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 distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.005 | 0.002 |
| Meta-epidemiology (narrow) | 0.004 | 0.005 |
| Meta-epidemiology (broad) | 0.002 | 0.006 |
| Bibliometrics | 0.001 | 0.003 |
| Science and technology studies | 0.005 | 0.005 |
| Scholarly communication | 0.004 | 0.005 |
| Open science | 0.008 | 0.008 |
| Research integrity | 0.004 | 0.007 |
| Insufficient payload (model declined to judge) | 0.016 | 0.010 |
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; both teacher heads agree on what is shown here.
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".