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That? >> a good five days. no question the winds are going to blow offshore for three days in japan. but i'm a little bit concerned say five days from now, a little particle does come off. later in the period, not right now, but say thursday. this piece could be picked up and sent into the central part of the pacific ocean and that would be a shorter trip to the u.s. now, remember, the radiation from chernobyl went around the world many, many times and we still here in america, even though it went over us a number of times, had less than 1/10th of a chest x-ray from that big disaster. >> we'll...

Part, we're not detecting radioactivity. you want to know how much exposure have you had. >> a machine doesn't tell you how much exposure you've had three days ago? >> no. think of it like a camera. you can hear it clicking off as it's giving readings here, which are all low. they're significantly low as compared to anything that would trigger an alarm. that measures alpha, beta and gamma rays. this is just measuring the air constantly around us, 13 microrads per hour, and that's, again, a very low number. >> professor, how does radiation spread over distance? if you are -- the u.s. government...