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Are compounds of Radioactive Isotopes - radioactive?


paulsutton
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I am trying to find out if compounds of Radioactive atoms such as Uranium are still radioactive.  From a search I found

https://web.evs.anl.gov/uranium/guide/overview/index.cfm

Which has lots of information, including information on the various Compounds of Uranium, but I can't see anything relating to radioactivity.

Just curious, I would suspect they may be in some cases.  

Paul

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1 hour ago, paulsutton said:

I am trying to find out if compounds of Radioactive atoms such as Uranium are still radioactive.  From a search I found

https://web.evs.anl.gov/uranium/guide/overview/index.cfm

Which has lots of information, including information on the various Compounds of Uranium, but I can't see anything relating to radioactivity.

Just curious, I would suspect they may be in some cases.  

Paul

Yes indeed they always are. Radioactivity is a function of the stability of atomic nuclei. These are not affected at all by the way atoms may be combined in chemical compounds. Chemical bonding is entirely due to the electrons in the atom, which lie far outside the nucleus.

In fact, to give you an example, the basis of carbon 14 dating relies on this. Carbon 14 is formed in the atmosphere due to its constant bombardment by cosmic rays. The result is that a certain proportion of atmospheric carbon dioxide molecules will have a C14 atom in place of the usual C12 one. When a plant absorbs this in photosynthesis, the carbon 14 is incorporated into a sugar molecule, generally used to build the cellulose skeleton of the plant. So a living plant always has the same ratio of C14 to C12 as the atmosphere does. However, when this is a tree that is cut down and used to build, say, a boat, if we dig the boat up 5000 years later we can tell when the tree was cut down by the amount of C14 that is left, the rest having decayed away, because C14 stopped being incorporated at that point and, being radioactive, it declines from that point on, so the ratio of C14 to C12 changes.    

Edited by exchemist
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Most compounds in nature have small amounts of radioactivity, which aren't a threat to people. The SI unit for radioactivity from a material is the becquerel, which is such a small unit (one nuclear decay per second) that it's usually used in multiples like mega or giga, MBq or GBq.  If we're taking about a compound, then calculation of radioactivity is about knowing the proportions of a radioisotope to other atoms in a sample, then using an equation, with the half life of the isotope, and Avogadro's number, to calculate the probable number of decays per second.  The numbers get significant, in terms of human health, when you get into the billions of becquerels.  37 GBq, for example, would be one Curie, an older measure, and could have negative effects if there were longterm exposure near to or inside a human body.  (The women who got sick painting the radium onto watch hands were in that range, IIRC)  1000 Curies, a common emission from a radiotherapy machine, and you could have serious tissue damage in a few minutes.  

 

 

 

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11 minutes ago, exchemist said:

Yes indeed they always are. Radioactivity is a function of the stability of atomic nuclei. These are not affected at all by the way atoms may be combined in chemical compounds. Chemical bonding is entirely due to the electrons in the atom, which lie far outside the nucleus.

In fact, to give you an example, the basis of carbon 14 dating relies on this. Carbon 14 is formed in the atmosphere due to its constant bombardment by cosmic rays. The result is that a certain proportion of atmospheric carbon dioxide molecules will have a C14 atom in place of the usual C12 one. When a plant absorbs this in photosynthesis, the carbon 14 is incorporated into a sugar molecule, generally used to build the cellulose skeleton of the plant. When this is a tree that is cut down and used to build, say, a boat, if we dig the boat up 5000 years later we can tell when the tree was cut down by the amount of C14 that is left, the rest having decayed away, because C14 stopped being incorporated at that point and, because it is radioactive, it decays away progressively.   

Thanks, this makes sense so I would guess that Carbon 13 is also perhaps made with cosmic radiation too, 

Paul

10 minutes ago, TheVat said:

Most compounds in nature have small amounts of radioactivity, which aren't a threat to people. The SI unit for radioactivity from a material is the becquerel, which is such a small unit (one nuclear decay per second) that it's usually used in multiples like mega or giga, MBq or GBq.  If we're taking about a compound, then calculation of radioactivity is about knowing the proportions of a radioisotope to other atoms in a sample, then using an equation, with the half life of the isotope, and Avogadro's number, to calculate the probable number of decays per second.  The numbers get significant, in terms of human health, when you get into the billions of becquerels.  37 GBq, for example, would be one Curie, an older measure, and could have negative effects if there were longterm exposure near to or inside a human body.  (The women who got sick painting the radium onto watch hands were in that range, IIRC)  1000 Curies, a common emission from a radiotherapy machine, and you could have serious tissue damage in a few minutes.  

 

 

 

So one example could be perhaps that Bananas contain radioactive isotopes of Potassium.

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3 minutes ago, paulsutton said:

Thanks, this makes sense so I would guess that Carbon 13 is also perhaps made with cosmic radiation too, 

Paul

So one example could be perhaps that Bananas contain radioactive isotopes of Potassium.

