Measurement of the Mg-24 (He-3, p) Al-26 cross section: Implication for Al-26 production in the early solar system
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15 pages
Published in:
- Phys.Rev.C 78 (2008) 044613
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Abstract: (APS)
The nucleosynthetic origin of Al26 (t1/2=0.72 Myr) in the early solar system is still an open question. Several models predict that short-lived radionuclides could be produced by irradiation of circumsolar material by light charged particles emitted by the young sun. Within some models, most of the Al26 is produced by He3-induced reactions on Mg24. Little experimental data exist on He3 reactions so that irradiation models have had to rely on theoretical cross sections deduced from statistical nuclear reaction codes. We performed a direct measurement of the Al26 production on Mg target by means of γ ray spectroscopy and accelerator mass spectrometry (AMS). The data indicate that the theoretical cross section used in previous approaches was overestimated by a factor of 3. Taking the particle spectra considered in theoretical approaches these data lead to a net reduction of the Al26 production of a factor of 2. We calculated the relative contribution of the different Al26 production channels depending on the irradiation scenario. We show that extremely large particles fluxes would be necessary to reach the canonical 26Al/27Al =5×10−5 in solids that were present in the early solar system. An in situ origin of this important isotopic chronometer by irradiation is unlikely.- 96.10.+i
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