Photoneutron cross sections were measured for 58Ni, 60Ni, 61Ni, and 64Ni at energies between the one-neutron and two-neutron thresholds using quasimonochromatic γ -ray beams produced in laser Compton ...scattering at the NewSUBARU synchrotron radiation facility. These photoneutron data are used to extract the γ -ray strength function above the neutron threshold, complementing the information obtained by the Oslo method below the threshold. We discuss radiative neutron-capture cross sections and the Maxwellian-averaged cross sections for Ni isotopes including 63Ni, a branching point nucleus along the weak s-process path. The cross sections are calculated with the experimentally constrained γ -ray strength functions from the Hartree-Fock-Bogolyubov plus quasiparticle–random-phase approximation based on the Gogny D1M interaction for both E1 and M1 components and supplemented with the M1 upbend.
The experimental set-up of the RIB in-flight facility EXOTIC Pierroutsakou, D.; Boiano, A.; Boiano, C. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
10/2016, Letnik:
834
Journal Article
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Odprti dostop
We describe the experimental set-up of the Radioactive Ion Beam (RIB) in-flight facility EXOTIC consisting of: (a) two position-sensitive Parallel Plate Avalanche Counters (PPACs), dedicated to the ...event-by-event tracking of the produced RIBs and to time of flight measurements and (b) the new high-granularity compact telescope array EXPADES (EXotic PArticle DEtection System), designed for nuclear physics and nuclear astrophysics experiments employing low-energy light RIBs. EXPADES consists of eight ΔE–Eres telescopes arranged in a cylindrical configuration around the target. Each telescope is made up of two Double Sided Silicon Strip Detectors (DSSSDs) with a thickness of 40/60μm and 300μm for the ΔE and Eres layer, respectively. Additionally, eight ionization chambers were constructed to be used as an alternative ΔE stage or, in conjunction with the entire DSSSD array, to build up more complex triple telescopes. New low-noise multi-channel charge-sensitive preamplifiers and spectroscopy amplifiers, associated with constant fraction discriminators, peak-and-hold and Time to Amplitude Converter circuits were developed for the electronic readout of the ΔE stage. Application Specific Integrated Circuit-based electronics was employed for the treatment of the Eres signals. An 8-channel, 12-bit multi-sampling 50MHz Analog to Digital Converter, a Trigger Supervisor Board for handling the trigger signals of the whole experimental set-up and an ad hoc data acquisition system were also developed. The performance of the PPACs, EXPADES and of the associated electronics was obtained offline with standard α calibration sources and in-beam by measuring the scattering process for the systems 17O+58Ni and 17O+208Pb at incident energies around their respective Coulomb barriers and, successively, during the first experimental runs with the RIBs of the EXOTIC facility.
•We realized a detection array for Exotic Radioactive Ion Beams.•High granularity (32×32 pixels 2×2mm wide for 8 telescopes).•High solid angle (8 telescopes 64×64mm wide in a cylindrical ...configuration covering up to 2.6sr).•We tested each component of the array by both alpha particles and in-beam environment.•We measured the angular distribution for 17O elastic scattering on a 58Ni target.
The EXPADES (EXotic PArticle DEtection System) detector array consists of 16 Double Side Silicon Strip Detectors (DSSSD) with active areas of 64×64mm2, arranged in 8 ΔE (40/50μm)–E (300μm) telescopes. All detector faces are segmented into 32×2-mm wide strips, ensuring a 2×2mm2 pixel configuration. Eight ionization chambers can be alternatively used as ΔE stages or, if needed, as an additional third layer for more complex triple telescopes. The signals from silicon ΔE layers and from ionization chambers are read by standard electronics, while innovative 32-channel ASIC chips are employed for the readout of the E stages. The results of off-line tests with alpha sources and from the first in-beam experiment with a 17O beam are presented.
•Production of in-flight Radioactive Ion Beams via two-body reactions.•Development of a cryogenic gas target.•Event-by-event tracking via Parallel Plate Avalanche Counters (PPACs).
The facility ...EXOTIC for the in-flight production of light weakly-bound Radioactive Ion Beams (RIBs) has been operating at INFN-LNL since 2004. RIBs are produced via two-body reactions induced by high intensity heavy-ion beams impinging on light gas targets and selected by means of a 30°-dipole bending magnet and a 1-m long Wien filter. The facility has been recently upgraded (i) by developing a cryogenic gas target, (ii) by replacing the power supplies of the middle lenses of the two quadrupole triplets, (iii) by installing two y-steerers and (iv) by placing two Parallel Plate Avalanche Counters upstream the secondary target to provide an event-by-event reconstruction of the position hit on the target. So far, RIBs of 7Be, 8B and 17F in the energy range 3–5MeV/u have been produced with intensities about 3×105, 1.6×103 and 105pps, respectively. Possible light RIBs (up to Z=10) deliverable by the facility EXOTIC are also reviewed.
