Answer to Question #4071 Submitted to "Ask the Experts"

There is a Web site that claims a small nuclear device can be made in the following way: (1) extract the americium-241 from 2,000 smoke detectors, (2) mix it with Elmer's glue and fill up two halves of a split tennis ball, and (3) bring the two halves of the tennis ball together by means of an M-80 firecracker in a two-foot length of pipe. Is it really that simple?

I think that your question stems from a book called The Radioactive Boy Scout that was published recently. There is a mixture of reality and fantasy in this, so let's try to untangle them. The short answer is that this will NOT make a nuclear weapon. The reason why is sort of interesting.

A smoke detector contains about 1 microcurie of radioactivity. One gram (there are 28 grams in one ounce) of ²⁴¹Am contains 3.4 million microcuries, so a smoke detector contains about one third of a millionth of a gram (about 0.3 micro-grams) of ²⁴¹Am. Two thousand smoke detectors, then, will contain 2 millicuries of ²⁴¹Am, which will weigh about half of a milligram (0.6 mg). To put this in perspective, one teaspoon of water holds 5 grams, or 5,000 mg of water, so we are talking about a half teaspoon of Am from 2,000 smoke detectors.

So let's do a reality check. A nuclear bomb made of uranium contains about 20 kilograms (over 40 pounds) of uranium and is the size of a softball. A plutonium weapon contains about 10 kg of plutonium and is about golf ball sized. Simply put, a half gram of ²⁴¹Am is not going to explode under any circumstances.

There are a lot of other problems here, too. What I think the Web page is trying to do is to give the plans for a "gun type" nuclear weapon, such as the one used in Hiroshima. However, that device used a few tens of kg of uranium instead of less than one gram of ²⁴¹Am. That device, too, used high explosives to shoot one half of a sphere of uranium down a modified naval gun barrel to form a critical mass. Two tennis ball halves, a firecracker (even an M-80), and a length of pipe just isn't going to do the trick. The authors of this Web site win a prize for imagination, but they lose in the physics category.

P. Andrew Karam, PhD, CHP