observed as quasi-molecular bands in both 12C+24Mg and 16O+20Ne reactions [10-12,17], and their related ternary clusterizations are also predicted theoretically [13,17].
[1] K.A. Erb and D.A. Bromley, "Treatise on Heavy Ion Science, Vol. 3, p. 201, Ed. Plenum, New York (1985).
[2] W. Greiner, J.-Y. Park, and W. Scheid, "Nuclear Molecules", Ed. World Scientific (1995).
[3] W. von Oertzen, M. Freer, and Y. Kanada-En'yo, Phys. Rep. 432(2006)43.
[4] M. Freer, Rep. Prog. Phys. 70(2007)2149.
[5] "Clusters in Nuclei" Vol.1, Lecture Notes in Physics 818, C. Beck (ed.) Springer-Verlag Berlin-Heidelberg, 2010.
[6] "in Nuclei", Vol.2, Lecture Notes in Physics 848, C. Beck (ed.) Springer-Verlag Berlin-Heidelberg, 2012.
[7] "Clusters in Nuclei", Vol.3, Lecture Notes in Physics 875, C. Beck (ed.) Springer-Verlag Berlin-Heidelberg, 2013.
[8] Y. Taniguchi et al., Phys. Rev. C 80(2009)044316.
[9] M. Kimura and H. Horiuchi, Phys. Rev. C 69(2004)051304.
[10] C. Beck et al., AIP Conf. Proc. 1098(2008)207.
[11] W. Sciani et al., Phys. Rev. C 80(2009)034319.
[12] J. Cseh {et al., Phys. Rev. C 80(2009)034320.
[13] Y. Kanada-En'yo and M. Kimura, Phys. Rev. C 72(2005)064322.
[14] M.-D. Salsac et al., Nucl. Phys. A 801(2008)1.
[15] E. Vardaci et al., Journal of Phys.: Conferences Series 436(2013)012054.
[16] C.E. Svensson et al., Phys. Rev. Lett. 85(2000)2693.
[17] C. Beck, Journal of Phys.: Conferences Series 436(2013012014).
Primary author
Dr
Christian BECK
(IPHC & Universite de Strasbourg)
