Fig. 1. Schematic diagram of detector structure

Fig. 2. Variation of penetration percentage of β-rays emitted from the decay of ⁴¹Ar with the thickness of BC404

Fig. 3. Variation of particle number percentage of 1 293.6 keV γ-rays deposit energy in BC404 with the thickness of BC404

Fig. 4. Variation of full-energy peak efficiency of 1 293.6 keV γ-ray with the thickness of CsI(Tl)

Fig. 5. Curves of F_D,m with various gas chamber diameter at different argon sampling rates (color online)

Fig. 6. Energy deposition diagram of ⁴¹Ar in CsI(Tl) scintillator simulated by Geant4

Fig. 7. Energy deposition diagram of ⁴¹Ar in BC404 and CsI(Tl) simulated by Geant4

Fig. 8. Variation of $F_{\mathrm{n},\mathrm{T}}$ with measurement time under different background counting rates (color online)