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International audience; The low-energy electromagnetic structure of 110Cd was studied using safe-energy Coulomb excitation at the Heavy Ion Laboratory, University of Warsaw. The preliminary results on the quadrupole deformation of lowlying 0+ states in 110Cd are presented and compared to the recent beyondmean-field and General Bohr Hamiltonian calculations.

International audience; A Coulomb excitation campaign on $^{106,108,110}$Sn at 4.4–4.5 MeV/u was launched at the HIE-ISOLDE facility at CERN. Larger excitation cross sections and γ-ray statistics were achieved compared to previous experiments at ∼2.8 MeV/u. More precise $(B(E2;0_{1}^{ + } \to 2_{1}^{ + }))$ values, lifetimes of states via the Doppler shift attenuation method, and new $(B(E2;0_{1}^{ + } \to 2_{x}^{ + })), (B(E2;2_{1}^{ + } \to 4_{1}^{ + }))$ and $(Q(2_{1}^{ + }))$ values from the new Miniball data will be obtained and applied to test modern nuclear structure theories.

A Coulomb-excitation experiment to study electromagnetic properties of Ca42 was performed using a 170-MeV calcium beam from the TANDEM XPU facility at INFN Laboratori Nazionali di Legnaro. γ rays from excited states in Ca42 were measured with the AGATA spectrometer. The magnitudes and relative signs of ten E2 matrix elements coupling six low-lying states in Ca42, including the diagonal E2 matrix elements of 21+ and 22+ states, were determined using the least-squares code gosia. The obtained set of reduced E2 matrix elements was analyzed using the quadrupole sum rule method and yielded overall quadrupole deformation for 01,2+ and 21,2+ states, as well as triaxiality for 01,2+ states, establishing the coexistence of a weakly deformed ground-state band and highly deformed slightly triaxial sideband in Ca42. The experimental results were compared with the state-of-the-art large-scale shell-model and beyond-mean-field calculations, which reproduce well the general picture of shape coexistence in Ca42.

International audience; A Coulomb excitation experiment to study electromagnetic properties of 45Sc was performed at the Heavy Ion Laboratory, University of Warsaw, using a 70 MeV 32S beam. Measured γ-ray intensities together with existing spectroscopic data were used to extract a set of matrix elements between the populated states. Upper limit on B(E3;7/2 − → 5/2 +) is given.

The neutron-deficient ${}^{\mathrm{196,198}}$Pb isotopes have been studied in Coulomb-excitation experiments employing the Miniball γ-ray spectrometer and radioactive ion beams from the REX-ISOLDE post-accelerator at CERN. The reduced transition probabilities of the first excited 2+ states in 196Pb and 198Pb nuclei have been measured for the first time. Values of $B(E2)={18.2}_{-4.1}^{+4.8}$ W.u. and $B(E2)={13.1}_{-3.5}^{+4.9}$ W.u., were obtained, respectively. The experiment sheds light on the development of collectivity when moving from the regime governed by the generalised seniority scheme to a region, where intruding structures, associated with different deformed shapes, start to come down in energy and approach the spherical ground state. journal_title: Journal of Physics G: Nuclear and Particle Physics article_type: paper article_title: Collectivity in ${}^{\mathrm{196,198}}$Pb isotopes probed in Coulomb-excitation experiments at REX-ISOLDE copyright_information: © 2017 IOP Publishing Ltd date_received: 2016-10-31 date_accepted: 2017-03-17 date_epub: 2017-05-03 ispartof: Journal of Physics G, Nuclear and Particle Physics vol:44 issue:6 status: published

The structure of neutron-rich 96,98Sr nuclei was investigated by low-energy safe Coulomb excitation of radioactive beams at the REX-ISOLDE facility, CERN, with the MINIBALL spectrometer. A rich set of transitional and diagonal E2 matrix elements, including those for non-yrast structures, has been extracted from the differential Coulomb-excitation cross sections. The results support the scenario of a shape transition at N = 60, giving rise to the coexistence of a highly deformed prolate and a spherical configuration in 98Sr, and are compared to predictions from several theoretical calculations. The experimental data suggest a significant contribution of the triaxal degree of freedom in the ground state of both isotopes. In addition, experimental information on low-lying states in 98Rb has been obtained.

