The root mean square radii of the proton density distribution in ^{16-24}O derived from measurements of charge changing cross sections with a carbon target at ∼900A  MeV together with the matter radii portray thick neutron skin for ^{22-24}O despite ^{22,24}O being doubly magic. Imprints of the shell closures at N=14 and 16 are reflected in local minima of their proton radii that provide evidence for the tensor interaction causing them. The radii agree with ab initio calculations employing the chiral NNLO_{sat} interaction, though skin thickness predictions are challenged. Shell model predictions agree well with the data.

The γ-ray emission from the nuclei 62,64Fe following Coulomb excitation at bombarding energy of 400-440 AMeV was measured with special focus on E1 transitions in the energy region 4-8 MeV. The unstable neutron-rich nuclei 62,64Fe were produced at the FAIR-GSI laboratories and selected with the FRS spectrometer. The γ decay was detected with AGATA. From the measured γ-ray spectra the summed E1 strength is extracted and compared to microscopic quasi-particle phonon model calculations. The trend of the E1 strength with increasing neutron number is found to be fairly well reproduced with calculations that assume a rather complex structure of the 1− states (three-phonon states) inducing a strong fragmentation of the E1 nuclear response below the neutron binding energy.

A first performance test of the Coulomb excitation multipolarimetry (Coulex-multipolarimetry) method is presented. It is based on a $$^{85}\hbox {Br}\,\pi p_{3/2}\rightarrow \pi p_{1/2}$$ spin-flip experiment performed as part of the PreSPEC-AGATA campaign at the GSI Helmholtzzentrum für Schwerionenforschung (GSI). Via determination of background levels around the expected $$^{85}\hbox {Br}$$ excitations as well as measured $$^{197}\hbox {Au}$$ excitations, an upper limit for the M1 transition strength of the $$1/2_1^-\rightarrow 3/2_\text {g.s.}^-$$ transition in $$^{85}\hbox {Br}$$ and a lower beam time limit for upcoming experimental campaigns utilizing Coulex-multipolarimetry have been inferred. The impact of the use of AGATA in its anticipated $$1\pi $$ configuration on these estimates is deduced via Geant4 simulations.

first performance test of the Coulomb excitation multipolarimetry ( Coulex-multipolarimetry ) method is presented. It is based on a ^85Br π p_3/2→π p_1/2 spin-flip experiment performed as part of the PreSPEC-AGATA campaign at the GSI Helmholtzzentrum für Schwerionenforschung (GSI). Via determination of background levels around the expected ^85Br excitations as well as measured ^197Au excitations, an upper limit for the M 1 transition strength of the 1/2_1^-→ 3/2_g.s.^- transition in ^85Br and a lower beam time limit for upcoming experimental campaigns utilizing Coulex-multipolarimetry have been inferred. The impact of the use of AGATA in its anticipated 1π configuration on these estimates is deduced via Geant4 simulations.

R. Avigo a,b, O. Wieland a,∗, A. Bracco a,b, F. Camera a,b, F. Ameil c, T. Arici c, A. Ataç d, D. Barrientos e, D. Bazzacco f, P. Bednarczyk h, G. Benzoni a, B. Birkenbach i, N. Blasi a, H.C. Boston j, S. Bottoni a,b, S. Brambilla a, B. Bruyneel k, M. Ciemała h, E. Clément l, M.L. Cortés m,c, F.C.L. Crespi a,b, D.M. Cullen n, D. Curien o, F. Didierjean o, C. Domingo-Pardo q, G. Duchêne o, J. Eberth i, A. Görgen p, A. Gadea q, J. Gerl c, N. Goel c, P. Golubev r, V. González q, M. Górska c, A. Gottardo f,u, E. Gregor c, G. Guastalla m,c, T. Habermann c, L.J. Harkness-Brennan j, A. Jungclaus s, M. Kmiecik h, I. Kojouharov c, W. Korten k, N. Kurz c, M. Labiche t, N. Lalović r, S. Leoni a,b, M. Lettmann m, A. Maj h, R. Menegazzo f, D. Mengoni f,g, E. Merchan c, B. Million a, A.I. Morales a,b, D.R. Napoli u, C. Nociforo c, J. Nyberg v, N. Pietralla m, S. Pietri c, Zs. Podolyák w, V.Yu. Ponomarev m, A. Pullia a,b, B. Quintana x, G. Rainovski y, D. Ralet c,m, F. Recchia f,g, M. Reese m, P. Regan w, P. Reiter i, S. Riboldi a,b, D. Rudolph r, M.D. Salsac k, E. Sanchis z, L.G. Sarmiento r, H. Schaffner c, J. Simpson t, O. Stezowski aa, J.J. Valiente-Dobón u, H.J. Wollersheim c

