Shape of the 4.438 MeV gamma-ray line of ^12C from proton and alpha-particle induced reactions on ^12C and ^16O

We calculated in detail the angular distribution of gamma-rays and the resulting shape of the gamma-ray line produced by the nuclear deexcitation of the 4.439 MeV state of ^12C following proton and alpha-particle interactions with ^12C and ^16O in the energy range from threshold to 100 MeV per nucleon, making use of available experimental data. In the proton energy range from 8.6 to 20 MeV, the extensive data set of a recent accelerator experiment on gamma-ray line shapes and angular distributions was used to deduce parameterizations for the gamma-ray emission of the 2^+, 4.439 MeV state of ^12C following inelastic proton scattering off ^12C and proton induced spallation of ^16O. At higher proton energies and for alpha-particle induced reactions, optical model calculations were the main source to obtain the needed reaction parameters for the calculation of gamma-ray line shapes and angular distributions. Line shapes are predicted for various interaction scenarios of accelerated protons and alpha-particles in solar flares.Comment: REVTeX, 9 pages, 8 figures, 4 tables, to be published by Phys. Rev.

A new experiment for the determination of the 18F(p,alpha) reaction rate at nova temperatures

The 18F(p,alpha) reaction was recognized as one of the most important for gamma ray astronomy in novae as it governs the early 511 keV emission. However, its rate remains largely uncertain at nova temperatures. A direct measurement of the cross section over the full range of nova energies is impossible because of its vanishing value at low energy and of the short 18F lifetime. Therefore, in order to better constrain this reaction rate, we have performed an indirect experiment taking advantage of the availability of a high purity and intense radioactive 18F beam at the Louvain La Neuve RIB facility. We present here the first results of the data analysis and discuss the consequences.Comment: Contribution to the Classical Novae Explosions conference, Sitges, Spain, 20-24 May 2002, 5 pages, 3 figure

Hydrogen Burning of 17-O in Classical Novae

We report on the observation of a previously unknown resonance at E=194.1+/-0.6 keV (lab) in the 17-O(p,alpha)14-N reaction, with a measured resonance strength omega_gamma(p,alpha)=1.6+/-0.2 meV. We studied in the same experiment the 17-O(p,gamma)18-F reaction by an activation method and the resonance-strength ratio was found to be omega_gamma(p,alpha)/omega_gamma(p,gamma)=470+/-50. The corresponding excitation energy in the 18-F compound nucleus was determined to be 5789.8+/-0.3 keV by gamma-ray measurements using the 14-N(alpha,gamma)18-F reaction. These new resonance properties have important consequences for 17-O nucleosynthesis and gamma-ray astronomy of classical novae.Comment: 4 pages, 4 figures. Accepted for publication in Physical Review Letter

Cross sections relevant to gamma-ray line emission in solar flares:3^3He-induced reactions on 16^{16}O nuclei

Gamma-ray production cross sections have been measured for gamma-ray lines copiously emitted in the $^3$He bombardment of $^{16}$O nuclei: the 937, 1042 and 1081 keV lines of $^{18}$F and the 1887 keV line of $^{18}$Ne. Four Ge detectors with BGO shielding for Compton suppression were used to measure the angular distributions of the gamma-rays. The excitation functions have been obtained for $^3$He bombarding energies from 3.7 to 36 MeV. Total cross sections are tabulated for calculations relevant to gamma-ray astronomy. The importance of these lines as diagnosis for the presence and properties of accelerated $^3$He in solar flares is discussed in light of the measured cross sections.Comment: Phys. Rev. C68 (2003) 0258XX, in pres

Gamma ray production cross sections in proton induced reactions on natural Mg, Si and Fe targets over the proton energy range 30 up to 66 MeV

Gamma-ray excitation functions have been measured for 30, 42, 54 and 66 MeV proton beams accelerated onto C + O (Mylar), Mg, Si, and Fe targets of astrophysical interest at the separate-sector cyclotron of iThemba LABS in Somerset West (Cape Town, South Africa). A large solid angle, high energy resolution detection system of the Eurogam type was used to record Gamma-ray energy spectra. Derived preliminary results of Gamma-ray line production cross sections for the Mg, Si and Fe target nuclei are reported and discussed. The current cross section data for known, intense Gamma-ray lines from these nuclei consistently extend to higher proton energies previous experimental data measured up to Ep ~ 25 MeV at the Orsay and Washington tandem accelerators. Data for new Gamma-ray lines observed for the first time in this work are also reported.Comment: 11 pages, 6 figures. IOP Institute of Physics Conference Nuclear Physics in Astrophysics VII, 28th EPF Nuclear Physics Divisional Conference, May 18-22 2015, York, U

D(18F,pa)15N reaction applied to nova gamma-ray emission

The 18F(p,alpha)15O reaction is recognized to be one of the most important reactions for nova gamma-ray astronomy as it governs the early E <= 511keV gamma emission. However in the nova temperature regime, its rate remains largely uncertain due to unknown low-energy resonance strengths. We report here the measurement of the D(18F,p)19F(alpha)15N one-nucleon transfer reaction, induced by a 14 MeV 18F radioactive beam impinging on a CD2 target; outgoing protons and 15N (or alpha-particles) were detected in coincidence in two silicon strip detectors. A DWBA analysis of the data resulted in new limits to the contribution of low-energy resonances to the rate of the 18F(p,alpha)15O reaction.Comment: Rapid Communication to appear in Phys. Rev. C., 4 pages and 4 figure

A runaway Wolf-Rayet star as the origin of 26-Al in the early solar system

Establishing the origin of the short-lived radionuclide (SLR) 26-Al, which was present in refractory inclusions in primitive meteorites, has profound implications for the astrophysical context of solar system formation. Recent observations that 26-Al was homogeneously distributed in the inner solar system prove that this SLR has a stellar origin. In this Letter, we address the issue of the incorporation of hot 26-Al-rich stellar ejecta into the cold protosolar nebula. We first show that the 26-Al atoms produced by a population of massive stars in an OB association cannot be injected into protostellar cores with enough efficiency. We then show that this SLR likely originated in a Wolf-Rayet star that escaped from its parent cluster and interacted with a neighboring molecular cloud. The explosion of this runaway star as a supernova probably triggered the formation of the solar system. This scenario also accounts for the meteoritic abundance of 41-Ca

Shape of the 4.438 MeV γ\gamma-ray line of 12^{12}C from proton and α\alpha-particle induced reactions on 12^{12}C and 16^{16}O

We calculated in detail the angular distribution of gamma-rays and the resulting shape of the gamma-ray line produced by the nuclear deexcitation of the 4.439 MeV state of ^12C following proton and alpha-particle interactions with ^12C and ^16O in the energy range from threshold to 100 MeV per nucleon, making use of available experimental data. In the proton energy range from 8.6 to 20 MeV, the extensive data set of a recent accelerator experiment on gamma-ray line shapes and angular distributions was used to deduce parameterizations for the gamma-ray emission of the 2^+, 4.439 MeV state of ^12C following inelastic proton scattering off ^12C and proton induced spallation of ^16O. At higher proton energies and for alpha-particle induced reactions, optical model calculations were the main source to obtain the needed reaction parameters for the calculation of gamma-ray line shapes and angular distributions. Line shapes are predicted for various interaction scenarios of accelerated protons and alpha-particles in solar flares