When does an isotope begin to decay?

[MarkL]

Take ⁶⁰Fe found in meteorites. Does it start to decay the moment it is created. Or does it start to decay when it cools to a solid (a meteorite)? Does heat have anything to do with it? Thanks

 

[A.T.]

Or does it start to decay when it cools to a solid (a meteorite)?

Are you asking if the decay rate depends on temperature?

https://physics.stackexchange.com/a/400132

 

[Nugatory]

Take ⁶⁰Fe found in meteorites. Does it start to decay the moment it is created. Or does it start to decay when it cools to a solid (a meteorite)? Does heat have anything to do with it? Thanks

The individual atoms start decaying probabilistically according to their half-life from the moment that they are created (perhaps as decay products of other unstable isotopes, perhaps by nucleosynthesis in stars). Whether these atoms are assembled into a lump of iron or floating around in the heart of a star, whether they're part of a mass of solidified iron or a puddle of molten iron is irrelevant to their individual decay probability.

So now you're probably wondering how we can do radioisotope dating if the solidification of the meteorite doesn't start a "decay clock" in the individual atoms?

 

[MarkL]

Yes. Thank you. So we measure the age of the isotope, not the meteorite.

 

[Vanadium 50]

So we measure the age of the isotope, not the meteorite.

No.

The isotope starts decaying from its inception. However, in radioisotope dating, we measure two things: the parent nucleus and the daughter nucleus. We pick pairs where the properties differ: e.g. in K-Ar dating, the argon is a gas, so if the rock is still in liquid form, the argon bubbles out. Only after the rock solidifies is the argon trapped, so K-Ar dating tells us when the sample was last liquid.

 

[sophiecentaur]

Yes. Thank you. So we measure the age of the isotope, not the meteorite.

I don't think I would put it that way.
You cannot know the age of an isotope (which particular nucleus would you be looking at?) and you can only do dating under particular conditions and with particular isotopes.
There's a general principle for radio isotope dating but different methods to achieve it. There needs to have been some physical or chemical process that isolates a suitable isotope with none of the daughter product there. Then you have a starting point for the process, after which there will be a steady exponential decay. As the parent decays, the proportion of parent to daughter after a given time will tell you how long that particular sample has been isolated (assuming you know the half life). The meteorite is assumed to have been formed with a particular concentration of the parent and the ratio that's measured will tell you how long since the meteorite was formed.
Radio Carbon dating looks at the Carbon isotopes that have been locked into plant tissue, from CO2 in the air. The proportion of C12 and C14 in the atmosphere is assumed to have been what it is now and the proportion of the two isotopes will change in time for the fixed C in the dead plant. The time is how long since the plant photosynthesised the food.