Higher-order hyperfine splitting

Higher-order hyperfine splitting ESR transitions with isotropic hyperfine (hf) and g values can be expressed as follows [36b] ... 

Note that we ignore higher-order contributions such as d2/2c2 in Eq. (5-3) this has consequences, as we will see later when we discuss the second-order Doppler shift. In order to detect shifts and splitting in the nuclear levels due to hyperfine interactions in iron, one needs an energy range of at most 5 10 8 eV around E0, which is achieved with Doppler velocities in the range of —10 to +10 mm s 1. 

Abstract. The usefulness of study of hyperfine splitting in the hydrogen atom is limited on a level of 10 ppm by our knowledge of the proton structure. One way to go beyond 10 ppm is to study a specific difference of the hyperfine structure intervals 8Au2 — Avi. Nuclear effects for axe not important this difference and it is of use to study higher-order QED corrections. 

Abstract. We review our recent results on higher order corrections in positronium physics. We discuss a calculation of the recoil 0(ma6) corrections to the hyperfine splitting [1] and energy levels of a positronium atom [2], 0(ma7 In2 a) contributions to the positronium S-wave energy levels [3] and Ola2) radiative corrections to the parapositronium decay rate [4],... 

There are several quantities in positronium physics where higher order radiative corrections have to be taken into account for the theoretical prediction to match the experimental precision. For the hyperfine splitting of the ground state, Av = E(13Si) — Eil1 So), the two best experimental values are [5,6]... 

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