Geant4 Simulations for the Radon Electric Dipole Moment Search at

γ-Ray and Internal Conversion Electron Emission
As described in Section 3.3, the γ-decay and internal conversion processes are
competitive. Level structure informationisrequired toaccurately describe their probabilities.
At any particular excited state in the daughter nucleus there are N number
of γ decays which can populate lower energy levels. The probability for a particular
transition is given by (1+α)I γ /I sum , where α is the internal conversion coefficient,
I γ is the measured γ-ray intensity and I sum = ∑ N (1+α N)I γN , such that the total
decay probability for that excited state is normalized to 100%. Through Monte Carlo
techniques, a decay branch is selected and the probabilities of γ decay versus internal
conversion are calculated from Equations 3.1, and again selected by Monte Carlo.
If the selected process is γ decay, the energy of the emitted γ ray is simply read
from the input data. If the selected process is internal conversion, the energy of the
emitted electron isthe γ-rayenergy minus the electron binding energy for theelectron
shell. The shell is determined from the probabilities given from the individual shell
internal conversion coefficients. Atomic electron binding energies [49] were directly
coded into the Geant4 simulation, resulting in accurate internal conversion electron
energies for shells K to N, and a general code that can be used in cases other than
the 223 Rn to 223 Fr decay studied here.
X-ray Emission
Following the emission of an internal conversion electron there exists a low lying
vacancy in the atomic shell structure of the daughter atom ( 223 Fr). An electron in a
higher orbital will prefer to occupy this lower energy state. As it transitions into the
vacancy energy is released in the form of a X ray.
The simulation of the X-ray emissions had two main user options. The first option
46