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Physical review / C 102(5), 054304 (2020). doi:10.1103/PhysRevC.102.054304, Published by Inst., Woodbury, NY

The European physical journal / A 56(4), 105 (2020). doi:10.1140/epja/s10050-020-00118-8, Published by Springer, Heidelberg

Data analysis of the Coulomb excitation experiment of the exotic 206Hg nucleus, recently performed at CERN’s HIE-ISOLDE facility, needs to account for the contribution to target excitation due to the strongly-present beam contaminant 130Xe. In this paper, the contamination subtraction procedure is presented.

8 pags., 9 figs., We measured absolute cross sections for neutron transfer channels populated in the Rb-94 + Pb-208 binary reaction. Cross sections have been extracted identifying directly the lead isotopes with the high efficiency MINIBALL gamma-ray array coupled to a particle detector combined with a radioactive Rb-94 beam delivered at E-lab = 6.2 MeV/nucleon by the HIE-ISOLDE facility. We observed sizable cross sections in the neutron-rich mass region, where the heavy partner acquires neutrons. A fair agreement between the measured cross sections with those from GRAZING calculations gives confidence in the cross-section predictions of more neutron-rich nuclei produced via a larger number of transferred nucleons., This work was partly supported by the HORIZON 2020 ENSAR2 Grant Agreement no. 654002, and Marie Skłodowska-Curie COFUND (EU-CERN) grant agreement no. 665779, and by STFC (U.K.). This work has been supported in part by the Croatian Science Foundation under Project no. 7194 and in part under Project no. IP-2018-01- 1257, and the German BMBF under contract 05P18PKCIA + Verbundprojekt 05P2018

The neutron-deficient mercury isotopes serve as a classical example of shape coexistence, whereby at low energy near-degenerate nuclear states characterized by different shapes appear. The electromagnetic structure of even-mass 182-188 Hg isotopes was studied using safe-energy Coulomb excitation of neutron-deficient mercury beams delivered by the REX-ISOLDE facility at CERN. The population of $ 0^{+}_{1,2}$01,2+, $ 2^{+}_{1,2}$21,2+and $ 4^{+}_{1}$41+states was observed in all nuclei under study. Reduced E2 matrix elements coupling populated yrast and non-yrast states were extracted, including their relative signs. These are a sensitive probe of shape coexistence and may be used to validate nuclear models. The experimental results are discussed in terms of mixing of two different configurations and are compared with three different model calculations: the Beyond Mean Field model, the Interacting Boson Model with configuration mixing and the General Bohr Hamiltonian. Partial agreement with experiment was observed, hinting to missing ingredients in the theoretical descriptions. The neutron-deficient mercury isotopes serve as a classical example of shape coexistence, whereby at low energy near-degenerate nuclear states characterized by different shapes appear. The electromagnetic structure of even-mass 182-188 Hg isotopes was studied using safe-energy Coulomb excitation of neutron-deficient mercury beams delivered by the REX-ISOLDE facility at CERN. The population of $ 0^{+}_{1,2}$01,2+, $ 2^{+}_{1,2}$21,2+and $ 4^{+}_{1}$41+states was observed in all nuclei under study. Reduced E2 matrix elements coupling populated yrast and non-yrast states were extracted, including their relative signs. These are a sensitive probe of shape coexistence and may be used to validate nuclear models. The experimental results are discussed in terms of mixing of two different configurations and are compared with three different model calculations: the Beyond Mean Field model, the Interacting Boson Model with configuration mixing and the General Bohr Hamiltonian. Partial agreement with experiment was observed, hinting to missing ingredients in the theoretical descriptions. ispartof: The European Physical Journal A - Hadrons and Nuclei vol:55 issue:8 pages:130-130 status: published

