Citation Hunt

The Wikipedia snippet below is not backed by a reliable source. Can you find one?

Click I got this! to go to Wikipedia and fix the snippet, or Next! to see another one. Good luck!

In page Protactinium:

"

Aristid von Grosse produced 2 milligrams of Pa2O5 in 1927,[15] and in 1934 first isolated elemental protactinium from 0.1 milligrams of Pa2O5.[16] He used two different procedures: in the first one, protactinium oxide was irradiated by 35 keV electrons in vacuum. In another method, called the van Arkel–de Boer process, the oxide was chemically converted to a halide (chloride, bromide or iodide) and then reduced in a vacuum with an electrically heated metallic filament:[12][17]