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Register a new userModes of decay in neutron-rich nuclei
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We calculate the ground, first intrinsic excited states and density distribution for neutron-rich thorium and uranium isotopes, within the framework of relativistic mean field(RMF) approach using axially deformed basis. The total nucleon densities are calculated, from which the cluster-structures inside the parent nuclei are determined. The possible modes of decay, like {alpha}-decay and b{eta} -decay are analyzed. We find the neutron-rich isotopes are stable against {alpha}-decay, however they are very much unstable against b{eta} -decay. The life time of these nuclei predicted to be tens of second against b{eta} -decay.
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We analyze the isoscalar response related to breathing modes with particular attention being paid to low-lying excitations in neutron--rich nuclei. We use the subtracted second random--phase approximation (SSRPA) to describe microscopically the response. By increasing the neutron excess, we study the evolution of the response in Ca isotopes going from $^{40}$Ca to $^{48}$Ca and to $^{60}$Ca as well as in $N=20$ isotones going from $^{40}$Ca to $^{36}$S and to $^{34}$Si. Finally, the case of $^{68}$Ni is investigated. We predict soft monopole modes in neutron--rich nuclei which are driven by neutron excitations. At variance with dipole pygmy modes, these neutron excitations are not only strongly dominant at the surface of the nucleus but over its entire volume. The effect of the mixing with two particle-two hole configurations induced by the SSRPA model is analyzed. The properties of such soft neutron modes are investigated in terms of their excitation energies, transition densities and wave--function components. Their collectivity is also discussed as a function of the isospin asymmetry and of the mass of the nucleus. The link between such low--energy compression modes and a compressibility modulus introduced for neutron--rich infinite matter is finally studied.
Both the incompressibility Ka of a finite nucleus of mass A and that ($K_{infty}$) of infinite nuclear matter are fundamentally important for many critical issues in nuclear physics and astrophysics. While some consensus has been reached about the $K_{infty}$, accurate theoretical predictions and experimental extractions of $K_{tau}$ characterizing the isospin dependence of Ka have been very difficult. We propose a differential approach to extract the Kt and Ki independently from the Ka data of any two nuclei in a given isotope chain. Applying this new method to the Ka data from isoscalar giant monopole resonances (ISGMR) in even-even Pb, Sn, Cd and Ca isotopes taken by U. Garg {it et al.} at the Research Center for Nuclear Physics (RCNP), Osaka University, Japan, we find that the $^{106}$Cd-$^{116}$Cd and $^{112}$Sn-$^{124}$Sn pairs having the largest differences in isospin asymmetries in their respective isotope chains measured so far provide consistently the most accurate up-to-date Kt value of $K_{tau}=-616pm 59$ MeV and $K_{tau}=-623pm 86$ MeV, respectively, largely independent of the remaining uncertainties of the surface and Coulomb terms in expanding the $K_{rm A}$, while the $K_{infty}$ values extracted from different isotopes chains are all well within the current uncertainty range of the community consensus for $K_{infty}$. Moreover, the size and origin of the Soft Sn Puzzle is studied with respect to the Stiff Pb Phenomenon. It is found that the latter is favored due to a much larger (by $sim 380$ MeV) Kt for Pb isotopes than for Sn isotopes, while the Ki from analyzing the Ka data of Sn isotopes is only about 5 MeV less than that from analyzing the Pb data.
We discuss the present status of the description of the structure of the very neutron rich nuclei, in the framework of modern large scale shell model calculations. Particular attention is paid to the interaction related issues, as well as to the problems of the shell model approach at the neutron drip line. We present detailed results for nuclei around N=20 and, more briefly, we discuss some salient features of the regions close to N=8, 28 and 40. We show that most experimental features can be understood in a shell model context.
The $beta$-decay and isomeric properties of $^{54}$Sc, $^{50}$K and $^{53}$Ca are presented, and their implications with respect to the goodness of the N=32 sub-shell closure discussed.
The signal of isospin-asymmetric phase transition in the evolution of the chemical potential was observed for hot quasi-projectiles produced in the reactions 40,48Ca + 27Al confirming an analogous observation in the lighter system 28Si + 112,124Sn. With increasing mass, the properties of hot quasi-projectiles become increasingly influenced by the secondary emission. Thermodynamical observables exhibit no sensitivity to the different number of missing neutrons in the two reactions 40,48Ca + 27Al, thus providing a signal of dynamical emission of neutrons, which can be related to formation of a very neutron-rich low-density region (neck) between the projectile and target.
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