The calculation changed the lifetimes
An analysis of earlier chromium-54 data says the lifetimes inferred for its excited states should be raised by 16% to 27%. The study revisits the Doppler-shift attenuation method, or DSAM, using contemporary stopping powers instead of the LSS values used in the original analysis. DSAM combines measured Doppler shifts with stopping-power calculations when inferring lifetimes. The larger revisions generally occurred among shorter lifetimes, where electronic stopping dominated.
The data came from an earlier 10-MeV alpha-induced 51V(alpha,pγ) reaction that produced the 54Cr excited-state measurements. The targets used enriched 51V, with 99.98% enrichment, on tantalum and molybdenum backings. The authors reconstructed and verified the analysis code, switched its stopping-power input to SRIM, and corrected errors in the energy-loss and average-scattering-angle calculations. They report that those corrections had a negligible effect on the lifetimes.
For the measured energy range, SRIM electronic stopping powers were about 60% of the LSS values, while the nuclear stopping powers agreed more closely. Electronic stopping dominated at first, but nuclear stopping became dominant after about 10 femtoseconds. With those inputs, the reanalysis reported lifetime increases of 16% to 27%, with the larger changes generally found among shorter lifetimes.
The authors compared the tantalum- and molybdenum-backed results and found that their lifetimes generally agreed within the uncertainties. They combined the results using a weighted average that handled asymmetric errors. The molybdenum-backed run, however, was cut short by an accelerator failure, and the paper says uncertainties remained large for both measurements.
The revised numbers change the model comparison
The revised lifetimes also changed the comparison with nuclear models. The shell-model calculations used NuShellX in the full fp-shell basis for both protons and neutrons, with the GXPF1A interaction. For reduced electric-quadrupole, or E2, transition rates through the first 6+ state, the paper reported better agreement when the model parameters called effective charges were set to 1.3 for protons and 0.45 for neutrons, rather than the standard values of 1.5 and 0.5. The authors caution that the available 54Cr and 58Fe cases are not enough to draw firm conclusions about effective charges for GXPF1A.
The results also bear on two tentative level assignments. The 3.786-MeV level, currently labeled (4)+, may instead be the 5+1 state, the paper argues. Its lifetime is greater than 3.7 ps, and among the theoretical states between 3.0 and 4.5 MeV, 5+1 is the one described as having a lifetime that long. The assignment remains a proposal and requires spectroscopic confirmation.
The 4.043-MeV level is also unsettled. The paper tentatively proposes a (6)+ or 6+2 assignment because its branching ratios and lifetime agree with the shell model under that interpretation. But the DCO data point in the opposite direction, leaving the assignment dependent on further spectroscopy.
What remains open
The work is a reanalysis of existing data, so its conclusions depend on the earlier Doppler-shift measurements, the reconstructed code and the stopping-power prescriptions used in the calculation. The paper also notes that the molybdenum-backed run was curtailed by an accelerator failure and that uncertainties remained large for both measurements. It says incorrect detector opening angles had been transcribed into earlier references, but that this did not affect the data analysis because detector dimensions and distances were used to determine the acceptance angles.
The authors recommend that the revised lifetimes replace the earlier values in future nuclear-data evaluations. They do not present the two level assignments as final, and both require additional spectroscopic confirmation. The document is an arXiv version 2 preprint dated 16 September 2026. The work was supported in part by Australian Research Council grants DP210101201 and DP250100400.
Paper data and sources
Original title: Doppler-shift attenuation method (DSAM) lifetimes in $^{54}$Cr - a re-evaluation
Authors: Andrew E. Stuchbery
Journal/Repository: arXiv
Status: Preprint, not yet peer-reviewed
First online: 2026-08-28
DOI: Not available
Original paper · Full text