Discovery ofRn229and the Structure of the Heaviest Rn and Ra Isotopes from Penning-Trap Mass Measurements

Abstract

The masses of the neutron-rich radon isotopes [223][224][225][226][227][228][229] Rn have been determined for the first time, using the ISOLTRAP setup at CERN ISOLDE. In addition, this experiment marks the first discovery of a new nuclide, 229 Rn, by Penning-trap mass measurement. The new, high-accuracy data allow a fine examination of the mass surface, via the valence-nucleon interaction V pn . The results reveal intriguing behavior, possibly reflecting either a N ¼ 134 subshell closure or an octupolar deformation in this region. DOI: 10.1103/PhysRevLett.102.112501 PACS numbers: 21.10.Dr, 21.30.Fe, 27.90.+b, 32.10.Bi The nuclear binding energy reflects the net effect of all aspects of the underlying fundamental forces [1]. Its evolution as a function of proton or neutron number provides information of great importance for nuclear structure. Joining the most basic nuclear characteristics of size and weight is that of shape, usually quantified by deformation, when a nucleus is considered not to be spherical.As the capacious valence orbitals of very heavy nuclides begin to fill with nucleons, increasing varieties of deformation become possible. It is well known [2] that one of these degrees of freedom, of importance in the light actinide nuclei, is that of octupole correlations and octupole deformations. Möller et al. [3] show octupole contributions to the binding energy and note that the strongest contribution is centered at 222 Rn. The role of octupole deformations, and therefore the study of their impact, is important in several respects. The existence of the actinides and the heaviest nuclei is specifically due to quantum effects in the underlying single particle levels which also manifest in associated collective correlations. The measurement of new masses in this region of octupole correlations therefore provides a significant constraint on future microscopic models, for example, in approaches exploiting density functional theory which is widely used in many areas of many-body physics [4]. Further, octupole correlations are known to greatly enhance the sensitivity to nuclear electric dipole moments: understanding the relations between masses and such correlations is therefore of importance in the wider context of tests of fundamental symmetries.Finally, another important impact of the study of masses in this region is to be found in the development of microscopic mass models for nucleosynthesis, which are particularly vulnerable in heavy nuclei.In this Letter we report on seven new masses of neutronrich radon nuclei including the new isotope 229 Rn, which marks the first discovery of a nuclide using a Penning-trap mass spectrometer. The results allow the extraction of important new values for the valence proton-neutron interaction in the A $ 222 mass region, confirming and significantly extending a unique anomaly in these interaction strengths that may indeed be related to octupole degrees of freedom in this region.Penning traps are used extensively [5] to provide accurate mass data of radionuclides wit...

Atomic physics techniques for studying nuclear ground state properties, fundamental interactions and symmetries: status and perspectives

“…Similarly, a new isotope, 229 Rn, was found by ISOLTRAP [129]. These two discoveries demonstrate the sensitivity and selectivity of Penning trap mass spectrometry.…”

Damping effects in Penning trap mass spectrometry

“…Penning traps have set milestones in high-precision mass spectrometry of stable and short-lived nuclei [1][2][3], including most recent investigations beyond the proton drip line [4] and of transfermium nuclides [5] as well as the discovery of a new radon isotope [6]. The mass of a charged particle is linked to the cyclotron frequency in a homogeneous magnetic field, c = qB/(2 m).…”

Radon Nuclides and Radon Generators

“…The neutron-rich isotopes of 227 Rn and 228 Rn were also prepared by the spallation of natural 232 Th target with 600 MeV proton beam [26]. The heaviest experimentally detected isotopes of radon, the [223][224][225][226][227][228][229] Rn, have been determined for the first time, using the ISOLTRAP setup at CERN ISOLDE experiment [27].…”