The atomic decay for a two level atom interacting with a single mode of electromagnetic
field is considered. In particular for a coherent state or statistical mixture (SM) of two opposite
coherent states as initial field states, the exact solution of the master equation is found. Effect of
the atomic damping on the partial entropies of the atom or the field and the total entropy as a measures of the purity loss is investigated. The degree of entanglement by the negativity and the mutual information and the atomic coherence through the master equation is studied.