MadSci Network: Medicine

Re: Can alpha emitters be dangerous when they are inhaled into the lungs?

Date: Fri Nov 14 00:35:19 2003
Posted By: Michael Kay, Haz. Mat Mgmt, Health Physics, Nuclear Science, President and Consultant AMBRY, Inc
Area of science: Medicine
ID: 1067895063.Me

The quick answer to your questions is "Yes, alpha emitters can be 
dangerous when inhaled into the lungs or consumed in water or food." 

The explaination is a bit more involved. The first stop is the chapter on 
Health Physics in Radiochemistry and Nuclear Methods of Analysis by W.D. 
Ehmann and D.E. Vance, John Wiley & Sons, Inc., New York, 1991. This is a 
bit technical but can be summarized as follows:
An alpha particle is a helium nucleus (2 protons and 2 neutrons totalling 
an atomic mass of 4) that can be emitted by many naturally occurring 
radioactive nuclides such as isotopes of Uranium, Thorium, Radium, Radon, 
and all the rest of the natural decay chains until they reach lead. For 
example, Uranium-238 ends up as Pb-206. The 32 mass unit difference means 
that 8 alpha particles are emitted in the complete decay of one U-238 
nucleus to Pb-206. If it is radon gas that is inhaled, then Rn-222 
decaying to Pb-206 emits 4 alpha particles to make the 16 mass unit 
difference. Polonium-210 only emits 1 alpha particle to arrive at Pb-206. 
Sometimes the chemistry of the radioactive nuclides in the decay chain 
causes them to be separated. Polonium-210 is naturally concentrated by 
tobacco leaves, and therefore is inhaled by smokers to a larger degree 
than by non-smokers. There are two additional natural decay chains; one 
begins with Th-232 and ends at Pb-208, and the other begins with U-235 
and ends with Pb-207. Those three chains, U-238, U-235, and Th-232, 
provide most of the alpha-particle emitting radionuclides we are exposed 
to in our lives.

Alpha particles outside the body are not dangerous to us. The outer layer 
of the skin is enough to stop alpha particles before they can contact any 
of our living cells. This is because alpha particles are large, heavy, 
charged nuclei compared to electrons. When an alpha particle is emitted, 
it travels in a straight line because a collision with a heavy nucleus is 
very rare compared to hitting an electron (remember, almost all of an 
atom is empty space occupied by electrons with the heavy nucleus a very 
small particle at the center). But because the alpha particle is so heavy 
compared to the electron, and because it is positively charged compared 
to the electron's negative charge, the alpha particle collides with and 
knocks electrons out of their orbits. This is called ionization, and is 
why alpha particles (along with beta particles and gamma rays) are called 
ionizing radiation. Alpha particles knock out a large number of electrons 
in a very short distance; that is how they are slowed down, and 
eventually pick up two electrons to become ordinary helium atoms. If you 
put an alpha emitting nuclide on a piece of photographic film (it has to 
be put directly on the emulsion because the paper cover would stop the 
alpha particles) you would see a small dark circle a few millimeters in 
diameter around the alpha emitting nuclide. This shows that a large 
amount of energy has been deposited in a small area, and many atoms were 
ionized by the alpha particle.

"Alpha particles will produce much more biological damage than the other 
two types of radiation [beta and gamma]. Therefore, alphas are the most 
biologically hazardous if they are ingested and incorporated into 
internal tissue." (Ehman & Vance page 181)

Alphas are very easy to shield against externally, and the usual way of 
entry into the body is inhalation or ingestion.

The next step is to look at the effects that may be caused by ingested 
alpha emitters. There is a lot of controversy over theories of causation 
of cancers or other abnormalities from alpha emitters. One theory is 
called the hot-particle theory. It says that cancer can be caused by the 
intense, local injury to a cell or group of cells caused by a particle 
containing an alpha emitter next to the cells. This is countered by the 
proponents of cell repair, or extermination by other body cells as part 
of the normal repair/replace function. 

I recommend going to:

This reference presents the answer to the question of ingesting 
radioactive material. The site is the Health Physics Society, and the 
information is considered to be reliable.

A way to obtain further information is to go to

and enter

biological effect of alpha radiation

in the search window. There is a lot of information out there on this 
question. But not all of it is correct, so be sure to look at the source 
of the information. One site talks about "microscopic nuclear explosions" 
that yield the alpha particles. This is not how alpha particles are 
emitted (actually by a complex quantum mechanical phenomenon called 
tunneling, where the alpha particle all of a sudden is outside the 
nucleus it was formerly inside by "tunneling through the wall".). 

One note on your question: all of the information you find is 
statistical, and would be called epidemiological statistics if applied to 
human populations. Epidemiological statistics can be applied to whole 
populations; THEY CANNOT BE APPLIED TO INDIVIDUALS. There are individuals 
who have never smoked who got lung cancer, and individuals who smoked all 
their lives who didn't get lung cancer. An individual either has lung 
cancer or doesn't have lung cancer (probability 1 or 0). Epidemiologic 
statistics say that out of a population of so many individuals with a 
given characteristic (such as smoker, or exposed to a radon concentration 
of so much in their house), there is a probability that so many of that 
group will develop lung cancer, but you cannot say which ones because 
that particular instance of the disease may have come from some other 


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