The Advanced GAmma Tracking Array (AGATA) has been installed at Laboratori Nazionali di Legnaro (LNL), Italy. In this installation, AGATA will consist, at the beginning, of 13 AGATA triple clusters (ATCs) with an angular coverage of 1π, and progressively the number of ATCs will increase up to a 2π angular coverage. This setup will exploit both stable and radioactive ion beams delivered by the Tandem–PIAVE-ALPI accelerator complex and the SPES facility. The new implementation of AGATA at LNL will be used in two different configurations, firstly one coupled to the PRISMA large-acceptance magnetic spectrometer and lately a second one at Zero Degrees, along the beam line. These two configurations will allow us to cover a broad physics program, using different reaction mechanisms, such as Coulomb excitation, fusion-evaporation, transfer and fission at energies close to the Coulomb barrier. These setups have been designed to be coupled with a large variety of complementary detectors such as charged particle detectors, neutron detectors, heavy-ion detectors, high-energy γ-ray arrays, cryogenic and gasjet targets and the plunger device for lifetime measurements. We present in this paper the conceptual design, characteristics and performance figures of this implementation of AGATA at LNL.

The excited states of unstable ^{20}O were investigated via γ-ray spectroscopy following the ^{19}O(d,p)^{20}O reaction at 8  AMeV. By exploiting the Doppler shift attenuation method, the lifetimes of the 2_{2}^{+} and 3_{1}^{+} states were firmly established. From the γ-ray branching and E2/M1 mixing ratios for transitions deexciting the 2_{2}^{+} and 3_{1}^{+} states, the B(E2) and B(M1) were determined. Various chiral effective field theory Hamiltonians, describing the nuclear properties beyond ground states, along with a standard USDB interaction, were compared with the experimentally obtained data. Such a comparison for a large set of γ-ray transition probabilities with the valence space in medium similarity renormalization group ab initio calculations was performed for the first time in a nucleus far from stability. It was shown that the ab initio approaches using chiral effective field theory forces are challenged by detailed high-precision spectroscopic properties of nuclei. The reduced transition probabilities were found to be a very constraining test of the performance of the ab initio models.

The Zirconium (Z = 40) isotopic chain has attracted interest for more than four decades. The abrupt lowering of the energy of the first 2^+ state and the increase in the transition strength B(E2; 2^+_1→ 0^+_1) going from ^98 Zr to ^100 Zr has been the first example of “quantum phase transition” in nuclear shapes, which has few equivalents in the nuclear chart. Although a multitude of experiments have been performed to measure nuclear properties related to nuclear shapes and collectivity in the region, none of the measured lifetimes were obtained using the Recoil Distance Doppler Shift method in the γγ -coincidence mode where a gate on the direct feeding transition of the state of interest allows a strict control of systematical errors. This work reports the results of lifetime measurements for the first yrast excited states in ^98-104 Zr carried out to extract reduced transition probabilities. The new lifetime values in γγ -coincidence and γ -single mode are compared with the results of former experiments. Recent predictions of the Interacting Boson Model with Configuration Mixing, the Symmetry Conserving Configuration Mixing model based on the Hartree–Fock–Bogoliubov approach and the Monte Carlo Shell Model are presented and compared with the experimental data.

Flerovium isotopes (element Z = 114) were produced in the fusion-evaporation reactions 48Ca + 242,244Pu and studied with an upgraded TASISpec decay station placed in the focal plane of the gas-filled separator TASCA at the GSI Helmholtzzentrum fur Schwerionenforschung in Darmstadt, Germany. Twenty-nine flerovium decay chains were identified by means of correlated implantation, alpha decay, and spontaneous fission events. Data analysis aspects and statistical assessments, primarily based on measured rates of various events, which laid the foundation for the comprehensive spectroscopic information on the flerovium decay chains, are presented in detail. Various decay scenarios of an excited state observed in 282Cn are examined in depth with the help of GEANT4 simulations and assessed by predictions of beyond mean-field calculations including triaxial shape degrees of freedom. Previous, revised, and newly derived fission probabilities of even-even superheavy nuclei are compared with various theoretical predictions.

γ -ray tracking is based on a new generation of position sensitive high-purity germanium (HPGe) detectors. A novel type of cluster detector was successfully developed and assembled for the high-resolution γ -ray spectrometer Advanced Gamma Tracking Array AGATA. The core part of the detector consists of three encapsulated, 36-fold segmented HPGe detectors which are operated in a common cryostat. The Ge crystal is hermetically sealed inside an aluminium can. All energy channels provide best energy resolution of core and segment signals for an extended energy range well above 50 MeV. A low cross-talk level was determined for the HPGe detectors and its preamplifier circuitry. Related cross-talk corrections are essential for highest energy resolution and improved position dependent pulse shape information. Recently a new encapsulation technology was put into operation which is based on a renewable metal elastic seal. HPGe detector developments are concerned with technologies for the production of p+ and n+ contacts, the segmentation and passivation of encapsulated HPGe crystals. Semiconductor processing research specifically aimed to develop a stable, thin and easy to segment n+ contact. A novel process, based on pulsed laser melting PLM, was successfully employed to produce very thin n+ and p+ contacts preserving the Ge purity. The contacts were segmented using a photolithographic process and then the intrinsic surface between contacts was passivated to assure the electrical insulation between them. A small detector prototype with three segments was made using these new techniques and then successfully tested.