Electric quadrupole matrix elements, Mp, for the Jπ=2+→0+, ΔT=0, T=1 transitions across the A=46 isobaric multiplet 46Cr-46V-46Ti have been measured at GSI with the FRS-LYCCA-AGATA setup. This allows direct insight into the isospin purity of the states of interest by testing the linearity of Mp with respect to Tz. Pairs of nuclei in the T=1 triplet were studied using identical reaction mechanisms in order to control systematic errors. The Mp values were obtained with two different methodologies: (i) a relativistic Coulomb excitation experiment was performed for 46Cr and 46Ti; (ii) a "stretched target" technique was adopted here, for the first time, for lifetime measurements in 46V and 46Ti. A constant value of Mp across the triplet has been observed. Shell-model calculations performed within the fp shell fail to reproduce this unexpected trend, pointing towards the need of a wider valence space. This result is confirmed by the good agreement with experimental data achieved with an interaction which allows excitations from the underlying sd shell. A test of the linearity rule for all published data on complete T=1 isospin triplets is presented.

The study of nuclei in the region around the N = Z doubly-magic nucleus Sn-100 has been of long standing interest for the nuclear structure and nuclear astrophysics. Recently, Park et al. have reported on properties of gamma-decaying isomers and isomeric ratios in the vicinity of Sn-100. That experiment was performed at the Radioactive Ion Beam Factory (RIBF) of the RIKEN Nishina Center in Japan as a part of the EURICA campaign. Neutron-deficient nuclei were produced in a fragmentation reaction of a Xe-124 primary beam on a 9 Be target at an energy of 345 MeV/A. Secondary ions were separated and identified in the BigRIPS fragment separator and implanted in the silicon detector array WAS3ABi. The data presented here were obtained in another experiment performed at the RIBF using the same reaction but slightly different separator settings. New results of ratios of isomeric population and half-lives of gamma-decaying isomers populated in the experiment are presented.

A gamma -decaying isomeric state (tau(1/2) = 197(-17)(+19) ns) has been identified in Cd-96, which is one alpha particle away from the last known bound N = Z nucleus, Sn-100. Comparison of the results with shell-model calculations has allowed a tentative experimental level scheme to be deduced and the isomer to be interpreted as a medium-spin negative-parity spin trap based on the coupling of isoscalar (T = 0) and isovector (T = 1) neutron-proton pairs. The data also suggest evidence for the population of a 9(+) T = 1 state, which is predicted by shell-model calculations to be yrast. Such a low-lying T = 1 state, which is unknown in lighter mass even-even self-conjugate nuclei, can also be interpreted in terms of the coupling of T = 0 and T = 1 neutron-proton pairs.

A systematic study was performed of microsecond gamma-decaying isomers around Sn-100 produced in a fragmentation reaction of a Xe-124 beam at 345 MeV/u at the Radioactive Ion Beam Factory of the RIKEN Nishina Center in Saitama, Japan. Half-lives of isomeric states in that region were remeasured allowing us to improve the currently available experimental information. Reduced transition probabilities were deduced and compared to shell-model calculations in various model spaces. The recently reported low-energy transitions in Rh-92 and Ag-96 were remeasured with improved precision. Additionally, experimental information on isomeric ratios, including five new ones, were extracted and compared to a previous experimental study and the sharp cutoff model of fragmentation reaction.

A thick neutron skin emerges from the first determination of root mean square radii of the proton distributions for $^{17-22}$N from charge changing cross section measurements around 900$A$ MeV at GSI. Neutron halo effects are signaled for $^{22}$N from an increase in the proton and matter radii. The radii suggest an unconventional shell gap at $N$ = 14 arising from the attractive proton-neutron tensor interaction, in good agreement with shell model calculations. $Ab$ $initio$, in-medium similarity re-normalization group, calculations with a state-of-the-art chiral nucleon-nucleon and three-nucleon interaction reproduce well the data approaching the neutron drip-line isotopes but are challenged in explaining the complete isotopic trend of the radii.

