While most of us tend to think that radioactivity is dangerous, experts say that, like beer, it’s actually good for you in moderation. We learned this while drinking radioactive beer at Bad Jimmy’s Brewing Company in Ballard on Wednesday during the “radioactive edition” of Astronomy on Tap Seattle.
University of Washington astrobiology professor Rory Barnes did the math on the beer. Figuring that a pint is about 90 percent water, carbon is about ten percent of the rest. That works out to 4.5 grams, or about 200 billion carbon-14 atoms. Carbon-14 has a half-life of 5,730 years, which Barnes said means that, in your glass, there’s about one atomic decay every second.
“You are all drinking radioactive beer,” he said. Nobody stopped. I was sipping on a red IPA which was delightful and may have been even a bit more radioactive than the others!
Barnes noted that while we think of Chernobyl or Fukushima when we think about radiation, the process of radioactive decay is pretty important.
Radioactivity is good
“If it weren’t for the radioactivity inside our planet we’d all be dead,” he said. Barnes explained that decay of uranium, thorium, and potassium inside the Earth produces about 50 terawatts of energy, or about 0.1 watt per square meter on the surface. That much energy could run our entire civilization if we could capture it. As it is, it drives geologic processes such as plate tectonics, which helps regulate the amount of carbon dioxide in our atmosphere.
“It’s really important that the planet does a good job of keeping it from building up to too high of a level or dropping down to too low of a level because then our Earth would not be habitable,” Barnes explained. “Without (plate tectonics) the carbon dioxide would either build up and our planet would roast or it would get drawn down and our planet would freeze.”
Earth is in a sweet spot as far as this internal energy goes. Mars generates less than half the energy Earth does and is geologically dead. Jupiter’s moon Io generates a whopping two watts per square meter and is wildly active volcanically. For life, conditions have to be just right.
Radioactivity may lead us to ET
Barnes said that this fact could help guide us to other planets that might be likely to harbor life. The trouble is that in order to determine a planet’s internal energy and radioactivity we would have to look inside a rock that is hundreds of light years away.
“It’s not really obvious how you do that, but that’s what we need to do,” he said. “I’m sorry to say that the answer is that we can’t at this point. This is the limit of our scientific research right now.”
The James Webb Space Telescope will be able to determine the elements in the atmospheres of distant planets. Barnes said it would make sense to use JWST to look at planets that are near where supernovae have occurred, because these stellar explosions spread the heavy elements needed for this sort of planetary energy generation.
Radioactivity and the ages of stars
UW astronomy post-doc Charli Sakari also uses radioactivity in her work. During her Astronomy on Tap talk she explained how she determines the makeup of stars by looking at spectra of the light they emit. Different elements leave a clear signature in the spectrum, absorption lines created when atoms in a star’s atmosphere absorb certain color wavelengths.
“If we measure how dark those lines are we can figure out how much of those elements is present in the atmospheres,” Sakari said.
It is especially informative to look for uranium and thorium.
“Uranium-238 has a half-life of 4.5 billion years, which is about the age of the Sun, whereas thorium-232 has a half life of 14 billion years,” Sakari explained. “These half-lives are long enough that we can use them to date the ages of the oldest stars in the universe.”
The oldest stars have few elements heavier than helium. Younger stars can contain many heavier elements fused in the cores of the generations of stars that preceded them.
Astronomy on Tap Seattle drew a big crowd to Bad Jimmy’s on a rainy Wednesday night. In fact astronomy and beer lovers were packed in so tightly, and were generating considerable warmth, that the staff popped the garage-type doors open to let in a little fresh air. One wag in the crowd speculated that the robust attendance may have been an indicator of the sorry state of network television. We would say that, in eleven months of events Astronomy on Tap, which is organized by astronomy graduate students at the UW, has delivered plenty of good information and tons of fun. The next gathering is scheduled for Feb. 24.