K. Hadyńska-Kl¸ek et al. ; 7 pags., 3 figs., 2 tabs., Shape parameters of a weakly deformed ground-state band and highly deformed slightly triaxial sideband in Ca42 were determined from E2 matrix elements measured in the first low-energy Coulomb excitation experiment performed with AGATA. The picture of two coexisting structures is well reproduced by new state-of-the-art large-scale shell model and beyond-mean-field calculations. Experimental evidence for superdeformation of the band built on 02+ has been obtained and the role of triaxiality in the A∼40 mass region is discussed. Furthermore, the potential of Coulomb excitation as a tool to study superdeformation has been demonstrated for the first time. © 2016 American Physical Society, Special gratitude goes to the INFN LNL and HIL Warsaw technical staff for their support and help, in particular, the accelerator crews for providing intense and good-quality 42Ca and 32S beams. K. H.-K. acknowledges support from the Research Council of Norway under the project Grant No. 213442. T. R. R. acknowledges computing time at GSI-Darmstadt and support from Spanish MINECO under Programa Ramon y Cajal 11420 and FIS-2014-53434-P, H. N. acknowledges support from Helmholtz Association through the Nuclear Astrophysics Virtual Institute NAVI (No. VH-VI-417). We also acknowledge the support by Generalitat Valenciana, Spain, under the grant PROMETEOII/2014/019 and by the FEDER funds of the European Commission (A. Gadea), Spanish Ministerio de Economía y Competitividad under Contract No. FPA2014-57196-C5 (A. J., A. Gadea), German Bundesministerium für Bildung und Forschung (BMBF) under Contract No. 05P12PKFNE TP4 (B. Birkenbach), the Polish National Science Centre under Projects No. DEC-2013/10/M/ST2/00427, No. DPN/N190/ AGATA/2009, No. 2011/03/B/ST2/01894, No. UMO- 2014/14/M/ST2/00738 (COPIN-INFN Collaboration), and No. 2015/17/B/ST2/01534.

States in the N = 28 nucleus Ar-46 have been studied by a two-neutron transfer reaction at REX-ISOLDE (CERN). A beam of radioactive Ar-44 at an energy of 2.16 AMeV and a tritium-loaded titanium target were used to populate Ar-46 by the H-3(Ar-44, p) two-neutron transfer reaction. Protons emitted from the target were identified in the T-REX silicon detector array. The excitation energies of states in Ar-46 have been reconstructed from the measured angles and energies of recoil protons. Angular distributions for three final states were measured and based on the shape of the differential cross section an excited state at 3695 keV was identified as J(pi) = 0(+). The angular differential cross section for the population of different states are compared to calculations using a reaction model employing both sequential and direct transfer of two neutrons. Results are compared to shell-model calculations using state-of-the-art effective interactions.

Neutron-rich {96,98}Sr isotopes have been investigated by safe Coulomb excitation of radioactive beams at the REX-ISOLDE facility. Reduced transition probabilities and spectroscopic quadrupole moments have been extracted from the differential Coulomb excitation cross sections. These results allow, for the first time, the drawing of definite conclusions about the shape coexistence of highly deformed prolate and spherical configurations. In particular, a very small mixing between the coexisting states is observed, contrary to other mass regions where strong mixing is present. Experimental results have been compared to beyond-mean-field calculations using the Gogny D1S interaction in a five-dimensional collective Hamiltonian formalism, which reproduce the shape change at N=60.

