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Here are 4 sources. There are dozens more though and there is some ambiguity as to whether their first detonation was February or early August 1945. There is also speculation that they delayed surrendering after Hiroshima, because they thought they might be able to nuke the US with their own bomb if they had only a few weeks more.
Also, at the end of the war, Russia took all of Japan’s nuclear scientists out of North Korea to keep for themselves.

https://en.wikipedia.org/wiki/Japanese_nuclear_weapon_program
https://foxtrotalpha.jalopnik.com/new-documents-found-pointing-to-japanese-atomic-bomb-pr-1722338915
https://www.atomicheritage.org/history/japanese-atomic-bomb-project
https://www.americanthinker.com/articles/2016/05/the_japanese_were_trying_to_make_an_atomic_bomb_too.html