Repulsive Four-Body Interactions of α\alpha Particles and Quasi-Stable Nuclear α\alpha-Particle Condensates in Heavy Self-Conjugate Nuclei

We study the effects of repulsive four-body interactions of $\alpha$ particles on nuclear $\alpha$-particle condensates in heavy self-conjugate nuclei using a semi-analytic approach, and find that the repulsive four-body interactions could decrease the critical number of $\alpha$ particles, beyond which quasi-stable $\alpha$-particle condensate states can no longer exist, even if these four-body interactions make only tiny contributions to the total energy of the Hoyle-like state of $^{16}$O. Explicitly, we study eight benchmark parameter sets, and find that the critical number $N_\text{cr}$ decreases by $|\Delta N_\text{cr}|\sim1-4$ from $N_\text{cr}\sim11$ with vanishing four-body interactions. We also discuss the effects of four-body interactions on energies and radii of $\alpha$-particle condensates. Our study can be useful for future experiments to study $\alpha$-particle condensates in heavy self-conjugate nuclei. Also, the experimental determination of $N_\text{cr}$ will eventually help establish a better understanding on the $\alpha$-particle interactions, especially the four-body interactions.Comment: 16 pages, 7 figures, accepted versio

Half-lives of α\alpha-emitters approaching the N=Z line

The half-lives of newly observed $\alpha$-emitters $^{105}$Te and $^{109}$Xe [Seweryniak \textit{et al.}, Phys. Rev. C \textbf{73}, 061301(R) (2006); Liddick \textit{et al.}, Phys. Rev. Lett. \textbf{97}, 082501 (2006)] are investigated by the density-dependent cluster model. The half-lives of $\alpha$-emitters close to the N=Z line are also studied in a unified framework where the influence of the nuclear deformation is properly taken into account. Good agreement between model and data is obtained and some possible $\alpha$-emitters are suggested for future experiments.Comment: 9 pages, 3 figures, To appear in Phys. Rev.

Cluster-Daughter Overlap as a New Probe of Alpha-Cluster Formation in Medium-Mass and Heavy Even-Even Nuclei

We study the possibility to use the cluster-daughter overlap as a new probe of alpha-cluster formation in medium-mass and heavy even-even nuclei. We introduce a dimensionless parameter $\mathfrak{O}$, which is the ratio between the root-mean-square (rms) intercluster separation and the sum of rms point radii of the daughter nucleus and the alpha particle, to measure the degree of the cluster-daughter overlap quantitatively. By using this parameter, a large (small) cluster-daughter overlap between the alpha cluster and daughter nucleus corresponds to a small (large) $\mathfrak{O}$ value. The alpha-cluster formation is shown explicitly, in the framework of the quartetting wave function approach, to be suppressed when the $\mathfrak{O}$ parameter is small, and be favored when the $\mathfrak{O}$ parameter is large. We then use this $\mathfrak{O}$ parameter to explore systematically the landscape of alpha-cluster formation probabilities in medium-mass and heavy even-even nuclei, with $\mathfrak{O}$ being calculated from experimentally measured charge radii. The trends of alpha-cluster formation probabilities are found to be generally consistent with previous studies. The effects of various shell closures on the alpha-cluster formation are identified, along with some hints on a possible subshell structure at $N=106$ along the Hg and Pb isotopic chains. The study here could be a useful complement to the traditional route to probe alpha-cluster formation in medium-mass and heavy even-even nuclei using alpha-decay data. Especially, it would be helpful in the cases where the target nucleus is stable against alpha decay or alpha-decay data are currently not available.Comment: 16 pages, 6 figures; accepted versio