Precision calculation of ^4,6,8He isotope shifts

Standard perturbation theory is employed to calculate the mass shifts of the 2 ¹S₀–2 ³S₁ and 2 ³S₁–2 ³P_J transitions for ^4,6,8He. High-precision results are obtained for the mass shifts in the isotope pairs ⁶He–⁴He and ⁸He–⁴He, with uncertainties below 1 part per million (ppm). Our analysis provides a complete set of isotope-shift results and systematically examines their sensitivity to nuclear charge-radius differences. Once experimental measurements reach a precision comparable to that of the calculated mass shifts, the squared differences of nuclear charge radii can be determined with an accuracy of approximately 0.4%–0.6%, representing an order-of-magnitude improvement over current values.