Yrast states ofRn216and the extent of a region of possible static intrinsic reflection asymmetry

Abstract

We report the results of a study of the yrast excitation spectrum for ' Rn via the Pb(' C,n2n) ' Rn reaction. Measurements of y-y coincidences, y-ray angular distributions, and y-x-ray coincidences were made. We propose a level spectrum up to J =(10+) which does not exhibit the alternating parity structure observed in several isotopes of radium and thorium. From an examination of information on ' Rn and the neighboring nuclei, we can tentatively determine that the radon isotopes of masses 216 to 222 and the N =128 isotones " Ra and "Th define a lower mass boundary of a region beyond which static intrinsic reflection asymmetric shapes may exist in the nuclear ground states.

High-spin octupole yrast levels inRn21686

“…To reduce this intense γ background, we used the ISIS array (40 telescopic E-E particle detectors) to trigger the GASP spectrometer, selecting the α particles emitted in coincidence with transitions between excited states in 216 Rn. This powerful technique and the transitions known from previous work [1] were used here to identify unambiguously the γ transitions belonging to this nucleus. At the bombarding energies used in the present reaction, the cross section for the 2α2n channel was estimated to be σ 40 µb.…”

“…The isotopic assignment of lines belonging to 216 Rn was based on the reaction energy and prior knowledge of a few transitions from previous work [1]. 1.…”

“…In fact, the transition between the spherical shell model and a collective regime seems to occur at N = 129 and Z = 87. The nucleus 216 Rn [1] shows evidence of the development of some quadrupole collectivity, but no low-lying negative parity states are observed. On the other hand, the Fr isotopes are located at the edge (Z = 87 in number of protons) of the region for which octupole collectivity starts.…”

“…The low-lying level scheme of 216 Rn has been previously studied up to J π = 10 + through the 208 Pb( 14 C, α2n) 216 Rn reaction [1]. In that study, the proposed level scheme did not exhibit at low spins the alternating parity structure observed in its heavier neighbors [2][3][4][5][6].…”

In-beam spectroscopy of215Rn86

“…[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].…”