Development of large area Silicon Photomultipliers arrays for gamma-ray spectroscopy applications

We report on the development of custom Front-End Electronics (FEE) dedicated to large area SiPM arrays for gamma-ray spectroscopy applications in high counting rate conditions. Two types of commercially available 8 x 8 arrays of 6 x 6 mm(2) Silicon Photomultipliers (SiPM) and a quasi-circular array of 30 SiPM cells were coupled to dedicated Front End Electronics (FEE) boards and tested in combination with LaBr3(Ce) crystals. Energy resolution measurements were taken with standard calibration radioactive sources (Co-60, Eu-152 and Co-56) while the timing response was studied in comparison with industry standard photomultiplier tubes. The energy resolution measured in this setup was down to 3.09(9)% at 661 keV, while the best timing resolution measured was 222.3(22) ps. Finally, the design of a SiPM based-ray detector, dedicated to fast-timing applications, is presented

Nuclear Structure Investigations in Yb isotopes

International audienceThe medium-to-heavy mass ytterbium isotopes (70Yb) in the rare-earth mass region are known to be well-deformed nuclei, which can be populated to very high spin, and are predicted to exhibit interesting phenomena, such as shape coexistence. The lack of any experimental information on the structure of the neutron-rich 180Yb isotope and the lifetime of the 21+ state of 178Yb have greatly motivated this study, which can offer useful information for the collective behavior of neutrons and protons in neutron-rich Yb isotopes. A measurement was performed to investigate the population of excited states and a first measurement of the unknown 21+ lifetime of 178Yb by means of a two neutron-transfer reaction 176Yb(18O,16O)178Yb at energies 68-74 MeV using the ROSPHERE array at IFIN-HH, Romania

Shape transitions between and within Zr isotopes

The Zirconium isotopes across the N=56,58 neutron sub­shell closures have been of special interest since years, sparked by the near doubly-magic features of 96Zr and the subsequent rapid onset of collectivity with a deformed ground-state structure already in 100Zr. Recent state-of-the-art shell model approaches did not only correctly describe this shape-phase transition in the Zr isotopic chain, but alsothe coexistence of non-collective structures and pronounced collectivity especially in 96,98Zr. Theisotope 98Zr is located on the transition from spherical to deformed ground state structures. We summarize recent experimental work to obtain the B(E2) excitation strengths of the first 2+ state of98Zr, including a new experiment employing the recoil-distance Doppler-shift method following a two-neutron transfer reaction

Shape transitions between and within Zr isotopes

The Zirconium isotopes across the N=56,58 neutron sub­shell closures have been of special interest since years, sparked by the near doubly-magic features of 96Zr and the subsequent rapid onset of collectivity with a deformed ground-state structure already in 100Zr. Recent state-of-the-art shell model approaches did not only correctly describe this shape-phase transition in the Zr isotopic chain, but alsothe coexistence of non-collective structures and pronounced collectivity especially in 96,98Zr. Theisotope 98Zr is located on the transition from spherical to deformed ground state structures. We summarize recent experimental work to obtain the B(E2) excitation strengths of the first 2+ state of98Zr, including a new experiment employing the recoil-distance Doppler-shift method following a two-neutron transfer reaction

Search for isospin-symmetry breaking in the A=62A=62 isovector triplet

The assignment of the first $2^+$ state in $^{62}$Ga has long been debated, due to its implications in triplet energy difference systematics in this mass region. An experiment has been performed at the IFIN-HH 9-MV Tandem accelerator using the ROSPHERE array in a mixed configuration of LaBr$_3$(Ce) and HPGe detectors, as well as an additional array of liquid scintillator neutron detectors. Excited states in $^{62}$Ga were populated through a $2n$ fusion-evaporation channel and an anisotropy ratio was obtained from neutron-filtered HPGe statistics of transitions observed at different angles. A $2^+$ state has been confirmed at an excitation energy of 978.1(1) keV. Theoretically, the interplay between isospin-symmetry breaking and shape-coexistence effects in the $A = 62$ isovector triplet is self-consistently treated within the beyond-mean-field complex excited Vampir variational model with symmetry projection before variation using an effective interaction obtained from a G matrix based on the charge-dependent Bonn CD potential adding the Coulomb interaction between the valence protons. Results are presented on Coulomb energy differences, mirror energy differences, triplet energy differences, and the superallowed Fermi $\beta$ decay of the ground state of $^{62}$Ge and $^{62}$Ga

Collective properties of neutron-deficient Nd isotopes: Lifetime measurements of the yrast states in 136^{136}Nd

International audienceLifetimes of the low-energy levels in Nd136, populated in the reaction Te124(O16,4n), were measured with the ROSPHERE array at the Horia Hulubei National Institute for Physics and Nuclear Engineering (IFIN-HH), Bucharest-Magurele. The data were analyzed using the recoil distance Doppler shift method, and, in the cases where lifetimes were τ⩽1 ps, Doppler attenuation effects were taken into account. The deduced electromagnetic transition probabilities are discussed in the framework of the five-dimensional collective Hamiltonian (5DCH) theoretical model implemented with the D1S Gogny force, and detailed systematics of several observables in the even-even Nd isotopic chain are presented that highlight the transitional character of the neutron-deficient Nd isotopes. The 5DCH predictions are in overall good agreement with the present experimental results

Nucleon-induced inelastic cross sections on Ni nat

International audienc

New evidence for alpha clustering structure in the ground state band of ²¹²Po

Half-lives of the low-lying yrast states of 212Po have been measured using the delayed coincidence fast-timing method. We report on the first measurement of the 41+ half-life, as well as a new measurement of the 61+ half-life with improved accuracy compared to previous studies. The extracted lifetime of the 41+ and 61+ state have been determined to be 100(14) ps and 1.66(28) ns respectively. With these measurements, precise values are now available for the reduced transition strengths B(E2) of all ground state band levels in 212Po up to the first 8+ state, in particular B(E2; 41+→21+) = 9.4(13) W.u. and B(E2;61+→41+) = 8.7(15) W.u. Comparison of the new available data with an α-clustering model calculation provides evidence that the inclusion of the α-cluster degree of freedom significantly improves agreement with experimental data compared to earlier shell model calculations

Multifaceted Quadruplet of Low-Lying Spin-Zero States in Ni-66: Emergence of Shape Isomerism in Light Nuclei

A search for shape isomers in the ^{66}Ni nucleus was performed, following old suggestions of various mean-field models and recent ones, based on state-of-the-art Monte Carlo shell model (MCSM), all considering ^{66}Ni as the lightest nuclear system with shape isomerism. By employing the two-neutron transfer reaction induced by an ^{18}O beam on a ^{64}Ni target, at the sub-Coulomb barrier energy of 39 MeV, all three lowest-excited 0^{+} states in ^{66}Ni were populated and their γ decay was observed by γ-coincidence technique. The 0^{+} states lifetimes were assessed with the plunger method, yielding for the 0_{2}^{+}, 0_{3}^{+}, and 0_{4}^{+} decay to the 2_{1}^{+} state the B(E2) values of 4.3, 0.1, and 0.2 Weisskopf units (W.u.), respectively. MCSM calculations correctly predict the existence of all three excited 0^{+} states, pointing to the oblate, spherical, and prolate nature of the consecutive excitations. In addition, they account for the hindrance of the E2 decay from the prolate 0_{4}^{+} to the spherical 2_{1}^{+} state, although overestimating its value. This result makes ^{66}Ni a unique nuclear system, apart from ^{236,238}U, in which a retarded γ transition from a 0^{+} deformed state to a spherical configuration is observed, resembling a shape-isomerlike behavior.status: publishe