Intermediate and weak coupling inRa219

Abstract

The level scheme of ' Ra established via a study of the 2 Pb('"C, 3n) ' Ra reaction is presented. The structure of the rotational band based on the ground state is interpreted as reflecting a g9~2 valence neutron weakly coupled to a spherical ' Ra core. A non-yrast side band is observed, having tentative 15-, . . . level assignments. An 2 state could result from the anomalous J= j -2 intermediatẽ 11strength coupling of a j1~~2 neutron to the ' Ra core. The relevance of a weak coupling model to the understanding of high spin (J )j) parity doublets and the surprisingly different experimentally observed level schemes of 2/Ra and 2QAc are discussed.Studies of odd-A nuclei have been shown to provide useful information on the structure of the even-even core as well as on the behavior of the valence nucleons. This is particularly the case where weak-coupling phenomena are observed for example, in Z & 50 odd-A nuclei. hen the core is a prolate spheroid, weak coupling of a valence nucleon in an orbit having total angular momentum j leads to the occurrence of the state J "=j+J""ata lo~er excitation than the state having J = J, "-1 and to a b J = 2 band; in contrast, for the case of a valence hole the order of the J,"and J, "-1 states is reversed and a 5J = 1 band occurs. The separation of the J,"and J, "-1 states is related directly to the diagonal (first order) matrix elements of the quadrupole operator for the core' ' and thus provides information on the core structure.Recently, a number of detailed studies~" on actinide nuclei and subsequent attempts' '4 at understanding the results on the basis of cluster configurations" or static octupole deformations' ' have focused attention on the validity and relationship of these two approaches. Comparable success in reproducing the known characteristics of even-even nuclei in this mass region has been obtained with the two approaches; both can reproduce the observed bands of states having alternating parities and strongly enhanced electric dipole intraband deexcitation transitions as collective phenomena. Thus far only the static octupole model has been applied to odd mass nuclei in this region. ' Both models, in which reflection symmetry is broken in the intrinsic frame, predict parity doublets in odd-A nuclei.In this short note, a detailed level spectrum for '9Ra is presented. These results are compared with recently published results for the neighboring nuclei 2"Ac (Refs. 16 and 17) and 2'9Ac (Refs. 18 and 19) in order to examine the underlying structure and to seek an appropriate description.Our study of 2'9Ra was carried out via the '08Pb('4C, 3ny)"9Ra reaction, using a '4C beam from the Brookhaven MP'7 tandem accelerator. Unambiguous identification of 2'9Ra was achieved in measurements of the excitation function for this reaction over the range 60~E(' C) «78 MeV using a target comprised of 450 p, g/cm' of '08Pb on a 225 p, g/cm2 Au backing. Gamma radiation was detected at 90' to the beam in a single Ge(Li) detector. Since detailed information on 2'sRa (the 4n channel) and ...

High-spin octupole yrast levels inRn21686

“…Such a low-seniority state has been found in the nearest lighter isotope 214 Rn [10] in which the 10 + state at 1928 keV excitation energy has predominantly seniority two, with the four protons coupled to zero. The state at 1837.5 keV is likely to be associated to the [h 4 (0)][g 2 (0)gi (8,9)] predominant configuration. [From a purely experimental point of view, the allowed spin-parity values are (8, 9, 10) + ].…”

“…Only a very small contamination from the α3n channel ( 219 Ra [8]) was present. A total of some 300,000 events were acquired from the γ -γ -E coincidences (2αxn channels, 2/3 of them corresponding to 216 Rn).…”

“…1). Only a few transitions belonging to 216 Rn are slightly contaminated with 219 Ra [8] transitions. This situation allows an intensity determination for the majority of the 216 Rn transitions.…”

In-beam spectroscopy of215Rn86

“…The predominant transitions could be assigned to 215 Rn and 216 Rn from the coincidence with 2α s in the E-E matrix of the ISIS array, where the separation between the alpha particles belonging to the 2α2n (and 2αn) channel and the charged particles arising from other reaction channels was very clear. (Only a very small contamination of the α2n channel, leading to 219 Ra [10], was present.) Approximately a total of 350 000 events were acquired from the γ -γ -E-E coincidences (2αxn channels, a third of them corresponding to 215 Rn).…”

“…[11]). This procedure of multipolarity assignment was consistently checked with transitions of known multipolarity belonging to 219,220 Ra [10] and the known transitions in 216 Rn [12,13].…”