Dear Science,
Despite going into the social sciences, I’ve always been
fascinated by nuclear physics. You mentioned heavy water in a recent
post on Slog, and it made me want to ask some questions about the
stuff: How is it made? Is it toxic at all—that is, could I drink
it and notice any difference? Is it actually heavier than “normal”
water? If it wouldn’t kill me to drink the stuff, is it expensive and
something I could buy a gallon of in order to impress my geek
friends?
If you want to build a backyard nuclear reactor, heavy water is
your best bet. It’s all about the hydrogen. Water—heavy or
light—comprises an oxygen atom and two hydrogen atoms. Most
hydrogen nuclei are just lonely little protons. (If you know who
Ronald McDonald is, but don’t know this about hydrogen, please go back
in time and slap yourself.) Rarely, a neutron or two accompanies
the proton in hydrogen—doubling or tripling its weight. Heavy
water is just regular old water, in which at least one of the hydrogen
atoms has a neutron.
So, is heavy water actually heavier than regular water? Yep, but not
by much. You drink heavy water all the time. It’s present in all water
in teeny, tiny amounts; 1 in about 3,000 water molecules is actually
heavy water. Since the chemical properties of the heavier
hydrogen-nucleus-with-a-neutron are slightly different, heavy water
starts to gum up all manner of body parts. Eventually, if you drank
enough purified heavy water—more than 20 gallons, at least a
quarter heavy—you’d die. A disgruntled Canadian tried to kill
his coworkers this way. He wasn’t all that successful.
Making heavy water is all about separating out the heavy water from
the light, through distillation or some other trickery. Given how close
chemically heavy water is to light, this is hideously expensive.
Only a few plants around the world can even do it. Buying five liters
of heavy water where both hydrogen atoms have the extra neutron would
cost you about $2,000. On the plus side, you could impress your geek
friends with sinking heavy-water ice
cubes.
Okay, but I promised you a backyard nuclear reactor. If you want to
start up a nuclear chain reaction, you need to purchase plutonium
(difficult, as even the Libyans aren’t selling any more), enrich
uranium for its more fissionable isotope 235, or use unenriched uranium
with heavy water. Given the choice between enriching
uranium—which has a tendency to explode violently when piled
too high—or enriching water (for heavy water), the sensible
among us choose the latter.
Incendiarily Yours,
Science
Send your questions to
dearscience@thestranger.com
