We picked up a radiation detector similar to the Radiation Alert Ranger / Radiation Survey Meter - a ß y x. I like this one better -- USB output and it runs on AA rather a 9V; I may upgrade. Then again, it's been 6 years since the Fukashima meltdown panic and no real need. The radiation panic following meltdown in Japan didn't really happen here, although I'm still not sure some of the oceanic die offs I read about aren't related.

Whatever, mine is only similar looking but not the same model. The specs below are quoted from the link and may be of interest.
Quote:
... Detector
Internal Halogen-quenched, uncompensated GM tube with thin mica window, 1.4-2.0 mg/cm2 areal density. Effective diameter of window is 45 mm (1.77 in.).

Operating Range
mR/hr - .001 (1µR) to 100
CPM - 0 to 350,000
µSv/hr - .01 to 1000
CPS - 0 to 5000
Total Counts- 1 to 9,999,000 counts
Accuracy (Referenced to Cs137)
Typically ±15% from factory, ±10% with NIST Source Calibration

Energy Sensitivity
Detects Alpha down to 2 MeV. Detects Beta down to .16 MeV; typical detection efficiency at 1 MeV is approx. 25%. Detects Gamma down to 10 KeV through the detector window. 3340 CPM/mR/hr (137Cs). Smallest detectable level for 125I is .02 µCi at contact. ...


Get a known radiation source you can use for testing.