Excellent video, thanks for sharing.

Bill Brodhead posted a link to the 1993 study on his website:

https://wpb-radon.com/Radon_research_papers/1993%20Denver,%20CO/1993_38_Initial%20Results%20From%20Follow-Up%20of%20New%20Jersey%20Homes%20Mitigated%20for%20Radon.pdf

We have used the Durridge (formerly Niton) RAD7 several times for paired (indoor air and sub-slab soil gas) radon testing. It works well for field investigations, provides timely results in the "sniff" mode, and can be rented or purchased from the manufacturer. It's also an approved continuous radon monitor:

http://aarst-nrpp.com/wp/approved-devices/

Here's some more information on it:

https://durridge.com/products_rad7.shtml