Yes in general there will be a small proportion of radioisotopes in everything. Life on Earth has evolved around this fact. Our cells have systems that repair DNA damage, to stop this wrecking the stability of cell replication. Nevertheless, DNA damage from radioactivity may be one of the driving forces behind evolution! You need mutations to come from somewhere, after all.    

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1 minute ago, exchemist said:

Yes in general there will be a small proportion of radioisotopes in everything. Life on Earth has evolved around this fact. Our cells have systems that repair DNA damage, to stop this wrecking the stability of cell replication. Nevertheless, DNA damage from radioactivity may be one of the driving forces behind evolution! You need mutations to come from somewhere, after all.    

So from this we can perhaps conclude there are both friendly and unfriendly mutations.  We have seen mutations at work with the variants of the Covid 19 virus.  So the virus adapts,  also with things like anti biotic resistant bacteria.   In terms of friendly, yes evolution, unfriendly Cancers etc.

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6 minutes ago, paulsutton said:

So from this we can perhaps conclude there are both friendly and unfriendly mutations.  We have seen mutations at work with the variants of the Covid 19 virus.  So the virus adapts,  also with things like anti biotic resistant bacteria.   In terms of friendly, yes evolution, unfriendly Cancers etc.

Sure. It's the job of Darwin's famous "natural selection" to weed out the useful mutations and ignore or discard those that are useless or actively harmful. (Nowadays we know the mechanisms are more complex than just that, but the basic principle remains valid.)

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33 minutes ago, exchemist said:

These are not affected at all by the way atoms may be combined in chemical compounds.

Sometimes this is the case. If the exclusive mode of decay is electron capture, then a fully ionized atom cannot decay because there are no electrons in the shell(s).

Beryllium-7 is an example of an isotope that has a slightly different half-life when metallic than in compounds.

https://www.google.com/search?q=Beryllium-7+half+life+change

 

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12 minutes ago, Sensei said:

Sometimes this is the case. If the exclusive mode of decay is electron capture, then a fully ionized atom cannot decay because there are no electrons in the shell(s).

Beryllium-7 is an example of an isotope that has a slightly different half-life when metallic than in compounds.

https://www.google.com/search?q=Beryllium-7+half+life+change

 

Interesting. But surely the only example of a chemically produced ion with no electrons is H+, isn't it (even that is doubtful)?  And the proton is stable.

Your beryllium example does not reflect that, obviously. The change they measured in electron capture rate was 1%   - and this process is highly exceptional, which is why it was newsworthy. 

For people like Paul, it seems to me the best answer remains that radioactivity is independent of the chemical environment of the atom. That is 99% true at least.

 

Edited by exchemist
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1 hour ago, Sensei said:

Sometimes this is the case. If the exclusive mode of decay is electron capture, then a fully ionized atom cannot decay because there are no electrons in the shell(s).

 

If the exclusive mode of decay is electron capture, then the emission is a neutrino, isn't it?  So not much impact in radiological terms.

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25 minutes ago, TheVat said:

If the exclusive mode of decay is electron capture, then the emission is a neutrino, isn't it?  So not much impact in radiological terms.

The electron that’s captured is an “inner” electron (1S) and bonding is via “outer” electron(s), so the effect on the decay is likely minimal. That Be sees an effect makes sense to me, since it only has the four electrons, so you would have the most possible effect on the 1S orbital depending on what bonds are formed.

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9 hours ago, TheVat said:

If the exclusive mode of decay is electron capture, then the emission is a neutrino, isn't it?  So not much impact in radiological terms.

Gamma photon(s) can be emitted by the nucleus, and X-rays and UV photon(s) can be emitted by electrons transitioning to the ground state of the daughter isotope.

The 1s orbital is vacant, so further electrons will have to decay via photon emission to reach their final states.

Edited by Sensei
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11 hours ago, exchemist said:

These are not affected at all by the way atoms may be combined in chemical compounds.

But the chemical compounds they are part of are affected when the atom undergoes radioactive decay. Not just the radiation from that decay damages biochemistry, the change from one element to another does too, both by breaking up the compound they were part of and from the chemical effects of the resultant compounds. I think the harms from radioactive materials are more biochemical in nature than direct radiation damage.

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9 hours ago, swansont said:

The electron that’s captured is an “inner” electron (1S) and bonding is via “outer” electron(s), so the effect on the decay is likely minimal. That Be sees an effect makes sense to me, since it only has the four electrons, so you would have the most possible effect on the 1S orbital depending on what bonds are formed.

I was going to make the same point. I suppose it is true that the 2s also has non-zero electron density at the nucleus, so capture could in principle take place from the 2s as well as from the 1s, though with lower probability since the 2s electrons spend more time further out. 

24 minutes ago, Ken Fabian said:

But the chemical compounds they are part of are affected when the atom undergoes radioactive decay. Not just the radiation from that decay damages biochemistry, the change from one element to another does too, both by breaking up the compound they were part of and from the chemical effects of the resultant compounds. I think the harms from radioactive materials are more biochemical in nature than direct radiation damage.

Undoubtedly.   

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