An Interstellar Origin for the Beryllium 10 in Calcium‐rich, Aluminum‐rich Inclusions
Bibliographic record
Abstract
Beryllium 10 is a short-lived radionuclide ( t 1/2 = 1.5 Myr) that was incorporated live into calcium-rich, aluminum-rich inclusions (CAIs) at the birth of our solar system. Beryllium 10 is unique among the short-lived radionuclides in that it is formed only by spallation reactions and not by nucleosynthesis, e.g., in a supernova. Recent work by McKeegan, Gounelle, and others has stated that the high initial abundance of 10 Be in CAIs ( 10 Be/ 9 Be ≈ 1 × 10 -3 ) cannot be attributed to galactic cosmic rays (GCRs) and therefore concluded that the spallation reactions must have occurred within the solar nebula itself, because of energetic particles emitted by the early Sun. In this paper we reexamine this conclusion. We calculate the contributions of GCRs to the 10 Be abundance in a molecular cloud core as it collapses to form a protostar and protoplanetary disk. We constrain the flux of protons and 10 Be GCRs in the Sun's molecular cloud core 4.5 Gyr ago. We use numerical magnetohydrodynamic simulations of star formation to model the time evolution of the magnetic field strength and column density of gas in a collapsing cloud core. We account for magnetic focusing and magnetic mirroring and the anisotropic distribution of GCR pitch angles in the cloud core. We calculate the rates at which GCR protons and α-particles induce spallation reactions producing 10 Be atoms, and the rates at which GCR 10 Be nuclei are trapped in the cloud core. Accounting also for the decay of 10 Be over the evolution of the cloud core, we calculate the time-varying 10 Be/ 9 Be ratio. We find that at the time of protostar formation 10 Be/ 9 Be ≈ 1 × 10 -3 , with an uncertainty of about a factor of 3. Spallation reactions account for 20% of the 10 Be in CAIs, while trapped GCR 10 Be nuclei account for the other 80%. The initial abundance of 10 Be in CAIs is therefore entirely attributable to cosmic rays. We discuss the implications of this finding for the origin of other short-lived radionuclides and for the use of 10 Be as a chronometer.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.001 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".