Cluster Emitters Research Articles

Extension of superasymmetric fission theory from cluster decay to nanophysics

The experimental half-lives of cluster emitters are in good agreement with our predictions within the analytical superasymmetric fission model. We extended the macroscopic-microscopic approach to study metallic cluster physics. Charged metallic clusters are ideal emitters of singly ionized trimers because both LDM and shell correction are reaching a minimum for the same mass asymmetry corresponding to the emission of a charged particle with two delocalized electrons. Maximum Q-value is obtained for transition metal clusters (high surface tension and low Wigner-Seitz radius).

CLUSTER RADIOACTIVITIES — PAST, PRESENT AND FUTURE

The half-lives of cluster emitters predicted by the analytical superasymmetric fission model have been experimentally confirmed. Potential energy surfaces of cluster emitters are showing deep valleys due to the strong shell effect of the doubly magic daughter 208 Pb . Cluster radioactivities allow us to study transitions from a deformed parent nucleus, with a complex structure resulted from mixing of several single-particle states, to a spherical daughter possessing a pure well known state. Recently, preliminary data concerning the 14 C radioactivity of 223 Ac were reported. The following modes have been experimentally confirmed: 14 C , 20 O , 24,25 Ne , 28,30 Mg , and 32,34 Si ; lower limits for 18 O , 23 F and 26 Ne are available. We give a list of some other experiments which have a good chance to be performed in the future. Applications for true ternary fission, 2α-accompanied fission, and atomic clusters are outlined.

HEAVY PARTICLE RADIOACTIVITIES

The potential energy surface for binary decay modes of 228 Th versus the distance between the fragment centers and the mass asymmetry is calculated by using the macroscopic-microscopic model with energy levels obtained within the most advanced asymmetric two center shell model. The valley due to 20 O radioactivity is evidenced as a result of the very strong shell effects due to the doubly magic daughter 208 Pb . For the first time the potential barrier of this decay mode is produced by adding the shell and pairing corrections to the phenomenological deformation energy. The half-lives of cluster emitters predicted by the analytical superasymmetric fission model have been confirmed in all measurements performed until now.

HALF-LIVES OF CLUSTER RADIOACTIVITY OF HEAVY NUCLEI

The half-lives of cluster radioactivity (14C-34Si) are well reproduced by a new formula between half-lives and decay energies. This formula is a natural extension of both the Geiger-Nuttall law and the Viola-Seaborg formula from α-decay to cluster radioactivity. The half-lives of new cluster emitters are predicted based on this formula. These are useful for future experimental researches of cluster radioactivity. The physics related to this formula is analyzed and discussed.

Even-even-like alpha- and cluster emitters

The strongest α- or cluster transitions in even-even nuclei usually occur from the ground state (g.s.) of the parent to the g.s. of the daughter nucleus. We perform a systematic search for transitions in nuclei with odd-number of protons and/or neutrons, obeying to the same rules. Universal curves, Geiger-Nuttall plots, and a semiempirical relationship derived from the fission theory of α-decay are used.

Proton-rich cluster emitter half-lives

The region of even - even proton-rich cluster emitters, Ba, Ce, Nd, Sm, Gd, and Dy isotopes, leading to daughter nuclei around the double magic , is studied within our analytical super-asymmetric fission model. The half-lives of various emitters of , , , and , plotted against the corresponding external barrier penetrability on a doubly logarithmic scale, lie on a straight line, unlike in the so-called `Geiger - Nuttal' plot, where the points versus are considerably scattered. Short half-lives and large branching ratios with respect to and decay could be found for disintegration of and , as well as for decay of and , in addition to the emission of already detected. These nuclei are emitters with estimated half-lives of seconds or fractions of a second.

Cluster radioactivities from an island of cluster emitters.

We have recently developed a realistic model for studying cluster radioactivities from actinide nuclei. This model uses a cubic potential in the overlapping region connected by a Yukawa-plus-exponential potential in the post-scission region. In the present work we use this model to study {sup 4}He, {sup 12}C, {sup 16}O, and {sup 28}Si radioactivities in the region of nuclides with proton and neutron number in the range {ital Z}=56--64 and {ital N}=58--72, which has been recently identified by Poenaru {ital et} {ital al}. as a new island of such cluster emitters. It is found that charge equilibration is not needed in the study of these radioactivities and the half-lives obtained for these decays lie very close to those reported by Poenaru {ital et} {ital al}. using their analytical super asymmetric fission model.

12C emission from 114Ba and nuclear properties.

We investigate the influence of nuclear masses, radii, and interaction potentials on $^{12}\mathrm{C}$ radioactivity of $^{114}\mathrm{the}$ best representative of a new island of cluster emitters leading to daughter nuclei around the doubly magic $^{100}\mathrm{Sn}$. Three different models are considered: one derived by Blendowske, Fliessbach, and Walliser (BFW) from the many-body theory of \ensuremath{\alpha} decay, as well as our analytical (ASAF) and numerical (NuSAF) superasymmetric fission models. A Q value larger by 1 MeV or an ASAF potential barrier reduced by 3% are producing a half-life shorter by 2 orders of magnitude. A similar effect can be obtained within BFW and NuSAF by a decrease of the action integral with less than 10% and 5%, respectively. By increasing the radius constant within ASAF or BFW models by 10%, the half-life becomes shorter by 3 orders of magnitude.

Some predictions of new spontaneous cluster emitters and mechanism of cluster decay

Two basic mechanisms of cluster radioactivity are discussed. The theoretical predictions for the new region of cluster emitters withA ∼ 110 are reported. The preliminary experimental results have indicated in favour of a nonadiabaticα-decay-like mechanism developed by the authors earlier.

New island of cluster emitters.

A new region of proton-rich parent nuclei decaying by spontaneous cluster emission with a measurable branching ratio relative to alpha decay is predicted within the analytical superasymmetric fission model. After a brief presentation of the model and of the seven mass tables used to calculate the released energy, the obtained results are discussed. Measurable half-lives and branching ratios are estimated for $^{12}\mathrm{C}$, $^{16}\mathrm{O}$, $^{28}\mathrm{Si}$, and other cluster radioactivities of some nuclides having proton and neutron numbers in the range Z=56--64 and N=58--72. Such nuclei far from stability could be produced in reactions induced by radioactive beams.