Geant4 Simulations for the Radon Electric Dipole Moment Search at

simulated given sufficient parent and daughter nucleus information. A natural extension
to the simulation would be the option of including of radioactive contamination.
The first tests with the ISAC uranium-carbide target in December 2010 indicated
an overwhelming presence of francium. Alkali metals, such as francium, are readily
ionized through surface ionization. It is very likely that the RnEDM experiment will
have some contamination from francium. Including radioactive contaminates into
the Geant4 simulation could help study the contamination effect on the observed
precession frequencies, and thus the EDM sensitivity.
The final design for the RnEDM measurement remains under development. The
Geant4 simulations can be used to study the effect of γ-ray scattering and backgrounds
in the experimental apparatus for various materials and geometries. The
optimization of the materials and geometries of the RnEDM apparatus can lead to
improved detection efficiencies.
Finally, the simulation of Saint-Gobain’s BrilLanCe 380 LaBr 3 (Ce) detector can
be improved by modeling the true aluminum construction around the crystal and
including the radioactive nature of 138 La. 138 La is a naturally occurring radioisotope
(0.09% abundance [41]) with a long half-life of 1.05×10 11 years[49]. It decays with
a 66.4% probability of electron capture into an excited state in 138 Ba, which in turn
decays by the emission of a 1426keV γ ray. The remaining 33.6%decays via β − decay
into an excited state in 138 Ce, which in turn decays by the emission of a 789 keV γ
ray in coincidence with the emitted electron [49]. Therefore the LaBr 3 (Ce) detectors
contain internal radiation peaks which can be incorporated into the Geant4
simulations for added realism.
The search for particle and atomic EDMs is an important area of physics research
today, as it directly probes the fundamental symmetries of the laws of physics.
81