Fifteen correlated alpha-decay chains starting from the odd-A superheavy nucleus 289Fl were observed following the fusion-evaporation reaction Ca-48 + Pu-244. The results call for at least two parallel alpha-decay sequences starting from at least two different states of (289)Fl. This implies that close-lying levels in nuclei along these chains have quite different spin-parity assignments. Further, observed alpha-electron and alpha-photon coincidences, as well as the alpha decay fine structure along the decay chains, suggest a change in the ground-state spin assignment between (285)Cn and (281)Ds. Our experimental results, on the excited level structure of the heaviest odd-N nuclei to date, provide a direct testing ground for theory. This is illustrated by comparison with new nuclear structure calculations based on the symmetry-conserving configuration mixing theory.

The very proton-rich 71 Kr isotope was produced through the in-flight fragmentation of 78 Kr on a beryllium target at RIKEN – Nishina Center in order to study its β-decay properties. A stack of double-sided silicon strip detectors, called WAS3ABi, was used as the decay station, where the detection of ion implants, β-decays and β-delayed protons took place. Beta-delayed γ-rays were measured using a system of 84 HPGe detectors, called EURICA, surrounding the decay station. The main goal of the present study was the precise measurement of the half-life of 71 Kr, as in the literature there is an almost 10 σ difference between the most precise independent results. Implant–β time correlations, implant–proton time correlations and implant–β–γ time correlations were all used to derive the half-life value, followed by a thorough investigation of systematic uncertainties for each method. As these values were found to be consistent, the weighted average t 1 / 2 = 94.40 +19 ms is reported as a new half-life value in this work. Furthermore a total of 26 previously unreported γ following the β-decay of 71 Kr were also identified in the analysis.

Level lifetimes for the candidate chiral doublet bands of 80Br were extracted by means of the Doppler-shift attenuation method. The absolute transition probabilities derived from the lifetimes agree well with the M1 and E2 chiral electromagnetic selection rules, and are well reproduced by the triaxial particle rotor model calculations. Such good agreements among the experimental data, selection rules of chiral doublet bands and theoretical calculations are rare and outstanding in researches of nuclear chirality. Besides odd-odd Cs isotopes, odd-odd Br isotopes in the A≈ 80 mass region represent another territory that exhibits the ideal selection rules expected for chiral doublet bands.

The β-decay of the even-even nucleus 70Kr with Z=N+2, has been investigated at the Radioactive Ion Beam Factory (RIBF) of the RIKEN Nishina Center using the BigRIPS fragment separator, the ZeroDegree Spectrometer, the WAS3ABI implantation station and the EURICA HPGe cluster array. Fifteen γ-rays associated with the β-decay of 70Kr into 70Br have been identified for the first time, defining ten populated states below Eexc=3300 keV. The half-life of 70Kr was derived with increased precision and found to be t1/2=45.19±0.14 ms. The β-delayed proton emission probability has also been determined as εp=0.545(23)%. An increase in the β-strength to the yrast 1+ state in comparison with the heaviest Z=N+2 system studied so far (62Ge decay) is observed that may indicate increased np correlations in the T=0 channel. The β-decay strength deduced from the results is interpreted in terms of the proton-neutron quasiparticle random-phase approximation (pnQRPA) and also with a schematic model that includes isoscalar and isovector pairing in addition to quadrupole deformation. The application of this last model indicates an approximate realization of pseudo-SU(4) symmetry in this system.

Excited states in the neutron-deficient nucleus Tc-87 have been studied via the fusion-evaporation reaction 54Fe(36Ar, 2n1p) Tc-87 at 115 MeV beam energy. The AGATA gamma-ray spectrometer coupled to the DIAMANT, NEDA, and Neutron Wall detector arrays for light-particle detection was used to measure the prompt coincidence of gamma rays and light particles. Six transitions from the deexcitation of excited states belonging to a new band in Tc-87 were identified by comparing gamma-ray intensities in the spectra gated under different reaction channel selection conditions. The constructed level structure was compared with the shell model and total Routhian surface calculations. The results indicate that the new band structure in 87Tc is built on a spherical configuration, which is different from that assigned to the previously identified oblate yrast rotational band.

