honestly if i was in your position i would vouch to go straight for the mitigation system. sealing the concrete might work for a the short term, but long term who knows. concrete will shift and crack over time and then the sealing is worthless.

Its good that the radon levels are not high yet, but overtime that could change, and you're trying to be proactive about it now instead of later where the price may be a multiple of what it is now.

im not a radon specialist, but common sense tells me to go full mitigation now.

First, has testing been done and a radon problem verified?

Testing is rather involved, since the better tests require at least three samples and the areas being tested have to remain undisturbed for a day or so.Radon testing

There are basically two types of radon mitigation systems, active and passive. Passive systems almost need to be installed during initial construction. Active systems have a fan which produces a pressure differential under the slab compared to above the slab. That draws the gas into the fan plumbing and it is exhausted outside the house.

"In many cases, simple systems using underground pipes and an exhaust fan
may be used to reduce radon. Such systems are called "sub-slab
depressurization," and do not require major changes to your home. These
systems remove radon gas from below the concrete floor and the
foundation before it can enter the home." From this article

Installing the mitigation system($600-$2,000) requires sealing all slab intrusion areas and cracks if a positive test indicates a radon problem.

Yes, radon was confirmed before I bought the house. The level I think was <5. I can't find the paperwork at the moment. I bought a digital electric monitor and it also shows low levels. I need to have it recalibrated however for a current number. House was built in 1965. When I initially talked with a mitigation specialist he said it's most difficult to reduce a low level which he thought mine is. That said, as I am undertaking a remodel it's something I'd like to address. I will call a mitigator again soonish for a cost estimate. And in the mean time I can also put down a vapor barrier above the slab before new flooring is laid. I don't expect a vapor barrier would be all I need. But why not try? It would be fairly low cost for the labor, barrier material and seam tape to be added under a padding that was already planned. The sealers have such a variety of toxic effects to not a good enough system that I can't seeing doing that now.

How are the intrusion areas and cracks sealed? I know if we see a crack after taking up the carpet then it can be addressed. Do they have to dig around the perimeter? Thanks.

The positive pressure type is basically a pipe inserted through the floor. That is connected to a pipe that extends through the roof (or outside) and has a small electric fan in the pipe and a gauge that shows the partial vacuum under the slab.

The sealers are of several types, depending on application.