Marie Curie studied radioactivity with pure and very active materials with no protection. The radioactivity of the notebook is indirect radioactivity, that is material that becomes radioactive after being exposed to powerful ionizing radiations. It must be noted that the notebook may not be deadly radioactive. And if it will be for 1500 years, it won't be deadly for 1500 years. For reference, bananas tend to be radioactive too. And you are exposed to ionizing radiations when you take the plane.

Chernobyl had two reactors burn iirc. Most of the radioactive material was in the reactor, but the fire made smoke out of radioactive materials. The quantity of smoke, in kg, that go out was significant, but it got diluted in the atmosphere and spread. Which means there wasn't so much dust, in mass, that got in any one place. The dust is also not only uranium, but a combination of uranium and materials that were contaminated like the notebook. With the rain, the dust was washed and distributed more, and with the time, materials become less and less radioactive.

Both the book and chernobyl are not dangerously radioactive. But because of the nature of radioactivity, care must always be taken.