Search

We have performed the first direct measurement of the 83Rb(p,g) radiative capture reaction cross section in inverse kinematics using a radioactive beam of 83Rb at incident energies of 2.4 and 2.7 A MeV. The measured cross section at an effective relative kinetic energy of Ecm = 2.393 MeV, which lies within the relevant energy window for core collapse supernovae, is smaller than the prediction of statistical model calculations. This leads to the abundance of 84Sr produced in the astrophysical p process being higher than previously calculated. Moreover, the discrepancy of the present data with theoretical predictions indicates that further experimental investigation of p-process reactions involving unstable projectiles is clearly warranted., 6 pages, 4 figures, published in Physical Review Letters

Nuclear reaction sensitivity studies have shown that the final isotopic abundance of O-Ne nova nucleosynthesis is dependent on the $^{34}\mathrm{S}(p,\ensuremath{\gamma})^{35}\mathrm{Cl}$ reaction at astrophysical energies corresponding to peak nova burning temperatures of 0.1--0.4 GK. Isotopic ratios of the S, Cl, and Ar products are all used in various methods of cosmochemical analysis of presolar meteoritic grains. Due to the lack of direct experimental data, the $^{34}\mathrm{S}+p$ reaction rate has been estimated using statistical modeling or information from indirect nucleon transfer experiments. In order to provide direct reaction information, the resonance strengths of several low energy resonances, ${E}_{\mathrm{c}.\mathrm{m}.}=272--495$ keV, in the $^{34}\mathrm{S}(p,\ensuremath{\gamma})^{35}\mathrm{Cl}$ reaction were measured for the first time in inverse kinematics using the DRAGON recoil separator located at TRIUMF, Canada's Particle Accelerator Centre in Vancouver.

The level structure of the very neutron rich and unbound $^9$He nucleus has been the subject of significant experimental and theoretical study. Many recent works have claimed that the two lowest energy $^9$He states exist with spins $J^\pi=1/2^+$ and $J^\pi=1/2^-$ and widths on the order of hundreds of keV. These findings cannot be reconciled with our contemporary understanding of nuclear structure. The present work is the first high-resolution study with low statistical uncertainty of the relevant excitation energy range in the $^8$He$+n$ system, performed via a search for the T=5/2 isobaric analog states in $^9$Li populated through $^8$He+p elastic scattering. The present data show no indication of any narrow structures. Instead, we find evidence for a broad $J^{\pi}=1/2^+$ state in $^9$He located approximately 3 MeV above the neutron decay threshold.

We present the first results of the experiment: “Examining the helium cluster decays of the \(^{12}\)Be excited states by triton transfer to the \(^9\)Li beam” (spokespersons: N. Soic, M. Freer), done at TRIUMF, Vancouver, CA, with the main goal of providing precise experimental data on the internal structure of the \(^{12}\)Be excited states.

The Electromagnetic Mass Analyser (EMMA) is a new vacuum-mode recoil mass spectrometer currently undergoing the final stages of commissioning at the ISAC-II facility of TRIUMF. EMMA employs a symmetric configuration of electrostatic and magnetic deflectors to separate the products of nuclear reactions from the beam, focus them in both energy and angle, and disperse them in a focal plane according to their mass/charge (m/q) ratios. The spectrometer was designed to accommodate the gamma-ray detector array TIGRESS around the target position in order to provide spectroscopic information from electromagnetic transitions. EMMA is intended to be used in the measurement of fusion evaporation, radiative capture, and transfer reactions for the study of nuclear structure and astrophysics. Its complement of focal plane detectors facilitates the identification of recoiling nuclei and subsequent recoil decay spectroscopy. Here we describe the facility and report on commissioning efforts., Comment: 5 figures

A sequence of low-energy levels in _{32}^{78}Ge_{46} has been identified with spins and parity of 2^{+}, 3^{+}, 4^{+}, 5^{+}, and 6^{+}. Decays within this band proceed strictly through ΔJ=1 transitions, unlike similar sequences in neighboring Ge and Se nuclei. Above the 2^{+} level, members of this sequence do not decay into the ground-state band. Moreover, the energy staggering of this sequence has the phase that would be expected for a γ-rigid structure. The energies and branching ratios of many of the levels are described well by shell-model calculations. However, the calculated reduced transition probabilities for the ΔJ=2 in-band transitions imply that they should have been observed, in contradiction with the experiment. Within the calculations of Davydov, Filippov, and Rostovsky for rigid-triaxial rotors with γ=30°, there are sequences of higher-spin levels connected by strong ΔJ=1 transitions which decay in the same manner as those observed experimentally, yet are calculated at too high an excitation energy.