S. Pietri, A.M. Bruce, T. Grahn, W.R. Plass, C. Scheidenberger, T. Dickel, A. Kelić-Heil, H. Geissel, H. Weick, F. Ameil, L. Audouin, J. Aysto, S. Bagchi, M. Bai, J. Benlliure, G. Benzoni, C. Bruno, D. Cortina, T. Davisson, J. Gerl, M. Gorska, E. Haettner, O. Hall, L. Harkness-Brennan, A. Heinz, A. Helert, J.P. Hucka, A. Jokinen, A. Kankainen, D. Kahl, B. Kindler, I. Kojuharov, D. Kostyleva, N. Kuzminchuk, M. Labiche, C. Lederer-Woods, B. Lommel, G. Matinez-Pinedo, G. Münzenberg, I. Mukha, R. Page, M. Pfutzner, Zs. Podolyak, A. Prochazka, S. Purushotaman, C. Rappold, P. Regan, M.V. Ricciardi, S. Rinta-Antila, S. Saha, T. Saito, H. Schaffner, F. Schirru, J. Simpson, H. Simon, P. Spiller, J. Stadlmann, J. Taieb, Y. Tanaka, I. Tanihata, J. Vesic, B. Voss, P.M. Walker, P.J. Woods, J. Winfield, M. Winkler.

Isomeric states in isotopes in the vicinity of doubly-magic Pb-208 were populated following reactions of a relativistic Pb-208 primary beam impinging on a Be-9 fragmentation target. Secondary beams of Pb-198,Pb-200,Pb-202,Pb-206 and Hg-206 were isotopically separated and implanted in a passive stopper positioned in the focal plane of the GSI Fragment Separator. Delayed gamma rays were detected with the Advanced Gamma Tracking Array (AGATA). Decay schemes were reevaluated and interpreted with shell-model calculations. The momentum-dependent population of isomeric states in the two-nucleon hole nuclei Pb-206/Hg-206 was found to differ from the population of multi neutron-hole isomeric states in Pb-198,Pb-200,Pb-202.

Isomeric states in isotopes in the vicinity of doubly-magic 208Pb were populated following reactions of a relativistic 208Pb primary beam impinging on a 9Be fragmentation target. Secondary beams of 198,200,202,206Pb and 206Hg were isotopically separated and implanted in a passive stopper positioned in the focal plane of the GSI Fragment Separator. Delayed γ rays were detected with the Advanced GAmma Tracking Array (AGATA). Decay schemes were re-evaluated and interpreted with shell-model calculations. The momentum-dependent population of isomeric states in the two-nucleon hole nuclei 206Pb/206Hg was found to differ from the population of multi neutron-hole isomeric states in 198,200,202Pb. PACS numbers: 29.30.Kv, 25.70.Mn, 24.50.+g, 23.20.-g, 21.60.Cs, 27.80.+w Submitted to: J. Phys. G: Nucl. Part. Phys.

Particle identification at radioactive ion beam facilities requires Time-of-Flight detectors with an optimal time resolution and high rate capability. Segmented plastic scintillators are a common option for such detectors. A promising approach to cope with the high segmentation of modern devices is the use of silicon photomultipliers (SiPMs) as readout of the Time-of-Flight detectors. A prototype device consisting of strips of plastic scintillator of 4.4 x 100 x 1 mm(3) readout at both ends by SiPMs of two different sizes was tested using a Xe-124 beam at 600 MeV/nucleon. Timing and time-over-threshold information were extracted. The time resolution of the prototype was found to vary with the applied voltage and the SiPM size. After optimizing the voltage, resolutions of 14.3(10) ps and 10.4(1) ps were obtained for SiPMs of 1 x 1 mm(2) and 3 x 3 mm(2) respectively. These results point to SiPMs being suitable as readout of plastic scintillators at radioactive ion beam facilities.

Isomeric states in isotopes in the vicinity of doubly-magic 208Pb were populated following reactions of a relativistic 208Pb primary beam impinging on a 9Be fragmentation target. Secondary beams of 198;200;202;206Pb and 206Hg were isotopically separated and implanted in a passive stopper positioned in the focal plane of the GSI Fragment Separator. Delayed γ rays were detected with the Advanced GAmma Tracking Array (AGATA). Decay schemes were re-evaluated and interpreted with shell-model calculations. The momentum-dependent population of isomeric states in the two-nucleon hole nuclei 206Pb/206Hg was found to differ from the population of multi neutron-hole isomeric states in 198;200;202Pb.

