Re: Alpha Radiation [was Re: The Extinction Challenge (fwd)] (fwd)
Wed, 4 Aug 1999 12:11:35 -0700

Robert J. Bradbury, <>, writes, quoting Hal:
> > As noted, this is consistent with John's statement, as absence of
> > interaction does not count as a "hit". The alpha particle would then
> > hit another cell.
> I suspect this is a semantic problem. In physical terms, a "hit" is
> an interaction with any atom. The way John (or Hal?) seem to be using
> it is to imply a "hit" is *only* an interaction that kills or mutates
> a cell.

No, I think there is a pretty well defined notion of what a hit means in this context, particularly when dealing with a neutrino. It passes completely through most atoms, then at some point it interacts with one and deposits its energy. The question at hand is whether this energy will kill the cell.

> Since the killing/mutating potential/probability varies with
> the energy/LET of the radiation/particle in my book this is overloading
> the term "hit". This is especially true if "hits" that do not kill
> or mutate the cell cause damage that causes an immune system reaction
> that produces free radicals that later produce mutations or cell death.
> The question is *what* is hit and how sensitive is your body to that?
> A "hit" to a lipid molecule might produce lipid peroxidation that will
> eventually go away (as the lipids get recycled). A "hit" to a protein
> molecule that causes mutations that are "seen" by the immune system
> can have cascading effects. A "hit" to a DNA moleucle (in the right
> place) can cause mutations that lead to cancer or cell death.

The neutrinos from supernova 1987A had energy 5 to 40 MeV. This is about 4 x 10^-5 ergs, or about 10^-7 calories. If this is deposited in a cell of size about 10 microns, the cell volume will be about 10^-9 cm^3. Depositing 10^-7 calories in 10^-9 g of water will raise its temperature by 100 degrees Celcius.

Granted the energy will need to go through a number of steps to be thermalized, but this still gives a good indication of the size of the interaction we are talking about here. Assuming these figures are corect, it would be like a tiny bomb going off in the cell, with enough energy to raise the entire cell to the boiling point of water. It is hard to see how it could survive a deposit of this much energy.