6 pags., 5 figs. -- 12th International Spring Seminar on Nuclear Physics, IOP Conf. Series. -- Open Access funded by Creative Commons Atribution Licence 3.0, In order to investigate the existence of molecular and/or exotic cluster configurations in Boron and Carbon n-rich isotopes we undertook two experiments: the first experimental study of exotic 9Li+¿ cluster states in 13B using the resonance scattering method at TRIUMF (Canada), and, with the same technique, the measurement of 10Be+¿ scattering at LNS in Catania, where a 10Be radioactive beam was produced for the first time. In order to measure the excitation function in a wide energy range, the beams were stopped in a Helium-flooded chamber. In the case of 13B, the elastic excitation function shows the presence of various peaks in an excitation energy region never explored before. In the case of 14C, our exclusive measurement of elastic scattering data with a high intensity beam, sheds some light on the contradictory previously published results [1, 2].

International audience; Carbon burning is a critical phase for nucleosynthesis in massive stars. The conditions for igniting this burning stage, and the subsequent isotope composition of the resulting ashes, depend strongly on the reaction rate for C12+C12 fusion at very low energies. Results for the cross sections for this reaction are influenced by various backgrounds encountered in measurements at such energies. In this paper, we report on a new measurement of C12+C12 fusion cross sections where these backgrounds have been minimized. It is found that the astrophysical S factor exhibits a maximum around Ecm=3.5–4.0 MeV, which leads to a reduction of the previously predicted astrophysical reaction rate.

Background: The $^{31}\mathrm{S}(p,\ensuremath{\gamma})\phantom{\rule{0.16em}{0ex}}^{32}\mathrm{Cl}$ reaction becomes important for sulfur production in novae if the $^{31}\mathrm{P}(p,\ensuremath{\alpha})^{28}\mathrm{Si}$ reaction rate is somewhat greater than currently accepted. The rate of the $^{31}\mathrm{S}(p,\ensuremath{\gamma})\phantom{\rule{0.16em}{0ex}}^{32}\mathrm{Cl}$ reaction is uncertain, primarily due to the properties of resonances at ${E}_{\mathrm{c}.\mathrm{m}.}=156$ and 549 keV.Purpose: We precisely determined the excitation energies of states in $^{32}\mathrm{Cl}$ through high-resolution $\ensuremath{\gamma}$ spectroscopy including the two states most important for the $^{31}\mathrm{S}(p,\ensuremath{\gamma})\phantom{\rule{0.16em}{0ex}}^{32}\mathrm{Cl}$ reaction at nova temperatures.Method: Excited states in $^{32}\mathrm{Cl}$ were populated using the $^{10}\mathrm{B}(^{24}\mathrm{Mg},2n)\phantom{\rule{0.16em}{0ex}}^{32}\mathrm{Cl}$ reaction with a $^{24}\mathrm{Mg}$ beam from the ATLAS facility at Argonne National Laboratory. The reaction channel of interest was selected using recoils in the Fragment Mass Analyzer, and precise level energies were determined by detecting $\ensuremath{\gamma}$ rays with Gammasphere.Results: We observed $\ensuremath{\gamma}$ rays from the decay of six excited states in $^{32}\mathrm{Cl}$. The excitation energies for two unbound levels at ${E}_{x}=1738.1$ (6) keV and 2130.5 (10) keV were determined and found to be in agreement with a previous high-precision measurement of the $^{32}\mathrm{S}(^{3}\mathrm{He},t)^{32}\mathrm{Cl}$ reaction [1].Conclusions: An updated $^{31}\mathrm{S}(p,\ensuremath{\gamma})\phantom{\rule{0.16em}{0ex}}^{32}\mathrm{Cl}$ reaction rate is presented. With the excitation energies of important levels firmly established, the dominant uncertainty in the reaction rate at nova temperatures is due to the strength of the resonance corresponding to the 2131-keV state in $^{32}\mathrm{Cl}$.

How does nature hold together protons and neutrons to form the wide variety of complex nuclei in the Universe? Describing many-nucleon systems from the fundamental theory of quantum chromodynamics has been the greatest challenge in answering this question. The chiral effective field theory description of the nuclear force now makes this possible but requires certain parameters that are not uniquely determined. Defining the nuclear force needs identification of observables sensitive to the different parametrizations. From a measurement of proton elastic scattering on ^{10}C at TRIUMF and ab initio nuclear reaction calculations, we show that the shape and magnitude of the measured differential cross section is strongly sensitive to the nuclear force prescription.

International audience; The 12C+12C fusion reaction is one of the most important for nuclear astrophysics since it determines the carbon ignition in stellar environments. Two experiments which make use of the gamma-particle coincidence technique to measure the 12C+12C S-factors at deep sub barrier energies are discussed. Results are presented showing a decrease of the S-factor below Ec.m. = 3 MeV.

