Question: how did scientists estimate how long areas around Chernobyl will be uninhabitable for, hence the substantial amount of radioactive particles and their different half-lifes?

Liam Gaffney answered on 20 Nov 2019:

Using the most advanced techniques of radiation detection it is possible to identify which radioactive isotopes are present in the area. Not only can they now identify the different isotopes, but scientists are also able to work out how much of the material is present and even locate hotspots by imaging the gamma-rays a bit like a camera.

Once you have all this information, you can use computer simulations to calculate how this will contamination will change over time. It’s all to do with the half-life of the different isotopes and the quantity of that material that still remains. Caesium-137 and strontium-90 were two of the most abundant isotopes produced and each have a half-life of around 30 year. After 150 years (5 half lives) there will be 32 times less of these isotopes than the original contamination.

Some other isotopes have a much longer half-life and will be around for thousands of years. However, this also means they are decaying and emitting radiation much more slowly and therefore the intensity of the radiation is quite low. They have to factor all of this into the simulations, including how the body might absorb the different elements.

Scientists need lots of data to make sure their calculations are accurate and radiation monitoring is done all of the time, all around the world. Some countries fly planes to measure radiation or have stations at various places. Here’s an online map that collects all this data in real time: http://safecast.org/tilemap/?y=51.331&x=29.944&z=10&l=0&m=0