DEPARTMENT OF NUCLEAR PHYSICS - NUCLEAR ENGINEERING - MEDICAL PHYSICS

Abstract :

The first laser spectroscopic determination of the change in the nuclear charge radius for a five-electron system is reported. This is achieved by combining high-accuracy ab initio mass-shift calculations and a high-accuracy measurement of the isotope shift in the $2s^{2}2p{2P}_{1/2}\to 2s^{2}3s{2S}_{1/2}$ ground state transition in boron atoms. Accuracy is increased by orders of magnitude for the stable isotopes $10,11B$ and the results are used to extract their difference in the mean-square charge radius $⟨r_c^2{⟩}^{11}-⟨r_c^2{⟩}^{10}=-0.49\left(12\right){\mathrm{fm}}^2$. The result is qualitatively explained by a possible cluster structure of the boron nuclei and quantitatively used to benchmark new ab initio nuclear structure calculations using the no-core shell model and Green’s function Monte Carlo approaches. These results are the foundation for a laser spectroscopic determination of the charge radius of the proton-halo candidate $8B$.

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