Deexcitation nuclear gamma-ray line emission from low-energy cosmic rays in the inner Galaxy

Recent observations of high ionization rates of molecular hydrogen in diffuse interstellar clouds point to a distinct low-energy cosmic-ray component. Supposing that this component is made of nuclei, two models for the origin of such particles are explored and low-energy cosmic-ray spectra are calculated which, added to the standard cosmic ray spectra, produce the observed ionization rates. The clearest evidence of the presence of such low-energy nuclei between a few MeV per nucleon and several hundred MeV per nucleon in the interstellar medium would be a detection of nuclear \gamma-ray line emission in the range E_ 0.1 - 10 MeV, which is strongly produced in their collisions with the interstellar gas and dust. Using a recent \gamma-ray cross section compilation for nuclear collisions, \gamma-ray line emission spectra are calculated alongside with the high-energy \gamma-ray emission due to {\pi} 0 decay, the latter providing normalization of the absolute fluxes by comparison with Fermi-LAT observations of the diffuse emission above E \gamma = 0.1 GeV. Our predicted fluxes of strong nuclear \gamma-ray lines from the inner Galaxy are well below the detection sensitivies of INTEGRAL, but a detection, especially of the 4.4-MeV line, seems possible with new-generation \gamma-ray telescopes based on available technology. We predict also strong \gamma-ray continuum emission in the 1-8 MeV range, which in a large part of our model space for low-energy cosmic rays exceeds considerably estimated instrument sensitivities of future telescopes.Comment: 22 pages, 7 figures, accepted for publication in ApJ; figures 6 and 7 replace

Measurement and analysis of nuclear γ-ray production cross sections in proton interactions with Mg, Si, and Fe nuclei abundant in astrophysical sites over the incident energy range E = 30–66 MeV

The modeling of nuclear γ -ray line emission induced by highly accelerated particles in astrophysical sites (e.g., solar flares, the gas and dust in the inner galaxy) and the comparison with observed emissions from these sites needs a comprehensive database of related production cross sections. The most important reactions of protons and α particles are those with abundant target elements like C, O, N, Ne, Mg, Si, and Fe at projectile energies extending from the reaction threshold to a few hundred MeV per nucleon. In this work, we have measured γ -ray production cross section excitation functions for 30, 42, 54, and 66 MeV proton beams accelerated onto nat C , C + O (Mylar), nat Mg , nat Si , and 56 Fe targets of astrophysical interest at the Separated Sector Cyclotron (SSC) of iThemba LABS (near Cape Town, South Africa). The AFRODITE array equipped with eight Compton suppressed high-purity (HPGe) clover detectors was used to record γ -ray line energy spectra. For known, intense lines previously reported experimental data measured up to E p ≃ 25 MeV at the Washington and Orsay tandem accelerators were thus extended to higher proton energies. Our experimental data for the last three targets are reported here and discussed with respect to previous data and to the Murphy et al. compilation [Astrophys. J. Suppl. Ser. 183, 142 (2009)]

Nuclear γ-ray line emission induced by energetic ions in solar flares and by galactic cosmic rays

International audienceThe γ-ray spectra ol the strongest solar flares often show a broad and complex structure in the 0.1-10 MeV region sitting on a bremsstrahlung continuum. This structure is composed of several outstanding narrow lines and of thousands of unresolved narrow and broad lines forming a quasi-continuum. The major part of this emission is due to prompt deexcitation lines following nuclear interactions of accelerated light and heavy ions with the atomic nuclei composing the solar atmosphere. A similar emission is expected from interactions of galactic cosmic rays with the interstellar gas and dust. Experimental nuclear reaction studies coupled with extensive calculations have been done in the last one and a half decade at Orsay for the modelisation of this γ-ray emission. After a description of the nuclear reaction studies the analysis of one solar flare spectrum and predictions for the emission from the inner Galaxy will be presented

gamma ray emission in alpha particle interactions with C, Mg, Si, and Fe at Ealpa 50 90 MeV