The angular distributions of the elastic, inelastic scattering and break-up cross sections of the one neutron halo $^{11}$Be on a heavy-mass target ($^{197}$Au) have been measured at laboratory energies below (31.9 MeV) and around (39.6 MeV) the Coulomb barrier ($V_b \sim$ 40 MeV). The elastic, inelastic channel and break-up channels of the $^{11}$Be + $^{197}$Au reaction have been experimentally separated for the first time in this energy range. The experiment was performed at TRIUMF, using four Silicon detectors in telescope configuration to separate the $^{11}$Be from the $^{10}$Be fragments and the High-Purity Germanium Detector Array TIGRESS for $\gamma$-ray detection. The break-up and inelastic scattering contributions are observed to be relevant even at energies well below the Coulomb barrier. Data are compared with different models of increasing degree of sophistication: semiclassical, inert-core continuum discretised coupled channel (CDCC) calculations and CDCC including core deformation and excitations (XCDCC). XCDCC calculations are necessary to reproduce simultaneously elastic, inelastic and break-up scattering data. The results show that the reaction mechanism is sensible to the entanglement of core and halo degrees of freedom in $^{197}$Au.

New, low-lying levels in the odd-odd, N=Z nucleus 62Ga have been identified using a sensitive technique, where in-beam γ rays from short-lived nuclei are tagged with β decays following recoil mass identification. A comparison of the results with shell-model and IBM-4 calculations demonstrates good agreement between theory and experiment, with the majority of predicted low-lying, low-spin T=0 states now identified. There is a dramatic change in the level density at low excitation energies for the N=Z nucleus 62Ga when compared with neighbouring odd-odd Ga isotopes where, in contrast, the low-lying level structure is dominated by configurations with T=1 pairing interactions between excess neutrons. This illustrates the distinctively different aspects of nuclear structure exhibited by nuclei with N=Z. © 2013 Elsevier B.V.

6 pags., 4 figs., -- Presented at the Zakopane Conference on Nuclear Physics “Extremes of the Nuclear Landscape”, Zakopane, Poland, August 28–September 4, 2016. -- Open Access funded by Creative Commons Atribution Licence 4.0, The excitation function of the resonant reaction He-4(Li-9,alpha) was measured with the aim of investigating the compound nucleus B-13. These measurements were performed in inverse kinematics at center-of-mass scattering angles close to 180 degrees by using a thick He-4 gas target and a Li-9 beam. The B-13 excitation energy region explored was 14-20 MeV where Li-9-alpha configurations of B-13 are predicted by Antysimmetrised Molecular Dynamics calculations. The measured excitation function at theta(cm) = 180 degrees shows different clear structures in a B-13 excitation energy region which was experimentally unknown.

Angular distributions of the elastic, inelastic, and breakup cross sections of the halo nucleus ^{11}Be on ^{197}Au were measured at energies below (E_{lab}=31.9 MeV) and around (39.6 MeV) the Coulomb barrier. These three channels were unambiguously separated for the first time for reactions of ^{11}Be on a high-Z target at low energies. The experiment was performed at TRIUMF (Vancouver, Canada). The differential cross sections were compared with three different calculations: semiclassical, inert-core continuum-coupled-channels and continuum-coupled-channels ones with including core deformation. These results show conclusively that the elastic and inelastic differential cross sections can only be accounted for if core-excited admixtures are taken into account. The cross sections for these channels strongly depend on the B(E1) distribution in ^{11}Be, and the reaction mechanism is sensitive to the entanglement of core and halo degrees of freedom in ^{11}Be.

Carbon burning plays a crucial role in stellar evolution, where this reaction is an important route for the production of heavier elements. A particle-γ coincidence technique that minimizes the backgrounds to which this reaction is subject and provides reliable cross sections has been used at the Argonne National Laboratory to measure fusion cross-sections at deep sub-barrier energies in the 12 C+12 C system. The corresponding excitation function has been extracted down to a cross section of about 6 nb. This indicates the existence of a broad S-factor maximum for this system. Experimental results are presented and discussed.

