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There is strong circumstantial evidence that certain heavy, unstable atomic nuclei are ‘octupole deformed’, that is, distorted into a pear shape. This contrasts with the more prevalent rugby-ball shape of nuclei with reflection-symmetric, quadrupole deformations. The elusive octupole deformed nuclei are of importance for nuclear structure theory, and also in searches for physics beyond the standard model; any measurable electric-dipole moment (a signature of the latter) is expected to be amplified in such nuclei. Here we determine electric octupole transition strengths (a direct measure of octupole correlations) for short-lived isotopes of radon and radium. Coulomb excitation experiments were performed using accelerated beams of heavy, radioactive ions. Our data on 220 Rn and 224 Ra show clear evidence for stronger octupole deformation in the latter. The results enable discrimination between differing theoretical approaches to octupole correlations, and help to constrain suitable candidates for experimental studies of atomic electric-dipole moments that might reveal extensions to the standard model. An experimental study of certain short-lived isotopes of radon and radium has found clear octupole deformation in the nuclei of the latter — that is, these nuclei are pear-shaped; the results enable discrimination between differing theoretical approaches to octupole correlations. Pear-shaped atomic nuclei The atomic nucleus is a many-body quantum system with a shape determined by the number of nucleons that it contains and the interactions between them. Most of the several thousand known stable and radioactive atomic nuclei, with differing numbers of protons and neutrons, are spherical or rugby-ball shaped. But there is circumstantial evidence that some heavy, unstable nuclides are distorted into a pear shape through the phenomenon of octupole deformation. Samples of these rare atomic species can be accelerated to 8% of the speed of light in the REX-ISOLDE facility at CERN, and now Coulomb excitation experiments on beams of the short-lived isotopes radium-224 and radon-220 have demonstrated clear octupole deformation in the former. The results make it possible to discriminate between the various theoretical models of octupole-deformed nuclei, and are also relevant to the pursuit of physics beyond the Standard Model.

A recoil-beta-tagging experiment has been performed to study the excited T = 0 and T = 1 states in the odd–odd N = Z nucleus 94 Ag, populated via the 40 Ca( 58 Ni,1p3n) 94 Ag reaction. The experiment was conducted using the MARA recoil separator and JUROGAM3 array at the Accelerator Laboratory of the University of Jyväskylä. Through correlating fast, high-energy beta decays at the MARA focal plane with prompt γ rays emitted at the reaction target, a number of transitions between excited states in 94 Ag have been identified. The timing characteristics of these transitions confirm that they fall within decay sequences that feed the short-lived T = 1 ground state of 94 Ag. The transitions are proposed to proceed within and between the sets of states with T = 0 and T = 1 . Possible correspondence between some of these transitions from analog states in 94 Pd has been discussed, and shell-model calculations including multipole and monopole electromagnetic effects have been presented, in order to enable predictions of the decay patterns between the T = 0 and T = 1 states and to allow a theoretical set of Coulomb energy differences to be calculated for the A = 94 T = 1 analog states.

The fusion evaporation reaction 40Ca(58Ni,p3n)94 Ag has been used to study the odd-odd N=Z nucleus 94Ag at JYFL-ACCLAB using the MARA recoil separator and the JUROGAM 3 HPGe detector array. The recoil-β-tagging technique has allowed the observation of γ rays de-exciting states in 94Ag for the first time. Shell model calculations using the JUN45 interaction including multipole and monopole electromagnetic effects are presented. Comparison with analog states observed in neighbor isobar nucleus 94Pd is also discussed.

In an experiment at RIKEN, radioactive ions were implanted in the SIMBA silicon detector array and the β particles from the subsequent decay detected. However, as SIMBA is not capable of complete calorimetry, it is not possible to extract Qβ values directly from the data. Geant4 simulations have been used to determine the response of SIMBA to a given β-emission spectrum. By simulating with different β spectra and calculating the detector response to each spectrum, it is possible to compare with experiment and deduce the Qβ values. The technique is validated using two nuclei, for which the expected β spectrum is known from the literature.

The decay of five neutron-heavy rhodium isotopes were studied at the Radioactive Isotope Beam Factory (RIBF) Facility at the RIKEN Nishina Center after relativistic fission of 238U beam on a thick beryllium target. Previously unknown associated gamma-ray decay energies are reported for each nuclide, and through evaluating the intensity of the 2+ → 0+ E2 transition in the even-even palladium daughter nuclei, 120,122,124Pd, from the beta-tagged gamma-ray spectra an upper or lower limit of beta-delayed neutron emission is deduced for each nuclei. A general, expected trend of increasing Pn is observed in the direction of the neutron drip line.

