Re: Dawkins and nuclear physics
- From: Hatunen <hatunen@xxxxxxx>
- Date: Mon, 28 Sep 2009 13:00:28 -0700
On 28 Sep 2009 07:09:45 -0700, TomS <TomS_member@xxxxxxxxxxx>
wrote:
In Dawkins' latest book, "The Greatest Show on Earth", he discusses
some of the nuclear physics involved in radioisotope dating.
It seems to me that this could be wrong on some of the details. (The
treatment is on pages 92 and following.)
He says, "There are several kinds of radioactive decay, which offer
opportunities for useful clocks." And, "All these kinds of instability
involve neutrons."
1) A neutron turns into a proton.
2) A proton turns into a neutron.
3) "A stray neutron happens to hit a nucleus and knocks out one proton,
taking its place."
4) "... an atom ejects a so-called alpha particle." "The atom changes
to whichever element is two below it in the periodic table."
My complaints about these:
1) Maybe I'm being nit-picking,
You are.
but I wouldn't say that a proton
turns into a neutron, but rather that a nucleus emits an electon and
an anti-neutrino with the effect that the number of neutrons goes down
by one and the number of protons increases by one. (If that were all I
had to complain about, I wouldn't say anything.)
That's like saying "I'm going to remove my shoes, socks, pants
shirt and underware and put on another set of shoes, socks, pants
and underware" instead of simply saying "I'm going to change
clothes."
2) This is really a nucleus emitting an anti-electron (positron) and
neutrino. (I think that's what he means.)
3) A neutron hitting a nucleus isn't very significant in radioisotope
dating, and I don't think that the effect of knocking out a proton is
characteristic of it. More often, doesn't the neutron initiate fission,
as in a chain reaction?
You seem to be doing well up to this point at being tendentious
and overly detailed. No. A neutron doesn't intitiate fission
unless the particular nucleus being struck is a fissionable
isotope.
4) My only complaint is about "two below it in the periodic table".
If you look at a periodic table, and look two *below* copper, you will
find gold. But an alpha-decay of copper (I don't think that there is
such a natural reaction in such a light nucleus, but if there were) would
take it to cobalt, two *before* (or to the left of) it.
I'm guessing that most of us took "two below in the periodic
table" to mean the element of atomic number two less than the
original nucleus, but you actually do have a point that the
periodic table is a specific thing laid out a specific way and
"two down" has quite a different meaning than that. "Up" and
"down" on a physical copy of the table would result in an element
with similar chemistry.
If I were describing the kinds of radioactive decay important in
dating, I would rather enumerate:
a) Alpha decay.
b) Beta decay.
c) Orbital electron capture.
There are other infelicities in the description that, I think, could
be misleading to the reader, but I won't go on at length.
I think you're being even more misleading by obfuscating with too
much detail a subject that only requires the layman's
approximation.
--
************* DAVE HATUNEN (hatunen@xxxxxxx) *************
* Tucson Arizona, out where the cacti grow *
* My typos & mispellings are intentional copyright traps *
.
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