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Yields of 7Be, 10Be, 26Al, 36Cl, 41Ca, and 53Mn for a chondritic chemistry and the spectral parameters p = 4 and 3He/1H = 0.3

圖片來源: Gounelle et al.

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Yields of 7Be, 10Be, 26Al, 36Cl, 41Ca, and 53Mn for a chondritic chemistry and the spectral parameters p = 4 and 3He/1H = 0.3

Yields of ⁷Be, ¹⁰Be, ²⁶Al, ³⁶Cl, ⁴¹Ca, and ⁵³Mn for a chondritic chemistry and the spectral parameters p = 4 and ³He/¹H = 0.3. The yields are normalized to the experimental values, corresponding to the horizontal dotted line. For ⁴¹Ca, we have adopted the initial value ⁴¹Ca/⁴⁰Ca = 3.9×10-7, more likely than the canonical ratio.

By modeling the abundance of radioactive elements found in calcium-aluminum-rich inclusions (CAIs) of meteorites, the origin and the evolution of the solar nebula is gradually being unraveled. Two explanations exist for the short-lived radionuclides (half-life T_1/2 < 5 Myr) present in the solar system when CAIs first formed. They originated either from the ejecta of a supernova or by the in situ irradiation of nebular dust by energetic particles. With a half-life of only 53 days,⁷Be is the key discriminant, since it can only be made by irradiation. Using the same irradiation model developed earlier, the yield of ⁷Be can be calculated. Within model uncertainties associated mainly with nuclear cross sections, the results agree with experimental values. Moreover, if ⁷Be and ¹⁰Be have the same origin, the irradiation time must be short (a few to tens of years), and the proton flux can be constrained as well. The X-wind model provides a natural astrophysical setting that gives the requisite conditions. In the same irradiation environment, ²⁶Al, ³⁶Cl, and ⁵³Mn are also generated at the measured levels within model uncertainties, provided that irradiation occurs under conditions reminiscent of solar impulsive events (steep energy spectra and high ³He abundance). The decoupling of the ²⁶Al and ¹⁰Be observed in some rare CAIs receives a quantitative explanation when rare gradual events (shallow energy spectra and low ³He abundance) are considered. The yields of ⁴¹Ca are compatible with an initial solar system value inferred from the measured initial ⁴¹Ca/⁴⁰Ca ratio and an estimate of the thermal metamorphism time, alleviating the need for two-layer proto-CAIs.