Low-spin states of neutron-rich 84,86,88Ge were measured by in-flight γ-ray spectroscopy at 270 MeV/u at the RIKEN-RIBF facility. The exotic beams have been produced by primary 238U in-flight fission reactions and impinged on the MINOS device. MINOS combines a 10-cm long LH2 target with a Time Projection Chamber (TPC) to reconstruct the reaction vertices. The reactions were selected by the BigRIPS and the ZeroDegree spectrometers for the incoming and outgoing channels, respectively. Emitted γ radiation was detected by the NaI-array DALI2. De-excitations from the 61+, 41,2+, and 21,2+ states of 84,86Ge and 41+ and 21,2+ states of 88Ge were observed. The data are compared to state-of-the-art shell model and beyond-mean-field calculations. Furthermore, a candidate for a 31+ state of 86Ge was identified. This state plays a key role in the discussion of ground-state triaxiality of 86Ge, along with other features of the low-energy level scheme. This work was published in [1].

A decay spectroscopy experiment was performed within the EURICA campaign at RIKEN in 2012. It aimed at the isomer and particle spectroscopy of excited states and ground states in the mass region below the doubly magic 100Sn. The N = Z nuclei 98In, 96Cd and 94Ag were of particular interest for the present study. Preliminary results on the neutron deficient nuclei 93Ag and 94Ag are presented. In 94Ag a more precise value for the half-life of the ground state’s superallowed Fermi transition was deduced. In addition the energy spectra of the mentioned decay could be reproduced through precise Geant4 simulations of the used active stopper SIMBA. This will enable us to extract Qβ values from the measured data. The decay of 93Ag is discussed based on the observed implantation-decay correlation events.

The first EURICA campaign with high intensity Uranium beams took place at RIKEN in November/December 2012. Within this campaign experiment NP1112-RIBF85 was performed dedicated to the study of the isomeric and beta decays of neutron-rich Cd, In, Sn and Sb isotopes towards and beyond the N=82 neutron shell closure. In this contribution we will first provide information about the status of the analysis of the extensive data set obtained in this experiment and close with a short outlook.

The IS475 collaboration conducted Coulomb-excitation experiments with post-accelerated radioactive 220Rn and 224Ra beams at the REX-ISOLDE facility. The beam particles (Ebeam: 2.83 MeV/u) were Coulomb excited using 60Ni, 114Cd, and 120Sn scattering targets. De-excitation γ-rays were detected employing the Miniball array and scattered particles were detected in a silicon detector. Exploiting the Coulomb-excitation code GOSIA for each nucleus several matrix elements could be obtained from the measured γ-ray yields. The extracted ‹3−||E3||0+› matrix element allows for the conclusion that, while 220Rn represents an octupole vibrational system, 224Ra has already substantial octupole correlations in its ground state. This finding has implications for the search of CP-violating Schiff moments in the atomic systems of the adjacent odd-mass nuclei.

A recoil-beta-tagging experiment has been performed to study the excited$$T=0$$T = 0 and$$T=1$$T = 1 states in the odd–odd$$N=Z$$N = Z nucleus$$^{94}$$94 Ag, populated via the$$^{40}$$40 Ca($$^{58}$$58 Ni,1p3n)$$^{94}$$94 Ag reaction. The experiment was conducted using the MARA recoil separator and JUROGAM3 array at the Accelerator Laboratory of the University of Jyväskylä. Through correlating fast, high-energy beta decays at the MARA focal plane with prompt$$\\gamma $$γ rays emitted at the reaction target, a number of transitions between excited states in$$^{94}$$94 Ag have been identified. The timing characteristics of these transitions confirm that they fall within decay sequences that feed the short-lived$$T=1$$T = 1 ground state of$$^{94}$$94 Ag. The transitions are proposed to proceed within and between the sets of states with$$T=0$$T = 0 and$$T=1$$T = 1 . Possible correspondence between some of these transitions from analog states in$$^{94}$$94 Pd has been discussed, and shell-model calculations including multipole and monopole electromagnetic effects have been presented, in order to enable predictions of the decay patterns between the$$T=0$$T = 0 and$$T=1$$T = 1 states and to allow a theoretical set of Coulomb energy differences to be calculated for the$$A = 94$$A = 94$$T=1$$T = 1 analog states.