God, how terrible the current systems are! E.g. looking for the Polonium publication from 1898 and can't find it easily! Presumably would be in the Comptes rendus de l'Académie des Sciences 1898. There are two per year, and from searches would be tome 127. Finally found at: archive.org/details/ComptesRendusAcademieDesSciences0127/page/n5/mode/2up
A decent manual list of publications from the Comptes rendus de l'Académie des Sciences: comptes-rendus.academie-sciences.fr/page/marie-skodowska-curie_fr/ They group Marie Curie's Polonium paper and Marie Curie's Radium paper together without giving the title of the second one though, but the page is given.
These must have been gamma rays.
Just before he left Cambridge for Montreal in 1898, Rutherford conducted a simple, systematic experiment to study the absorption of rays from uranium. [...] In 1901 he determined that Becquerel's rays are indeed electromagnetic rays. He called them γ (gamma) rays.
This terminology is used e.g. in Marie Curie's Polonium paper:
Some minerals containing uranium and thorium (pitchblende, chalcolite, uranite) are very active from the point of view of the emission of Becquerel rays.
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