Carbon burning powers scenarios that influence the fate of stars, such as the late evolutionary stages of massive stars (exceeding eight solar masses) and superbursts from accreting neutron stars. It ...proceeds through the12C +12C fusion reactions that produce an alpha particle and neon-20 or a proton and sodium-23-that is,12C(12C, a,)20Ne and12C(12C, p)23Na-at temperatures greater than 0.4 X 109 kelvin, corresponding to astrophysical energies exceeding a megaelectronvolt, at which such nuclear reactions are more likely to occur in stars. The cross-sections for those carbon fusion reactions (probabilities that are required to calculate the rate of the reactions) have hitherto not been measured at the Gamow peaks below 2 megaelectronvolts because of exponential suppression arising from the Coulomb barrier. The reference rate at temperatures below 1.2 X 109 kelvin relies on extrapolations that ignore the effects of possible low-lying resonances. Here we report the measurement of the12C(12C, a0,1)20Ne and12C(12C, p0,1)23Na reaction rates (where the subscripts 0 and 1 stand for the ground and first excited states of20Ne and23Na, respectively) at centre-of-mass energies from 2.7 to 0.8 megaelectronvolts using the Trojan Horse method and the deuteron in 14N. The cross-sections deduced exhibit several resonances that are responsible for very large increases of the reaction rate at relevant temperatures. In particular, around 5 X 108 kelvin, the reaction rate is boosted to more than 25 times larger than the reference value. This finding may have implications such as lowering the temperatures and densities8 required for the ignition of carbon burning in massive stars and decreasing the superburst ignition depth in accreting neutron stars to reconcile observations with theoretical models.
Abstract
The study of heavy-ions induced double charge-exchange (HI-DCE) nuclear reactions is a promising way to access data-driven information on neutrino-less double-beta decay nuclear matrix ...elements. In the following, particular attention is given to the (
18
O,
18
Ne) and (
20
Ne,
20
O) HI-DCE reactions as tools for
β
+
β
+
and
β
−
β
−
decays, respectively. The experiments are performed in Catania at the Laboratori Nazionali del Sud of the Istituto Nazionale di Fisica Nucleare (INFN-LNS). The MAGNEX magnetic spectrometer is used to momentum analyse the ejectiles of a large network of nuclear reactions. New preliminary experimental data for the
76
Se(
18
O,
18
F)
76
As and
76
Ge(
20
Ne,
20
F)
76
As single charge exchange (SCE) and for the
76
Se(
18
O,
18
Ne)
76
Ge and
76
Ge(
20
Ne,
20
O)
76
Se DCE nuclear reactions were also investigated.
Abstract
Heavy-ion one-nucleon transfer reactions are promising tools to investigate single-particle configurations in nuclear states, with and without the excitation of the core degrees of freedom. ...An accurate determination of the spectroscopic amplitudes of these configurations is essential for the study of other direct reactions as well as beta-decays. In this context, the
76
Se(
18
O,
17
O)
77
Se one-neutron transfer reaction gives a quantitative access to the relevant single particle orbitals and core polarization transitions built on
76
Se. This is particularly relevant, since it provides data-driven information to constrain nuclear structure models for the
76
Se nucleus.
The excitation energy spectrum and the differential cross section angular distributions of this nucleon transfer reaction was measured at 275 MeV incident energy for the first time using the MAGNEX large acceptance magnetic spectrometer. The data are compared with calculations based on distorted wave Born approximation and coupled channel Born approximation adopting spectroscopic amplitudes for the projectile and target overlaps derived by large-scale shell model calculations and interacting boson-fermion model.
These reactions are studied in the frame of the NUMEN project. The NUMEN (NUclear Matrix Elements for Neutrinoless double beta decay) project was conceived at the Istituto Nazionale di Fisica Nucleare–Laboratori Nazionali del Sud (INFN-LNS) in Catania, Italy, aiming at accessing information about the nuclear matrix elements (NME) of neutrinoless double beta decay (0
νββ
) through the study of the heavy-ion induced double charge exchange (DCE) reactions on various 0
νββ
decay candidate targets. Among these, the
76
Se nucleus is under investigation since it is the daughter nucleus of
76
Ge in the 0
νββ
decay process.
The broad network of nuclear reactions populated in the 18O + 12C collision was studied to test the capability of state-of-art nuclear structure and reaction theories to describe both the direct and ...sequential components of the (18O, 18F) single charge exchange nuclear reaction. The experiment was performed using the 18O beam at 275 MeV incident energy produced by the K800 superconducting cyclotron and the MAGNEX magnetic spectrometer at the Laboratori Nazionali del Sud of the Istituto Nazionale di Fisica Nucleare. A unique comprehensive and coherent theoretical calculation, able to describe the whole network of direct reactions, is the approach proposed for the first time to analyse this large set of experimental data. This holistic approach, applied both to the experimental and theoretical analysis, is the main feature and novelty of the work here presented.
