Now KTS, you know like I know you nor science nor Naturalists can prove there is no God.
The title of the OP is correct, Atheistic Scientists. It is their faith, not proof that is foundational.
Most people who call themselves atheist, are agnostic atheists who do not claim to actively know that god does not exist, but simply do not believe in things for which they have no evidence. Let me ask you a question. Do you believe in fairies? If not, what evidence do you have that fairies cannot exist? Or do you simply feel that not believing in fairies is the reasonable default position until someone gives you positive evidence for them?
Richard Dawkins, perhaps the world's most famous atheist, proposed a 7-point scale:
1) Absolute, 100% certainty that there is a god.
2) Strong confidence that there is a god.
3) Slightly lean toward belief in god.
4) Exact 50/50.
5) Slightly lean against belief in god.
6) Strong confidence that there is no god.
7) Absolute, 100% certainty that there is no god.
Dawkins called himself a "6" on this scale. I don't know any atheist who is a "7". The closest thing to a "7" that I have seen is one atheist who argues that the concept of god is incoherent.