Chapter 31 - Nuclear Physics and Radioactivity - Problems - Page 901: 34

$5.62\times10^{-7}\,s^{-1}$

$T_{\frac{1}{2}}=14.28\,day= 14.28\,day\times\frac{(60\times60\times24)s}{1\,day}$$=1.234\times10^{6}\,s$ Thus, we find: Decay constant $\lambda= \frac{0.693}{T_{\frac{1}{2}}}=\frac{0.693}{1.234\times10^{6}s}= 5.62\times10^{-7}s^{-1}$