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It’s All About the Number 220 Today


by Bill Chameides | February 20th, 2012
posted by Erica Rowell (Editor)

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What’s in a number.

Numbers are all around us. Today we look at one.

Say you eschewed NPR on this morning’s drive to work for some soothing classical music — or maybe some classic rock, depending on how you roll — to begin the workweek on a stress-free note. Chances are, you would have heard the number 220 along the drive. Musically, a sound vibrating at 220 cycles per second (also referred to as 220 Hertz) is the A note below the middle C on a piano. (The A an octave above the 220 frequency — 440 Hertz — is known as the standard pitch; it’s the most common note on a tuning fork.)

Reading the news also might turn up 220. On a major downside, earlier this month it was reported that Europe’s recent deep freeze was responsible for the deaths of more than 220 people in just one week. Lows dropped to almost minus 40 degrees Fahrenheit in some places as a strong negative phase of the Arctic Oscillation developed. The current death toll has risen to over 650.

On a less depressing note, it also turns out that 220 miles is the maximum distance an all-electric Tesla Roadster can travel on a single charge.

On the science front, here’s a little tidbit on the radon isotope 220Rn, also known as thoron. Like other isotopes of radon, 220Rn has 86 protons — called its atomic weight. What distinguishes 220Rn from other radon isotopes are its 134 neutrons. 220Rn is a natural decay product of the most stable of the thorium isotopes (232Th), and in turn decays in a little less than a minute, eventually leading to the generation of lead.

Even though 220Rn is radioactive, it’s not much of a health threat. Couple reasons why. First, thorium, its parent compound, is relatively stable. Second, 220Rn decays so quickly that very little of the gas diffuses out of the ground to where people can inhale it.

It’s quite a different story for another radon isotope, 222Rn. This one is produced from a decay series initiated by the most abundant of the isotopes of uranium, 238U. But unlike the very short decay rate of 220Rn, 222Rn takes about four days to decay, which gives it enough time to diffuse out of the ground and build up inside of poorly ventilated basements and crawlspaces. Believe it or not, this isotope is connected to a major health problem: According to the Environmental Protection Agency, exposure to 222Rn is responsible for about 20,000 lung-cancer deaths per year. Not a bad idea, therefore, to have your home tested for radon. You can do it yourself — go to EPA’s radon information page to find out how.

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