The quadrupole shape evolution in heaviest stable Mo isotopes is studied in terms of the shape coexistence phenomenon occurrence in this region of nuclear chart. Quadrupole deformation parameters of the 96,98,100 Mo isotopes in the low-lying (ground and excited) 0+ states were deduced using Coulomb excitation method. In all cases rich sets of electromagnetic reduced matrix elements were determined using the GOSIA code and then analysed using the Quadrupole Sum Rules formalism. Discussion of the experimental results in comparison with the predictions of microscopic calculations within the general quadrupole collective Bohr Hamiltonian model is presented for 100 Mo .

The light krypton isotopes were studied in a series of Coulomb excitation experiments using radioactive beams at GANIL. The static quadrupole moments found in these experiments give firm experimental evidence for the shape coexistence scenario that is based on theoretical calculations and on the systematics of low-lying excited 0+ states. The experimental results are interpreted within a phenomenological two-band mixing model. Configuration mixing calculations based on triaxial Hartree-Fock-Bogolyubov calculations with the Gogny D1S effective interaction have been performed and compared to experimental data.

The low-lying states in the odd-odd and unstable isotopes 106, 108In have been Coulomb excited from the ground state and the first excited isomeric state at the REX-ISOLDE facility at CERN. With the additional data provided here the $ \pi$ g 9/2 -1 ⊗ $ \nu$ d 5/2 and $ \pi$ g 9/2 -1 ⊗ $ \nu$ g 7/2 multiplets have been re-analyzed and are modified compared to previous results. The observed $ \gamma$ -ray de-excitation patterns were interpreted within a shell model calculation based on a realistic effective interaction. The agreement between theory and experiment is satisfactory and the calculations reproduce the observed differences in the excitation pattern of the two isotopes. The calculations exclude a 6+ ground state in 106In . This is in agreement with the conclusions drawn using other techniques. Furthermore, based on the experimental results, it is also concluded that the ordering of the isomeric and ground state in 108In is inverted compared to the shell model prediction. Limits on B(E2) values have been extracted where possible. A previously unknown low-lying state at 367keV in 106In is also reported.

Large area thin strip detectors with build-in electric field are among possible choices to provide radiation-hard detectors for future high-energy physics experiments and heavy ion applications. Among the advantages of thin detectors with build in field are the very low detector bias voltage and reduced material cost. A new technology for silicon detector production called Planar Process Partially Performed on the Thin Silicon Membrane (PPPP process) is described. Using this method the transmission Δ E , 52 and 22 μ m thick strip detectors operated at 5 V bias potential were produced and tested. The n - – n + structures produced by about 50 μ m of high resistivity ( 2000 Ω cm ) layer epitaxially grown on 400 μ m of low resistivity substrate were used for the detector construction. The n - – n + wafers were manufactured in the Institute of Electronic Materials Technology. The detectors performance as E – Δ E telescopes (associated with an independent 400 μ m E detector) was tested using the light charged particles from the reaction 12 C( 14 N,X) and heavy ions (Li, Be, B, C, N) produced in the 9 B( 14 N,X) reaction at 89.6 MeV beam energy. An energy resolution of the Δ E detector measured with the 6.05 and 6.09 MeV α -particles from 212 Bi was about 110 keV. This paper describes the new technological approach used for fabrication of the devices and reports some results from light charged particles and heavy ion measurements.

