I used a product called radon seal. Sprayed the walls and floor. I have not tested it. I only did it to be safe. Check this web site. Its a spray on app.

Here is a link that might be useful: radonseal

I used radon seal on my basement floor and walls, followed by Drylok on the walls and a latex floor paint on the floor. This was in addition to sealing the gap around the slab. After all that the Radon reading went from about 6 to about 1. I didn't test at each step, so I can't say for sure how much each step helped.

The Radonseal web site is a bit overstated I think, but when I researched this, I couldn't find any complaints about the company. The product soaks right in to the concrete and leaves no visible residue on the surface. I also let some dry up in a jar to see what was left, and there was a clear crystalline residue (quite a bit compared to the amount of liquid I put in the jar), obviously the silicate compound. Given those two observations, it seems to me that the silicate must do something to clog up the pores in the concrete. In other words, the silicate goes into the concrete as a solution, and doesn't come out, so the crystals that form must be taking up pore space, but to what extent, I can't say.

I can confirm that it has no odor, and feels like water that has a little soap in it.

Alex

Thank you, Alex and Mike. The only reason I am asking about alternatives to RadonSeal is that they are significantly cheaper.
CP-1007 is potassium silicate and X-1 is sodium silicate blends. RadonSeal does not provide any details, saying only that it is a silicate based sealer. Is there any difference in performance? Who knows...
Had anybody else used similar products in the past? What was the result?