Ernest Rutherford (right) & Hans Geiger in their laboratory at Manchester University in about 1908. They are seen with the instrumentation they used to detect & count alpha particles from a radio- active source. The experiment led to Rutherford identifying alpha particles as helium ions (they were later shown to be helium nuclei). Rutherford (1871-1937) elucidated the nature of radioactivity & the structure of the atom. Born in New Zealand, he worked in England & Canada & was the greatest experimental physicist of his day. Geiger (1882- 1945) was a German who is best known for his invention of the Geiger counter.