If it only glows after exposure to light it isn't radium.
CMOS sensors can detect gamma particles. If you have an android phone there's an app that actually works (assuming you follow the calibration steps properly)[1]. Apparently Radium mostly emits alpha particles so I'm not sure how effective this would be.
If you are thinking about buying an actual geiger counter make sure to get one with a working probe assembly. A lot of surplus geiger counters are sold without the probe assembly with is the expensive part and the thing that wears out[2]. The probe assembly also needs to be properly calibrated.
CMOS sensors can detect gamma particles. If you have an android phone there's an app that actually works (assuming you follow the calibration steps properly)[1]. Apparently Radium mostly emits alpha particles so I'm not sure how effective this would be.
If you are thinking about buying an actual geiger counter make sure to get one with a working probe assembly. A lot of surplus geiger counters are sold without the probe assembly with is the expensive part and the thing that wears out[2]. The probe assembly also needs to be properly calibrated.
[1]: https://play.google.com/store/apps/details?id=com.rdklein.ra...
[2]: https://www.amazon.com/Atomic-Adventures-Islands-Forgotten-I...