The scientific journal is located in the North-West area of the main building in Sector 12.
There is a combination for the safe to the journal from 3 torn pieces of paper. If not, you could try the following:
1) Use an Explosive to open the wall next to the safe. (2) Have a very strong merc like Mike waiting in the corner and using a lock kit to open the safe, then move one step away. (3) A third merc comes and picks up the journal
If you merged the combination from the scraps of paper from sectors 47, 44 and 32 (spoiler), you will get the safe combination and need not do the above steps.
After your team retrieve the Journal, the day will END!
Sadly no monetary awards or boost to guards. You may only hear Brenda's joy on retrieving here journal and some notification of the baby fallow free, which you would have heard from Hervos' note in Sector 33.
However, ending the day earlier without any penalty is helpful, as it allows you to load your "mules" and ship a lot of equipment right back to camp.
(Spoiler)The outcome of this quest it will affect the final cut scene.(Spoiler)