Poltinnik alloy 1924

Hello,

I'm looking for the exact metal composition of the Poltinnik coin from 1924.
(https://en.numista.com/catalogue/pieces4623.html)
I found that it is made from 900 silver. However I'm not sure about the other metals used in this alloy. Does anyone know if it consists only of silver and copper or are also other metals (zinc, nickel, ...) used in this alloy?

Thank you.

Copper according to this X-Ray fluoresnce analysis, for sure concerning 50 Kopecks 1924 London & Leningrad

Pretty sure that the silver is alloyed with copper.