[填空题]
A radioactivematerialc8nu 2,*cl33lsx.oo g n)pnr a produces 1280 decays per minute ugobp,l( *k n4a6 iku0wtg0j 4ady-x/at one time, and 4.6 h later produces320 decays per minu ua*(,p o-6i ylg/g4akdjn0txukwb4 0te. What is its half-life? $T_{\frac{1}{2}}$= $h$
