I have a question about my Chemistry Stack Exchange post: Transition contraction for D series Someone please just take a look at the question I had asked. Everyone is downvoting it instead of answering it. I don't know why? If something is wrong on my part, please do tell me

I reasearched about the history of the discovery of neutrons and couldn't find who found out that isotopes are a change in the number of neutrons. Can you please tell me who it was that made this discovery?