Answer to Question #1449 Submitted to "Ask the Experts"

Q

Earlier I submitted Question #573 and was pleased with the answer. That question dealt with gamma radiation from mineral specimens I harvest. I now have a breakdown of the percent of alpha, beta, and gamma and would like to know, considering this new information, what my risks are. Our autunite produces 3% gamma, 62% beta, and 35% alpha. Our specimens will average 3 to 6 mR/hr gamma.

A

As you may know, autunite is Ca(UO₂)₂(PO₄)₂-10H₂O, Hydrated Calcium Uranyl Phosphate, and poses and very minimal risk to you. The radiation from uranium is a very low external hazard. The dead layer of the skin stops the alphas that are emitted from this mineral. Only a small percentage of the betas emitted are energetic enough to get through the skin. With both the alphas and betas, one only needs to worry about the ones that are released from the material that is on the very outside of the sample; all others are shielded by the mineral itself. As a matter of fact, the gammas that are emitted are of very low energy as well and many of them do not get out of the sample either. As was mentioned, this sample is a very minimal external hazard and the only way that it would give you any appreciative dose would be if you ate it. And even then, given the dose rate that you gave (I assumed that the dose rate was on contact with the sample), the dose received would not be substantial enough to cause any harm. The thing that you have to worry about most is the degradation of your sample. I have read that over time autunite loses water and becomes meta-autunite. Many museums try very hard to maintain the integrity of their good autunite samples. Kenneth Krieger