Simultaneous observation of Lyman- $α$ and Balmer- $β$ transitions in hydrogenic iron, ${Fe}^{25 +}$ : A novel technique for $1 s$ Lamb-shift measurement

The

n = 2

n = 4

Balmer-

β

transitions in hydrogenic

{Fe}^{25 +}

have been observed in the first order of Bragg diffraction in a beam-foil light source. Simultaneous observation of the

1 s - 2 p

Lyman-

α

transitions from the same source in the fourth diffraction order leads to a new method for the measurement of the

1 s

ground-state Lamb shift which is less sensitive to uncertainties arising from Doppler shifts than previous work. With the use of the Balmer-

β

transitions for calibration, the Lyman-

α

wavelengths are, for the

1 s {}^{2}S_{\frac{1}{2}} - 2 p {}^{2}P_{\frac{3}{2}}

transition, 1.778 15±0.000 19 Å, and for the

1 s {}^{2}S_{\frac{1}{2}} - 2 p {}^{2}P_{\frac{1}{2}}

transition, 1.783 64±0.000 19 Å. Values of the Lamb-shift contributions to the

1 s - 2 p

transitions, and the

2 p_{\frac{1}{2}, \frac{3}{2}}

fine structure, are extracted.

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Simultaneous observation of Lyman-α and Balmer-β transitions in hydrogenic iron, Fe25+: A novel technique for 1s Lamb-shift measurement