Abstract
The broad network of nuclear reactions populated in the
18
O +
12
C collision was studied to test the capability of state-of-art nuclear structure and reaction theories to describe both the ...direct and sequential components of the (
18
O,
18
F) single charge exchange nuclear reaction. The experiment was performed using the
18
O beam at 275 MeV incident energy produced by the K800 superconducting cyclotron and the MAGNEX magnetic spectrometer at the Laboratori Nazionali del Sud of the Istituto Nazionale di Fisica Nucleare. A unique comprehensive and coherent theoretical calculation, able to describe the whole network of direct reactions, is the approach proposed for the first time to analyse this large set of experimental data. This holistic approach, applied both to the experimental and theoretical analysis, is the main feature and novelty of the work here presented.
The FAZIA project in Europe: R&D phase Bougault, R.; Poggi, G.; Barlini, S. ...
The European physical journal. A, Hadrons and nuclei,
2014/2, Letnik:
50, Številka:
2
Journal Article
Recenzirano
Odprti dostop
The goal of the FAZIA Collaboration is the design of a new-generation 4
π
detector array for heavy-ion collisions with radioactive beams. This article summarizes the main results of the R&D phase, ...devoted to the search for significant improvements of the techniques for charge and mass identification of reaction products. This was obtained by means of a systematic study of the basic detection module, consisting of two transmission-mounted silicon detectors followed by a CsI(Tl) scintillator. Significant improvements in
ΔE
-
E
and pulse-shape techniques were obtained by controlling the doping homogeneity and the cutting angles of silicon and by putting severe constraints on thickness uniformity. Purposely designed digital electronics contributed to identification quality. The issue of possible degradation related to radiation damage of silicon was also addressed. The experimental activity was accompanied by studies on the physics governing signal evolution in silicon. The good identification quality obtained with the prototypes during the R&D phase, allowed us to investigate also some aspects of isospin physics, namely isospin transport and odd-even staggering. Now, after the conclusion of the R&D period, the FAZIA Collaboration has entered the demonstrator phase, with the aim of verifying the applicability of the devised solutions for the realization of a larger-scale experimental set-up.
A systematic study of the nuclei that can be described as an integer number of a particles plus three neutrons via the (7Li,7Be) reaction at about 8 MeV/u has shown the presence of Bound States ...Embedded in the Continuum in the energy spectra. These are experimental signatures of the dynamical correlations of an easily polarizable core with a single-particle state of the valence neutron.
The MAGNEX large-acceptance spectrometer was commissioned with beams from the LNS Tandem. First results of physical interest are presented. The obtained 10-3 energy resolution confirms the ambitious ...characteristic of the calculations and allows considering the instrument as an ideal tool for future studies in the field of nuclear spectroscopy and reaction mechanisms at incident energies not far form the Coulomb barrier.
The response of silicon–silicon–CsI(Tl) telescopes, developed within the FAZIA collaboration, to fragments produced in nuclear reactions 84Kr+120-124Sn at 35AMeV, has been used to study ion ...identification methods. Two techniques are considered for the identification of the nuclear products in the silicon stages. The standard ΔE−E one requires signals induced in two detection layers by ions punching through the first one. Conversely, the digital Pulse Shape Analysis (PSA) allows the identification of ions stopped in the first silicon layer. The capabilities of these two identification methods have been compared for different mountings of the silicons, i.e. rear (particles entering through the low electric field side) or front (particles entering through the high electric field side) side injection. The ΔE−E identification method gives exactly the same results in both configurations. At variance, the pulse shape discrimination is very sensitive to the detector mounting. In case of rear side injection, the identification with the “energy vs. charge rise time” PSA method presents energy thresholds which are significantly lower than in the case of front side injection.
The preemission of neutrons from 11Li halo nuclei is considered. The present problems of investigation of 11Li halo nucleus structure by means of the Cnn correlation function are briefly presented. ...The influence of the target screening on the halo neutron preemission is described. It is shown that, owing to the diminishing of the screening effect, the yield of preemission neutron pairs is expected to be much larger in the case of 12C than in the case of Si target. It is shown that a new experiment on a 12C target will allow one to solve the standing problems of Cnn and to test experimentally a recent new theory of Cnn.
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