Fine Structure In Proton Emission Research Articles

Nuclear Structure Studies at the Borders of Stability

We have performed theoretical calculations to describe the structure of nuclei at the extremes of stability, using the nonadiabatic quasiparticle approach. With this approach, for the first time clear evidence has been obtained for partial rotation alignment in a proton emitting nucleus (121Pr). Recent findings suggest the departure from axial deformation in the region of proton emitting nuclei. Our calculation for 145Tm, giving the energy spectra of parent and daughter nuclei, half-life and fine structure, confirmed a large triaxiality. Similarly, we have studied decay of 141Ho, the only known nucleus for which fine structure in proton emission from both ground and isomeric states was observed. The interpretation of the data pointed out to the breaking of axial symmetry in this nucleus as well. The present studies provide new and precise theoretical tools to access nuclear structure properties far from the stability domain.

Proton emission, gamma deformation, and the spin of the isomeric state of 141Ho

The nonadiabatic quasiparticle model for triaxial shapes is used to perform calculations for decay of 141Ho, the only known odd-Z even-N deformed nucleus for which fine structure in proton emission from both ground and isomeric states was observed. All experimental data corresponding to this unique case namely, the rotational spectra of parent and daughter nuclei, decay widths and branching ratios for ground and isomeric states, could be well explained with a strong triaxial deformation γ∼20°. The recent experimental observation of fine structure decay from the isomeric state, can be explained only with an assignment of I=3/2+ as the decaying state, in contradiction with the previous assignment, of I=1/2+, based on adiabatic calculations. This study reveals that proton emission measurements could be a precise tool to probe triaxial deformations and other structural properties of exotic nuclei beyond the proton drip-line.

Shell structure beyond the proton drip line studied via proton emission from deformed 141Ho

Fine structure in proton emission from the 7/2−[523] ground state and from the 1/2+[411] isomer in deformed nucleus 141Ho was studied by means of fusion-evaporation reactions and digital signal processing. Proton transitions to the first excited 2+ state in 140Dy, with the branching ratio of Ipgs(2+)=0.9±0.2% and Ipm(2+)=1.7±0.5%, were observed. The data are analyzed within the non-adiabatic weak coupling model assuming a large quadrupole deformation of the daughter nucleus 140Dy as predicted by the self-consistent theory. Implications of this result on coexistence effects around N=74 are discussed. Significant modifications of the proton shell structure when going from the valley of beta stability to the proton drip line are discussed in terms of self-consistent theory involving the two-body tensor interaction.

Study of fine structure in the proton radioactivity of 146Tm

Measurement of fine structure in proton emission allows one to deduce the composition of the parent and daughter state’s wavefunction populated by proton emission. This paper presents new experimental data on the fine-structure decay of 146Tm, and a new interpretation of its decay properties.

Neutron single-particle states populated via proton emission from146Tmand150Lu

Proton emission from the odd-odd nuclei ${}^{146}\mathrm{Tm}$ and ${}^{150}\mathrm{Lu}$ has been reinvestigated by means of the recoil mass spectrometer. In the ${}^{146}\mathrm{Tm}$ study, the strongest proton transitions at 1.12 MeV and at 1.19 MeV have been assigned to the decay of ${}^{146m}\mathrm{Tm}$ ${(T}_{1/2}=200\ifmmode\pm\else\textpm\fi{}10\mathrm{ms})$ and to the ${}^{146gs}\mathrm{Tm}$ decay ${(T}_{1/2}=80\ifmmode\pm\else\textpm\fi{}10\mathrm{ms}),$ respectively. Three new proton lines were identified at 0.89 MeV, 0.94 MeV, and 1.01 MeV. The observed decay pattern has been interpreted by using spherical estimates of emission probabilities. The decays of ${}^{146m,gs}\mathrm{Tm}$ to the $\ensuremath{\nu}{s}_{1/2}$ ${}^{145}\mathrm{Er}$ ground state and to excited neutron states originating from the $\ensuremath{\nu}{h}_{11/2}$ orbital are reported. This work represents the first observation of fine structure in proton emission from an odd-odd nucleus. In the ${}^{150}\mathrm{Lu}$ study, the proton energy and half-life values of ${E}_{p}=1277\ifmmode\pm\else\textpm\fi{}8\mathrm{keV}$ and ${T}_{1/2}{=39}_{\ensuremath{-}6}^{+8}\ensuremath{\mu}\mathrm{s}$ for the decay of ${}^{150m}\mathrm{Lu}$ were obtained with better precision, but no evidence for fine structure in the proton emission was found.

Fine structure in proton emission from 145Tm discovered with digital signal processing.

Fine structure in proton emission from the 3.1(3) mus activity of 145Tm was discovered by using a novel technique of digital processing of overlapping recoil implantation and decay signals. Proton transitions to the ground state of 144Er and to its first excited 2(+) state at 0.33(1) MeV with a branching ratio I(p)(2(+))=9.6+/-1.5% were observed. The structure of the 145Tm wave function and the emission process were analyzed by using particle-core vibration coupling models.

New experimental results in proton radioactivity

A review of experimental data obtained recently on proton-radioactive nuclei is presented. The highlights include the observation of fine structure in proton emission, for the decays of 131Eu, 145Tm and 146Tm, and the studies of the excited states in proton-emitting nuclei. The observation limits are extended to few nanobarns cross-sections ( 140Ho, 164Ir and 130Eu) and few microsecond half-lives (e.g., 145Tm). Measured decay properties for thirty-nine proton-emitting ground and isomeric states contributed to the understanding of nuclear masses and evolution of single-particle states at and beyond the proton drip line. Experimental results have stimulated new theoretical approaches to proton emission and the structure of unbound narrow resonance states.

Towards new proton radioactivities with radioactive beams and digital signal processing

Particle radioactivity studies using the XIA DGF-4C digital signal processing units at the Recoil Mass Separator of Oak Ridge National Laboratory are presented. Proton emission signals were observed starting from 500 ns after recoil implantation. An energy threshold below 100 keV for particle detection was achieved. For the 145Tm and 146Tm decay, evidence for the fine structure in proton emission was obtained. An experiment to search for a new proton emitter 149Lu is described as an example where the combination of a 56Ni radioactive beam and digital signal processing is a major advantage.

Fine structure in proton emission from deformed131Eu

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