[ajax0604]

I've been reading up on AAS and I am confused on a few points. I read that a chopper is used which has alternating mirror and "open" sections. When the mirror is in line, it reflects all the light from the hollow lamp to the detector for a reference reading. Is that correct? When the "open" section is in line, does all of the light go to the flame where the sample atoms are, or is the light split somehow so that some of it is diverted straight to the detector as before?

[marquis]

Yes, you have the right idea.

It's the way the instrument is made into a "double beam" instrument. 

The last AAS I used was still using photomultiplier detectors.  Then you
have the lamps, which can also be variable.  By splitting the beam,
you can adjust (instrumentally) for these variations.