Towards High-Precision Mass Measurements at the N=126 Factory
Bibliographic record
Abstract
Precise atomic mass measurements are essential for a wide range of nuclear physics studies. Particularly, it is important for studying the rapid neutron capture process (r-process), which is responsible for producing almost half of the heavy elements in the universe. The Canadian Penning Trap (CPT) mass spectrometer at Argonne National Laboratory has been central to these endeavors by measuring radioactive ion masses with high precision through their cyclotron frequency determinations. This dissertation covers the CPT’s transition from the CARIBU facility towards the new N=126 Factory. During its final two years at the CARIBU facility, a series of measurements were conducted including mass measurements of rhodium isotopes (108, 110, 112, 114, 116, 118Rh) and lanthanide isotopes (149La, 149Ce, 149Pr) presented in this work. For rhodium isotopes, the masses of both the ground state and an isomeric state were determined for 108, 110, 112, 114, 116Rh, and a new possible isomeric state of 114 Rh was observed. Additionally, the measurements of 149La, 149Ce and 149Pr significantly reduced the uncertainties compared to the Atomic Mass Evaluation (AME) values, which are all based on beta-endpoint measurements of Q_beta values, known for their low precision and possible inaccuracy. This work also presents a comprehensive study of systematic effects observed using the Phase-Imaging Ion-Cyclotron-Resonance (PI-ICR) technique. The measurement procedures and data analysis methods, incorporating the impact of systematic effects, are summarized. By the end of April 2023, the CPT was decommissioned and removed from the CARIBU facility in preparation for its installation at the N=126 Factory, a new radioactive beam (RIB) facility at Argonne National Laboratory (ANL). The N=126 Factory is designed to produce very neutron-rich isotopes, particularly around the N=126 closed shell for the study of the last r-process abundance peak. This dissertation presents the simulation, design, and production yield calculations for the new facility. A key component of the N=126 Factory, the Notre Dame Multi-Reflection Time-of-Flight (ND MR-TOF) spectrometer, will be employed to remove isobaric contaminants accompanying the isotopes of interest. The commissioning and simulation studies of the MR-TOF are presented. Once the N=126 Factory is fully operational, the first planned measurements at the N=126 Factory will target unknown masses of the isotopes of Au (Z=79), Pt (Z=78), Ir (Z=77), and Os (Z=76) near the N=126 shell closure. These measurements will provide vital insights into the robustness of the shell closure and serve as a key test for theoretical mass models.
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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 | 0.013 | 0.009 |
| Meta-epidemiology (narrow) | 0.001 | 0.001 |
| Meta-epidemiology (broad) | 0.001 | 0.001 |
| Bibliometrics | 0.002 | 0.002 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.003 | 0.003 |
| Open science | 0.003 | 0.003 |
| Research integrity | 0.002 | 0.003 |
| Insufficient payload (model declined to judge) | 0.004 | 0.004 |
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".