J/ApJ/748/L25 Li-Be-B measurements using SIMS (Wielandt+, 2012)
Evidence for multiple sources of 10Be in the early solar system.
Wielandt D., Nagashima K., Krot A.N., Huss G.R., Ivanova M.A., Bizzarro M.
<Astrophys. J., 748, L25 (2012)>
=2012ApJ...748L..25W 2012ApJ...748L..25W
ADC_Keywords: Abundances ; Atomic physics ; Comets ; Solar system
Keywords: astrochemistry - meteorites, meteors, meteoroids -
nuclear reactions, nucleosynthesis, abundances - protoplanetary disks
Abstract:
Beryllium-10 is a short-lived radionuclide (t1/2=1.4Myr) uniquely
synthesized by spallation reactions and inferred to have been present
when the solar system's oldest solids (calcium-aluminum-rich
inclusions, CAIs) formed. Yet, the astrophysical site of 10Be
nucleosynthesis is uncertain. We report Li-Be-B isotope measurements
of CAIs from CV chondrites, including CAIs that formed with the
canonical 26Al/27Al ratio of ∼5x10-5 (canonical CAIs) and CAIs
with Fractionation and Unidentified Nuclear isotope effects (FUN-CAIs)
characterized by 26Al/27Al ratios much lower than the canonical
value. Our measurements demonstrate the presence of four distinct
fossil 10Be/9Be isochrons, lower in the FUN-CAIs than in the
canonical CAIs, and variable within these classes. Given that FUN-CAI
precursors escaped evaporation-recondensation prior to evaporative
melting, we suggest that the 10Be/9Be ratio recorded by FUN-CAIs
represents a baseline level present in presolar material inherited
from the protosolar molecular cloud, generated via enhanced trapping
of galactic cosmic rays. The higher and possibly variable apparent
10Be/9Be ratios of canonical CAIs reflect additional
spallogenesis, either in the gaseous CAI-forming reservoir, or in the
inclusions themselves: this indicates at least two nucleosynthetic
sources of 10Be in the early solar system. The most promising locale
for 10Be synthesis is close to the proto-Sun during its early
mass-accreting stages, as these are thought to coincide with periods
of intense particle irradiation occurring on timescales significantly
shorter than the formation interval of canonical CAIs.
Description:
We studied four canonical calcium-aluminum-rich inclusions (CAIs)
(31E, E38, E48, and E104) from the reduced CV carbonaceous chondrite
Efremovka and two FUN-CAIs (KT-1 and AXCAI 2771) from the oxidized CV
chondrites NWA 779 and Axtell.
The Li-Be-B measurements were conducted by secondary ion-mass
spectrometry (SIMS) using the University of Hawaii's (UH) Cameca
ims-1280. The primary beam was O- and the mass resolving power was
set to 2400. Measuring sequence and counting times were 6Li (6s),
7Li (2s), and 9Be (2s) in mono-collection mode, while 10B and
11B were measured simultaneously (20s), all on electron multipliers.
Finally, 24Mg was measured with a Faraday for 1.6s. The analyses
were mostly carried out in melilite, with a few analyses in pyroxene,
and avoided any regions that experienced obvious alteration.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 113 59 Li-Be-B isotope and concentration data
table2.dat 75 7 Summary of Be/B and 1/B regressions
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See also:
J/ApJ/743/140 : Abundances (Be,α) in metal-poor stars (Boesgaard+, 2011)
J/A+A/319/593 : [Be] abundances in low-metallicity stars (Molaro+ 1997)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 10 A10 --- CAI The calcium-aluminum-rich inclusion name
12- 17 A6 --- Sample Sample identifier (mel=melilite, px=pyroxene)
19 A1 --- f_Sample [cf] coarse- or fine-grained region
21- 26 F6.2 10-9 Li [0.5/264] The Li abundance (1)
28- 32 F5.2 10-9 e_Li Uncertainty in Li
34- 39 F6.1 10-9 Be [13.5/1677] The Be abundance (1)
41- 45 F5.1 10-9 e_Be Uncertainty in Be
47- 53 F7.2 10-9 B [0.2/5929] The B abundance (1)
55- 60 F6.2 10-9 e_B Uncertainty in B
62- 67 F6.1 --- 9Be/6Li [12/7031] Ratio of 9Be to 6Li abundance
69- 73 F5.1 --- e_9Be/6Li Uncertainty in 9Be/6Li
75- 79 F5.2 --- 7Li/6Li [9/13] Ratio of 7Li to 6Li abundance
81- 84 F4.2 --- e_7Li/6Li Uncertainty in 7Li/6Li
86- 92 F7.2 --- 9Be/11B [0.04/2048] Ratio of 9Be to 11B abundance
94- 99 F6.2 --- e_9Be/11B Uncertainty in 9Be/11B
101-106 F6.4 --- 10B/11B [0.2/0.9] Ratio of 10B to 11B abundance
108-113 F6.4 --- e_10B/11B Uncertainty in 10B/11B
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Note (1): The Li, Be, and B concentrations are calculated based on
secondary ion-mass spectrometry (SIMS) measurements of 7Li, 9Be,
11B and 24Mg and electron-microprobe measurements of Mg-content.
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Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 10 A10 --- CAI The calcium-aluminum-rich inclusion name
12- 13 I2 --- n [5/12] Sample size
15- 18 F4.2 10+4 10Be/9Be [2.75/6.7] Ratio of 10Be to 9Be abundance
20- 23 F4.2 10+4 e_10Be/9Be [0.2/1.4] 10Be/9Be uncertainty
25- 30 F6.4 --- 10B/11B [0.2427/0.2544] Ratio of 10B to 11B
abundance (Be/B regression)
32- 37 F6.4 --- e_10B/11B [0.0006/0.006] 10B/11B uncertainty
39- 42 F4.2 --- MSWD [0.52/1.19] Be/B mean square of weighted
deviation
44- 48 F5.3 10+4 1/B [0.005/4] 1/B slope (1)
50- 55 F6.4 10+4 e_1/B [0.0007/1.8] 1/B uncertainty (1)
57- 62 F6.4 --- 10B/11B2 [0.24/0.273] Ratio of 10B to 11B abundance
(1/B regression) (1)
64- 69 F6.4 --- e_10B/11B2 [0.0006/0.021] 10B/11B2 uncertainty (1)
71- 75 F5.2 --- MSWD2 [0.4/28] 1/B mean square of weighted
deviation (1)
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Note (1): 1/B correlations are based on B concentration measurements in ppm
(parts per million).
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History:
From electronic version of the journal
(End) Greg Schwarz [AAS], Emmanuelle Perret [CDS] 23-Oct-2013