Chelsie, this might be a good place to begin.
cpm vs energy units
https://www.youtube.com/watch?v=laWJ4KXxPLkConverting cpm to uSv/hr
https://www.youtube.com/watch?v=RjLXaags0CgI like Tom and his presentations.
He is an enthusiast.
If you take the time to review the titles of videos he has created, watching whatever catches your eye, you will begin to get a reasonable handle upon what is going on.
Some detectors are more sensitive than others,
Some are optimized for certain ranges,
Some are only valuable in nuclear war!!!
and almost NONE of them are suitable for inspecting food, properly.
Good luck.
rc
On the youtube, William Milberry has also made an excellent presentation on the truth of the matter regarding food testing with a Geiger-Muller counter.
https://www.youtube.com/watch?v=oc6FPIK1VaYand, food testing
https://www.youtube.com/watch?v=BIKro3s6eU4.