The extinct p-process nuclide 146Sm (t1/2 = 103 ± 5 Myr) is known to have been present in the Early-Solar System and has been proposed as an astrophysical chronometer. 146Sm is also intensely used to date meteorite and planetary differentiation processes, enhancing the importance of an accurate knowledge of the 146Sm half-life. We are engaged in a new determination of the 146Sm half-life in which the 146Sm/147Sm atom ratio is determined by accelerator mass spectrometry at the ATLAS facility of Argonne National Laboratory. In order to reduce systematic errors in the AMS determination of the 146Sm/147Sm ratios (in the range of 10-7-10-9), 146Sm and 147Sm ions were alternately counted in the same detector in the focal plane of a gas-filled magnet, respectively in continuous-wave and attenuated mode. Quantitative attenuation is obtained with the 12 MHz pulsed and ns-bunched ATLAS beam by chopping beam pulses with an RF sweeper in a ratio (digitally determined) down to 1:106. The experiments and preliminary results are discussed. © 2012 Elsevier B.V. All rights reserved., SCOPUS: cp.j, info:eu-repo/semantics/published

International audience; Superheavy nuclei exist solely due to quantum shell effects,which create a pocket in the potential-energy surface of the nucleus, thusproviding a barrier against spontaneous fission. Determining the height ofthe fission barrier and its angular-momentum dependence is important toquantify the role that microscopic shell corrections play in enhancing andextending the limits of nuclear stability. In this talk, the first measurement ofa fission barrier in the very heavy nucleus 254No will be presented.

A particle- γ coincidence technique has been used to measure the fusion cross-section in the system 12C+12C at low beam energies. Based on these results, it should be possible to measure this important fusion cross-section down to the 10 pb level within a week-long run.

6 pags., 4 figs., 2 tabs. -- PACS:27.20.+n25.55.Hp23.20.-g29.85.-c, The reactions 10B (3He, p α α α) at 4.9 MeV and 11B (3He, d α α α) at 8.5 MeV have been used to investigate the γ decay of states in 12C. By measuring the four-body final state in complete kinematics we are able to detect γ transitions indirectly. We find γ transitions from the 15.11 MeV state in 12C to the 12.71, 11.83, 10.3 and 7.65 MeV states followed by their breakup into three α particles. The relative γ-ray branching ratios obtained are (1.2 ± 0.3), (0.32 ± 0.12), (1.4 ± 0.2) and (4.4 ± 0.8) %, respectively, with the remaining (92.7 ± 1.0) % of the γ decays going to the bound states. We obtain Γα / Γ = (2.8 ± 1.2) % for the isospin-forbidden α decay of the 15.11 MeV state. From the 12.71 MeV state we find γ transitions to the 10.3 and 7.65 MeV states. The relative γ-ray branching ratios are (0.9- 0.5 + 0.6) and (2.6- 1.2 + 1.6) %, respectively, with the remaining (96.6- 1.3 + 1.7) % of the γ decays going to the bound states. Finally, we discuss the relation between the β decay of 12N and 12B to states in 12C and the γ decay of the 15.11 MeV analog in 12C to the same states. © 2009 Elsevier B.V., We would like to acknowledge the support of the Spanish CICYT research grant FPA2007-62170 and the MICINN Consolider Project CSD 2007-00042 as well as the support of the European Union VI Framework through RII3-EURONS/JRA4-DLEP (contract number 506065). D.G. is a Juan de la Cierva fellow.

We have studied C-12 in full kinematics via the B-10(He-3, p alpha alpha alpha) reaction at an energy of 2.45 MeV. In our data we have identified states in C-12 from the ground state up to about 18 MeV, with spins ranging from 0 to 4. Due to the very good resolution, we are able to determine properties of these C-12 resonances, such as their energy, width, and spin. In this contribution preliminary results from the ongoing analysis are presented. Main focus on the precise determination of the breakup spectra for all resonances.

We present a detailed analysis of the elastic scattering and breakup channel for the reaction of Li-11 on Pb-208 at incident laboratory energies of 24.3 and 29.8 MeV, measured at the radioactive ion beam facility of TRIUMF, in Vancouver, Canada. A large yield of Li-9 fragments was detected by four charged particle telescopes in a wide angular range. The experimental angular and energy distributions of these Li-9 fragments have been compared to coupled-reaction-channel and continuum-discretized coupled-channel calculations. The large production of Li-9 fragments at small angles can be explained by considering a direct breakup mechanism, while at medium-large angles a competition between direct breakup and neutron transfer to the continuum of the Pb-208 target was observed.

Two isomers decaying by electromagnetic transitions with half-lives of 4.7(1.1) and 247(73) μs have been discovered in the heavy ^{254}Rf nucleus. The observation of the shorter-lived isomer was made possible by a novel application of a digital data acquisition system. The isomers were interpreted as the K^{π}=8^{-}, ν^{2}(7/2^{+}[624],9/2^{-}[734]) two-quasineutron and the K^{π}=16^{+}, 8^{-}ν^{2}(7/2^{+}[624],9/2^{-}[734])⊗8^{-}π^{2}(7/2^{-}[514],9/2^{+}[624]) four-quasiparticle configurations, respectively. Surprisingly, the lifetime of the two-quasiparticle isomer is more than 4 orders of magnitude shorter than what has been observed for analogous isomers in the lighter N=150 isotones. The four-quasiparticle isomer is longer lived than the ^{254}Rf ground state that decays exclusively by spontaneous fission with a half-life of 23.2(1.1) μs. The absence of sizable fission branches from either of the isomers implies unprecedented fission hindrance relative to the ground state.

