Considering it was the Japanese that brought about the martial circumstances that led to the need for the bombs in the Pacfic the first place, a donation to the aggressors and authors of Rape and Massacre of Nanking as well as the invasions and murders of so many other nations and peoples, any gift that would contribute to the popular but false notion of the Japanese as hapless victims of the Atomic Bomb is wildly inappropriate, IMO.
As an atomic vet, I worked as a Dust-Off medic on the Enewetak Clean-up Project, I have lost comrades as well as suffered myself, the result of radiation injuries, I know what it is like to have been poisoned for life by this Nations abysmal and, often times criminal, atomic and nuclear policies.
However, the World War being what it was, those bombs were the right tool at the right time and by all counts, saved many, many more lives, Japanese, American and Allied, than those souls lost in those two attacks.
I suggest you either sell it outright to whomever will compensate you fairly or considering making it available as a loaned display to schools and museums that need help explaining what the war time demands, plans and technology were that went into the ending of the war, the way it did, without all the political spin we tend to attach to all such artifacts and events these days.