Hi catsmom,
This is the way I did it:

Wait and watch for the pattern of movement of the scientists. The female scientist goes clockwise and stops in front of airlock. She goes to right frame and back to left frame. The male scientist also goes clockwise.
One way to get by is to wait for the female scientist to be on the left side in front of the airlock, sneak towards the core, sneak to the right and then run to the stairs.
Go down and go clockwise behind the stairs on this level so as not to meet the male scientist.
Go around to the stand close to the stairs and insert the encapsulated worm on the core stand. Watch the cutscene.