To detect radiation for what was released at Fukushima, yes a Geiger counter is something you could use. I have a few myself but haven't bothered to check any pcbs.
The primary radionuclides of concern released during the accident were I-131, Cs-137, and Cs-134.
The I-131 is long gone. Short half life.
Cs-137 has a longer half life and has a decay mode with a high branching ratio in gamma decay. It releases a very distinct gamma ray at 662 keV that is very central to radiation detection and nuclear physics.
Cs-134 having a ~2y half life and decaying mostly via beta decay.
They surveyed a couple hundred thousand people at the end of 2011 who lived "near" the plant and like 10 fucking people received anything close to a notable dose. 10. And the doses were equivalent to a CT or some bullshit.
If you are worried about radiation on your pcbs, take them to your local university and visit the nuclear engineering or physics department and have them survey them. Be prepared to lose that pcb if there is a postive result(there won't be).
While you're at it, stop eating bananas, throw away your Brazil nuts, tear our your granite counter tops, and for heaven sakes stay out of your basement. There is spooky gas down there dontyaknow!