5He radioactivity

The disintegration of a metastable nuclear state by emission of a light particle can be considered to be a very asymmetric fission process. An approximation of the potential barrier in the overlapping region of the two fragments leads to an analytic relationship for the life-time, allowing us to handle a large number of cases to search for new kinds of radioactivities. In this way, it is predicted that some nuclei with Z = 83-92, N = 127-137 and 97-105,145-157 are able to decay spontaneously by emission of 5 He particles. A tentative optimistic estimation leads to the result that only 15 radionuclides should have partial life-times in the range 10 14-1038 years; all others, except some superheavies, are longer lived. The best candidate is 213Po for which the daughter is a double magic nucleus. Smaller life-times, with a better chance to be experimentally confirmed have some β-delayed 5He emitters, as for example 155Yb, 175Pt, 209-217Ra, 9-11Be, 13-14B, 13-17C and 19-21O.La désintégration d'un état nucléaire métastable par émission d'une particule légère peut être considérée comme un processus de fission très asymétrique. Une approximation de la barrière de potentiel dans la région de recouvrement des deux fragments conduit à une relation analytique pour la durée de vie, permettant de traiter un grand nombre de cas dans une recherche de nouveaux modes de radioactivité. On découvre ainsi que certains noyaux ayant Z = 83-92, N = 127-137 et 97-105, 145-157 peuvent émettre spontanément des particules 5He. D'après une estimation optimiste, 15 noyaux seulement ont des durées de vie partielles dans l'intervalle 1014-1038 ans; les autres, à l'exception de quelques noyaux superlourds, vivent un temps encore plus long. Le meilleur candidat est 213Po, conduisant à un noyau doublement magique. Quelques émetteurs 5He-β retardés, comme par exemple 155Yb, 175Pt, 209-217Ra, 9-11Be, 13-14B, 13-17C et 19-21O, ont des durées de vie plus brèves, et une meilleure chance de confirmation expérimentale

Study of the 86Sr(ρ, α)85Sr reaction

The structure of the 85Sr nucleus has been investigated by measuring the angular distributions of α-particles from the 86Sr(ρ, α)85Sr reaction at a bombarding energy of 17.5 MeV, with a 90 cm split-pole magnetic spectrograph. Angular distributions from 6° to 80° have been obtained for the ground state and levels with excitation energies of 0.23, 0,74, 0.90, 1.14, 1.23, 1.62, 1.96 and 2.14 MeV. A DWBA analysis provides l-values and spectroscopic factors for all but one of these levels

Gamma-ray spectroscopy of the nucleus

Gamma-ray coincidence techniques are used to determine new level structures in the N = 81 nucleus 139Ce, at low spins and excitation energies with the 139La(p, nγ) reaction at 5.0 and 6.0MeV incident energy, and at high spins with the 130Te(12C, 3nγ) reaction at 50.5MeV, respectively. Lifetime determinations are also made in the (p, nγ) reaction with the centroid DSA method. The observed level structures are discussed by comparison with existing calculations and with those in the neighbouring nucleus 140Ce

Evidence for the two-body nature of the E1 transition operator in the sdf-interacting boson model

Two new absolute transition rates are reported for the nucleus144Sm following an ( α, α') Coulomb excitation study. They are B(E3; 3-→ 0+)=(38±3) W.u. and B(E1;3- → 2+)=(2.8±0.4)×10-3 W.u. This large E1 matrix element, along with the previously known B(E1; 1- →+) value support the interpretation of the 1- state in this nucleus as 2-phonon 2+ × 3- excitation. In the frame of the IBM-1 + f-boson model we show the need for a two-body term in the E1 transition operator. Estimates for the strengths of the one and two-body parts of the E1 transition operator are obtained from these experimental data