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A new measurement of γ decay from the states above the neutron threshold in Pb208 has been performed at Cyclotron Centre Bronowice in Kraków, Poland. The main goal of the experiment was to observe the γ decay to the ground state from the isoscalar giant quadrupole resonance (ISGQR). To this day, the only published observation of this phenomenon dates back to the late 1980s, where γ decay to the ground state branching ratio was reported. At variance with the existing measurement using inelastic scattering of O17, here proton inelastic scattering is employed. In particular, data were obtained for Pb208(p,p′γ) at 85 MeV beam energy, where γ rays were measured for proton scattering angles 8.9∘, 10.7∘, 12.5∘, and 14.3∘. By applying a similar analysis method as in the previous experiment, the branching ratio of ISGQR gamma decay to the ground state was extracted from the data.

Background: Superdeformed (SD) bands are suggested by theory around Ca40 and in lighter alpha-conjugate nuclei such as Mg24, Si28, and S32. Such predictions originate from a number of theoretical models including mean-field models and antisymmetrized molecular dynamics (AMD) calculations. While SD bands have been identified in Ca40 and its near neighbors, evidence of their existence in the lighter, midshell nuclei is circumstantial at best. The key evidence of superdeformation would be the observation of transitions with high B(E2) transition strengths connecting states in a rotational sequence. This is challenging information to obtain since the bands lie at a high excitation energy and competition from out-of-band decay is dominant. Purpose: The purpose of the present study is to establish a new methodology to circumvent the difficulties in identifying and quantifying in-band transitions through directly populating candidate states in the SD band in Si28 through inelastic alpha scattering, selecting such states with a spectrometer, and measuring their gamma-ray decay with a large array of high-purity germanium detectors, allowing direct access to electromagnetic transition strengths. Methods: Excited states in Si28 were populated in the Si28(α,α′) reaction using a 130-MeV He4 beam from the K140 AVF cyclotron at the Research Center for Nuclear Physics. Outgoing alpha particles were analyzed using the Grand Raiden spectrometer positioned at an angle of 9.1° to favor the population of states with J≈4. Coincident gamma rays were detected with the CAGRA array of 12 HPGe clover detectors augmented by a set of four large LaBr3 detectors. Results: Data analysis showed that it was possible to identify additional low-energy transitions in competition with high-energy decays from excited states in Si28 in the vicinity of 10 MeV. However, while the candidate 4+ SD state at 10.944 MeV was populated, a 1148-keV transition to the candidate 2+ SD state at 9.796 MeV was not observed, and only an upper limit for its transition strength of B(E2)

The low-lying excited states in the neutron-deficient N=Z+1 nucleus Tc444387 have been studied via the fusion-evaporation reaction Fe54(Ar36, 2n1p)Tc87 at the Grand Accélérateur National d'Ions Lourds (GANIL), France. The AGATA spectrometer was used in conjunction with the auxiliary NEDA, Neutron Wall, and DIAMANT detector arrays to measure coincident prompt γ rays, neutrons, and charged particles emitted in the reaction. A level scheme of Tc87 from the (9/2g.s.+) state to the (33/21+) state was established based on six mutually coincident γ-ray transitions. The constructed level structure exhibits a rotational behavior with a sharp backbending at ω≈0.50 MeV. A decrease in alignment frequency and increase in alignment sharpness in the odd-mass isotonic chains around N=44 is proposed as an effect of the enhanced isoscalar neutron-proton interactions in odd-mass nuclei when approaching the N=Z line.

International audience; A recent extension of the Doppler-shift attenuation method to measure short lifetimes of states populated in low-energy binary reactions is applied to the case of 17N. The reliability of the technique is confirmed by measuring the lifetime of the 5515 keV 3/2− state, which is depopulated by two different γ rays. The method is used to measure the lifetime of the 5170 keV (9/2+) state in the same nucleus. Comparisons with large-scale shell-model predictions are given as well.

To test the predictive power of ab initio nuclear structure theory, the lifetime of the second 2+ state in neutron-rich O20,τ(22+)=150-30+80fs, and an estimate for the lifetime of the second 2+ state in C16 have been obtained for the first time. The results were achieved via a novel Monte Carlo technique that allowed us to measure nuclear state lifetimes in the tens-to-hundreds of femtoseconds range by analyzing the Doppler-shifted γ-transition line shapes of products of low-energy transfer and deep-inelastic processes in the reaction O18(7.0MeV/u)+Ta181. The requested sensitivity could only be reached owing to the excellent performances of the Advanced γ-Tracking Array AGATA, coupled to the PARIS scintillator array and to the VAMOS++ magnetic spectrometer. The experimental lifetimes agree with predictions of ab initio calculations using two-and three-nucleon interactions, obtained with the valence-space in-medium similarity renormalization group for O20 and with the no-core shell model for C16. The present measurement shows the power of electromagnetic observables, determined with high-precision γ spectroscopy, to assess the quality of first-principles nuclear structure calculations, complementing common benchmarks based on nuclear energies. The proposed experimental approach will be essential for short lifetime measurements in unexplored regions of the nuclear chart, including r-process nuclei, when intense beams, produced by Isotope Separation On-Line (ISOL) techniques, become available.

The low-lying energy spectrum of the extremely neutron-deficient self-conjugate (N=Z) nuclide Ru448844 has been measured using the combination of the Advanced Gamma Tracking Array (AGATA) spectrometer, the NEDA and Neutron Wall neutron detector arrays, and the DIAMANT charged particle detector array. Excited states in Ru88 were populated via the Fe54(Ar36,2nγ)Ru88∗ fusion-evaporation reaction at the Grand Accélérateur National d'Ions Lourds (GANIL) accelerator complex. The observed γ-ray cascade is assigned to Ru88 using clean prompt γ-γ-2-neutron coincidences in anticoincidence with the detection of charged particles, confirming and extending the previously assigned sequence of low-lying excited states. It is consistent with a moderately deformed rotating system exhibiting a band crossing at a rotational frequency that is significantly higher than standard theoretical predictions with isovector pairing, as well as observations in neighboring N>Z nuclides. The direct observation of such a "delayed" rotational alignment in a deformed N=Z nucleus is in agreement with theoretical predictions related to the presence of strong isoscalar neutron-proton pair correlations.