A detection technique for high-efficiency measurements of fusion reactions with low-intensity radioactive beams was developed. The technique is based on a Multi-Sampling Ionization Chamber (MUSIC) operating as an active target and detection system, where the ionization gas acts as both target and counting gas. In this way, we can sample an excitation function in an energy range determined by the gas pressure, without changing the beam energy. The detector provides internal normalization to the incident beam and drastically reduces the measuring time. In a first experiment we tested the performance of the technique by measuring the 10,13,15C+12C fusion reactions at energies around the Coulomb barrier. Fil: Carnelli, Patricio Francisco Florencio. Argonne National Laboratory; Estados Unidos. Comisión Nacional de Energía Atómica. Gerencia del Área de Investigación y Aplicaciones No Nucleares. Gerencia Física (Centro Atómico Constituyentes). Proyecto Tandar; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Almaraz Calderón, S.. Argonne National Laboratory; Estados Unidos Fil: Rehm, K. E.. Argonne National Laboratory; Estados Unidos Fil: Albers, M.. Argonne National Laboratory; Estados Unidos Fil: Alcorta, M.. Argonne National Laboratory; Estados Unidos Fil: Bertone, P. F.. Argonne National Laboratory; Estados Unidos Fil: Digiovine, B.. Argonne National Laboratory; Estados Unidos Fil: Esbensen, H.. Argonne National Laboratory; Estados Unidos Fil: Fernandez Niello, Jorge Oscar. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Comisión Nacional de Energía Atómica. Gerencia del Área de Investigación y Aplicaciones No Nucleares. Gerencia Física (Centro Atómico Constituyentes). Proyecto Tandar; Argentina Fil: Henderson, D.. Argonne National Laboratory; Estados Unidos Fil: Jiang, C. L.. Argonne National Laboratory; Estados Unidos Fil: Lai, J.. Argonne National Laboratory; Estados Unidos Fil: Marley, S. T.. Argonne National Laboratory; Estados Unidos Fil: Nusair, O.. Argonne National Laboratory; Estados Unidos Fil: Palchan Hazan, T.. Argonne National Laboratory; Estados Unidos Fil: Pardo, R.. Argonne National Laboratory; Estados Unidos Fil: Paul, M.. The Hebrew University of Jerusalem; Israel Fil: Ugalde, C.. Argonne National Laboratory; Estados Unidos

26Al is an important radioisotope in astrophysics that provides evidence of ongoing nucleosynthesis in the Galaxy. The 23Na(α, p)26Mg reaction has been identified by a sensitivity study as being one of the most important reactions for the production of 26Al in the convective C/Ne burning shell of massive stars. Owing to large uncertainties in previous experimental data, model calculations are used for the reaction rate of 23Na(α, p)26Mg in this sensitivity study. Current experimental data suggest a reaction rate a factor of ∼40 higher than model calculations. However, a new measurement of this reaction cross section has been made in inverse kinematics in the energy range E(c.m.)=1.28-3.15 MeV at TRIUMF, and found to be in reasonable agreement with the model calculation. A new reaction rate is calculated and tight constraints on the uncertainty in the production of 26Al, due to this reaction, are determined.

International audience; The cross section of the ^12C+^12C fusion reaction at low energies is of paramount importance for models of stellar nucleosynthesis in different astrophysical scenarios, such as Type Ia supernovae and Xray superbursts, where this reaction is a primary route for the production of heavier elements. In a series of experiments performed at Argonne National Laboratory, using Gammasphere and an array of Silicon detectors, measurements of the fusion cross section of ^12C+^12C were successfully carried out with the gamma and charged-particle coincidence technique in the center-of-mass energy range of 3-5 MeV. These were the first background-free fusion cross section measurements for ^12C+^12C at energies of astrophysical interest. Our results are consistent with previous measurements in the high-energy region; however, our lowest energy measurement indicates a fusion cross section slightly lower than those obtained with other techniques.