Coulomb-excitation experiments are performed with postaccelerated beams of neutron-deficient Po196,198,200,202 isotopes at the REX-ISOLDE facility. A set of matrix elements, coupling the low-lying states in these isotopes, is extracted. In the two heaviest isotopes, Po200,202, the transitional and diagonal matrix elements of the 2+1 state are determined. In Po196,198 multistep Coulomb excitation is observed, populating the 4+1,0+2, and 2+2 states. The experimental results are compared to the results from the measurement of mean-square charge radii in polonium isotopes, confirming the onset of deformation from Po196 onwards. Three model descriptions are used to compare to the data. Calculations with the beyond-mean-field model, the interacting boson model, and the general Bohr Hamiltonian model show partial agreement with the experimental data. Finally, calculations with a phenomenological two-level mixing model hint at the mixing of a spherical structure with a weakly deformed rotational structure., We acknowledge the support of the ISOLDE Collaboration and technical teams and, especially, the support of RILIS and REX. This work was supported by FWO-Vlaanderen (Belgium), by GOA/2010/010 (BOF KU Leuven), by the Interuniversity Attraction Poles Programme initiated by the Belgian Science Policy Office (BriX network P7/12), by the European Commission within the Seventh Framework Programme through I3-ENSAR (Contract No. RII3-CT-2010-262010), by the German BMBF under Contract Nos. 05P12PKFNE, 06DA9036I 05P12RDCIA, and 05P12RDCIB, by the UK Science and Technology Facilities Council, by the Spanish MINECO under Project No. FIS2011-28738-C02-02, by Narodowe Centrum Nauki (Polish Center for Scientific Research) Grant No. UMO-2013/10/M/ST2/00427, by the Academy of Finland (Contract No. 131665), and by the European Commission through the Marie Curie Actions call PIEFGA-2008-219174 (J.P.).

Two monolithic E – Δ E charged particle telescopes with Δ E layers of 11 and 20 μ m thick, respectively, produced with the Quasi-Selective Epitaxy method were tested at the Heavy Ion Laboratory in Warsaw. Thorium source α -particles and 12C(14N,X) reaction products at 80 MeV beam energy were used. During on-beam tests, detectors were placed at 20 ∘ laboratory angle with respect to the beam axis. Among the reaction products, ions of Li, Be, B, C, N, O, F were identified (using the telescope with 20 μ m Δ E layer). Pulses from both E and Δ E components of the telescope were digitalized with a digital oscilloscope, sent to a PC machine and recorded. Pulse shape analysis technique was then applied to obtain the final two dimensional spectrum. The E – Δ E two-dimensional scatter plots obtained after irradiation of the monolithic E – Δ E telescopes by α -particles from the calibration source are presented. The energy resolution of the monolithic E – Δ E telescope measured using α -particles was about 0.7 MeV for telescope with 20 μ m thick Δ E layer and 0.4 MeV for telescope with 11 μ m Δ E layer. Response of the monolythic E – Δ E telescopes for Po 212 8.78 MeV α -particles registered at different impact positions at the telescope face was measured. Cross-talk signals in the monolithic E – Δ E telescope as a function of position and the Δ E detector capacitance were simulated using the numerical solution of the telegraphic equation describing time-dependent evolution of the cross-talk potentials in the Δ E detector RC network.

Coulomb excitation experiments were performed with 96 Mo , 98 Mo and 100 Mo isotopes using both beam and target excitation. As a result, quadrupole deformation parameters were deduced for two lowest-lying (ground and excited) 0+ states. Surprising shape changes of these states were observed.

Excited states in 110Sn and 111Sn nuclei have been investigated using in-beam γ-ray spectroscopic methods. An 16O beam with an energy of 60-80MeV was used to bombard a 98Mo target. On the basis of the relative excitation functions, γ-ray angular distributions, γ-γ and γ-time distributions, γ-ray multiplicity and total energy data, the level schemes of 110Sn and 111Sn have been studied and extended up to Eexc ∼ 11.5MeV, I = 24ℏ, and Eexc ∼ 11.1MeV and I = (51/2)ℏ, respectively. An extension of the intruder, g.s. and negative-parity bands, as well as 5 new band-like structures are proposed in 110Sn. The nature of newly introduced collective band 8 as well as 10+ states fed in the decay of the collective band is discussed. In the 111Sn nucleus an intruder band based on the 23/2- state has been reinvestigated and the extension of the g.s. band and second negative-parity band is given. Evidence for neutron-core coupling in 111Sn is found. The structure and systematics of excited states in light Sn isotopes is discussed.

