The question is that if they drop atomic bomb the radiation from some radioactive isotopes has a really long half-life, and not sure if you can create a bomb only with isotopes who have short half-life. I am definitely not an expert and now I am curious if someone managed to achieve that.

For perspective, and don't tell me that dropping nuclear bombs over civilians was the necessary evil to do during WWII. Because if it was, how would you explain this:

The atomic bomb that detonated over Hiroshima used Uranium-235, while the Nagasaki bomb had Plutonium-239. The half-life of U-235 is 700 million years, while that of Pu-239 is 24,000 years. In other words, once on the ground, they will be there for a very long time.