Actually, atheism is a belief system as it is predicated on the disbelief in the existence of God or gods.  As such, it is no more rational than any other belief system or religion.  Agnosticism, on the other hand, relates to a person who believes that nothing is known or can be known of the existence or nature of God or of anything beyond material phenomena; a person who claims neither faith nor disbelief in God.    Agnosticism is therefore scientific and rational.  Atheism, on the other hand, much to your chagrin I'm sure, is a religion.