Author(s): Vogt, A; Siciliano, M; Birkenbach, B; Reiter, P; Hadynska-Klȩk, K; Wheldon, C; Valiente-Dobon, JJ; Teruya, E; Yoshinaga, N; Arnswald, K; Bazzacco, D; Blazhev, A; Bracco, A; Bruyneel, B; Chakrawarthy, RS; Chapman, R; Cline, D; Corradi, L; Crespi, FCL; Cromaz, M; De Angelis, G; Eberth, J; Fallon, P; Farnea, E; Fioretto, E; Fransen, C; Freeman, SJ; Fu, B; Gadea, A; Gelletly, W; Giaz, A; Gorgen, A; Gottardo, A; Hayes, AB; Hess, H; Hetzenegger, R; Hirsch, R; Hua, H; John, PR; Jolie, J; Jungclaus, A; Karayonchev, V; Kaya, L; Korten, W; Lee, IY; Leoni, S; Liang, X; Lunardi, S; MacChiavelli, AO; Menegazzo, R; Mengoni, D; Michelagnoli, C; Mijatovic, T; Montagnoli, G; Montanari, D; Muller-Gatermann, C; Napoli, D; Pearson, CJ; Podolyak, Z; Pollarolo, G; Pullia, A; Queiser, M; Recchia, F; Regan, PH; Regis, JM; Saed-Samii, N; Sahin, E; Scarlassara, F; Seidlitz, M; Siebeck, B; Sletten, G; Smith, JF; Soderstrom, PA; Stefanini, AM; Stezowski, O; Szilner, S; Szpak, B; Teng, R; Ur, C; Warner, DD; Wolf, K; Wu, CY; Zell, KO | Abstract: The transitional nuclei Xe132 and Xe133 are investigated after multinucleon-transfer (MNT) and fusion-evaporation reactions. Both nuclei are populated (i) in Xe136+Pb208 MNT reactions employing the high-resolution Advanced GAmma Tracking Array (AGATA) coupled to the magnetic spectrometer PRISMA, (ii) in the Xe136+Pt198 MNT reaction employing the GAMMASPHERE spectrometer in combination with the gas-detector array CHICO, and (iii) as an evaporation residue after a Te130(α,xn)Xe134-xn fusion-evaporation reaction employing the HORUS γ-ray array at the University of Cologne. The high-spin level schemes are considerably extended above the Jπ=(7-) and (10+) isomers in Xe132 and above the 11/2- isomer in Xe133. The results are compared to the high-spin systematics of the Z=54 as well as the N=78 and N=79 chains. Furthermore, evidence is found for a long-lived (T1/2â‰1μs) isomer in Xe133 which closes a gap along the N=79 isotones. Shell-model calculations employing the SN100PN and PQM130 effective interactions reproduce the experimental findings and provide guidance to the interpretation of the observed high-spin features.

The νg9/2, d5/2, s1/2 orbitals are assumed to be responsible for the swift onset of collectivity observed in the region below 68 Ni. Especially the single-particle energies and strengths of these orbitals are of importance. We studied such properties in the nearby

The first measurement of $\ensuremath{\gamma}$ rays from the $^{114}\mathrm{Sn}(n,\ensuremath{\gamma})$ reaction using cold neutrons, performed with an array of Ge detectors at the PF1B facility of the Institute Laue-Langevin in Grenoble, has provided the most accurate energy, ${Q}_{\ensuremath{\beta}}=173(12)$ eV, of ${\ensuremath{\beta}}^{\ensuremath{-}}$ decay of the $^{115}\mathrm{In}$ ground state to the first excited state in $^{115}\mathrm{Sn}$. This is the lowest of all such energies in the known nuclear landscape. The accuracy of the neutron binding energy of $^{115}\mathrm{Sn}$ and the mass of $^{114}\mathrm{Sn}$ have been improved.

