Examination of how properties of a fissioning system impact isomeric yield ratios of the fragments
Bibliographic record
Abstract
The population of isomeric states in the prompt decay of fission fragments---so-called isomeric yield ratios (IYRs)---is known to be sensitive to the angular momentum $J$ that the fragment emerged with, and may therefore contain valuable information on the mechanism behind the fission process. In this work, we investigate how changes in the fissioning system impact the measured IYRs of fission fragments to learn more about what parameters affect angular momentum generation. To enable this, a new technique for measuring IYRs is first demonstrated. It is based on the time of arrival of discrete $\ensuremath{\gamma}$ rays, and has the advantage that it enables the study of the IYR as a function of properties of the partner nucleus. This technique is used to extract the IYR of $^{134}\mathrm{Te}$, strongly populated in actinide fission, from the three different fissioning systems: $^{232}\mathrm{Th}(n,\mathrm{f}), ^{238}\mathrm{U}(n,\mathrm{f})$, at two different neutron energies, as well as $^{252}\mathrm{Cf}$(sf). The impacts of changing the fissioning system, the compound nuclear excitation energy, the minimum $J$ of the binary partner, and the number of neutrons emitted on the IYR of $^{134}\mathrm{Te}$ are determined. The decay code talys is used in combination with the fission simulation code freya to calculate the primary fragment angular momentum from the IYR. We find that the IYR of $^{134}\mathrm{Te}$ has a slope of $0.004\ifmmode\pm\else\textpm\fi{}0.002$ with increase in compound nucleus (CN) mass. When investigating the impact on the IYR of increased CN excitation energy, we find no change with an energy increase similar to the difference between thermal and fast fission. By varying the mass of the partner fragment emerging with $^{134}\mathrm{Te}$, it is revealed that the IYR of $^{134}\mathrm{Te}$ is independent of the total amount of prompt neutrons emitted from the fragment pair. This indicates that neutrons carry minimal angular momentum away from the fission fragments. Comparisons with the freya$+$talys simulations reveal that the average angular momentum in $^{134}\mathrm{Te}$ following $^{238}\mathrm{U}(n,\mathrm{f})$ is $6.0\ensuremath{\hbar}$. This is not consistent with the value deduced from recent cgmf calculations. Finally, the IYR sensitivity to the angular momentum of the primary fragment is discussed. These results are not only important to help understanding the underlying mechanism in nuclear fission, but can also be used to constrain and benchmark fission models, and are relevant to the $\ensuremath{\gamma}$-ray heating problem of reactors.
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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 | 0.002 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.001 |
| Insufficient payload (model declined to judge) | 0.003 | 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".