International audience; Analyses of data from both deep inelastic reactions at Argonne National Laboratory and single-and multiple-particle knockout reactions at Michigan State University revealed new gamma-ray transitions in even-even Ni-66,68,70,72(38,40,42,44) and in Co-67(40) that provide strong evidence for multiple shape coexistence at N = 38 and 40 and deep prolate minima in Ni-70(42) and isotonic Cu-71(42). A new transition at 642 keV is proposed for Ni-66 as the prolate 2(+) to 0(+) transition. Two new transitions in Ni-72 at 915 and 1225 keV were identified in the knock-out reaction study and could represent de-population of prolate states. Taken together with recent theoretical work using the Monte Carlo shell model, a well defined region of shape coexistence can be seen existing precisely between 38

An extensive study of the level structure of $^{61}\mathrm{Co}$ has been performed following the complex $^{26}\mathrm{Mg}(^{48}\mathrm{Ca},2\ensuremath{\alpha}4np\ensuremath{\gamma})^{61}\mathrm{Co}$ reaction at beam energies of 275, 290, and 320 MeV using Gammasphere and the Fragment Mass Analyzer (FMA). The low-spin structure is discussed within the framework of shell-model calculations using the GXPF1A effective interaction. Two quasirotational bands consisting of stretched-$E2$ transitions have been established up to spins $I=41/2$ and $(43/2)$, and excitation energies of $\ensuremath{\sim}17$ and $\ensuremath{\sim}20$ MeV, respectively. These are interpreted as signature partners built on a neutron $\ensuremath{\nu}{({g}_{9/2})}^{2}$ configuration coupled to a proton $\ensuremath{\pi}{p}_{3/2}$ state, based on cranked shell model (CSM) calculations and comparisons with observations in neighboring nuclei. In addition, four $\ensuremath{\Delta}I=1$ bands were populated to high spin, with the yrast dipole band interpreted as a possible candidate for the shears mechanism, a process seldom observed thus far in this mass region.

The structure of semi-magic Ni-70(28)42 was investigated following complementary multinucleon-transfer and secondary fragmentation reactions. Changes to the higher-spin, presumed negative-parity states based on observed gamma-ray coincidence relationships result in better agreement with shell-model calculations using effective interactions in the neutron f(5/2)pg(9/2) model space. The second 2(+) and (4(+)) states, however, can only be successfully described when proton excitations across the Z = 28 shell gap are included. Monte Carlo shell-model calculations suggest that the latter two states are part of a prolate-deformed intruder sequence, establishing an instance of shape coexistence at low excitation energies similar to that observed recently in neighboring Ni-68.

IWM-EC 2014 – International Workshop on Multi facets of EoS and Clustering.-- et al., Structure information of 11Li halo nucleus has been obtained from the inclusive break-up measurements of the 11Li+208Pb reactions at energies around the Coulomb barrier (Elab = 24.3 and 29.8 MeV). The effective break-up energy and the slope of B(E1) distribution close to the threshold have been extracted from the experimental data.

Total fusion cross section of carbon isotopes were obtained using the newly developed MUSIC detector. MUSIC is a highly efficient, active target-detector system designed to measure fusion excitation functions with radioactive beams. The present measurements are relevant for understanding x-ray superbursts. The results of the first MUSIC campaign as well as the astrophysical implications are presented in this work.

The $(d,\ensuremath{\alpha})$ reaction is highly selective, favoring final states in which the removed neutron and proton are completely aligned in a $J=2j$ configuration. We have studied the $^{14,15}\mathrm{C}(d,\ensuremath{\alpha})^{12,13}\mathrm{B}$ reactions in inverse kinematics using the Helical Orbit Spectrometer (HELIOS) at Argonne National Laboratory. In $^{12}\mathrm{B}$, the reaction strongly favors the population of a known ${3}^{+}$ state at 5.61 MeV, and for $^{13}\mathrm{B}$, we observe a possible unreported doublet of states at high excitation energy, probably corresponding to the $^{12}\mathrm{B}({3}^{+})$ state coupled to the $1{s}_{1/2}$ neutron from the $^{15}\mathrm{C}$ ground state. In contrast to single-nucleon transfer, deuteron-transfer reactions have not been widely studied with exotic nuclei.

Background: Two-photon emission, while well known in atomic physics, is a rare second-order process in nuclear physics with only three cases where a two-photon branch is measured. The limited knowledge stems from the experimental difficulty in resolving two-photon emission from dominant single-photon emission, restricting practical cases for study to ${0}^{+}\ensuremath{\rightarrow}{0}^{+}$ ($E0$) transitions, since single-photon emission is forbidden. In practical terms, this limits the range of easily accessible cases to even-even nuclei with the unusual property of a first excited state with spin/parity of 0${}^{+}$.Purpose: Two-photon branches are measured for the closed-shell nuclei, ${}^{16}\mathrm{O}$, ${}^{40}\mathrm{Ca}$, and ${}^{90}\mathrm{Zr}$. The intention of the present work was to obtain data for a case which was not a closed-shell nucleus. Of the possible nuclei relevant to such a study, ${}^{98}Mo$ was chosen as its first-excited state is 0${}^{+}$ and lies below 1 MeV, meaning that internal pair transitions are not allowed.Method: The first excited state (${J}^{\ensuremath{\pi}}={0}^{+}$) in ${}^{98}Mo$ was excited in resonant inelastic proton scattering using a 6.7-MeV proton beam. The population of the state was selected using an annular double-sided silicon strip detector (DSSD). The decay of the state by conversion electrons was observed using the same DSSD, while Gammasphere was used to detect possible two-photon events.Results: An upper limit on the two-photon branch obtained was 1 $\ifmmode\times\else\texttimes\fi{}$ 10${}^{\ensuremath{-}4}$ at the 95% confidence level (CL). Conclusions The upper limit obtained is smaller than any other previously obtained two-photon branch. Phase space considerations suggest that the actual value of the branching ratio in this case may be significantly smaller than the upper limit obtained.

