Re: Alpha Radiation [was Re: The Extinction Challenge (fwd)]

hal@finney.org
Mon, 2 Aug 1999 21:29:09 -0700

Robert J. Bradbury, <bradbury@www.aeiveos.com>, writes:
> "Previous studies by Lloyd et al. (Ll79) showed that at a dose correspinding
> to a surviving fraction of 37%, about 14 particles traversed the nucleus
> for each cell killed. The fact that on average 13 particles may traverse
> a cell nucleus without killing the cell may explain the high efficiency
> with which high-LET particles induce transformed loci."
>
> So, cells *can* survive alpha particles and in most cases it takes a number
> of alpha particles to transform or kill cells. Obviously if 13+ particles
> traverse the nuclei, then many more particles are traversing other areas
> of the cell.

What does this mean, "traverse"? Does that refer to alpha particles which passed through the nucleus without interacting with any atoms there (i.e. alpha particles which don't "hit")? Or does it mean alpha particles which hit and interacted with atoms but without fatal effects?

I have the impression that the alpha particle travels for some distance without interacting with any atoms, then at some point it does pass near an atom's nucleus and causes a large energy deposit there. This is what we are calling a "hit".

John seemed to be saying that *if* an alpha particle "hits", that is, it is absorbed and interacts with atoms in the cell, it causes so much damage that it is virtually certain to kill or mutate the cell it "hits". That is consistent with the statement above if we assume that the 13 particles traversed the nucleus without interacting with any atoms there, and the 14th killed the cell.

> So regarding your original statement:
> >> An Alpha particle will kill or mutate any cell it hits, a rare neutrino that hits
> >> would be almost as deadly.
>
> - Many alpha particles can pass through a cell with no effect.

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.

> - If "sufficient" alpha particles pass through the nucleus and cause
> enough mutations the cell will become cancerous.
> - If *more* alpha particles pass through the nucleus and cause double
> strand breaks, the cell may die.

I think the question is whether you are counting alpha particles which don't interact, or only alpha particles which "hit". If the latter, what do your sources say about the cellular survivability of such an interaction?

> - It takes many more low-LET neutrinos passing through a cell to cause
> damage corresponding to that of a high-LET (but low energy) alpha particle.
> So neutrinos *are not* as deadly as alpha particles.

I think John meant, per interaction. Obviously a neutrino, which John has said can pass through light-years of lead, will go through a cell more easily than an alpha particle which is stopped by a sheet of paper. The question is, for these high-energy supernova neutrinos, *if* one interacts with a cell, how would the damage compare with that caused by an alpha particle which "hits".

> ... Return safety interlocks to normal position....
>
> John, you should assume in any discussions that if the material relates
> to biology and/or nanotechnology that I am likely to have in my personal
> library the relevant sources. If I suggest that you may be inaccurate,
> it is because I have good sources to back up those opinions. My education
> includes computer science, chemistry, microbiology, biochemistry and
> some physics and astronomy. I will willingly and freely admit when I
> am wrong or on swampy ground. However, if you make a claim without being
> able to back it up, I will slice you and dice you and nail you to the wall.

Does this kind of rhetoric move the discussion forward?

Hal