Background: In the neutron-rich A approximate to 100 mass region, rapid shape changes as a function of nucleon number as well as coexistence of prolate, oblate, and triaxial shapes are predicted by various theoretical models. Lifetime measurements of excited levels in the molybdenum isotopes allow the determination of transitional quadrupole moments, which in turn provides structural information regarding the predicted shape change.Purpose: The present paper reports on the experimental setup, the method that allowed one to measure the lifetimes of excited states in even-even molybdenum isotopes from mass A = 100 up to mass A = 108, and the results that were obtained.Method: The isotopes of interest were populated by secondary knock-out reaction of neutron-rich nuclei separated and identified by the GSI fragment separator at relativistic beam energies and detected by the sensitive PreSPEC-AGATA experimental setup. The latter included the Lund-York-Cologne calorimeter for identification, tracking, and velocity measurement of ejectiles, and AGATA, an array of position sensitive segmented HPGe detectors, used to determine the interaction positions of the gamma ray enabling a precise Doppler correction. The lifetimes were determined with a relativistic version of the Doppler-shift-attenuation method using the systematic shift of the energy after Doppler correction of a gamma-ray transition with a known energy. This relativistic Doppler-shift-attenuation method allowed the determination of mean lifetimes from 2 to 250 ps.Results: Even-even molybdenum isotopes from mass A = 100 to A = 108 were studied. The decays of the low-lying states in the ground-state band were observed. In particular, two mean lifetimes were measured for the first time: tau = 29.7(-9.1)(+11.3) ps for the 4(+) state of Mo-108 and tau = 3.2(-0.7)(+ 0.7) ps for the 6(+) state of Mo-102.Conclusions: The reduced transition strengths B(E2), calculated from lifetimes measured in this experiment, compared to beyond-mean-field calculations, indicate a gradual shape transition in the chain of molybdenum isotopes when going from A = 100 to A = 108 with a maximum reached at N = 64. The transition probabilities decrease for Mo-108 which may be related to its well-pronounced triaxial shape indicated by the calculations.

The first evidence for β-delayed proton emission from the 16+ spin gap isomer in 96Cd is presented. The data were obtained from the Rare Isotope Beam Factory, at the RIKEN Nishina Center, using the BigRIPS spectrometer and the EURICA decay station. βp branching ratios for the ground state and 16+ isomer have been extracted along with more precise lifetimes for these states and the lifetime for the ground state decay of 95Cd. Large scale shell model (LSSM) calculations have been performed and WKB estimates made for ℓ=0,2,4 proton emission from three resonance-like states in 96Ag, that are populated by the β decay of the isomer, and the results compared to the new data. The calculations suggest that ℓ=2 proton emission from the resonance states, which reside ∼5 MeV above the proton separation energy, dominates the proton decay. The results highlight the importance of core-excited wavefunction components for the 16+ state.

Background: There have been measurements on roughly 230 nuclei that are beta-delayed neutron emitters. They range from He-8 up to La-150. Apart from 210Tl, with a branching ratio of only 0.007%, no other neutron emitter has been measured beyond A = 150. Therefore, new data are needed, particularly in the region of heavy nuclei around N = 126, in order to guide theoretical models and help understand the formation of the third r-process peak at A similar to 195.Purpose: To measure both beta-decay half-lives and neutron branching ratios of several neutron-rich Au, Hg, Tl, Pb, and Bi isotopes beyond N = 126.Method: Ions of interest were produced by fragmentation of a U-238 beam, selected and identified via the GSI-FRS fragment separator. A stack of segmented silicon detectors (SIMBA) was used to measure ion implants and beta decays. An array of 30 He-3 tubes embedded in a polyethylene matrix (BELEN) was used to detect neutrons with high efficiency and selectivity. A self-triggered digital system is employed to acquire data and to enable time correlations. The latter were analyzed with an analytical model and results for the half-lives and neutron-branching ratios were derived by using the binned maximum-likelihood method.Results: Twenty new beta-decay half-lives are reported for Au204-206, Hg208-211, Tl211-216, Pb215-218, and Bi218-220, nine of them for the first time. Neutron emission probabilities are reported for Hg-210,Hg-211 and Tl211-216.Conclusions: The new beta-decay half-lives are in good agreement with previous measurements on nuclei in this region. The measured neutron emission probabilities are comparable to or smaller than values predicted by global models such as relativistic Hartree Bogoliubov plus the relativistic quasi-particle random phase approximation (RHB + RQRPA).

Citation for published version (APA): Cullen, D., Podolyak, Z., Shand, C. M., Lalovic, N., Gerl, J., Rudolph, D., Alexander, T., Boutachkov, P., Cortes, M. L., Gorska, M., Kojouharov, I., & Kurz, N. (2016). Role of the \Delta resonance in the population of a four-nucleon state in the 56Fe \rightarrow 54Fe reaction at relativistic energies. Physical Review Letters, 117(22). https://doi.org/10.1103/PhysRevLett.117.222302

The β-delayed neutron emission probabilities of neutron rich Hg and Tl nuclei have been measured together with β-decay half-lives for 20 isotopes of Au, Hg, Tl, Pb, and Bi in the mass region N≳126. These are the heaviest species where neutron emission has been observed so far. These measurements provide key information to evaluate the performance of nuclear microscopic and phenomenological models in reproducing the high-energy part of the β-decay strength distribution. This provides important constraints on global theoretical models currently used in r-process nucleosynthesis.