Penning-Trap Mass Measurement of Helium-4

Abstract

Light-ion trap (LIONTRAP), a high-precision Penning-trap mass spectrometer, was used to determine the atomic mass of $^{4}\mathrm{He}$. Here, we report a 12 parts-per-trillion measurement of the mass of a $^{4}{\mathrm{He}}^{2+}$ ion, $m(^{4}{\mathrm{He}}^{2+})=4.001\text{ }506\text{ }179\text{ }651(48)\text{ }\text{ }\mathrm{u}$. From this, the atomic mass of the neutral atom can be determined without loss of precision: $m(^{4}\mathrm{He})=4.002\text{ }603\text{ }254\text{ }653(48)\text{ }\text{ }\mathrm{u}$. This result is slightly more precise than the current CODATA18 literature value but deviates by 6.6 standard deviations.

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