Coulomb excitation experiment of 100 Mo has recently been performed using 40 Ar beam from the Warsaw Cyclotron. Three lowest 2+ states, two 4+ and one 0+ excited states have been observed. It is a continuation of the systematic study of 96 Mo and 98 Mo nuclei having low lying 0+ excited state, with energy very close to the first 2+ state.

A new technology for silicon detector production called Planar Process Partially Performed on the Thin Silicon Membrane (PPPP process) is described. Using this method a self-biased, transmission Δ E , 52 μ m thick strip detector was produced and tested. The detector sensitive depth (region of the detector from which created electron–hole pairs are collected) was about 36 μ m . The n - – n + structure produced by about 50 μ m of high-resistivity ( 2000 Ω cm ) layer epitaxially grown on 300 μ m of low-resistivity substrate was used for the detector construction. The n - – n + wafer was manufactured in the Institute of Electronic Materials Technology. The detector performance as a E – Δ E telescope (formed with an independent 400 μ m E detector) was tested using light charged particles (p,d,t, α ) produced in the p(9Be,X) reaction at 22 MeV energy. An energy resolution of the Δ E detector was measured to be about 100 keV.

We report experimental attempts to determine the sign of the electric dipole moment (relative to the electric octupole moment) in the octupole deformed nucleus 226 Ra. Sensitivity to this quantity is observed in the measured yields of γ-ray transitions following very low energy Coulomb excitation.

The level structure of 231 Pa was investigated by Coulomb excitation using 148 MeV 32 S and 255, 260 and 261 MeV 58 Ni projectiles and the NORDBALL detector array. The 1/2[530] ground-state rotational band was excited up to spin 39/2 − . The 3/2[651] band, established up to spin 37/2 + , was observed to be populated apart from direct Coulomb excitation by the de-excitation of the 1/2[530] band. The 1/2[400] band could be followed up to spin 23/2 + . Weak excitation of the bands 5/2[642], 5/2[512], 3/2[532] and 3/2[521] was seen up to spins 11/2 + , 15/2 − , 9/2 − and 9/2 − , respectively. Matrix elements were extracted from the γ -ray yields with the help of the semi-classical Coulomb-excitation least-squares search code GOSIA. The level scheme and transition intensities were analyzed in the framework of the quasiparticle-plus-phonon model including Coriolis-coupling (QPMC).

Collective structures in 180 Ta built on the meta-stable K π =9 − high-spin isomer were investigated using two types of Coulomb excitation experiments. In-beam studies identify γ -vibrational bands with typical bandhead E2 excitation strengths of 6 Weisskopf units (W.u.). Coulomb activation of the 180 Ta ground state was measured with 36 S and 64 Ni projectiles using thin targets. The excitation functions and the 180 Ta recoil angular distributions favor a K π =7 + octupole vibration at E x =1155(40) keV as intermediate state in the population of the ground state.

The nucleus 98 Mo was multiply Coulomb excited using 20 Ne, 84 Kr and 136 Xe beams. Eighteen E2 and M1 reduced matrix elements connecting 7 low-lying levels have been determined using the least-squares code GOSIA. The results are compared with the predictions of an extended version of the IBM1 model. The quadrupole sum rules approach was used to determine the shape parameters in two 0 + (ground and first excited) states. The rotational invariants 〈Q 2 〉 and 〈 cos 3δ〉 obtained show the shape coexistence in 98 Mo nucleus: the triaxial ground state and the prolate first excited state.

