Measurement of the Lamb shift in n = 2 to n = 1 transitions of hydrogen-like and helium-like uranium.
Lupton, James Harold
1994
Abstract
Precision experimental tests in high Z atoms have important implications for current theories of quantum electrodynamics (QED). Of particular interest are tests in hydrogen-like and helium-like ions, where the energy levels can be measured to high precision, probing QED effects without complications from multi-electron interactions. Hydrogen-like and helium-like uranium are the current limit of high field atomic measurements on few electron systems. I report a measurement of the $2p\sb{3/2}$-$1s\sb{1/2}$ transition in hydrogen-like uranium. I have measured 102, 130 $\pm$ 87eV statistical, $\pm$36eV systematic uncertainty for this transition energy. The measurement is in agreement with theoretical calculations which predict 102,180(1)eV. Simultaneously, I measure the ($1s2p)\sp1 P\sb1$-$(1s\sp2)\sp1S\sb0$ transition in helium-like uranium as an unresolved doublet. This allows a relative measurement to the nearby hydrogen-like transition allowing a direct probe of the electron-electron correlations in the helium-like system. The difference is 1532 $\pm$ 105eV and agrees with the theoretical calculations of 1573(1)eV for the 2$\sp{1}P\sb1$-$1\sp1{S}\sb0$ transition and 1647(1)eV for the 2$\sp{3}P\sb2$-$1\sp1S\sb0$ transition. These measurements were obtained with a Doppler tuned spectrometer, a proven technique at lower Z and lower energies, though new at the stiff x-ray energies ($\sim$100keV) of the n = 2 to n = 1 transitions in hydrogen-like uranium. Our Doppler spectrometer produced a measurement with a systematic uncertainty of $\pm 36$eV. Our measurement is competitive to better than a factor of two with current measurements using proven but limited techniques at significantly more integrated beam intensity. The Doppler spectrometer is currently capable of a measurement of the ground state Lamb shift in uranium to an accuracy of $\pm2.5eV$ systematic uncertainty which would be competitive with the current theoretical uncertainties. The Doppler spectrometer beam velocity systematic and alignment systematics can be eliminated with proven experimental techniques. This is in marked contrast with other measurements of the 1s uranium Lamb shift made with germanium detectors which are limited by its fundamental line width. Predictions of the 2$p\sb{3/2}$-$1s\sb{1/2}$ transition energy are shifted 450eV from the value given by the Dirac equation. This shift, primarily effecting the $1s$ state, is due to quantum electrodynamics (QED) and nuclear size corrections. Together, these comprise the Lamb shift. The Lamb shift in hydrogen-like, high Z ions, is dominated by the QED self energy correction. Measurements in hydrogen-like uranium are singularly important in experimental tests of QED because the vacuum polarization and nuclear size corrections can be measured in other high Z systems but the 353eV QED electron self energy shift is unique to the ground state of hydrogen-like uranium.Other Identifiers
(UMI)AAI9423254
Subjects
Physics, Nuclear Physics, Atomic
Types
Thesis
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