Abstract
The dynamics of a nuclear open quantum system could be revealed in the correlations between the breakup fragments of halo nuclei. The breakup mechanism of a proton halo nuclear system is of ...particular interest as the Coulomb polarization may play an important role, which, however, remains an open question. Here we use a highly efficient silicon detector array and measure the correlations between the breakup fragments of
8
B incident on
120
Sn at near-barrier energies. The energy and angular correlations can be explained by a fully quantum mechanical method based on the state-of-the-art continuum discretized coupled channel calculations. The results indicate that, compared to the neutron halo nucleus
6
He,
8
B presents distinctive reaction dynamics: the dominance of the elastic breakup. This breakup occurs mainly via the short-lived continuum states, almost exhausts the
7
Be yield, indicating the effect of Coulomb polarization on the proton halo state. The correlation information reveals that the prompt breakup mechanism dominates, occurring predominantly on the outgoing trajectory. We also show that, as a large environment, the continuum of
8
B breakup may not significantly influence elastic scattering and complete fusion.
The cosmological lithium problem (CLP) stems from the outstanding discrepancy between theoretical predictions and astronomical observations of primordial lithium abundances. For the radiogenic ...production of 7Li, 7Be plays a pivotal role in the Big Bang nucleosynthesis (BBN). Nevertheless, the data for neutron-induced 7Be destruction processes were still sparse, and especially lacked information on the contributions of transitions to the 7Li excited states. In this work, we have determined the 7Be\({(n,{p}_{0})}^{7}\)Li, 7Be\({(n,{p}_{1})}^{7}\)Li*, and 7Be\({(n,\alpha )}^{4}\)He reaction cross sections by means of the Trojan Horse method. The present and the previous data were analyzed together by a multichannel R-matrix fit, providing an improved uncertainty evaluation of the \((n,{p}_{0})\) channel and the first-ever quantification of the \((n,{p}_{1})\) contribution in the BBN-relevant energy range. We implemented the revised total reaction rate summing both the \((n,{p}_{0})\) and \((n,{p}_{1})\) contributions in a state-of-the-art BBN code PRIMAT. As a consequence, the present nuclear-physics data offers a reduction of the predicted 7Li abundance by about one-tenth, which would impose a stricter constraint on BBN and head us in the correct direction to the CLP solution.
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.
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.
.
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.
The elastic scattering in the reaction
7
Li+
208
Pb was investigated in the bombarding energy range from 25 to 39 MeV. The real and imaginary parts of the optical potential were analyzed by using a ...phenomenological potential. A dispersion relation analysis is presented in order to investigate the threshold anomaly effect. It is concluded that
7
Li has an intermediate behavior between the tightly bound nuclei such as
16
O and the loosely bound nuclei such as
6
Li where the lack of the threshold anomaly is unambiguously observed. Reaction cross sections are also extracted from the elastic scattering data and its comparison with the ones of other systems has been performed to draw hints on the effect of the breakup channel.
•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.
Abstract
The
$$^{27}\hbox {Al}(\hbox {p},\alpha )^{24}\hbox {Mg}$$
27
Al
(
p
,
α
)
24
Mg
reaction, which drives the destruction of
$$^{27}$$
27
Al and the production of
$$^{24}\hbox {Mg}$$
24
Mg
in ...stellar hydrogen burning, has been investigated via the Trojan Horse Method (THM), by measuring the
$$^2\hbox {H}(^{27}\hbox {Al},\alpha ^{24}\hbox {Mg})\hbox {n}$$
2
H
(
27
Al
,
α
24
Mg
)
n
three-body reaction. The experiment covered a broad energy range (
$$E_\mathrm{c.m.}\le \,1.5\,\hbox {MeV}$$
E
c
.
m
.
≤
1.5
MeV
), aiming to investigate those of interest for astrophysics. The results confirm the THM as a valuable technique for the experimental study of fusion reactions at very low energies and suggest the presence of a rich pattern of resonances in the energy region close to the Gamow window of stellar hydrogen burning (70–120 keV), with potential impact on astrophysics. To estimate such an impact a second run of the experiment is needed, since the background due the three-body reaction hampered to collect enough data to resolve the resonant structures and extract the reaction rate.
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