Nuclear deexcitation lines are regularly observed in the amp; 947; ray emission spectra of strong solar flares. The most prominent lines are produced by interactions of protons and amp; 945; particles, accelerated up to hundreds of MeV, with abundant nuclei of the solar atmosphere. Analysis and interpretation of these lines, which carry valuable information on the solar flare properties, need cross section data for the amp; 947; ray line emission in these interactions for a wide particle energy range. To this purpose, we measured the amp; 947; ray emission in interactions of amp; 945; particle beams of E amp; 945; 50 90 MeV with target foils of C, Mg, Si, and Fe at the center for proton therapy of the Helmholtz Zentrum Berlin. Setups of three high purity Ge detectors and one LaBr3 Ce detector have been employed to detect the amp; 947; rays in two experiment campaigns. Relatively large distances of the detectors from the target and pulsed beams with sub ns wide pulses allowed the separation of beam induced prompt amp; 947; ray emission from the targets from other amp; 947; rays and neutron induced background. amp; 947; ray production cross sections for about 60 deexcitation lines from excited target nuclei or reaction products have been determined. For the strongest deexcitation lines from the major target isotopes, 12C, 24Mg, 28Si, 56Fe, there are now measured cross section data from reaction threshold to E amp; 945; 90 MeV that can be directly used for astrophysical applications like solar flares. Comparison of the results with a cross section compilation for strong amp; 947; ray lines in solar flare emissions and the predictions of the talys nuclear reaction code were done. They underline the importance of cross section determinations at accelerator laboratories for the establishment of an accurate cross section data base in a wide projectile energy rang

γ\gamma-ray emission in α\alpha-particle interactions with C, Mg, Si, and Fe at Eα=50–90{E}_{\alpha}=50\text{--}90 MeV

International audienceNuclear deexcitation lines are regularly observed in the γ-ray emission spectra of strong solar flares. The most prominent lines are produced by interactions of protons and α particles, accelerated up to hundreds of MeV, with abundant nuclei of the solar atmosphere. Analysis and interpretation of these lines, which carry valuable information on the solar flare properties, need cross-section data for the γ-ray line emission in these interactions for a wide particle energy range. To this purpose, we measured the γ-ray emission in interactions of α-particle beams of Eα=50–90 MeV with target foils of C, Mg, Si, and Fe at the center for proton therapy of the Helmholtz-Zentrum Berlin. Setups of three high-purity Ge detectors and one LaBr3:Ce detector have been employed to detect the γ rays in two experiment campaigns. Relatively large distances of the detectors from the target and pulsed beams with sub-ns-wide pulses allowed the separation of beam-induced prompt γ-ray emission from the targets from other γ rays and neutron-induced background. γ-ray production cross sections for about 60 deexcitation lines from excited target nuclei or reaction products have been determined. For the strongest deexcitation lines from the major target isotopes, C12, Mg24, Si28, Fe56, there are now measured cross-section data from reaction threshold to Eα=90 MeV that can be directly used for astrophysical applications like solar flares. Comparison of the results with a cross-section compilation for strong γ-ray lines in solar flare emissions and the predictions of the talys nuclear reaction code were done. They underline the importance of cross-section determinations at accelerator laboratories for the establishment of an accurate cross-section data base in a wide projectile energy range

Gamma-ray emission in alpha-particle reactions with C, Mg, Si, Fe

International audienceCross sections for the strongest gamma-ray emission lines produced in alpha-particle reactions with C, Mg, Si, Fe have been measured in the range E_alpha = 50 - 90 MeV at the center for proton therapy at the Helmholtz-Zentrum Berlin. Data for more than 60 different gamma-ray lines were determined, with particular efforts for lines that are in cross section compilations/evaluations with astrophysical purpose, and where data exist at lower projectile energies. The data are compared with predictions of a modern nuclear reaction code and cross-section curves of the latest evaluation for gamma-ray line emission in accelerated-particle interactions in solar flares

γ\gamma-ray production by proton and α\alpha-particle induced reactions on 12^{12}C, 16^{16}O, 24^{24}Mg, and Fe

$\gamma$-ray production cross sections for proton and $\alpha$-particle interactions with $^{12}$C, $^{16}$O, $^{24}$Mg, and Fe have been measured in the energy range 5–25 MeV with proton beams and 5–40 MeV with -particle beams. Isotopically pure foils of $^{24}$Mg and foils of natural isotopical composition of C, MgO, and Fe have been used. $\gamma$-ray angular distributions were obtained with five high-purity Ge detectors with bismuth germanate Compton shields placed at angles of 45° to 157.5°. Cross sections for more than 50 different $\gamma$-ray transitions were extracted, and for many of them no data have been published before. Comparison of present data with data available in the literature shows mostly good to excellent agreement. In addition to the production cross sections, high-statistics, low-background line shapes of the 4.438 MeV $^{12}$C ray from inelastic scattering off $^{12}$C and spallation of $^{16}$O were obtained. Comparison with nuclear reaction calculations shows that these data place interesting constraints on nuclear reaction models