WOS: 000295765100014, The first implementation of the AGATA spectrometer consisting of five triple germanium detector clusters has been installed at Laboratori Nazionali di Legnaro, INFN. This setup has two major goals, the first one is to validate the gamma-tracking concept and the second is to perform an experimental physics program using the stable beams delivered by the Tandem-PIAVE-ALPI accelerator complex. A large variety of physics topics will be addressed during this campaign, aiming to investigate both neutron and proton-rich nuclei. The setup has been designed to be coupled with the large-acceptance magnetic-spectrometer PRISMA. Therefore, the in-beam prompt gamma rays detected with AGATA will be measured in coincidence with the products of multinucleon-transfer and deep-inelastic reactions measured by PRISMA. Moreover, the setup is versatile enough to host ancillary detectors, including the heavy-ion detector DANTE, the gamma-ray detector array HELENA, the Cologne plunger for lifetime measurements and the Si-pad telescope TRACE. In this paper the design; characteristics and performance figures of the setup will be described.

Conversion electron spectroscopy constitutes an important tool in nuclear structure physics. A high efficiency iron-free Orange type electron spectrometer with an energy resolution of 1–2% has been installed at a beam line of the Cologne 10 MV FN Tandem Van-de-Graaff accelerator for in-beam studies of conversion electrons. In combination with a γ -ray detector array, high efficiency e - – γ -coincidences can be performed. The newly developed very fast LaBr 3 ( Ce ) scintillator detector with an energy resolution of about 4% makes it also possible to use e - – γ -coincidences for lifetime measurements of nuclear excited states. A second iron-free Orange spectrometer can be connected to perform e - – e - -coincidences. Because of the higher efficiency and the better energy resolution, the use of the Double Orange Spectrometer for lifetime measurements is more powerful. Lifetimes down to 100 ps and even less can be determined with an accuracy of about 10 ps. The working principle of the Orange spectrometer and the setup of the Double Orange Spectrometer are described. The performances are illustrated by examples of in-beam experiments with a main focus on high precision lifetime measurements.

Background: Shape coexistence in heavy nuclei poses a strong challenge to state-of-the-art nuclear models, where several competing shape minima are found close to the ground state. A classic region for investigating this phenomenon is in the region around Z=82 and the neutron midshell at N=104. Purpose: Evidence for shape coexistence has been inferred from α-decay measurements, laser spectroscopy, and in-beam measurements. While the latter allow the pattern of excited states and rotational band structures to be mapped out, a detailed understanding of shape coexistence can only come from measurements of electromagnetic matrix elements. Method: Secondary, radioactive ion beams of Rn202 and Rn204 were studied by means of low-energy Coulomb excitation at the REX-ISOLDE in CERN. Results: The electric-quadrupole (E2) matrix element connecting the ground state and first excited 21+ state was extracted for both Rn202 and Rn204, corresponding to B(E2;21+→01+)=29-8+8 and 43-12+17 W.u. respectively. Additionally, E2 matrix elements connecting the 21+ state with the 41+ and 22+ states were determined in Rn202. No excited 0+ states were observed in the current data set, possibly owing to a limited population of second-order processes at the currently available beam energies. Conclusions: The results are discussed in terms of collectivity and the deformation of both nuclei studied is deduced to be weak, as expected from the low-lying level-energy schemes. Comparisons are also made to state-of-the-art beyond-mean-field model calculations and the magnitude of the transitional quadrupole moments are well reproduced., 0, SCOPUS: ar.j, info:eu-repo/semantics/published

The quasi-SU(3) sequence of the positive parity $\ensuremath{\nu}{g}_{9/2},{d}_{5/2},{s}_{1/2}$ orbitals above the $N=40$ shell gap are assumed to induce strong quadrupole collectivity in the neutron-rich Fe $(Z=26)$ and Cr $(Z=24)$ isotopes below the nickel region. In this paper the position and strength of these single-particle orbitals are characterized in the neighborhood of $^{68}\mathrm{Ni} (Z=28,\phantom{\rule{0.16em}{0ex}}N=40)$ through the $^{66}\mathrm{Ni}(d,p)^{67}\mathrm{Ni}$ one-neutron transfer reaction at 2.95 MeV/nucleon in inverse kinematics, performed at the REX-ISOLDE facility in CERN. A combination of the Miniball $\ensuremath{\gamma}$-array and T-REX particle-detection setup was used and a delayed coincidence technique was employed to investigate the 13.3-$\ensuremath{\mu}\mathrm{s}$ isomer at 1007 keV in $^{67}\mathrm{Ni}$. Excited states up to an excitation energy of 5.8 MeV have been populated. Feeding of the $\ensuremath{\nu}{g}_{9/2}$ (1007 keV) and $\ensuremath{\nu}{d}_{5/2}$ (2207 keV and 3277 keV) positive-parity neutron states and negative parity $(\ensuremath{\nu}pf)$ states have been observed at low excitation energy. The extracted relative spectroscopic factors, based on a distorted-wave Born approximation analysis, show that the $\ensuremath{\nu}{d}_{5/2}$ single-particle strength is mostly split over these two excited states. The results are also compared to the distribution of the proton single-particle strength in the $^{90}\mathrm{Zr}$ region $(Z=40,N=50)$.

