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I watching some TV program some time ago and a guy in it mentioned that when-ever museums display real dinosaur bones (as opposed to a replica) the bones are painted over with a lead paint, because they are radioactive.

The sentence was not qualified (so he did not e.g. say that just some bones found somewhere are radioactive).

So is this true of most or all dinosaur bones, or just some of them? If I ever find a huge dino fossil somewhere, should I be concerned?

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    $\begingroup$ I think I've seen that show, were they claiming that the dinosaurs were killed off by ancient aliens using nuclear weapons? $\endgroup$ – user137 Mar 2 '15 at 20:09
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    $\begingroup$ Partially definitely yes - that's the principle of radiocarbon dating ;-) $\endgroup$ – Probably Mar 2 '15 at 20:41
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    $\begingroup$ @Probably: Not in fossils that are millions of years old. C14 (the isotope used for radio carbon dating) has a half life of roughly 5700 years. The isotopes which are interesting here are potassium 40, various uranium isotopes and probably thorium and radium. $\endgroup$ – Chris Mar 2 '15 at 20:57
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    $\begingroup$ Here's one theory: truthisscary.com/2012/05/… $\endgroup$ – Memming Mar 2 '15 at 21:11
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    $\begingroup$ The paragraph "Elemental uranium does not occur in nature. This isotope forms through combination with oxygen and several uranium oxidized minerals and compounds." form truthisscary.com/2012/05/… is pure nonsense. $\endgroup$ – Martín-Blas Pérez Pinilla Mar 3 '15 at 8:24
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While it is true that some fossils can be radioactive, not all of them are. According to the ressources I have found, it depends on the place where these minerals are found and also the other minerals present at this place.

When there are uranium and or potassium rich ores available, the fossils seem to enrich these radioactive isotopes in the calcium matrix of the bone during fossilation. See the reference for some more details on this.

The isotopes which are occurring there are Uranium (U235 and U238), Potassium (K40)) and Rubidium (Rb87), all of them with half lives in the billion years. Carbon does not play a role in these very old fossils (millions of years old), as the half life of the relevant carbon isotope is to short. These elements are also used for radiodating these fossils, see the table below (from here):

enter image description here

Regarding the radioactive safety I think there are some fossils where you should be cautious and carry them around all day long in your pocket. Most of these isotopes release $\alpha$ and $\beta$ radiation, some $\gamma$. While the $\alpha$ radiation is relatively easy to shield, lead can have detrimental effects due to the occurance of retardation radiation of the slowed down particles. In the lab we use thick acrylic glass shields to protect us from $\beta$ radiation.

Additionally I have found some secondary sources for painting the dinosaur bones with lead paint, but no real first hand source from a museum or so. Additionally the rules for radiation safety are pretty strict. If the bones would be so radioactive that a short visit would endanger you (how long are you looking at such pieces, a few minutes at maximum I would say) than they couldn't be shown anyway. Let alone the dangers for the scientists which analyze them. So I would think this is an urban legend.

Reference:

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    $\begingroup$ The Uranium or other radioisotopes are not present in such levels as to cause problems. This much of radioisotopes even living organisms accumulate. The possible radioactivity could be only because of proximity to radioactive minerals. This should not be because of bioaccumulation. $\endgroup$ – WYSIWYG Mar 3 '15 at 5:56
  • $\begingroup$ @WYSIWYG This process happen not via bioaccumulation but after the death of the animals. If the rock in which it is embedded contain radioactive isotopes the enrich in the bones. $\endgroup$ – Chris Mar 3 '15 at 7:26
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    $\begingroup$ All fossils are radioactive, because to some degree everything is radioactive, including the human body. It's simply a question of how radioactive. Dinosaur bones are probably just as radioactive as any other sedimentary rock. See e.g. hps.org/publicinformation/ate/faqs/faqradbods.html and sciencedirect.com/science/article/pii/S1001804206600249 $\endgroup$ – jamesqf Mar 3 '15 at 18:06
  • $\begingroup$ Some rare fossils are radioactive enough to be dangerous (don't keep them in your pocket dangerous) others are less radioactive than the person looking at them. lead paint sounds like a total urban legend likely caused by some confusion, no one paints real bone, However repaired sections or missing pieces (replaced by sculptures or casts for mother individuals) are usually painted however and some older ones will of course be painted with lead paint which was really common at one time. likely some one head about some museum cleaning lead paint off older mounts and jumped to a conclusion. $\endgroup$ – John Jun 1 at 4:57

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