Re: The Extinction Challenge (fwd)

Robert J. Bradbury (
Sat, 31 Jul 1999 10:25:07 -0700 (PDT)

> Michael S. Lorrey <> wrote:

> John Clark wrote:
> >
> > Billy Brown <> Wrote:
> >
> > >If it were all neutrinos an average human would stop a grand total of maybe
> > >10^-17 % of that flux, which amounts to around 10^-7 electron volts -
> > >in other words, less than one interaction.
> >
> > I have no idea what you're talking about. You seem to saying that a human
> > body would not absorb even one neutrino from a nearby supernova, but
> > you can't possibly mean that.
> Then why did you say a body the size of a planet would not stop it? 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.
This gets messy, though the mass of the Earth exceeds the mass of a human by 10^23, the vertical column above a human (on the side away from the SN) exceeds the height of a human by ~6 million. The mass of the atmospheric column has to be much much less (when you are on the side facing the SN). The interaction rate though depends on the neutrino density and the number of atoms in the body.

Since a big tank of water or chlorine containing liquid (i.e. current neutrino detectors) will interact with 5-20 neutrinos for a SN event (at some distance like a nearby galaxy), I would have to believe that the neutrino density for a nearby event would be sufficient to cause at least a few interactions with the mass of the human body.

But I would argue that the event would have to be *very* close to have a life-span decreasing effect. [Otherwise we wouldn't be here today!]