Sub-barrier Coulomb-excitation was performed on a mixed beam of $^{62}$Mn and $^{62}$Fe, following in-trap $\beta^{-}$ decay of $^{62}$Mn at REX-ISOLDE, CERN. The trapping and charge breeding times were varied in order to alter the composition of the beam, which was measured by means of an ionisation chamber at the zero-angle position of the Miniball array. A new transition was observed at 418~keV, which has been tentatively associated to a $(2^{+},3^{+})\rightarrow1^{+}_{g.s.}$ transition. This fixes the relative positions of the $\beta$-decaying $4^{+}$ and $1^{+}$ states in $^{62}$Mn for the first time. Population of the $2^{+}_{1}$ state was observed in $^{62}$Fe and the cross-section determined by normalisation to the $^{109}$Ag target excitation, confirming the $B(E2)$ value measured in recoil-distance lifetime experiments., Comment: 9 pages, 10 figures

Coulomb-excitation experiments to study electromagnetic properties of radioactive even-even Hg isotopes were performed with 2.85 MeV/nucleon mercury beams from REX-ISOLDE. Magnitudes and relative signs of the reduced E2 matrix elements that couple the ground state and low-lying excited states in Hg182-188 were extracted. Information on the deformation of the ground and the first excited 0(+) states was deduced using the quadrupole sum rules approach. Results show that the ground state is slightly deformed and of oblate nature, while a larger deformation for the excited 0(+) state was noted in Hg-182; 184. The results are compared to beyond mean field and interacting-boson based models and interpreted within a two-state mixing model. Partial agreement with the model calculations was obtained. The presence of two different structures in the light even-mass mercury isotopes that coexist at low excitation energy is firmly established.

Lifetimes of the low-lying (11/2-) states in 63,65Co have been measured employing the recoil distance doppler shift method (RDDS) with the AGATA γ-ray array and the PRISMA mass spectrometer. These nuclei were populated via a multinucleon transfer reaction by bombarding a 238U target with a beam of 64Ni. The experimental B(E2) reduced transition probabilities for 63,65Co are well reproduced by large-scale shell-model calculations that predict a constant trend of the B(E2) values up to the N=40 67Co isotope

The radioactive isotope 107In was studied using sub-barrier Coulomb excitation at the REX-ISOLDE facility at CERN. Two γ rays were observed during the experiment, corresponding to the low-lying 11/2+ and 3/2− states. The reduced transition probability of the 11/2+ state was determined with the semiclassical Coulomb excitation code GOSIA2. The result is discussed in comparison to large-scale shell-model calculations, previous unified-model calculations, and earlier Coulomb excitation measurements in the odd-mass In isotopes. ispartof: Physical Review C, Nuclear Physics vol:87 issue:1 status: published

A set of B(E2) values for the low-lying excited states in the radioactive isotope Sn-109 were deduced from a Coulomb excitation experiment. The 2.87-MeV/u radioactive beam was produced at the REX-ISOLDE facility at CERN and was incident on a secondary Ni-58 target. The B(E2) values were determined using the known 2(+) -> 0(+) reduced transition probability in Ni-58 as normalization with the semiclassical Coulomb excitation code GOSIA2. The transition probabilities are compared to shell-model calculations based on a realistic nucleon-nucleon interaction and the predictions of a simple core-excitation model. This measurement represents the first determination of multiple B(E2) values in a light Sn nucleus using the Coulomb excitation technique with low-energy radioactive beams. The results provide constraints for the single-neutron states relative to Sn-100 and also indicate the importance of both single-neutron and collective excitations in the light Sn isotopes. (Less)

