A radionuclide \(A_{1}\) with decay constant \(\lambda_{1}\) transforms into a radionuclide \(A_{2}\) with decay constant \(\lambda_{2}\). Assuming that at the initial moment the preparation contained only the radionuclide \(A_{1}\), find: (a) the equation describing accumulation of the radionuclide \(A_{2}\) with time; (b) the time interval after which the activity of radionuclide \(A_{2}\) reaches the maximum value.