Well spotted Lou, and yes it is particularly intriguing. A couple of
pointers.
First, describing it as an after glow is potentially misleading, in that
it is not necessarily after anything. It is something that is seen at
and around the time when lightning occurs, but can be seen when there is
no actual lightning.
Secondly, the current density in the air sparks is probably not
important as the gamma rays occur during the forked leader when the
current is comparatively low. The high currents are seen in the return
stroke, when far less gamma ray emission is seen associated with the
stroke. In lab experiments they sometimes see gamma ray emission above
the spark at that point.
Nigel
On 06/11/2012 20:43, [email protected] wrote:
Thanks, Nigel
A very good reference. There are certainly lots of variables to consider.
I've only perused it, but I found the long (- 50 minute half-life)
gamma/x-ray after-glow (described on pp.24-5) particularly intriguing.
I haven't had time to look into the lab spark experiments cited, but it
seems important (if difficult) to determine the current density in the
air sparks to get a complete picture.
-- Lou Pagnucco
Lou, the answer is, its complicated, but very interesting and conditions
can be recreated in the lab, and the guy who knows all about this is Joe
Dwyer. He has done an excellent review
http://www.springerlink.com/content/l112wv31n5446564/
You also get gamma rays, and he has shown that these are generated with
a down stroke (ie the bit that you don't see) and appear to be
associated with the formation of each fork in the stepped leader (see
fig 18).
Nigel
