Isobaric multiplet mass equation in the<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mi>A</mml:mi><mml:mo>=</mml:mo><mml:mn>31</mml:mn><mml:mo>,</mml:mo><mml:mspace width="0.16em"/><mml:mi>T</mml:mi><mml:mo>=</mml:mo><mml:mn>3</mml:mn><mml:mo>/</mml:mo><mml:mn>2</mml:mn></mml:mrow></mml:math>quartets
Bibliographic record
Abstract
Background: The observed mass excesses of analog nuclear states with the same mass number $A$ and isospin $T$ can be used to test the isobaric multiplet mass equation (IMME), which has, in most cases, been validated to a high degree of precision. A recent measurement [Kankainen et al., Phys. Rev. C 93, 041304(R) (2016)] of the ground-state mass of $^{31}\mathrm{Cl}$ led to a substantial breakdown of the IMME for the lowest $A=31,\phantom{\rule{0.16em}{0ex}}T=3/2$ quartet. The second-lowest $A=31,\phantom{\rule{0.16em}{0ex}}T=3/2$ quartet is not complete, due to uncertainties associated with the identity of the $^{31}\mathrm{S}$ member state.Purpose: Our goal is to populate the two lowest $T=3/2$ states in $^{31}\mathrm{S}$ and use the data to investigate the influence of isospin mixing on tests of the IMME in the two lowest $A=31,\phantom{\rule{0.16em}{0ex}}T=3/2$ quartets.Methods: Using a fast $^{31}\mathrm{Cl}$ beam implanted into a plastic scintillator and a high-purity Ge $\ensuremath{\gamma}$-ray detection array, $\ensuremath{\gamma}$ rays from the $^{31}\mathrm{Cl}(\ensuremath{\beta}\ensuremath{\gamma})^{31}\mathrm{S}$ sequence were measured. Shell-model calculations using USDB and the recently-developed USDE interactions were performed for comparison.Results: Isospin mixing between the $^{31}\mathrm{S}$ isobaric analog state (IAS) at 6279.0(6) keV and a nearby state at 6390.2(7) keV was observed. The second $T=3/2$ state in $^{31}\mathrm{S}$ was observed at ${E}_{x}=7050.0(8)$ keV. Calculations using both USDB and USDE predict a triplet of isospin-mixed states, including the lowest $T=3/2$ state in $^{31}\mathrm{P}$, mirroring the observed mixing in $^{31}\mathrm{S}$, and two isospin-mixed triplets including the second-lowest $T=3/2$ states in both $^{31}\mathrm{S}$ and $^{31}\mathrm{P}$.Conclusions: Isospin mixing in $^{31}\mathrm{S}$ does not by itself explain the IMME breakdown in the lowest quartet, but it likely points to similar isospin mixing in the mirror nucleus $^{31}\mathrm{P}$, which would result in a perturbation of the $^{31}\mathrm{P}$ IAS energy. USDB and USDE calculations both predict candidate $^{31}\mathrm{P}$ states responsible for the mixing in the energy region slightly above ${E}_{x}=6400$ keV. The second quartet has been completed thanks to the identification of the second $^{31}\mathrm{S} T=3/2$ state, and the IMME is validated in this quartet.
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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 | 0.006 | 0.005 |
| Meta-epidemiology (narrow) | 0.004 | 0.005 |
| Meta-epidemiology (broad) | 0.002 | 0.007 |
| Bibliometrics | 0.001 | 0.005 |
| Science and technology studies | 0.005 | 0.005 |
| Scholarly communication | 0.004 | 0.005 |
| Open science | 0.007 | 0.006 |
| Research integrity | 0.004 | 0.006 |
| Insufficient payload (model declined to judge) | 0.055 | 0.014 |
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".