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what happens to substances when they undergo radioactive decay
February 6, 2014 9:28 AM   Subscribe

Radioisotopes decay into a different element (usually) based on what they emit, and the decay chain is easy to follow, well understood, etc. But what happens when the radioisotope is part of a ionic compound ?

The cesium compound in the Goiania incident was cesium chloride. That cesium isotope decays into stable barium.

So when the cesium decays, you're left with barium chloride ? That seems wrong because the chloride ion count would be different. (CsCl vs BaCl2), not to mention the crystal/lattice structure would probably be different.

So what happens ?

Similarly, for non-ionic bound radioisotopes, when the isotope is in a rock or metal compound, and decays, what happens ? The bonds/structure should seemingly change ..
posted by k5.user to Science & Nature (5 answers total) 1 user marked this as a favorite
 
The most extreme (and common) example of that is when Potassium-40 beta decays into Argon-40, which of course is a noble gas. The argon won't bond with anything, and whatever the potassium atom was hooked to becomes a radical.

So what happens? Eventually it bonds with something. It's entirely a function of the specific circumstance, and what's around it at the time.
posted by Chocolate Pickle at 9:32 AM on February 6 [2 favorites]


some of the incomplete barium chloride molecules will grab another chlorine atom from nearby to become complete. some of the bariums will have their chlorine taken away, but they will find solace in the loose electrons zipping around from the beta decay and be reduced to nonionic form.
posted by bruce at 10:03 AM on February 6 [2 favorites]


The short answer is indeed free radicals, and the occasional stable gaseous products.

When I worked with spent nuclear fuel, we had a handful of isotopes that the spent fuel would slowly emit and had to get filtered for: krypton, xenon, and iodine being the common ones, and in the cases of Kr and Xe, the radioactive gaseous products had short half lives. Iodine was the product of most concern.
posted by kaszeta at 11:54 AM on February 6 [1 favorite]


Molecules that contain an atom that radioactively decays will break up.

The odds are very good that whatever the atom decays into will not be chemically appropriate, and even if it was, the energies associated with decay are large compared to molecular bond strengths.

As others have said, the new atom and the remnants of the old molecule will both float around naturally and either bond or not as their chemical nature and surroundings dictate.

I should note that in the case of a CsCl source of any plausible strength after 100 half-lives what you essentially have is stable CsCl with a barely measurable quantity of Ba. Only a tiny, tiny, tiny, fraction of the CsCl molecules were initially (Cs-137)Cl molecules, so the bulk properties of the material would be unchanged.

Funny story, not decay, but similar nuclear interactions: I was trying to make Cl-36 in a reactor by irradiating MgCl powder, for various reasons that seemed good to me. MgCl is soluble in water, and I took my irradiated mixture of MgCl and added water to it. My hope was to end up with a solution that had some Cl-36. Apparently (this is what I assume) its time in the reactor had broken some bonds and I ended up with certain amount of elemental magnesium which did not appreciate being added to water.
posted by pseudonick at 1:29 PM on February 6 [3 favorites]


Others are correct that any molecule which has a constituent decay to a different element will probably break up. There's another effect, too: the energetic particles emitted during the decay deposit their energy in the material by breaking chemical bonds in nearby molecules. A typical nuclear decay has a few mega-eV of energy, while a typical chemical bond has a few eV of energy to break, so a single decay can break many thousands of neighboring bonds, introduce crystal defects, etc. This is for instance why irradiated glass turns dark.
posted by fantabulous timewaster at 11:07 AM on February 7


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