Double internal bremsstrahlung in the electron-capture decay of 55Fe

The energy distribution of photons emitted in double internal bremsstrahlung accompanying the electron-capture decay of ⁵⁵Fe has been investigated. For sum photon energies in the range of 44–230 keV and at an emission angle of 90°, the ratio of transition probabilities of double to single internal bremsstrahlung processes has been found to be (5.6±0.5) × 10^?5. The experimental data are compared with the existing theoretical predictions.