. Research Paper . Radioactive Nuclear Beam Physics and Nuclear Astrophysics SCIENCE CHINA Physics, Mechanics & Astronomy August 2011 Vol. 54 Suppl. 1: s130–s135 doi: 10.1007/s11433-011-4420-z c  Science China Press and Springer-Verlag Berlin Heidelberg 2011 phys.scichina.com www.springerlink.com Alpha-particle decays from excited states in 24 Mg WANG SiMin 1 , XU Chen 2 , LIOTTA R J 3 , QI Chong 3 , XU FuRong 1* & JIANG DongXing 1 1 School of Physics and State Key Laboratory of Nuclear Physics and Technology, Peking University, Beijing 100871, China; 2 School of Physics, Peking University, Beijing 100871, China; 3 Royal Institute of Technology (KTH), AlbaNova University Center, Stockholm S-10691, Sweden Received January 7, 2011; accepted March 15, 2011; published online July 18, 2011 Using a cluster model based on the Woods-Saxon potential, alpha-particle decays from excited states in 24 Mg have been system- atically investigated. Calculations can in general reproduce experimental data, noticing the fact that the preformation factor P of alpha particle in alpha-decaying nuclei is of order from 10 0 to 10 -2 . This can be the evidence for the α+ 20 Ne structure in 24 Mg. Meanwhile, the results also show the existence of other configurations, such as 16 O+2α. Since the calculated decay widths are very sensitive to the angular momentum carried by the outgoing cluster (α particle), our results could serve as a guide to experimental spin assignments. alpha decay, cluster structure, cluster model, 24 Mg PACS: 21.10.Tg, 21.60.Gx, 23.60.+e, 27.30.+t 1 Introduction As a useful tool to probe nuclear structure, α decay has made great success in heavy nuclei, such as providing unique shell structure information [1,2] and evidence for shape coexis- tence [3]. Theoretically, in the framework of a cluster model based on Gamow picture [4], a nucleus which has α radioac- tivity can be simply described as an α particle moving around a frozen core. Simple calculations within this model can well reproduce the experimental data of α decays for nuclei A > 100, e.g., studies in refs. [5–10]. On the other hand, α particle emissions play a crucial role in the search for exotic molecular states in light nuclei [11], which is of increasing in- terest recently. However, such systematic calculations within Gamow model are still lacking, especially for favored α de- cays. In this article, we will extend this kind of cluster model to the area of light nuclei. The nucleus 24 Mg has been a typical example for vari- ous cluster structures, with many experimental and theoret- ical studies. As early as the 1960s, the pioneering work of Bromley et al. [12] suggested that the resonances observed in 12 C- 12 C reactions close to Coulomb barrier corresponded *Corresponding author (email: frxu@pku.edu.cn) to quasimolecular structures in the compound nucleus 24 Mg. Thenceforth, a variety of reaction experiments were per- formed where different cluster-decay channels were observed (e.g., α+ 20 Ne ∗ [13,14], 8 Be + 16 O [15–21], 12 C + 12 C [20– 26], and α chain [27]). Nilsson-Strutinsky [28,29], α clus- ter model (ACM) [30] and Hartree-Fock [31] calculations gave evidence for largely deformed configurations. Recently, we calculated the decay widths of 8 Be + 16 O and 12 C + 12 C channels which corresponded to resonant states in the exci- tation energy range of 20–35 MeV for 24 Mg, demonstrating 8 Be+ 16 O and 12 C + 12 C structures [32]. We investigate the α cluster states of 24 Mg in this paper. According to ref. [22], 8 Be + 16 O and 12 C + 12 C decays are dominant in the highly excited resonant states of 24 Mg (in the energy range ≈ 20–35 MeV). Nevertheless, alpha de- cays take over their place when excitation energy is between 10 and 20 MeV. Our calculations will focus on this energy range. The spectroscopy of the resonant states in 24 Mg has also been an interesting topic. Based on the microscopic gen- erator coordinate method, Descouvement and Baye [33,34] investigated the spectroscopy with α cluster configuration. This was also discussed by Kato [35] with the orthogonality condition model (OCM). Buck et al. [36] studied the clus- ter structure and spectroscopy within the 12 C + 12 C coupling