The WMAP satellite, devoted to the observations of the anisotropies of the Cosmic Microwave Background (CMB) radiation, has recently provided a determination of the baryonic density of the Universe ...with unprecedented precision. Using this, Big Bang Nucleosynthesis (BBN) calculations predict a primordial 7Li abundance which is a factor 2-3 higher than that observed in galactic halo dwarf stars. It has been argued that this discrepancy could be resolved if the 7Be(d,p)2alpha reaction rate is around a factor of 100 larger than has previously been considered. We have now studied this reaction, for the first time at energies appropriate to the Big Bang environment, at the CYCLONE radioactive beam facility at Louvain-la-Neuve. The cross section was found to be a factor of 10 smaller than derived from earlier measurements. It is concluded therefore that nuclear uncertainties cannot explain the discrepancy between observed and predicted primordial 7Li abundances, and an alternative astrophysical solution must be investigated.
Phys.Rev.C67:052801,2003 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.
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.
Three calibration campaigns of the spectrometer SPI have been performed
before launch in order to determine the instrument characteristics, such as the
effective detection area, the spectral ...resolution and the angular resolution.
Absolute determination of the effective area has been obtained from simulations
and measurements. At 1 MeV, the effective area is 65 cm^2 for a point source on
the optical axis, the spectral resolution ~2.3 keV. The angular resolution is
better than 2.5 deg and the source separation capability about 1 deg. Some
temperature dependant parameters will require permanent in-flight calibration.
The early E < 511 keV gamma-ray emission from novae depends critically on the 18F(p,a)15O reaction. Unfortunately the reaction rate of the 18F(p,a)15O reaction is still largely uncertain due to the ...unknown strengths of low-lying proton resonances near the 18F+p threshold which play an important role in the nova temperature regime. We report here our last results concerning the study of the d(18F,p)19F(alpha)15N transfer reaction. We show in particular that these two low-lying resonances cannot be neglected. These results are then used to perform a careful study of the remaining uncertainties associated to the 18F(p,a)15O and 18F(p,g)19Ne reaction rates.
Nucl.Phys. A718 (2003) 259-262 The ^18F(p, alpha)^15O reaction is recognized as one of the most important
reaction for nova gamma-ray astronomy as it governs the early =< 511 keV
emission. However, ...its rate remains largely uncertain at nova temperatures due
to unknown low-energy resonance strengths. In order to better constrain this
reaction rate, we have studied the one-nucleon transfer reaction, D(^18F,p
alpha)^15N, at the CRC-RIB facility at Louvain La Neuve.
AIP Conf.Proc. 637 (2003) 420-424 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.
We propose the sequential reaction process \(^{15}\)O(\(p\),\(\gamma)(\beta^{+}\))\(^{16}\)O as a new pathway to bypass of the \(^{15}\)O waiting point. This exotic reaction is found to have a ...surprisingly high cross section, approximately 10\(^{10}\) times higher than the \(^{15}\)O(\(p\),\(\beta^{+}\))\(^{16}\)O. These cross sections were calculated after precise measurements of energies and widths of the proton-unbound \(^{16}\)F low lying states, obtained using the H(\(^{15}\)O,p)\(^{15}\)O reaction. The large \((p,\gamma)(\beta^{+})\) cross section can be understood to arise from the more efficient feeding of the low energy wing of the ground state resonance by the gamma decay. The implications of the new reaction in novae explosions and X-ray bursts are discussed.
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.
Core-collapse supernovae as cosmic ray sources Marcowith, Alexandre; Dwarkadas, Vikram V; Renaud, Matthieu ...
Monthly notices of the Royal Astronomical Society,
10/2018, Volume:
479, Issue:
4
Journal Article
Peer reviewed
Open access
Core-collapse supernovae produce fast shocks which pervade the dense circumstellar medium (CSM) of the stellar progenitor. Cosmic rays (CRs) if accelerated at these shocks can induce the growth of ...electromagnetic fluctuations in the foreshock medium. In this study, using a self-similar description of the shock evolution, we calculate the growth time-scales of CR-driven instabilities. We select a sample of nearby core-collapse radio supernova of type II and Ib/Ic. From radio data, we infer the parameters which enter in the calculation of the instability growth times. We find that extended IIb SNe shocks can trigger fast intra-day instabilities, strong magnetic field amplification, and CR acceleration. In particular, the non-resonant streaming instability can contribute to about 50 percent of the magnetic field intensity deduced from radio data. This results in the acceleration of CRs in the range 1-10 PeV within a few days after the shock breakout. In order to produce strong magnetic field amplification and CR acceleration, a fast shock pervading a dense CSM is necessary. In that aspect, IIn supernovæ are also good candidates. But a detailed modelling of the blast wave dynamics coupled with particle acceleration is mandatory for this class of object before providing any firm conclusions. Finally, we find that the trans-relativistic object SN 2009bb even if it produces more modest magnetic field amplification can accelerate CRs up to 2-3 PeV within 20 d after the outburst.
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