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 the C +C fusion reactions that produce an alpha particle and neon-20 or a proton and sodium-23-that is, C(C, α)Ne and C(C, p)Na-at temperatures greater than 0.4 × 10 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 × 10 kelvin relies on extrapolations that ignore the effects of possible low-lying resonances. Here we report the measurement of the C(C, α)Ne and C(C, p)Na reaction rates (where the subscripts 0 and 1 stand for the ground and first excited states of Ne andNa, respectively) at centre-of-mass energies from 2.7 to 0.8 megaelectronvolts using the Trojan Horse method and the deuteron in N. 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 × 10 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 densities 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 .

The transfer reaction p͑ 8 He, d͒ 7 He has been studied by correlational measurements, and an excited state of 7 He was observed (E ‫ء‬ 2.9 6 0.3 MeV, G 2.2 6 0.3 MeV) which decays mainly into 3n 1 4 He. Most likely, it has a structure with a neutron in an excited state coupled to the 6 He core which itself is in the excited 2 1 state. [S0031-9007(99)09012-2] 23.20.En, 27.20. + n, 21.45. + v We report on such a novel step, in the experiments with beams of exotic nuclei, as the investigation of transfer reactions. Namely, we studied the p͑ 8 He, d͒ 7 He reaction for the spectroscopy of 7 He.It is well known that nuclei have excited states. There is a famous exception from this rule-the absence of excited states in 3 He and 3 H. Another kind of exception was 7 He. This nucleus was investigated for 30 years in many reactions with stable beams, and no excited states were found. As a result, 7 He began to be considered as a nucleus which may not have excited states. It can be explained by a large width for decay 7 He ‫ء‬ ! n 1 6 He. The ground state of 7 He is a well established resonance that decays into n 1 6 He.Radioactive nuclear beams are the most promising tool to study as neutron-rich systems as 7 He. Since the projectiles in reactions are already neutron rich, reaction mechanisms are simpler than those with stable beams, cross sections are higher, and physical backgrounds are lower. We used a beam of 8 He at 50A MeV, that was produced by the fragment separator RIPS at RIKEN, and studied the p͑ 8 He, d͒ 7 He reaction with the CH 2 and C targets. To study transfer reactions with beams of exotic nuclei, a special detection system, the RIKEN telescope, was designed (Fig. 1). It represents a stack of solidstate position-sensitive detectors (strip detectors) that have large area and annular hole. Using this telescope, we detected deuterons at small angles in the laboratory system (10 ± -25 ± ) corresponding to a high cross section.In addition to the deuterons, we detected other particles emitted from the decay of 7 He. Neutrons were measured by the neutron walls of plastic scintillators, while charged particles were bent in the dipole magnet and detected by the drift chamber and the plastic scintillators' hodoscope (Fig. 1). These parts of the detection system allowed us to study spectra of deuterons detected in coincidences with 6 He, 4 He, and neutrons. Other detectors in Fig. 1, the beam scintillators and multiwire proportional counters, were used for identification of each beam particle, determination of its energy, and for its tracking.The resulting deuteron spectra are presented in Figs. 2 and 3 as a function of energy in the center of mass of 7 He relative to the n 1 6 He threshold. In each graph, the upper histogram with pronounced peak corresponds to measurements with CH 2 target; the lower structureless histogram shows total background from materials other than protons in the target (it was obtained with the C and empty targets). The cutoff of spectra at energy of ϳ30 MeV reflects the energy range meas...

The article describes the main achievements of the NUMEN project together with an updated and detailed overview of the related R&D activities and theoretical developments. NUMEN proposes an innovative technique to access the nuclear matrix elements entering the expression of the lifetime of the double beta decay by cross section measurements of heavy-ion induced Double Charge Exchange (DCE) reactions. Despite the two processes, namely neutrinoless double beta decay and DCE reactions, are triggered by the weak and strong interaction respectively, important analogies are suggested. The basic point is the coincidence of the initial and final state many-body wave-functions in the two types of processes and the formal similarity of the transition operators. First experimental results obtained at the INFN-LNS laboratory for the 40 Ca( 18 O, 18 Ne) 40 Ar reaction at 270 MeV, give encouraging indication on the capability of the proposed technique to access relevant quantitative information.The two major aspects for this project are the K800 Superconducting Cyclotron and MAGNEX spectrometer. The former is used for the acceleration of the required high resolution and low emittance heavy ion beams and the latter is the large acceptance magnetic spectrometer for the detection of the ejectiles. The use of the high-order trajectory reconstruction technique, implemented in MAGNEX, allows to reach the experimental resolution and sensitivity required for the accurate measurement of the DCE cross sections at forward angles. However, the tiny values of such cross sections and the resolution requirements demand beam intensities much larger than manageable with the present facility. The on-going upgrade of the INFN-LNS facilities in this perspective is part of the NUMEN project and will be discussed in the article.3

No abstract