7-radiation Lamb shift

The nonrelativistic estimate of the contribution of B<3> to the Lamb shift was first carried out by Crowell [17] as follows. The interaction of the radiation field with the electron is given by... 

The technique for studying the 2S1/2 2P3/2 transitions in Si13+ by laser spectroscopy is illustrated in Fig. 1. Laser radiation at 734 nm is used to excite ions from the metastable 2S]y2 state to the 2P3/2 state, from which they rapidly decay to the ground state via an allowed electric dipole transition. The resonance is monitored by observing the rate of emission of 2 keV Lyman-a X-ray photons as a function of the laser frequency. The 2S Lamb shift may be deduced from such a measurement of the 2S1/2-ZP3/2 interval because the n = 2 fine structure splitting is more accurately known theoretically. 

Mention should be made here of a new experiment using millimetre radiation (about 256 GHz) to determine the Rydberg constant from the energy spacings of neighbouring circular Rydberg states of atomic hydrogen [43] in a way essentially free of QED and the Lamb shift. 

Herzberg s paper [61] also reports measurements on the He+ line 1640 A (n = 3—2), excited and analysed in the same way as 4686 A. The fine structure is the same as that of Ha enlarged by the factor 16, except that the Lamb shifts are increased by a slightly smaller factor. All seven predicted components can be seen (one with difficulty), in disagreement with the exact coincidences of some of them which one would expect on the Dirac theory. The measured intervals agree with the radiation theory to within the accuracy of measurement ( 0 02 cm 1),... 

Lamb shift - The small energy difference between the and levels in the hydrogen atom, which results from interactions between the electron and the radiation field. 

Lamb shift A small energy difference between two levels ( Si/2 and Pi/2) in the hydrogen spectrum. The shift results from the quantum Interaction between the atomic electron and the electromagnetic radiation. 

The interaction of the Rydberg atoms with the thermal radiation field results in a small shift of the Rydberg levels (Lamb shift), which only amounts to Av/y 2x 10 for rubidium. It has recently been measured with extremely well stabilized lasers [10.56]. In order to eliminate the influence of the thermal radiation field one has to enclose the interaction zone of the laser and atomic beam by walls cooled to a few degrees Kelvin. 

Ah 1/10 Hz = 100 MHz). The measurement yields a Lamb shift of the Is state of about 8170MHz (best value is 8172.876(29) MHz [9.396]), which is in close agreement with the theoretical predictions. Since the natural life-time of the 2s state is about 10 s, extremely narrow lines should, in principle, be attainable. Narrow-band 243 mn radiation has been genera-... 

In the historical development of science, experimental progress in the accuracy of measurements have often brought about a refinement of theoretical models or even the introduction of new concepts [14.1]. Examples are A. Einstein s theory of special relativity based on the interferometric experiments of Michel son and Morley [14.2] M. Planck s introduction of quantum physics for the correct explanation of the measured spectral distribution of black-body radiation, the introduction of the concept of electron spin after the spectroscopic discovery of the fine structure in atomic spectra [14.3] or the test of quantum-electrodynamics by precision measurements of the Lamb shift [14.4]. 

This effect may be explained in terms of the quantum theory of electrodynamics. According to this theory each mode of the quantized radiation field possesses a zero-point energy of hu)/2. This implies that, even in the absence of external radiation, the mean square value of the time-depen-dent electric field is finite and that a hydrogen atom will experience a perturbation produced by the fluctuations in this field. These zero-point fluctuations cause the electron to wobble randomly in its orbit and so smear the charge over a greater volume of space. Since the electron is bound to the nucleus by a non-uniform electric field, the reduction in electron density causes a shift in the atomic energy levels. This Lamb shift, as it is now called, is greatest for those states in which iK0) is finite, i.e. the n states. 

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