The structure of the unbound F-15 nucleus is investigated using the inverse kinematics resonant scattering of a radioactive O-14 beam impinging on a CH2 target. The analysis of H-1(O-14, p) O-14 and H-1(O-14, 2p) N-13 reactions allowed the confirmation of the previously observed narrow 1/2(-) resonance, near the two-proton decay threshold, and the identification of two new narrow 5/2(-) and 3/2(-) resonances. The newly observed levels decay by 1p emission to the ground of O-14, and by sequential 2p emission to the ground state of N-13 via the 1(-) resonance of O-14. Gamow shell model (GSM) analysis of the experimental data suggests that the wave functions of the 5/2(-) and 3/2(-) resonances may be collectivized by the continuum coupling to nearby 2p- and 1p-decay channels. The observed excitation function H-1(O-14, p) O-14 and resonance spectrum in F-15 are well reproduced in the unified framework of the GSM.

The reduced transition probabilities for the 4_{1}^{+}→2_{1}^{+} and 2_{1}^{+}→0_{1}^{+} transitions in ^{92}Mo and ^{94}Ru and for the 4_{1}^{+}→2_{1}^{+} and 6_{1}^{+}→4_{1}^{+} transitions in ^{90}Zr have been determined in this experiment making use of a multinucleon transfer reaction. These results have been interpreted on the basis of realistic shell-model calculations in the f_{5/2}, p_{3/2}, p_{1/2}, and g_{9/2} proton valence space. Only the combination of extensive lifetime information and large scale shell-model calculations allowed the extent of the seniority conservation in the N=50 g_{9/2} orbital to be understood. The conclusion is that seniority is largely conserved in the first πg_{9/2} orbital.

The structure of the unbound $^{15}$F nucleus is investigated using the inverse kinematics resonant scattering of a radioactive $^{14}$O beam impinging on a CH$_2$ target. The analysis of $^{1}$H($^{14}$O,p)$^{14}$O and $^{1}$H($^{14}$O,2p)$^{13}$N reactions allowed the confirmation of the previously observed narrow $1/2^{-}$ resonance, near the two-proton decay threshold, and the identification of two new narrow 5/2$^{-}$ and 3/2$^{-}$ resonances. The newly observed levels decay by 1p emission to the ground of $^{14}$O, and by sequential 2p emission to the ground state (g.s.) of $^{13}$N via the $1^-$ resonance of $^{14}$O. Gamow shell model (GSM) analysis of the experimental data suggests that the wave functions of the 5/2$^{-}$ and 3/2$^{-}$ resonances may be collectivized by the continuum coupling to nearby 2p- and 1p- decay channels. The observed excitation function $^{1}$H($^{14}$O,p)$^{14}$O and resonance spectrum in $^{15}$F are well reproduced in the unified framework of the GSM.

A nuclear spectroscopy experiment was conducted to study α-decay chains stemming from isotopes of flerovium (element Z=114). An upgraded TASISpec decay station was placed behind the gas-filled separator TASCA at the GSI Helmholtzzentrum für Schwerionenforschung in Darmstadt, Germany. The fusion-evaporation reactions ^{48}Ca+^{242}Pu and ^{48}Ca+^{244}Pu provided a total of 32 flerovium-candidate decay chains, of which two and eleven were firmly assigned to ^{286}Fl and ^{288}Fl, respectively. A prompt coincidence between a 9.60(1)-MeV α particle event and a 0.36(1)-MeV conversion electron marked the first observation of an excited state in an even-even isotope of the heaviest man-made elements, namely ^{282}Cn. Spectroscopy of ^{288}Fl decay chains fixed Q_{α}=10.06(1)  MeV. In one case, a Q_{α}=9.46(1)-MeV decay from ^{284}Cn into ^{280}Ds was observed, with ^{280}Ds fissioning after only 518  μs. The impact of these findings, aggregated with existing data on decay chains of ^{286,288}Fl, on the size of an anticipated shell gap at proton number Z=114 is discussed in light of predictions from two beyond-mean-field calculations, which take into account triaxial deformation.

A gamma-ray spectroscopic study of Po-212 was performed at the Grand Accelerateur National d'Ions Lourds, using the inverse kinematics alpha-transfer reaction C-12(Pb-208, Po-212) Be-8 and the AGATA spectrometer. A careful analysis based on gamma gamma coincidence relations allowed us to establish 14 new excited states in the energy range between 1.9 and 3.3 MeV. None of these states, however, can be considered as candidates for the levels with spins and parities of 1(-) and 2(-) and excitation energies below 2.1 MeV, which have been predicted by recent alpha-cluster model calculations. A systematic comparison of the experimentally established excitation scheme of Po-212 with shell-model calculations was performed. This comparison suggests that the six states with excitation energies (spins and parities) of 1744 (4(-)), 1751 (8(-)), 1787 (6(-)), 1946 (4(-)), 1986 (8(-)), and 2016 (6(-)) keV, which previously were interpreted as alpha-cluster states, may in fact be of positive parity and belong to low-lying shell-model multiplets. This reinterpretation of the structure of Po-212 is supported by experimental information with respect to the linear polarization of gamma rays, which suggests a magnetic character of the 432-keV gamma ray decaying from the state at an excitation energy of 1787 keV to the 6(1)(+) yrast state, and exclusive reaction cross sections.

