I think the OP is talking about the 2 or so giant radscorpions that live north of the Yangzee Memorial. At level 4 it's pretty hard to deal with those with the equipment a normal level 4 player wojuld have.
Hehe

you really think there are just two of them there? Just go and explore bit more

As for question, normal radscorpions are easy to kill. Just "dance" around them always staying on their side or back. Newer put yourself in front of them. I use just any melee weapon for this as they seem to have trouble turning after you. Melee works well also since it prevents them to get too close, each hit seems to throw them back a little. Of course, do not fight more than one at the time.
As for giant radscorpions -they are difficult. Very difficult. I was unable to use same tactics as on normal ones, for some reason they are hard to get to their sides. They are very fast. Early on only working tactics is to get in to place where they can not reach you and shoot. Fortunately their big size makes this easy in some locations. Caravan wrecks are excellent as are some trucks. Some destroyed buildings work also well. Rocks do not work nearly as well since they can reach you on most of them with their stinger.
Preparing minefield in front of you and then luring them inside is also working, especially later when you have some better weapons to finish them off if mines are not sufficient. Cowboy repeater works well for me as it can unload its ammo load very fast. I place row of mines between me and scorpion, then start shooting as fast as I can and hope mines and bullets will finish it before it can reach me. Of course its very important not to get attention of more than one at the time.
In any case, always try to keep as much distance between you and them as you can. Meeting one in close quarters means always trouble unless you play unarmed character and use some knock down moves (which requires VATS if I am not mistaken so if you are playing without VATS as a rule like I do, bad luck).