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A fast-timing method to determine lifetimes of nuclear states in the sub-nanosecond domain is presented. It is based on in-beam measurements of triple-gamma coincidences in heavy-ion ...fusion-evaporation reactions, performed with an array of HPGe and LaBr
3
:Ce detectors. The high-energy resolution HPGe detectors are used to define de-exciting cascades, while the fast LaBr
3
:Ce detectors are used to determine the decay time spectra of selected levels fed by these cascades. A special method to treat the time information of an array of fast detectors is employed in order to fully use the efficiency of the array. Two measurements are presented to illustrate the method: a re-determination of the known half-life
ns of the
keV,
level in
107
Cd (test experiment), and the determination of a half-life
ps for the
keV,
state of
199
Tl .
The present paper describes preparation and characterization of strontium targets for nuclear astrophysical experiments with alpha particles accelerated near the Gamow window energy. SrF
2
and SrCO
3
...targets were obtained by thermal evaporation in similar conditions. Target characteristics (thickness, chemical purity and surface morphology) were determined via α transmission measurements, XRD and SEM/EDX analysis. The results reveal the SrF
2
target exhibits better properties compared to the SrCO
3
one for our nuclear astrophysics experiments. This result was supported by nuclear activation measurements with an α beam at the Bucharest Tandem 9 MV accelerator.
Nuclei are complex quantum objects due to complex nucleon-nucleon interactions. They can undergo rather rapid changes in structure as a function of nucleon number. A well known region of such a shape ...transition is the rare-earth region around N = 90, where accessible nuclei range from spherical nuclei at the closed neutron shell at N = 82 to deformed nuclei. For a better understanding of this phenomenon, it is of interest to study empirical signatures like the E2 transition strength \(B(E2;{2}_{1}^{+}\to {0}_{1}^{+})\) or the E0 excitation strength \({\rho }^{2}(E0;{0}_{1}^{+}\to {0}_{2}^{+})\). The nuclide 152Gd with 88 neutrons is located close to the quantum phase transition at N = 90. The lifetime \(\tau ({0}_{2}^{+})\) of 152Gd has been measured using fast electronic scintillation timing (FEST) with an array of HPGe- and LaBr3- detectors. Excited states of 152Gd were populated via an (α,n)-reaction on a gold-backed 149Sm target. The measured lifetime of \(\tau ({0}_{2}^{+})=96(6)\text{ps}\) corresponds to a reduced transition strength of \(B(E2;{0}_{2}^{+}\to {2}_{1}^{+})=111(7)\) W.u. and an E0 transition strength of ρ 2(E0) = 39(3) · 10−3 to the ground state. This result provides experimental support for the validity of a correlation between E0 and E2 strengths that is a novel indicator for a quantum phase transition. This work was published as J. Wiederhold et al., Phys. Rev. C 94, 044302 (2016).
The (J,T)=(1,1) parity doublet in 20Ne at 11.26 MeV is a good candidate to study parity violation in nuclei. However, its energy splitting is known with insufficient accuracy for quantitative ...estimates of parity violating effects. To improve on this unsatisfactory situation, nuclear resonance fluorescence experiments using linearly and circularly polarized γ-ray beams were used to determine the energy difference of the parity doublet ΔE=E(1−)−E(1+)=−3.2(±0.7)stat(−1.2+0.6)sys keV and the ratio of their integrated cross sections Is,0(+)/Is,0(−)=29(±3)stat(−7+14)sys. Shell-model calculations predict a parity-violating matrix element having a value in the range 0.46–0.83 eV for the parity doublet. The small energy difference of the parity doublet makes 20Ne an excellent candidate to study parity violation in nuclear excitations.
The prompt γ-ray emission is investigated in the 16A MeV energy region by means of the 36,40Ar + 96,92Zr fusion reactions leading to a compound nucleus in the vicinity of 132Ce. The dynamical nature ...of this radiation is confirmed. We show that the prompt γ radiation has an angular distribution pattern consistent with a dipole oscillation along the symmetry axis of the dinuclear system. The data are compared with calculations based on a collective bremsstrahlung analysis of the reaction dynamics.
Highly-monochromatic γ-ray beams are produced at the NewSUBARU synchrotron radiation facility by the inverse Compton scattering of laser photons from relativistic electrons. The latest s-process ...study in nuclear astrophysics with the γ-ray beam is presented.
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