1. Us-uk no, ussr in a heartbeat.There doesn't seem to have ever been much discussion amongst the US and British about using an atomic bomb in the European theater. The war ended before practical deployment could be achieved, but there does not seem to have been any planning to ever use one. Why? The attached article gives some reasons, fear of an unexploded bomb falling into the hands of German scientists, and the bombs being best suited to the B-29. The second one seems to be a weak argument. The British Lancaster could do the job, and I don't believe transferring a wing of B-29s to England would have been that difficult as it is suggested to be. The vulnerability of the B-29 to a still potent Luftwaffe seems to be a bigger concern.
Of all the articles I could find no concerns were stated about collateral damage or fallout. Even those relatively weak atom bombs produced radioactive fallout. If the war in Europe had stalled in the Fall of 1944, and the Russians had been held back, would we have dropped an atom bomb that might have produced fallout that would have affected Soviet troops?
Interesting notes in the article about the early target planning done in 1943. I was somewhat surprised to see the Japanese fleet at Truk so prominently mentioned. However, a bomb dropped into that harbor, ringed by mountains, would have been devastating.
Discuss.
https://ieer.org/resource/commentary/always-the-target/
2. At the end of the day it was clearly not going to be needed in germany. I suspect that’s the main reason.
3. Japan was perceived to be a different story in light of the island hopping campaign, whether rightfully or wrongfully. And yes there are ultimately racial and vengeance overtones. American boys in1942 signed up to go kill japs, not Germans.