Geant4 Simulations for the Radon Electric Dipole Moment Search at

30
Absolute Efficiency (%)
25
20
15
10
RnEDM Components
no cell, oven or magnet
cell and oven only
magnet only
cell, oven and magnet
5
0
10 100 1000 10000
γ-ray Energy (keV)
Figure 4.2: Geant4 generated absolute efficiency curves for a ring of eight GRIFFIN
detectors in the highest efficiency mode (forward configuration) including various
components of the RnEDM apparatus.
4.1.2 223 Rn β-Decay Spectra
The β decay of 223 Rn into 223 Fr was simulated to include all known β decay
branches and subsequent γ-ray, conversion electron and X-ray decays. The full γ-
ray spectrum for the β decay of 223 Rn is presented in Figure 4.4(a). The Geant4
simulation consisted of 1.2 billion β decay events from an initial sample of 8 ×10 10
nucleiinsidetheEDMcell. TheEDMcell, oven, magnetand1mmofµMetalshielding
were included in the simulation. The initial polarization was assumed to be 100% and
boththespin-relaxation(T 1 )andthespin-decoherence(T 2 )timesweresimulatedtobe
30 seconds, resulting in a combined depolarization time of 15 seconds. The simulated
decay scheme (See Appendix A) includes 136 levels and 294 γ-ray transitions. The
inclusion of the internal conversion process is shown to be important as the resulting
X-rays dominate the spectrum at low energies.
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