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The alpha emission rate from some older americium-241 school cup sources, detected by a GM tube, appears much lower than when the sources were new. Strangely, the sources perform as expected when used with spark counters and ionisation chambers. This apparent reduction of emission rate adversely affects the demonstration of blocking alpha radiation with paper. The research jointly by the University of Liverpool and CLEAPSS revealed an increase in alpha energy straggling caused by a net migration of americium deeper into the source foil. The article gives advice to schools that have such a source behaving oddly
