More radiation questions

Is a radioactive element with a short half-life more intensly radioactive than an element with a long half-life? It seems to me that a kilogram of material with a ten-day half life would be “more” radioactive than a kilgram of stuff with a ten-year half life.

Also, are the multiple decade half-life of some nuclides the reason that people can suffer an “outbreak” of cancer years after the initial exposure?

Well, both of them are radioactive. During the time before the ten-day half life material expires, it is certainly decaying at a faster rate than the ten-year half life material. But 5 years later, the ten-year half life stuff is still going strong. So I think it depends on the time frame you’re asking about. In terms of danger to people, it is more dangerous to be exposed to a certain amount of radiation over a short period of time than it is to be exposed to that same amount of radiation over a long period of time.

No, that’s not accurate. There is no way to determine when the effects of radiation exposure are going to show up. If the radiation is external to your body, then it only affects you as long as you are in it’s vicinity (however far reaching that is). But that doesn’t mean the affects of that exposure will be immediately apparent.

Yes, other factors being equal, (which they almost never are, exactly,) a shorter half-life will mean that more of the element is decaying per unit time.

Some of the factors that might complicate this simple explanation is the fact of decay chains, (element A breaks down into element B with a half-life of ten years, element B then breaks down into element C with a half-life of ten minutes, element C then breaks down into element D with a half-life of ten days, and element D is relatively stable,) and the fact that different radioactive decays generate different kinds of radiation, which can be like comparing cherries and watermelons.

And yes, long half-life nuclides can definitely be a factor in delayed radiation illness - I’m not sure about cancer specifically, but probably it could apply there. Cancer also has its own way of going into sleeper mode I believe.

Strontium 90 is a particularly nasty nuclide - not only does it have a half-life of nearly 30 years and a double-beta decay chain, but it is chemically similar enough to calcium to get deposited into your bones. :eek:

::waves hi to Jsb5391 on preview::

Yes - short half-life material is more radioactive than long half-life material, so with used nuclear fuel, the first 10 years are the worst, requiring lots of cooling and shielding (usually in large cooling ponds). However, it does depend on the sort of radiation - alpha and beta are easily shielded against, neutron and gamma, less so.

However, long half-life absorption is not always the reason for delayed cancers in radiation exposure. In general, the genetic damage is done during initial exposure, but the cancer has to develop from a single cell. In slow growing tissue, this can take years. Also, the initial genetic damage does not cause cancer immediately, but subsequent replication errors in combination with the radiation damage trigger the cancerous phase.

Some radioisotopes have higher bio-activity than others - radioactive [sup]90[/sup]Strontium (1/2 life is ~30ys) gets absorbed into bone, as it is chemically related to Calcium. [sup]131[/sup]I (1/2 life 8 days) gets concentrated into the thyroid, causing selective damage. Supplements containing Iodine and Calcium can be used to (or at least attempt to) limit bio-absorption.

I see good answers on preview, but am posting anyhow.


Are any of the effects of radiation sickness caused by elements in a irradiated body decaying into elements that are toxic or which combine into toxic compounds?

No, not really. Radiation sickness is caused by radiation damage - no actual ingestion or absorption of radioactive materials is required.

And the LD50 due to radiation of a nucleotide is almost certainly far higher than the LD50 of any toxic decay product.

Some isotopes have toxic effects, though. Replace enough (about 50%) [sup]1[/sup]H[sub]2[/sub]O with [sup]2[/sup]H[sub]2[/sub]O (heavy water) in the human body and the subject will die, due to reaction rate/thermodynamic differences between water and heavy water.


Just to clarify, although in principle ingestion is not required, ingestion (or entry to the body through some other route) is required for radiation sickness due to alpha emitters as the skin will effectively block alpha particles. Once they are inside you they will do considerable damage!

I’m not talking about ingesting radioactive materials. I’m talking about being exposed to ionizing radiation which can result in the bodies own atoms decaying into toxic materials.

Both Alpha and Beta radiation (from outside the body) have limited penetration, and the primary effects are chemical - damaging cell walls and structures, damaging dna bonds/bases and creating free radicals.

Gamma Radiation is highly penetrating, and weakly interacting. However, gamma rays do dump energy into the body, and produce both heat and electrons, giving similar results to alpha and beta radiation, albeit throughout the body due to deeper penetration.

Neutrons do not interact with electrons (being electrically neutral), so do not directly impact the body chemically. Neutrons can hit nuclei and create nuclear changes, as well as displacing atoms from chemical structures. These can then trigger decay chains that emit other forms of ionizing radiation, as well. This is the only way you could get non-toxic elements to turn into toxic elements within the body, but the toxic effects are going to be minimal compared to the other effects.

You could argue that the chemical changes induced by ionising radiation could produce toxic molecules (especially free radicals which can be extremely damaging), but I would call that a stretch. I guess that the impact of massive radiation-induced cell death will dump toxins into the body, but that is not something I can comment on.