The low-lying excited states in the neutron-deficient N = Z + 1 nucleus (87)(43)Tcc(44) have been studied via the fusion-evaporation reaction Fe-54(Ar-36, 2n1p)Tc-87 at the Grand Accelerateur 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 gamma rays, neutrons, and charged particles emitted in the reaction. A level scheme of Tc-87 from the (9/2(g.s.)(+)) state to the (33/2(1)(+)) state was established based on six mutually coincident gamma-ray transitions. The constructed level structure exhibits a rotational behavior with a sharp backbending at (h) over bar omega approximate to 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.

V. Girard-Alcindor, 2 A. Mercenne, I. Stefan, F. de Oliveira Santos, N. Michel, M. P loszajczak, M. Assié, A. Lemasson, E. Clément, F. Flavigny, A. Matta, D. Ramos, M. Rejmund, J. Dudouet, D. Ackermann, P. Adsley, M. Assunção, B. Bastin, D. Beaumel, G. Benzoni, R. Borcea, A.J. Boston, L. Cáceres, B. Cederwall, I. Celikovic, V. Chudoba, M. Ciemala, J. Collado, F. C. L. Crespi, 16 G. D’Agata, G. De France, F. Delaunay, C. Diget, C. Domingo-Pardo, J. Eberth, C. Fougères, S. Franchoo, F. Galtarossa, A. Georgiadou, J. Gibelin, S. Giraud, V. González, N. Goyal, A. Gottardo, J. Goupil, S. Grévy, V. Guimaraes, F. Hammache, L. J. Harkness-Brennan, H. Hess, D.S. Judson Oliver, O. Kamalou, A. Kameneyero, J. Kiener, W. Korten, S. Koyama, M. Labiche, L. Lalanne, V. Lapoux, S. Leblond, A. Lefevre, C. Lenain, S.Leoni, 16 H. Li, A. Lopez-Martens, A. Maj, I. Matea, R. Menegazzo, D. Mengoni, 25 A. Meyer, B. Million, B. Monteagudo, P. Morfouace, J. Mrazek, M. Niikura, J. Piot, Zs. Podolyak, C. Portail, A. Pullia, B. Quintana, F. Recchia, 25 P. Reiter, K. Rezynkina, 25 T. Roger, J. S. Rojo, F. Rotaru, M.D. Salsac, A. M. Sánchez Beńıtez, E. Sanchis, M. Şenyig̈it, N. de Séréville, M. Siciliano, 22, 32 J. Simpson, D. Sohler, O. Sorlin, M. Stanoiu, C. Stodel, D. Suzuki, C. Theisen, J. C. Thomas, P. Ujic, J.J. Valiente-Dobón, and M. Zielińska Grand Accélérateur National d’Ions Lourds (GANIL),

The low-lying excited states in the neutron-deficient $N=Z+1$ nucleus $_{43}^{87}\mathrm{Tc}_{44}$ have been studied via the fusion-evaporation reaction $^{54}\mathrm{Fe}(^{36}\mathrm{Ar}, 2n1p)^{87}\mathrm{Tc}$ at the Grand Acc\'el\'erateur 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 $\ensuremath{\gamma}$ rays, neutrons, and charged particles emitted in the reaction. A level scheme of $^{87}\mathrm{Tc}$ from the ($9/{2}_{\mathrm{g}.\mathrm{s}.}^{+}$) state to the ($33/{2}_{1}^{+}$) state was established based on six mutually coincident $\ensuremath{\gamma}$-ray transitions. The constructed level structure exhibits a rotational behavior with a sharp backbending at $\ensuremath{\hbar}\ensuremath{\omega}\ensuremath{\approx}0.50$ 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.

Citation for published version (APA): Goldkuhle, A., Blazhev, A., Fransen, C., Dewald, A., Beckers, M., Birkenbach, B., Braunroth, T., Clément, E., Dudouet, J., Eberth, J., Hess, H., Jacquot, B., Jolie, J., Kim, Y-H., Lemasson, A., Lenzi, S. M., Li, H. J., Litzinger, J., Michelagnoli, C., ... Zell, K. O. (2020). Lifetime measurements of excited states in neutron-rich 53 Ti: benchmarking effective shell-model interactions. Physical Review C, 102(5), [054334]. https://doi.org/10.1103/PhysRevC.102.054334