Certificate issued by the Institute de Radium, December 1926.

FRANCE - SEPTEMBER 11: Certificate to specify radium content signed by Marie Curie in her role as director of the Institute de Radium. Pierre Curie (1859-1906) and his wife Marie (1867-1934) were two of the first people to work on radioactivity, which was originally discovered by Henri Becquerel (1852-1908). The Curies investigated it further to produce radium and polonium, and won the Nobel Prize for Physics in 1903 for their work on radioactivity. After Pierre Curie was killed in a street accident in Paris, Marie continued her research, becoming the first woman professor at the Sorbonne. She won the Nobel Prize for a second time in 1911. (Photo by SSPL/Getty Images)