Geant4 Simulations for the Radon Electric Dipole Moment Search at

anaverageof120kHzphotopeakcountrateispossible. Thus, for100daysofcounting
we would expect approximately N = 1 × 10 12 photopeak counts, with negligable
background when gated on the γ-ray photopeaks. Studies with 209 Rn at Stony Brook
[32]havedemonstrated30secondsforthespin-decoherence time, andavalueof0.2for
theanalyzingpower istypical forγ-rayanisotropies. Withanelectric fieldof5kV/cm
we calculate the sensitivity for the EDM measurement (σ d ) to be approximately
1×10 −26 e-cmusing theγ-rayanisotropytechnique. Fortheβ asymmetry method, we
expect larger backgrounds, B ≈ 0.2, but a significantly higher count-rate capability.
Thecount rateintheβ detectorswillonlybelimitedbythedecay rateoftheavailable
number ofradonnuclei, allowing atotaldetected count rateoforder 5MHz. AnEDM
sensitivity of 2×10 −27 e-cm is thus expected for 100 days of counting using the betaasymmetry
technique [32].
These estimates are statistical limits and do not account for the realistic sources
of backgrounds in the actual γ-ray experiment caused by bremsstrahlung production
from the stopping β-particles and Compton scattering of photons both into and out
of the γ-ray detectors which can lead to backgrounds underneath the γ-ray photopeaks
with different angular distributions than the γ-rays of interest. The detailed
simulations presented in this thesis are motivated by the need to study the realistic
signal for the precession frequencies that will ultimately determine the sensitivity of
the RnEDM measurement using the γ-ray anisotropy technique (see Chapter 3).
2.4 GRIFFIN Spectrometer
To observe the γ radiation in the RnEDM experiment the recently funded GRIF-
FIN spectrometer will be utilized. GRIFFIN stands for Gamma-Ray Infrastructure
27