Uranium Basics
https://www.umrc.net/uranium_basics.aspx

Uranium occurs in trace amounts in nature about 3 parts per million (ppm) or 3 micrograms of uranium per gram of dry soil, the equivalent of 1 teaspoon of natural uranium per 5 tonnes of earth.
An infinitesimal quantity of natural uranium is ingested in the body on a daily basis. It passes through the body with minimal effects. It is absorbed very poorly in the gastrointestinal tract (only 2% absorption). Approximately 10 nanograms (a nanogram is 1 one-billionth of a gram) is excreted daily in human urine.

Once mined, uranium is refined into concentrated packets of almost pure uranium. It is this highly concentrated �natural� uranium which is processed to produce enriched uranium. The enrichment process increases the isotope U235 concentration to create Enriched Uranium which is more easily fissionable for use in nuclear weapons and reactors. This process also creates depleted uranium (DU) as a byproduct.

All uranium whether �natural�, �depleted� or �enriched� is a chemical and radiological toxic substance emitting alpha, beta and gamma particles. All forms of uranium differ from each other by only a fraction of one percent. Both natural and depleted uranium are over 99% composed of the isotope U238. The ratio of isotope U238/U235 gives the unique signature that identifies whether the uranium is enriched, natural, or depleted.

Radioactivity (disintegrations per second) in 1 milligram of U-238 at Secular Equilibrium

U-238 Th-234 Pa-234 U-234
12.4 alpha particles 12.4 beta particles 12.4 beta particles 0.017 alpha particles
In the course of one year, 1 milligram of uranium emits 390 million alpha particles, 780 million beta particles and associated gamma rays. This is over one billion high-energy, ionizing, radioactive particles and rays which can produce extensive biological damage.

The energy of a single alpha particle exceeds the amount required to damage important macromolecules such as DNA, RNA, enzymes and proteins. It does this by breaking molecular bonds and by chemical reactions, which alter or destroy the shape, organization, and function of these molecules.

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As the table shows, U-238 emits only alpha waves. The beta particles come from Th-234 and Pa-234.

How was this calculated (beta particles)? With the half life of U-238, 1 milligram would give half a milligram of Th-234 every 4.6 billion years. And the resulting Th-234 decays to half every 21 days. I really think there's some switching of facts here, making us believe that we instantly get a lot of Th-234 from U-238. Don't we spread out that half milligram over 4.6 billion years?

As for the gamma rays, where would they come from? It's nowhere in the decay series of U-238. From the beta particles? If so (which I don't see how) we expect it also spread over the 4.6 billion year half-life of U-238.

Gamma rays are what we should worry about because these are what can penetrate deeply. Even beta rays are easily blocked by thick clothing.

I don't see how alpha from the environment does. Other forms of radiation like X and gamma, yes.

I now see that alpha harms only if it enters the body.

But this only occurs if the alpha emitting substance enters the body. Alpha rays from the outside don't cause any harm. So for all the DU spread about in war zones, our only concern is if we inhale or ingest them. Which is just about the same as other heavy metals.

Gerry