The interaction between neutron-rich nuclei plays an important role for understanding the reaction mechanism of the fusion process as well as for the energy production through pycnonuclear reactions in the crust of neutron stars. We have performed the first measurements of the total fusion cross sections in the systems (10,14,15)C+(12)C using a new active target-detector system. In the energy region accessible with existing radioactive beams, a good agreement between the experimental and theoretical cross sections is observed. This gives confidence in our ability to calculate fusion cross sections for systems which are outside the range of today's radioactive beam facilities.

The 1809-keV $\ensuremath{\gamma}$ ray from the decay of $^{26}{\mathrm{Al}}^{g}$ is an important target for $\ensuremath{\gamma}$-ray astronomy. In the convective C/Ne burning shell of massive presupernova stars, the $^{23}\mathrm{Na}(\ensuremath{\alpha},p)^{26}\mathrm{Mg}$ reaction directly influences the production of $^{26}\mathrm{Al}$. We have performed a direct measurement of the $^{23}\mathrm{Na}(\ensuremath{\alpha},p)^{26}\mathrm{Mg}$ reaction cross section at the appropriate astrophysically important energies. The stellar rate calculated in the present work is larger than the recommended rate by nearly a factor of 40 and could strongly affect the production of $^{26}\mathrm{Al}$ in massive stars.

We have studied the fission-neutron emission competition in highly excited $^{274}$Hs (Z=108) (where the fission barrier is due to shell effects) formed by a hot fusion reaction. Matching cross bombardments ($^{26}$Mg + $^{248}$Cm and $^{25}$Mg + $^{248}$Cm) were used to identify the properties of first chance fission of $^{274}$Hs. A Harding-Farley analysis of the fission neutrons emitted in the $^{25,26}$Mg + $^{248}$Cm was performed to identify the pre- and post-scission components of the neutron multiplicities in each system. ($\Gamma$$_{n}$/$\Gamma$$_{t}$) for the first chance fission of $^{274}$Hs (E$^{\ast}$ = 63 MeV) is 0.89 $\pm$ 0.13, i.e., $\sim$ 90 $%$ of the highly excited nuclei survive.The high value of that survival probability is due to dissipative effects during de-excitation. A proper description of the survival probabilities of excited superheavy nuclei formed in hot fusion reactions requires consideration of both dynamic and static (shell-related) effects.

The β −decay branching ratio of 12 B to the Hoyle state in 12 C was measured by detection of γ rays. 12 B nuclei were produced via the 11 B(d,p)12 B reaction in inverse kinematics on a TiD2 target. The present results corroborate those obtained recently for the β branch by implantation. The value from both experiments is inconsistent with that accepted in the literature.

States in ${}^{18}$N have been populated in the neutron-adding $(d,p)$ reaction on the short-lived ${}^{17}$N beam. Previously observed levels, found in this work at excitation energies of 0.12(1) MeV and 0.74(1) MeV, have been identified as those expected from a proton $0{p}_{1/2}$ hole coupled to the ${}^{19}$O $5/{2}^{+}$ ground state. A new state at 1.17(2) MeV is consistent with the coupling of the $1/{2}^{\ensuremath{-}}$ proton-hole state to the excited $1/{2}^{+}$ state in ${}^{19}$O. Orbital angular momentum assignments and spectroscopic factors were determined from the measured angular distributions through a distorted wave Born approximation analysis. Systematics for the ${(0{d}_{5/2}1{s}_{1/2})}^{3}$ neutron configurations in the $N=11$ isotones, ${}^{17}$C, ${}^{18}$N, and ${}^{19}$O are discussed and comparisons to $p$-$sd$ shell-model calculations are made.

