\(\frac{{\Delta N}}{{\Delta N'}} = \frac{{{N_0}\left( {1 - {2^{ - \frac{{ - t}}{T}}}} \right)}}{{{N_0}{2^{ - \frac{T}}}\left( {1 - {2^{ - \frac{{ - t}}{T}}}} \right)}} = \frac{n} =  > \frac{1}{{{2^{ - \frac{T}}}}} = 16 =  > \frac{T} = 4 =  > T = 138\) ngày