Trapped-Ion Technique for Measuring the Nuclear Charge Radii of Highly Charged Radioactive Isotopes

We present the first measurement to isolate the variation of nuclear effects in the x-ray transitions of few-electron heavy ions. Using a novel technique to produce and trap radioactive ions we measured the energy difference between 2s1/2-2p3/2 transitions in Li-, Be-, B-, and C-like ²³³U and ²³⁸U. We show that because of the simplified atomic structure of few-electron ions the data are readily interpreted in terms of the variation in the mean nuclear radius. A value δ〈r²〉233,2380ex0ex=0ex0ex-0.457±0.043 fm² is found, which lies between earlier measurements based on different techniques.