Communication between neurons in neuronal networks is associated with changes in neuronal membrane potentials. The ability to image these changes on sub-ms timescales is vital for better understanding of inter-neuronal connections. Inorganic probes have been developed for this purpose and proved to be fast enough to detect neuronal action potentials with sufficient time resolution. However, these probes non-selectively partition into membranes other than plasma membranes and they cannot be targeted to specific cells. Protein-based optical voltage-sensing probes can address this problem, but current genetically encoded voltage indicators (GEVIs) lack behind the inorganic probes in speed and amplitude. Here, we present the design and characterization of new sensors that are based on artificial proteins (maquettes). These artificial membrane maquettes contain four membrane-spanning α-helices that are linked into a single protein chain and form electron transfer chain across a lipid bilayer. To facilitate in vitro characterization, they have been expressed in high yields in inclusion bodies of E. coli, purified and refolded in charged and uncharged detergent micelles, as well as in lipid vesicles. Circular dichroism studies revealed 70% α-helicity in SDS and no melting in high temperatures and common denaturants, indicating their strong structural stability. The maquettes assemble in different membrane environments and bind 3 hemes upon assembly in vesicles (two hemes strongly with 150 nM affinity and third one more weakly with kd ∼ 1 µM). The redox midpoint potentials of the three hemes at pH=8.0 are −38, −150, and −203 mV, suggesting that they will be in mixed oxidation states when incorporated in resting plasma membranes. We are currently conjugating these maquettes with fluorescent proteins and nanoparticles to enable fast electron and energy transfers that will lead to strong fluorescent signals deltaF/F as a function of transmembrane voltage.

The isotopes 122,124,126Cd were studied in a “safe” Coulomb-excitation experiment at the radioactive ion-beam facility REX-ISOLDE at CERN. The reduced transition probabilities B(E2; 0+g.s. →2+1) and limits for the quadrupole moments of the first 2+ excited states in the three isotopes were determined. The onset of collectivity in the vicinity of theZ=50 andN=82 shell closures is discussed by comparison with shell model and beyond mean-field calculations. ispartof: Physical Review C, Nuclear Physics vol:89 issue:1 pages:1-10 status: published

Multiple Coulomb excitation with heavy-ion beams offers an unique opportunity to study model-independently the collective properties of the nuclear structure. Existing detector systems and data analysis methods allow not only to measure complete sets of parameters describing the electromagnetic properties of the nuclei-electric and magnetic multipole matrix elements-but also by using sum rules to translate these results to the shape evolution of the charge distributions independently for each level. The technique of Coulomb excitation can also be used to answer specific questions, as illustrated in this paper.

The antiprotonic x-ray cascade in ${}^{172}\mathrm{Yb}$ and ${}^{176}\mathrm{Yb}$ was studied and the widths and shifts of the levels which are affected by the strong interaction were deduced. A large number of transitions up to $\ensuremath{\Delta}n=5$ could be observed. This opened the possibility to determine for the first time also the widths of noncircular orbits. In ${}^{172}\mathrm{Yb}$ and ${}^{176}\mathrm{Yb}$ four level shifts and seven level widths were measured in each case. The widths are slightly increasing from ${}^{172}\mathrm{Yb}$ to ${}^{176}\mathrm{Yb}$ whereas the shifts stay roughly constant. The experimental intensities of the transitions are compared with results from calculations of the antiproton cascade. Using a Fermi distribution for the nucleon densities the neutron diffuseness parameter was deduced to be for ${}^{172}\mathrm{Yb} (0.58\ifmmode\pm\else\textpm\fi{}0.04) \mathrm{fm}$ larger than the proton diffuseness parameter. For ${}^{176}\mathrm{Yb}$ this value is $(0.71\ifmmode\pm\else\textpm\fi{}0.04) \mathrm{fm}.$

We have studied collective properties of the unstable 88Kr and 92Kr nuclei using Coulomb excitation in inverse kinematics at the REX-ISOLDE facility at CERN. We present preliminary results for both nuclei and give a short discussion in the framework of valence mirror symmetry.

Excited states of Cd-103 were studied in the reaction Ni-58(Cr-50,4pn)Cd-103. The NORDBALL array with neutron and charged particle detectors was employed for the detection of gamma rays and light evaporated particles. The level scheme of Cd-103 was significantly extended. A strong cascade of E2 transitions connecting negative parity states was found, Shell model calculations were performed and positive parity excited states were interpreted in terms of neutron-particle and proton-hole excitations with respect to the doubly magic N = Z = 50 core. The negative parity band was well reproduced by the total routhian surface calculations. (C) 1997 Elsevier Science B.V.

