Re: The Extinction Challenge

John Clark (
Sat, 31 Jul 1999 13:27:07 -0400

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Michael S. Lorrey <> Wrote:

>Then why did you say a body the size of a planet would not stop it?

Because it's true, solar neutrino are as common at night as they are in the day, they just come from the ground to the sky not the sky to the ground. Neutrinos don't like to react with matter very much so If you want to build a neutrino observatory you'll need a big target like a 1000 ton tank of distilled water, and you'll need to protect it from the noise of other cosmic rays so you'll have to put it in the deepest mine shafts on the planet, 1.5 to 2 miles deep. Next you'll need to line the tank with very sensitive light detectors. A huge number of neutrinos pass through the tank every second but almost always the do absolutely nothing, however on very rare occasions they turn a neutron into an electron and a proton moving at enormous speed, faster even than the speed of light in water (but not of course in a vacuum), this produces a characteristic flash of blue light that can be picked up by your detectors. Normally you'll see between one and two flashes a month. In the 1987 supernova that happened 200,000 light years away they saw about 20 flashes in one second.

>It follows that if a whole planet will not stop even a large fraction of
>the neutrinos, then a puny human body will not absorb any.

That follows only if the number of neutrinos you're dealing with is small, but they never are. neutrinos are by far the most ubiquitous particle in the universe, far more of them in the universe than atoms or electrons or even photons. The sun alone produces about 1.8 X 10^38 neutrinos a second (there is some controversy over that figure, but it's accurate to within a factor of 3), and that's a trivial amount compared to what a supernova can do.

>What flavor of neutrinos are we talking about here?

I'm talking about electron neutrinos, the other 2 types are even harder to detect.

John K Clark

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