Đáp án:

 \(X = 2,3\)

Giải thích các bước giải:

Ta có: 

\(\begin{array}{l}
\dfrac{{{N_1}}}{{{N_0}}} = {2^{ - \dfrac{{{t_1}}}{T}}} \Rightarrow \dfrac{1}{2} = {2^{ - \dfrac{{{t_1}}}{T}}} \Rightarrow \dfrac{{{t_1}}}{T} = 1\\
 \Rightarrow {t_1} = T\\
\dfrac{{{N_2}}}{{{N_0}}} = {2^{ - \dfrac{{{t_2}}}{T}}} \Rightarrow \dfrac{1}{{64}} = {2^{ - \dfrac{{{t_2}}}{T}}} \Rightarrow \dfrac{{{t_2}}}{T} = 6\\
 \Rightarrow {t_2} = 6T\\
 \Rightarrow {t_2} - {t_1} = 5T \Rightarrow 40 = 5T\\
 \Rightarrow T = 8ngay\\
H = \lambda {N_0} = \dfrac{{\ln 2}}{T}.\dfrac{{{m_0}}}{A}.{N_A}\\
 \Rightarrow H = \dfrac{{\ln 2}}{{8.24.3600}}.\dfrac{{50}}{{1000.131}}.6,{02.10^{23}}\\
 \Rightarrow H = 2,{3.10^{14}}Bq\\
 \Rightarrow X = 2,3
\end{array}\)