Low energy fast events from radon progenies at the surface of a CsI(Tℓ) scintillator

► 222Rn progenies easily stick to the detector surfaces. ► It causes the background even at the low energy region. ► This is the serious background in the rare phenomena search. ► With CsI(Tℓ) scintillator, we demonstrate that they decay fast. ► We show that they are distintively faster than neutron or gamma events.