A radioactive isotope of gold, Au-198, is used in the diagnosis and treatment of liver disease. Suppose that a 6.0-mg sample of Au-198 is injected into a liver, and that this sample decays to 4.6 mg after 1 day. Assume the amount of Au-198 remaining after t minutes is given by N(t)=N0e-t.

a) Determine the disintegration constant for Au-198. b) Determine the half-life of Au-198. c) Write the equation that gives the amount of Au-198 remaining as a function of time, in terms of its half-life. d) How fast is the sample decaying after 3 days?