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

The Miniball germanium detector array has been operational at the REX (Radioactive ion beam EXperiment) post accelerator at the Isotope Separator On-Line facility ISOLDE at CERN since 2001. During the last decade, a series of successful Coulomb excitation and transfer reaction studies have been performed with this array, utilizing the unique and high-quality radioactive ion beams which are available at ISOLDE. In this article, an overview is given of the technical details of the full Miniball setup, including a description of the γ-ray and particle detectors, beam monitoring devices and methods to deal with beam contamination. The specific timing properties of the REX-ISOLDE facility are highlighted to indicate the sensitivity that can be achieved with the full Miniball setup. The article is finalized with a summary of some physics highlights at REX-ISOLDE and the utilization of the Miniball germanium detectors at other facilities. © The Author(s) 2013. ispartof: European Physical Journal A, Hadrons and Nuclei vol:49 issue:3 pages:1-32 status: published

A rapid onset of quadrupole deformation is known to occur around the neutron number 60 in the neutron-rich Zr and Sr isotopes. This shape change has made the neutron-rich A = 100 region an active area of experimental and theoretical studies for many decades now. We report in this contribution new experimental results in the neutron rich 96,98Sr investigated by safe Coulomb excitation of radioactive beams at the REX-ISOLDE facility, CERN. Reduced transition probabilities and spectroscopic quadrupole moments have been extracted from the differential Coulomb excitation cross section supporting the scenario of shape coexistence/change at N = 60. Future perspectives are presented including the recent experimental campaign performed at ILL-Grenoble. ispartof: EPJ Web of Conferences vol:62 ispartof: 5th International Workshop on Nuclear Fission and Fission Product Spectroscopy (FISSION) location:Caen: FRANCE date:28 May - 31 May 2013 status: published

Coulomb fission of 238U has been studied in the interaction of a 24.3 MeV/nucleon U beam with a Au target. A novel experimental approach is followed, aiming at distinguishing fission of Coulomb origin from nuclear fission. The Z distribution of the fragments is studied for both fission processes.

The Coulomb excitation experiment to study electromagnetic properties of the heaviest stable Mo isotope, ${}^{100}$Mo, was performed using a 76 MeV ${}^{32}$S beam from the Warsaw cyclotron U-200P. Magnitudes and relative signs of 26 $E1$, $E2$, $E3$, and $M1$ matrix elements coupling nine low-lying states in ${}^{100}$Mo were determined using the least-squares code gosia. Diagonal matrix elements (related to the spectroscopic quadrupole moments) of the 2${}_{1}^{+}$, 2${}_{2}^{+}$, and 2${}_{3}^{+}$ states as well as the 4${}_{1}^{+}$ state were extracted. The resulting set of reduced $E2$ matrix elements was complete and precise enough to obtain, using the quadrupole sum rules approach, quadrupole deformation parameters of ${}^{100}$Mo in its two lowest 0${}^{+}$ states: ground and excited. The overall deformation of the 0${}_{1}^{+}$ and 0${}_{2}^{+}$ states in ${}^{100}$Mo is of similar magnitude, in both cases larger compared to what was found for the neighboring isotopes ${}^{96}$Mo and ${}^{98}$Mo. At the same time, the asymetry parameters obtained for both states strongly differ, indicating a triaxial shape of the ${}^{100}$Mo nucleus in the ground state and a prolate shape in the excited 0${}^{+}$ state. Low-energy quadrupole excitations of the ${}^{100}$Mo nucleus were studied in the frame of the general quadrupole collective Bohr Hamiltonian model (GBH). The potential energy and inertial functions were calculated using the adiabatic time-dependent Hartree-Fock-Bogoliubov (ATDHFB) method starting from two possible variants of the Skyrme effective interaction: SIII and Sly4. The overall quadrupole deformation parameters resulting from the GBH calculations with the SLy4 variant of the Skyrme interaction are slightly closer to the experimentally obtained values than those obtained using SIII.