We have used the ${}^{13}$B($d,p$)${}^{14}$B reaction in inverse kinematics to study the properties of states in ${}^{14}$B, the lightest particle-bound $N=9$ isotone. The spectroscopic information, including spins, parities, and spectroscopic factors for the states observed in ${}^{14}$B are used to deduce the wave functions for the low-lying negative parity $\ensuremath{\nu}(\mathit{sd})$ levels, as well as provide information about the evolution of the effective neutron $1{s}_{1/2}\ensuremath{-}0{d}_{5/2}$ single-particle energies. The data confirm that the ground and first-excited states are predominantly $s$ wave in character and are single-neutron halo states. The effective single-particle energies are found to match the trends set by other $N=9$ isotones.

The gamma-ray multiplicity and total energy emitted by the heavy nucleus 254No have been measured at 2 different beam energies. From these measurements, the initial distributions of spin I and excitation energy E * of 254No were constructed. The distributions display a saturation in excitation energy, which allows a direct determination of the fission barrier. 254No is the heaviest shell-stabilized nucleus with a measured fission barrier. © Owned by the authors, published by EDP Sciences, 2014.

The inclusive breakup for the Li-11 + Pb-208 reaction at energies around the Coulomb barrier has been measured for the first time. A sizable yield of Li-9 following the Li-11 dissociation has been observed, even at energies well below the Coulomb barrier. Using the first-order semiclassical perturbation theory of Coulomb excitation it is shown that the breakup probability data measured at small angles can be used to extract effective breakup energy as well as the slope of B(E1) distribution close to the threshold. Four-body continuum-discretized coupled-channels calculations, including both nuclear and Coulomb couplings between the target and projectile to all orders, reproduce the measured inclusive breakup cross sections and support the presence of a dipole resonance in the Li-11 continuum at low excitation energy.

This work reports on the scattering of 11Be on 197Au at energies around and below the Coulomb barrier. By experimentally identifying the elastic scattering, inelastic scattering and breakup channels, and comparing them with different calculations, valuable information on the 11Be structure and its B(E1) distribution to the continuum are obtained. On top of that, a deeper understanding of the scattering process at low energies is achieved for reactions of this kind, making these studies extendable to other loosely-bound systems like 17,19C Gobierno de España FPA2015-64969-P, FIS2014-53448-C2-1-P, FPA2013-47327-c02-01-R, FPA2012-32443, FIS2013-41994-P, CSD2007-00042 EUROCORES EUI-2009-04162 European Union 654002

The low-spin level scheme of ${}^{68}$Ni was investigated following two-neutron-knockout and multinucleon-transfer reactions. The energy of the first excited state was determined to be ${E}_{x}({0}_{2}^{+})=1603.5(3)$ keV. Relative $B(E2)$ transition probabilities were deduced and compared with shell-model calculations using several modern effective interactions. Theory reproduces the data well, but indicates substantial mixing of multi-particle, multi-hole configurations for the lowest observed ${0}^{+}$ and ${2}^{+}$ states.

We have used the B-10(He-3, paaa) reaction at 4.9 MeV and the B-11(He-3, daaa) reaction at 8.5 MeV to determine the energy, width, and decay mechanism of resonances in C-12 above the triple-alpha threshold up to 21 MeV in excitation energy. Comparison with various models has allowed us to estimate the degree of clustering of the states studied.

The low-spin level scheme of ${}^{68}$Ni was investigated with the Gammasphere array following reactions between a ${}^{70}$Zn beam and ${}^{238}$U, ${}^{208}$Pb, and ${}^{197}$Au targets. Spin assignments for some states have been verified through $\ensuremath{\gamma}$-ray angular correlations, including the ${0}^{+}$ assignment for the 2511-keV level. Two previously unknown states at 3302 and 3405 keV have been identified. No evidence was found for a recently reported 216-ns, ${0}^{+}$ isomer at 2202 keV that was attributed to a proton two-particle, two-hole intruder configuration, despite experimental conditions similar to those used in the measurement reporting its discovery.

A new data acquisition system for experiments using the Gammasphere detector array and associated detectors including the double-sided silicon strip detector (DSSD) is under development. Waveform digitization and triggering hardware identical to that developed for GRETINA has been procured and interfaced to the both the existing Gammasphere and DSSD detectors to provide significantly increased data throughput and increased event rates. A new parasitic signal connection and cable plant provides the ability to simultaneously measure the same events using both the old and new systems. A triggering interface module has been manufactured that connects the Gammasphere trigger and clock to the new system. A second digital data acquisition system has been attached to the DSSD detector located downstream from Gammasphere. The trigger systems of Gammasphere, Digital Gammasphere and Digital DSSD have successfully synchronized the clocks of all three data acquisition systems demonstrating timestamp correlation across multiple detector systems. New firmware for the digitizer modules specific to the signals provided by the Gammasphere detector has been developed and is currently being tested in situ to directly compare the energy resolution of the two data acquisition systems. We describe the system as implemented and show test results to date, where significantly faster event processing rates have been obtained with nearly equivalent energy resolution.