do american scientists use metric units? if not why not?

They do, for the obvious reasons that it's easier to do the math, and it's easier to communicate with scientists worldwide. Some non-metric units are still sometimes used, simply by convention or history. The first that come to mind are the light year and the AU (astronomical unit). They just use a familiar reference. But then, that's how all the other units started. The meter hasn't changed much in size, but its definition changed over time to become more precise.

They use metric units for most things. Temperature, while metic, is usually in k (Kelvin) as opposed to centigrade.

The term is International system of units, which is abbreviated SI (for the french term)

for the most part yes.

base 10 verses base 12

yes they do cause it's the universal language of science. i think it's kind of gay though when some pinhead goes out of his way to use metric units. not many people outside of science use it. tell me miles and feet, please no kilometers and meters. that's enough said about that.

amongst one-another, they do. unfortunately, we don't