Step 1 :The decay rate of a radioactive substance is related to its half-life by the formula: \(k = \frac{\ln(2)}{T}\), where \(k\) is the decay constant, \(T\) is the half-life of the substance, and \(\ln\) is the natural logarithm function.
Step 2 :In this case, the half-life \(T\) is given as 11.5 days. We can substitute this into the formula to find the decay rate \(k\).
Step 3 :Substituting \(T = 11.5\) into the formula, we get \(k = \frac{\ln(2)}{11.5}\).
Step 4 :Calculating the above expression, we get \(k = 0.06027366787477785\).
Step 5 :Rounding to six decimal places, we get \(k = 0.060274\).
Step 6 :Final Answer: The decay rate, \(k\), for the radioactive substance with a half-life of 11.5 days is approximately \(\boxed{0.060274}\).