Strong one-neutron emission from two-neutron unbound states in <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mi>β</mml:mi></mml:math> decays of the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mi>r</mml:mi></mml:math>-process nuclei <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mmultiscripts><mml:mi mathvariant="normal">Ga</mml:mi><mml:mprescripts/><mml:none/><mml:mrow><mml:mn>86</mml:mn><mml:mo>,</mml:mo><mml:mn>87</mml:mn></mml:mrow></mml:mmultiscripts></mml:math>
Bibliographic record
Abstract
$\ensuremath{\beta}$-delayed one-neutron and two-neutron branching ratios $({P}_{1n}$ and ${P}_{2n})$ have been measured in the decay of $A=84$ to 87 Ga isotopes at the Radioactive-Isotope Beam Factory (RIBF) at the RIKEN Nishina Center using a high-efficiency array of $^{3}\mathrm{He}$ neutron counters (BRIKEN). Two-neutron emission was observed in the decay of $^{84,85,87}\mathrm{Ga}$ for the first time and the branching ratios were measured to be ${P}_{2n}=1.6(2)%,1.3(2)%$, and $10.2{(28)}_{\mathrm{stat}}{(5)}_{\mathrm{sys}}%$, respectively. One-neutron branching ratio of $^{87}\mathrm{Ga}\phantom{\rule{4pt}{0ex}}({P}_{1n}=81{(9)}_{\mathrm{stat}}{(8)}_{\mathrm{sys}}%)$ and half-life of 29(4) ms were measured for the first time. The branching ratios of $^{86}\mathrm{Ga}$ were also measured to be ${P}_{1n}=74{(2)}_{\mathrm{stat}}{(8)}_{\mathrm{sys}}%$ and $16.2{(9)}_{\mathrm{stat}}{(6)}_{\mathrm{sys}}%$ with better precision than a previous study. The observation that ${P}_{1n}>{P}_{2n}$ for both $^{86,87}\mathrm{Ga}$ was unexpected and is interpreted as a signature of dominating one-neutron emission from the two-neutron unbound excited states in $^{86,87}\mathrm{Ge}$. In order to interpret the experimental results, shell-model and Hauser-Feshbach statistical model calculations of delayed particle and $\ensuremath{\gamma}$-ray emission probabilities were performed. This model framework reproduces the experimental results. The shell model alone predicts ${P}_{2n}$ significantly larger than ${P}_{1n}$ for the $^{87}\mathrm{Ga}$ decay, and it is necessary to invoke a statistical description to successfully explain the observation that ${P}_{1n}>{P}_{2n}$. Our new results demonstrate the relevance and importance of a statistical description of neutron emission for the prediction of the decay properties of multineutron emitters and that it must be included in the $r$-process modeling.
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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 | 0.001 | 0.001 |
| Meta-epidemiology (narrow) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.001 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.002 | 0.001 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.001 | 0.002 |
| Insufficient payload (model declined to judge) | 0.024 | 0.005 |
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".