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One half went to Henri Becquerel for discovering spontaneous radioactivity. Pierre Curie and Marie Curie each received one quarter for investigating that radiation.^[ref] Becquerel's uranium-radiation experiment and Curie ionization-current measurement expose two complementary experimental routes into radioactivity.

A physicist who investigated magnetism, piezoelectricity and radioactivity. He built delicate balances, electrometers and piezoelectric crystals; this work on instruments helped make weak electrical effects measurable. With Marie Curie, he investigated radioactive substances under difficult laboratory conditions. The Curie ionization-current measurement illustrates how such instrumentation can turn a small signal into a quantitative comparison.^[ref]