LITHIUM–BERYLLIUM–BORON ISOTOPIC COMPOSITIONS IN METEORITIC HIBONITE: IMPLICATIONS FOR ORIGIN OF ¹⁰ Be AND EARLY SOLAR SYSTEM IRRADIATION

Abstract

ABSTRACTin CV Ca-Al-rich inclusions supports a heterogeneous distribution of 10 Be and its protosolar irradiation origin. We consider two possible irradiation scenarios that could potentially lead to the observed Li-Be-B isotopic compositions in PLACs. Although in situ irradiation of solids with hibonite chemistry seems to provide the simplest explanation, more high quality data will be needed for quantitatively constraining the irradiation history.

Short-Lived Radionuclides and Early Solar System Chronology

“…The significance of this lack of correlation, for both chronology and source of radionuclides, is discussed further in the succeeding text. More PLAC hibonite grains were analyzed by Liu et al (2009) and Liu et al (2010), for which the combined data are consistent with single inferred 10 Be/ 9 Be ratios of (5.3AE 1.0) Â 10 À4 .…”

Beryllium-10 production in gaseous protoplanetary disks and implications for the astrophysical setting of refractory inclusions

“…This expectation would provide an explanation for the lower 10 Be/ 9 Be of FUN CAIs in CV chondrites (MacPherson et al 2003;Wielandt et al 2012) and PLACs in CM chondrites (Liu et al 2010) compared to "'regular"' CAIs. Indeed these CAIs are characterized by nucleosynthetic stable isotopic anomalies (e.g.…”

“…upon the last equilibration) 10 Be/ 9 Be ratios averaging ∼ 6 × 10 −4 in CV chondrite (type A and B) CAIs (Davis and McKeegan 2014), with less than a factor of two spread. Yet systematically lower values around 3 × 10 −4 and 5 × 10 −4 have been found for two CV chondrite FUN CAIs ("Fractionated and Unknown Nuclear effects";MacPherson et al (2003); Wielandt et al (2012)) and platy hibonite crystals (PLAC) in CM chondrites (Liu et al 2009(Liu et al , 2010, respectively, and, conversely, values up to 10 −2 have been found for Isheyevo CAI 411 (Gounelle et al 2013) and more recently, fine-grained group II CV chondrite CAIs (Sossi et al 2017). The overall spread, along with correlated 50 V excesses (also ascribed to spallation) in the latter objects (Sossi et al 2017), is difficult to reconcile with simple 10 Be inheritance from the (galactic cosmic ray-irradiated) protosolar cloud (Desch et al 2004), which should be largely homogeneous, and argues in favor of local production in the disk following flares from the young Sun (Gounelle et al , 2006(Gounelle et al , 2013Sossi et al 2017), such as those manifested in X-rays by present-day protostars (e.g.…”

Heterogeneous distribution of 26Al at the birth of the solar system: Evidence from refractory grains and inclusions

“…A local, solar energetic particle irradiation origin of 26 Al received some support after discovery in CAIs of shortlived radionuclides, which could be produced only by irradiation-10 Be , and, possibly, 7 Be ). However, the difficulties in explaining the apparently uniform distribution of 26 Al with the inferred initial 26 Al ⁄ 27 Al ratio of approximately 5.2 · 10 )5 (e.g., Jacobsen et al 2008) and the lack of correlation between 26 Al ⁄ 27 Al ratio and 10 Be ⁄ 9 Be ratio in CAIs MacPherson et al 2003;Liu et al 2010;Wielandt et al 2012) make the irradiation model for the origin of 26 Al doubtful. Recently, Duprat and Tatischeff (2007) showed that the maximum amount of irradiation-induced 26 Al can only account for a homogeneous distribution of this radionuclide over a rocky reservoir of only 2-3 Earth's masses (not over the minimum mass solar nebula of 0.01 solar mass, Weidenschilling [1977]) and that the well-defined canonical 26 Al ⁄ 27 Al ratio observed in CAIs is probably incompatible with an in situ production in the embedded phase of the Sun.…”