In this post we describe a sensor for gamma rays based on a scintillator crystal with a well for housing the sample to be measured. This type of sensor allows to perform measurements with 4π geometry on small samples. With this type of sensor very high count sensitivity is achieved.
With this equipment, the sample must be inserted in the well present in the scintillator crystal. We did a test by making a measurement with two watch hands with radium paint. With geiger counter the measured activity level is rather low, with a normal NaI scintillator the measured level is higher, given the greater sensitivity of this type of detector, but still does not exceed the value of 100 pulses/sec. With the well detector the measured activity is very high and exceeds 400 pulses/sec.
From the above gamma spectrum we notice the main peaks due to radium and its progeny, the detector resolution is however rather poor, both because of the inherent geometry of the scintillator crystal and because the not so high quality of the chain crystal / PMT / HV power supply.
For completeness we report below the results that you get with americium-241 and Sodium 22 :