Nuclear reaction mechanisms for systems characterized by very different asymmetries (U + C, Si, Ni, Au) have been investigated at 24.3 MeV / nucleon, using as observables both the fission products and the neutron multiplicity. It is clearly observed that the fusion process — whatever its completeness — can only occur with rather light target nuclei, indicating the persistence of potential energy effects much above the interaction barrier.

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 four-proton hole Pd-96 neighbor of the doubly-magic Sn-100 nucleus was studied in-beam, using a fusion-evaporation reaction of a Ni-58 beam on a Sc-45 target. States of Pd-96 were established up to an excitation energy of 9707 keV. A core-excited odd-parity isomer with T-1/2 = 37.7(1.1) ns was identified. Shell model calculations were performed in four different model spaces. Even-parity states of Pd-96 are very well reproduced in large-scale shell model (LSSM) calculations in which excitations are allowed of up to five g(9/2) protons and neutrons across the N = Z = 50 gap, to the g(7/2), d(5/2), d(3/2), and s(1/2) orbitals. The odd-parity isomer can be only qualitatively interpreted though, employing calculation in the full fpg shell model space, with just one particle-hole core excitation.

Post-accelerated isomerically purified radioactive beams, available at the CERN On-Line Isotope Mass Separator facility using the resonant ionization laser technique, have been used to study the Coulomb excitation of the I-pi = 3(-) state in Cu-70 (Z = 29, N = 41). While first results using a I-pi = 6(-) beam were reported previously, the present complementary experiment allows us to complete the study of the multiplet of states (3(-), 4(-), 5(-), 6(-)) arising from the pi 2p(3)/(2)nu 1g(9/2) configuration. Besides the known gamma-ray transition deexciting the 4(-) state, a ground-state. ray of 511(3) keV was observed for the first time and was unambiguously associated with the 5(-) state deexcitation. This observation fixes the energy, spin, and parity of this state, completing the low-energy level scheme of Cu-70. B(E2) values for all possible E2 transitions within the multiplet were determined. A comparison with large-scale shell model calculations using different interactions and valence spaces shows the importance of proton excitation across the Z = 28 shell gap and the role of the 2d(5/2) neutron orbital.

Excited states of the nucleus Er-170 have been studied by Coulomb excitation using the GASP gamma-ray detector system at the Laboratori Nazionali di Legnaro. The ground-state band along with a low-lying K-pi = 0(+) band and gamma-vibrational band were populated during the experiment. Based on the measured gamma-ray yields, a set of interband and intraband matrix elements has been extracted using the Coulomb excitation code GOSIA. The resulting E2 matrix elements are compared to collective model predictions.

The B(E2; I-i -> I-f) values for transitions in Ga-71(31)40 and Ga-73(31)42 were deduced from a Coulomb excitation experiment at the safe energy of 2.95 MeV/nucleon using post-accelerated beams of Ga-71,Ga-73 at the REX-ISOLDE on-line isotope mass separator facility. The emitted gamma rays were detected by the MINIBALL gamma-detector array, and B(E2; I-i -> I-f) values were obtained from the yields normalized to the known strength of the 2(+) -> 0(+) transition in the Sn-120 target. The comparison of these new results with the data of less neutron-rich gallium isotopes shows a shift of the E2 collectivity toward lower excitation energy when adding neutrons beyond N = 40. This supports conclusions from previous studies of the gallium isotopes, which indicated a structural change in this isotopic chain between N = 40 and 42. Combined with recent measurements from collinear laser spectroscopy showing a 1/2(-) spin and parity for the ground state, the extracted results revealed evidence for a 1/2(-), 3/2(-) doublet near the ground state in Ga-73(31)42 differing by at most 0.8 keV in energy.