The X(5) symmetry describes nuclei at the critical point of the shape phase transition from axially deformed rotor nuclei to spherical vibrators. 150Nd, 152Sm, and 154Gd were the first nuclei where the predicted charateristics of the X(5) symmetry were observed. Later it was shown that also 176,178,180Os can be successfully described with the X(5) symmetry.In the close vicinity of shape phase transitions one expects strongly changing nuclear shapes. In the X(5) region around A = 150 this was observed for nuclei with different neutron numbers, whereas in the X(5) region around A = 180 this is to be expected for different proton numbers. The aim of the work presented here is the confirmation of a rapid shape change for nuclei close to 178Os. Besides the knowledge on the level scheme of the nuclei of interest, especially absolute E2 transition strengths are crucial for the interpretation of nuclear structure. Prolate deformation is expected for 176W. Thus we performed a recoil distance Doppler shift (RDDS) m...

Recently, an Orange spectrometer, a focusing iron‐free magnetic spectrometer, has been installed at a beam line of the 10 MV Tandem accelerator of the IKP of the University of Cologne. The high efficiency of 15% of 4π for the detection of conversion electrons and the energy resolution of 1% makes the Orange spectrometer a powerful instrument. From the conversion electron spectrum, transition multipolarities can be determined using the so called K to L ratio. In combination with an array of germanium and lanthanum bromide detectors, e−‐γ‐coincidences can be performed to investigate the level scheme. Moreover, the very fast lanthanum bromide scintillator with an energy resolution of 3% allows e−‐γ lifetime measurements down to 0.3 ns. A second Orange spectrometer can be added to build the Double Orange Spectrometer for e−‐e−‐coincidences. It is indispensable for lifetime measurements of low intensity or nearby lying transitions as often occur in odd‐A and odd‐odd nuclei. The capabilities are illustrated wit...

An array of eight Ge detectors for coincidence measurements of γ rays from neutron-capture reactions has been constructed at the PF1B cold-neutron facility of the Institut Laue-Langevin. The detectors arranged in one plane every 45° can be used for angular correlation measurements. The neutron collimation line of the setup provides a neutron beam of 12 mm in diameter and the capture flux of about 108/(s × cm2) at the target position, with a negligible neutron halo. With the setup up to 109 γγ and up to 108 triple-γ coincidence events have been collected in a day measurement. Precise energy and efficiency calibrations up to 10 MeV are easily performed with 27Al(n,γ)28Al and 35Cl(n,γ)36Cl reactions. Test measurements have shown that neutron binding energies can be determined with an accuracy down to a few eV and angular correlation coefficients measured with a precision down to a percent level. The triggerless data collected with a digital electronics and acquisition allows to determine half-lives of excited levels in the nano- to microsecond range. The high resolving power of double- and triple-γ time coincidences allows significant improvements of excitation schemes reported in previous (n,γ) works and complements high-resolution γ-energy measurements at the double-crystal Bragg spectrometer GAMS of ILL.

The radioactive isotope 107Sn was studied using Coulomb excitation at the REX-ISOLDE facility at CERN. This is the lightest odd-Sn nucleus examined using this technique. The reduced transition probability of the lowest-lying 3/2+ state was measured and is compared to shell-model predictions based on several sets of single-neutron energies relative to 100Sn. Similar to the transition probabilities for the 2+ states in the neutron-deficient even-even Sn nuclei, the measured value is underestimated by shell-model calculations. Part of the strength may be recovered by considering the ordering of the d5/2 and g7/2 single-neutron states. ispartof: European Physical Journal A, Hadrons and Nuclei vol:48 issue:7 status: published