Frédéric Joliot and Irène Joliot-Curie demonstrated that irradiation can create material that still exhibits radioactivity after the irradiating source is removed. In their 1934 report, aluminium exposed to a polonium source continued to emit Positrons afterward, with an exponentially decreasing count rate. Similar behavior in other light elements showed that irradiation had produced unstable nuclear species. Measuring the subsequent radioactive decay separated this persistent activity from radiation produced only during the incoming-particle collisions.[ref]
Artificial Production of a New Kind of Radio-Element by Frédéric Joliot and Irène Joliot-Curie. 1934 abstract, continued positron emission after removal of the polonium preparation
A physicist.[ref]
https://www.nobelprize.org/prizes/chemistry/1935/joliot-fred/biographical/?print=1. Independent professional biography and identity
Portrait of Frédéric Joliot-Curie
. Studio Harcourt / Wellcome Images, via Wikimedia Commons. Creative Commons Attribution 4.0 International., via Wikimedia Commons. Source. Articles by others on the same topic
Frédéric Joliot-Curie was a French physicist and Nobel laureate, known for his work in nuclear physics and radioactivity. He was born on March 19, 1900, and passed away on August 14, 1958.