The nuclear charge radius of <sup>13</sup>C.
basic_science · Level V
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- Record sourced from PubMed, PMID 40623998.
- Also identified by DOI 10.1038/s41467-025-60280-9 and PMC identifier 12234786.
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Abstract
The size is a key property of a nucleus. Accurate nuclear radii are extracted from elastic electron scattering, laser spectroscopy, and muonic atom spectroscopy. The results are not always compatible, as the proton-radius puzzle has shown most dramatically. Beyond helium, precision data from muonic and electronic sources are scarce in the light-mass region. The stable isotopes of carbon are an exception. We present a laser spectroscopic measurement of the root-mean-square (rms) charge radius of <sup>13</sup>C and compare this with ab initio nuclear structure calculations. Measuring all hyperfine components of the 2 <sup>3</sup>S <math xmlns="http://www.w3.org/1998/Math/MathML"><mo>→</mo></math> 2 <sup>3</sup>P fine-structure triplet in <sup>13</sup>C<sup>4+</sup> ions referenced to a frequency comb allows us to determine its center-of-gravity with accuracy better than 2 MHz although second-order hyperfine-structure effects shift individual lines by several GHz. We improved the uncertainty of R<sub>c</sub>(<sup>13</sup>C) determined with electrons by a factor of 6 and found a 3σ discrepancy with the muonic atom result of similar accuracy.