What element did Rutherford use to obtain alpha particles in his experiment of gold foil?
Initially, I stated in the comments(now deleted) that the source for alpha-particles was either Am-241 or radium metal. Both are incorrect as @M. Farooq said. The actual source was called radium-emanation which was basically radon gas or Rn-222 which was several times more radioactive than uranium. Researching a little bit more on the history of Rutherford's gold-foil experiment gave me following references. Have a look if you want to know more about the "inspiration/motivation" of this experiment:
- Boltwood, Bertram B. “Radioactivity.” Proceedings of the American Philosophical Society, vol. 50, no. 200, 1911, pp. 333–346. JSTOR, www.jstor.org/stable/983927.