CLEAPSS Supporting practical science and technology
GL145 - Odd behaviour of some americium‐241 cup style sources
Several schools have told us that when detecting alpha emissions with a GM tube, their americium‐241 source appeared to have become less radioactive than when it was new1. The source worked as expected with spark counters and open ionisation chambers. But using a sheet of paper to block alpha particles in front of their GM tube made little difference to the count rate.