Octupole correlations in the structure of O2 bands in the N=88 nuclei150Sm Gd

Knowledge of the exact microscopic structure of the 01 + ground state and first excited 02 + state in 150Sm is required to understand the branching of double β decay to these states from 150Nd. The detailed spectroscopy of 150Sm and 152Gd has been studied using (α,xn) reactions and the γ -ray arrays AFRODITE and JUROGAM II. Consistently strong E1 transitions are observed between the excited Kπ = 02 + bands and the lowest negative parity bands in both nuclei. These results are discussed in terms of the possible permanent octupole deformation in the first excited Kπ = 02 + band and also in terms of the “tidal wave” model of Frauendorf.Web of Scienc

Lifetime measurements of excited states in ¹⁶³W and the implications for the anomalous B(E2) ratios in transitional nuclei

This letter reports lifetime measurements of excited states in the odd-N nucleus 163W using the recoil-distance Doppler shift method to probe the core polarising effect of the i13/2 neutron orbital on the underlying soft triaxial even-even core. The ratio B(E2:21/2⁺ → 17/2⁺)/B(E2:17/2⁺ → 13/2⁺) is consistent with the predictions of the collective rotational model. The deduced B(E2) values provide insights into the validity of collective model predictions for heavy transitional nuclei and a geometric origin for the anomalous B(E2) ratios observed in nearby even-even nuclei is proposed

Shape evolution in even-even N≤126, Z≥82 nuclei

The shape evolution in the neutron-de cient lead, polonium and radium nuclei has been investigated via in-beam and delayed y-ray and conversion electron spectroscopy. The lead isotope 180Pb is found to still exhibit prolate excited structure, related to the known intruder structures in the heavier isotopes. The production cross-section of 180Pb was only 10 nb, one of the lowest ever employed in an in-beam experiment. A candidate for an excited prolate band was found in 192Po, making it the rst polonium isotope for which both oblate and prolate rotational bands have been established. Contrary to the previous results, the current experiments indicate that the onset of deformation in the radium isotopic chain seems not to take place yet in 206Ra. Based on the very similar decay patterns obtained in several in-beam experiments on the neutronde cient nuclei in the region and on the statistical limits of detection, three possible further cases for experiments are proposed. Methods developed for the data analysis, specially aimed at the studies of exotic nuclei, are presented.    

A simple timestamping data acquisition system for ToF-ERDA

A new data acquisition system, ToF-DAQ, has been developed for a ToF-ERDA telescope and other ToF-E and ToF-ToF measurement systems. ToF-DAQ combines an analogue electronics front-end to asynchronous time stamped data acquisition by means of a FPGA device. Coincidences are sought solely in software based on the timestamps. Timestamping offers more options for data analysis as coincidence events can be built also in offline analysis. The system utilises a National Instruments R-series FPGA device and a Windows PC as a host computer. Both the FPGA code and the host software were developed using the National Instruments LabVIEW graphical programming environment. Up to eight NIM ADCs can be handled by a single FPGA. The host computer and the FPGA can process total continuous count rates of over 750000 counts/s with a timestamping resolution of 8.33 ns.peerReviewe

In-beam spectroscopic studies of shape coexistence and collectivity in the neutron-deficient Z ≈ 82 nuclei

In the present paper we focus on studies of shape coexistence in even-mass nuclei in the neutron-deficient Pb region. They are based on experiments carried out using tagging techniques in the Accelerator Laboratory of the University of Jyväskylä, Finland. Excited states in many of these nuclei can only be accessed via fusion-evaporation reactions employing high-intensity stable-ion beams. The key features in these experiments are high selectivity, clean spectra and instrumentation that enables high count rates. We review three spectroscopic highlights in this region.peerReviewe

A Geant4 simulation package for the SAGE spectrometer

A comprehensive Geant4 simulation was built for the sage spectrometer. The simulation package includes the silicon and germanium detectors, the mechanical structure and the electromagnetic fields present in sage. This simulation can be used for making predictions through simulating experiments and for comparing simulated and experimental data to better understand the underlying physics.peerReviewe

Recoil-decay tagging study of 205Fr

The nucleus 205Fr has been studied through γ -ray and electron spectroscopy using the recoil-decay tagging technique. The resulting level scheme presents a spherical structure built on the 9/2− ground state and a rotational structure on top of a short-lived isomer. The isomer, with a spin and parity of 13/2+ and a half-life of 80(20) ns, de-excites by an M2 transition directly to the 9/2− ground state. Another, longer-lived, isomer, with a half-life of 1.15(4) ms, has also been found and assigned a spin and parity of 1/2+. Transitions populating and de-exciting this isomer have been observed as well.peerReviewe

Spectroscopy of the proton drip-line nucleus 203Fr

The nucleus 203Fr has been studied through γ -ray and electron spectroscopy, using the recoil-decay tagging technique. A 13/2+ state, with a half-life of 0.37(5) μs, has been observed in 203Fr. Both the α-decay branch and the internal de-excitation of the 1/2+ isomer in 203Fr have been studied. Furthermore, the corresponding 1/2+ state, with a half-life of 0.31(8) s, has been found in 199At. In addition, transitions feeding the 9/2− ground state of 203Fr have been identified. The observed level pattern suggests that the ground state is still spherical.peerReviewe

Alpha-decay studies of the nuclides 195Rn and 196Rn

The new neutron deficient nuclide 195 Rn and the nuclide 196 Rn have been produced in fusion evaporation reactions using 56 Fe ions on 142 Nd targets. A gas-filled recoil separator was used to separate the fusion products from the scattered beam. The activities were implanted in a position sensitive silicon detector. The isotopes were identified using spatial and time correlations between implants and decays. Two α decaying isomeric states, with E α = 7536 ( 11 ) keV [ T 1 / 2 = ( 6 + 3 − 2 ) ms ] for the ground state and E α = 7555 ( 11 ) keV [ T 1 / 2 = ( 5 + 3 − 2 ) ms ] for an isomeric state were identified in 195 Rn . In addition, the half-life and α decay energy of 196 Rn were measured with improved precision. The reduced widths deduced for the neutron deficient even-mass Rn isotopes suggest an onset of substantial deformation at N = 110.peerReviewe

Search for the terminating 27- state in 140Nd

In the search for the fully aligned 27− state in 140Nd predicted by cranked Nilsson-Strutinsky calculations, new close-to-spherical high-spin states have been discovered. Both the close-to-spherical and the triaxial calculated states are in good agreement with the experimental results, supporting the existence of shape coexistence up to very high spins. Shell-model calculations using a newly developed effective interaction for the 50 N ,Z 82 mass region are in good agreement with the observed spherical states. The comparison between the experimental and calculated level energies allowed the relative energy to be established between several proton and neutron orbitals at high energy and spins.peerReviewe