Eh, it could be non-radioactive next week. That's not very likely, but it could be

If you only think about half live then yes it would be radioactive forever but in reality after a long time every atom would've decayed into non radioactive elements.

You can even calculate the expected time it would take for the random process of decay to terminate.

I wonder how long it would take for the radioactivity to be indistinguishable from the atmospheric average.

Um, Chernobyl is still extremely radioactive. You probably mean the exclusion zone which is really not that bad, there's even tourists going there. But it's still not recommended to live there due to cumulative exposure.

they didn't say the book is dangerous, they said it's radioactive

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.

It isn't "safe" it's "safe enough" for limited visits to the exclusion zone and VERY limited visits to the sarcophagus that enclosed the old reactor

Chernobyl was made into a TV show while this book appears to be just a book.

fun fact: the other three reactors in Chernobyl were put in operation again AFTER reactor 4 blew up
I believe the last one for 14 additional years

how safe that was is another question though

Different radioactive materials have different half-life periods.

Chernobyl isn't safe safe, it's just safe enough for wildlife to survive there, possibly with lowered life span and quality of life.

Also, there's a decent danger of radioactive dust coming off the book if it's handled. It may not be that radioactive, but if it clings to you, or you breathe it in, it will do considerably more damage than if it was all one solid rock that made geiger counters click.

I'm guessing we don't know the particulars of what radium isotope Curie was working with?

It should be noted that big chunks of radioactive materials are generally safe same with just generally high radiation under a certain threshold, we are illuminated by a big ball of fuck you radiation after all. The problem is radioactive dust and particulates, once its in your body you are fucked and its pretty random on what amount will kill you. This is what happened to those Russian dumbasses who dug trenches around Chernobyl, they breathed in radioactive dust and it wreaked havoc on their bodies. This is also one of the main reasons you wear gas masks around such things.