Paleomagnetic analysis and radiocarbon dating of an expanded Holocene deep‐sea sediment sequence recovered by Integrated Ocean Drilling Program (IODP) Expedition 303 from Labrador Sea Site U1305 ...(Lat.: 57°28.5 N, Long.: 48°31.8 W, water depth 3459 m) provides insights into mechanisms that drive both paleomagnetic secular variation (PSV) and magnetization acquisition in deep‐sea sediments. Seventeen radiocarbon dates on planktonic foraminifera define postglacial (ca. 8 ka) sedimentation rates as ranging from 35 to > 90 cm/kyr. Alternating field (AF) demagnetization of u‐channel samples show that these homogeneous sediments preserve a strong, stable, and consistently well‐defined component magnetization. Normalized remanence records pass reliability criteria for relative paleointensity (RPI) estimates. Assuming that the age of magnetization is most accurately defined by well dated PSV records with the highest sedimentation rates, allows us to estimate and correct for temporal offsets at Site U1305 interpreted to result from postdepositional remanence acquisition at a depth of ∼20 cm. Comparisons indicate that the northern North Atlantic PSV and RPI records are more consistent with European than North American records, and the evolution of virtual geomagnetic poles (VGP) are temporally and longitudinally similar to global reconstructions, though with much larger latitudinal variation. The largest deviations from a geocentric axial dipole (GAD) are observed during times of the highest intensities, in contrast to the usual assumption. These observations are consistent with the idea that PSV in the North Atlantic and elsewhere during the Holocene results from temporal oscillations of high‐latitude flux concentrations at a few recurrent locations.
Key Points
Deep‐sea sediments provide insights into geomagnetic change
North Atlantic is characterized by high amplitude PSV
PSV results from temporal oscillations of flux at a few recurrent locations
Studying interactions of radioactive ions with neutrons is particularly demanding and has been performed only in a few cases. Some of these interactions are crucial in several astrophysical contexts. ...In the present work, the case of the 7Be destruction induced by the (n, ) reaction is investigated at the energies typical of the primordial nucleosynthesis by means of the Trojan Horse Method applied to the 2H(7Be, )p quasi-free reaction. The 7Be(n, )4He cross-section has been measured in a single experiment from ∼2 MeV down to cosmological energies. The corresponding deduced reaction rate has been adopted to evaluate the impact on big bang nucleosynthesis and on the lithium problem.
Fluorine abundance determination is of great importance in stellar physics to understand s-elements production and mixing processes in asymptotic giant branch (AGB) stars. Up to now, theoretical ...models overproduce F abundances in AGB stars with respect to the observed values, thus calling for further investigation of the reactions involving fluorine. In particular, the 19F(p, )16O reaction is the main destruction channel of fluorine at the bottom of the convective envelope in AGB stars, an H-rich environment where it can experience temperatures high enough to determine its destruction, owing to additional mixing processes. In this paper the Trojan horse method (THM) was used to extract the 19F(p, 0)16O S-factor in the energy range of astrophysical interest (Ecm 0-1 MeV). This is the most relevant channel at the low temperatures (few 107 K) characterizing the bottom of the convective envelope, according to current knowledge. A previous indirect experiment using the THM has observed three resonances in the energy regions below Ecm 450 keV. These energies correspond to typical AGB temperatures, thus implying a significant increase in the reaction rate. Statistics are scarce for performing an accurate separation between resonances, preventing one from drawing a quantitative conclusion about their total widths and spin parities. Before THM measurement, only extrapolations were available below about 500 keV, showing a non-resonant behavior that sharply contradicts the trend of the astrophysical factor at higher energies. A new experiment has been performed to verify the measured TH astrophysical factor and to perform more accurate spectroscopy of the involved resonances.
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
Recenzirano
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.
The mechanism of reactions with weakly-bound proton-rich nuclei at energies near the Coulomb barrier is a long-standing open question owing to the paucity of experimental data. In this study, a ...complete kinematics measurement was performed for the proton drip-line nucleus 17F interacting with 58Ni at four energies near the Coulomb barrier. Thanks to the powerful performance of the detector array, exhaustive information on the reaction channels, such as the differential cross sections for quasielastic scattering, exclusive and inclusive breakup, as well as for fusion-evaporation protons and alphas, was derived for the first time. The angular distributions of quasielastic scattering and exclusive breakup can be described reasonably well by the continuum-discretized coupled-channels calculations. The inclusive breakup was investigated using the three-body model proposed by Ichimura, Austern, and Vincent, and results indicate the non-elastic breakup is the dominant component. The total fusion cross sections were determined by the fusion-evaporation protons and alphas. Based on the measured exclusive breakup data, the analysis of the classical dynamical simulation code PLATYPUS demonstrates that the incomplete fusion plays a minor role. Moreover, compared with 16O+58Ni, both the reaction and total fusion cross sections of 17F+58Ni exhibit an enhancement in the sub-barrier energy region, which mainly arises from couplings to the continuum states. This work indicates that the information of full reaction channels is crucially important to comprehensively understand the reaction mechanisms of weakly bound nuclear systems.
Double Sided Silicon Strip Detectors (DSSSD) are highly segmented detectors that are widely used in nuclear physics especially in radioactive beam experiments where, due to the low beam intensities, ...one needs to cover large solid angles with high granularity. A study of the response of DSSSDs, using 7Li and 16O beams at different energies is presented. In order to characterize the detector behavior for events corresponding to particles entering the detector in the interstrip gap both for ohmic and junction sides, signals of positive and negative polarities were acquired at the same time. Different procedures for the selection of full energy events and for the determination of the corresponding efficiencies are shown and discussed.
.
We report on the development of a new, portable detector array for charged particles with a low detection threshold to study the reaction mechanisms of exotic nuclear systems at energies around the ...Coulomb barrier. In order to identify both light and heavy particles simultaneously, the array consists of ten units of
Δ
E
-
E
R
telescopes, where each one is made up of four detection layers: one ionization chamber, one 40 (or 60)μm double-sided silicon strip detector and two quadrant silicon detectors with thicknesses of 300μm and 1000 (or 1500)μm, respectively. The frame of the ionization chamber is innovatively designed with printed circuit boards, thus the mass of each telescopic unit was reduced significantly which eases transport and installation requirements to different radioactive ion beam lines around the globe. The commissioning experiments focused on elucidating several reaction mechanisms encountered in the
17
F +
58
Ni and
17
F +
208
Pb systems, and we demonstrated that the array has a sufficient capability to enable charged particle identification over a large range of
Z
. Light particles like
p
,
d
,
α
as well as heavy ions like
16
O and
17
F can be clearly distinguished. Considering these properties, this newly developed array enables in-depth investigation of the novel reaction mechanisms which are manifested in the collisions of exotic nuclei with differing isotopes.
•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.
.
Sub-barrier fusion of the two near-by systems
36
S +
50
Ti,
51
V has been measured at the Laboratori Nazionali di Legnaro (INFN). Motivation for the experiment came from the possible effect of the ...non-zero spin of the ground state of the
51
V nucleus on the sub-barrier excitation function, and in particular on the shape of the barrier distribution. No previous data were available for these two systems near the barrier. Our results show that the two measured excitation functions are very similar down to the level of 20-30μb. The same is true for the two barrier distributions. Coupled-channel calculations have been performed including the low energy excitations of both projectile and the two targets. We have indication that the low-lying levels in
51
V can be interpreted in the weak-coupling scheme, that is,
51
V (
I
) =
50
Ti(2
+
) ⊗
p
(1
f
7/2
) and that the extra proton in the
1
f
7
/
2
shell does not have a significant influence on sub-barrier fusion.
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