I've done physics, I completely understand what nuclear radiation is and why it is harmful. What I can't seem to figure out are the rules surrounding radioactive emitters/items on flights. Surely it's not just any radioactive items, because everything is at least slightly radioactive.

You get about 12 times the sieverts per hour at 35,000 feet than you generally do at sea level (3 μSv/hr in the air, 0.25 μSv/hr at sea level). And even then it's essentially harmless.

What if I had a strong radiation source, but encased in thick lead shielding? Or a strong emitter of only alpha particles? Do they measure it in Sieverts per hour, or Becquerels? Or Gray? All of it makes a difference.

Something that measures high in Gray or Becquerels could be damn near close to undetectable in Sieverts per hour - arguably the only relevant unit in terms of radiation effects on human health.

There's not enough info available to nerds like me, so insight would be greatly appreciated.

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    $\begingroup$ It messes with the x ray machines. $\endgroup$ – Ron Beyer Feb 15 at 15:14
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    $\begingroup$ Radioactive materials, like several other hazardous materials, are allowed on cargo flights. I often handle radioactive packages. There’s a limit of 2 mSv/hr on the exterior surface, but the ones I handle are x-ray sources for testing welds, so they have to be very strong emitters on the inside. They are required to have labeling that includes a “cargo aircraft only” label. Even lithium batteries now must have a CAO label if not contained in a device. So it’s clearly for safety in case of an emergency $\endgroup$ – TomMcW Feb 15 at 16:04
  • $\begingroup$ I'm quite curious. What are the forbidden items you are referring to? Some items brought back by tourists might be radioactive (e.g. rocks sample such as granite) and I doubt there radioactivity is measured before boarding. $\endgroup$ – Manu H Feb 15 at 16:42
  • $\begingroup$ @TomMcW: Lithium batteries not contained in a device are completely prohibited even on cargo aircraft; did you mean to say lithium-ion batteries? $\endgroup$ – Sean Feb 15 at 21:37
  • $\begingroup$ @Sean We accept undamaged lithium metal batteries not contained in a device for transport. They must be shipped as hazmat and there are two labels required: a UN3090 label and a Cargo aircraft only label. The quantity is limited, but I’d have to ask my haz specialist what that is since I never pick those up, but I do sometimes deliver them. Usually it’s hearing aid batteries which are obviously very small. $\endgroup$ – TomMcW Feb 16 at 2:19

Radioactive substances are potentially hazardous to people.

It is correct that many radioactive items would be perfectly safe to carry onboard, e.g. a key hanger with an alpha or beta particle emitter cast in acrylic, or a radioactive source for scientific purpose, if that source is properly packaged.

enter image description here Glowing key hanger containing tritium. Image source: Nite GlowRing

Travelers usually do not carry radioactive items with them. If there is the need or wish to bring a radioactive item along, there is normally no need to have it in the hand luggage. This makes radioactive items different from lithium ion batteries. While potentially hazardous, there is a strong demand for lithium ion batteries on board. Banning them would essentially ban mobile phones and laptops.

Airport security staff as well as airline ground and cabin crew are neither qualified nor equipped to inspect and judge the safety of radioactive items. Opening the safe packaging of radioactive items might be dangerous. An item that cannot be opened cannot be checked if something else is hidden inside.

Finally, radioactivity stirs an irrational fear in many (if not most) people.

Given the need to restrict the transport of radioactive material somehow, and the difficulties in controlling it in a more sophisticated manner, the ban of such material from hand luggage seems comprehensible.

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