"To successfully get the achievement for this quest, you must speak with Three Dog in the Galaxy News Radio quest, and have him give you the quest, as opposed to going to Rivet City and getting the quest from Dr. Li. Receiving the quest from Dr. Li disqualifies you from getting the achievement, as the first objective in the quest is to find Rivet City, and completing objectives out of order or before getting the quest can disqualify you from certain quest-based achievements (Yes, it WILL disqualify you if you don't get the objectives in order. It will skip all the Rivet City and Doctor Li Stuff). It is also possible to skip to the mission "Gain Access to Vault 112" if you have already travelled to Jefferson Memorial (on your own, not as part of the mission), and found the holotapes. After this, Three Dog and Doctor Li will not give you any information about your dads whereabouts whatsoever. Also, if you have already visited Smith Casey's Garage before you acquire the holotapes, then there is a chance that you will not get the achievement upon completion of the quest. "
http://fallout.wikia.com/wiki/Scientific_Pursuits
