Delayed Radiation From Lightning Storms

[ChrisSmolinski]

Science, Vol 304, Issue 5667, 43 , 2 April 2004

AMERICAN PHYSICAL SOCIETY MEETING:
Lightning Strikes and Gammas Follow?
Kim Krieger

MONTREAL, CANADA--More than 6000 physicists braved an early spring
freeze here from 22 to 26 March for the American Physical Society's
largest-ever March Meeting.
The next time an electrical storm lights up a summer night, be aware--
the sky's glowing in the dark for longer than you might imagine.
Gamma rays shoot out of the sky minutes to hours after lightning
strikes. Nuclear reactions fizzing in the atmosphere may be the
source, and lightning could be the trigger, researchers reported at
the meeting. The late-blooming rays, discovered by Mark Greenfield
and colleagues at the International Christian University in Tokyo,
Japan, could point to an unsuspected source of nuclear processes in
the atmosphere and may give physicists new insights into how
lightning forms.
"[Greenfield] seems to be on to something very intriguing," says
Joseph Dwyer, a physicist at Florida Institute of Technology in
Melbourne. "The implications are big."

Greenfield's group began chasing lightning in 1999, after gamma ray
detectors atop the university's physics building recorded radioactive
rain--a documented result of radon gas in the atmosphere, but one the
physicists had never heard of. Their interest piqued, they started to
pay closer attention to the weather. Another surprise came after a
lightning storm. Immediately after lightning crackled through the
atmosphere, the detectors would register a burst of gamma rays,
followed about 15 minutes later by an extended shower of gamma rays
that peaked after about 70 minutes and then tapered off with a
distinctive 50-minute half-life.

Lightning packs a 10-million-volt punch, rending the sky with massive
electric fields. Physicists know that the fields accelerate
electrons, which streak upward and release gamma rays as they
decelerate. These gamma rays burst just microseconds after the
lightning irradiates the sky. Delayed gamma rays, though, had never
been reported before. The timing of the gamma rays--the delay of a
few tens of minutes, and the characteristic 50-minute half-life --
suggests that they come from nuclear reactions in the atmosphere,
Greenfield says. But it would take millions of electron volts of
energy to spark such reactions--an amount some physicists think could
be supplied only by lightning-triggering cosmic rays, so for now the
ultimate source of the reactions is anybody's guess.



Whatever the cause, Greenfield and colleagues suspect that the
lightning's electric field sends positive particles, perhaps ionized
hydrogen atoms, careening into other atoms in Earth's atmosphere
powerfully enough to cause nuclear reactions. The researchers suggest
that accelerated protons slam into argon-40, a common isotope in the
atmosphere, and transform it into chlorine-39. The chlorine then
decays into excited argon-39, immediately giving off a gamma ray as
it relaxes. Chlorine-39 has a 56-minute half-life, which fits nicely
with the observed gamma rays. But Greenfield says the gamma rays
could also come from many different reactions with an average half-
life that just happens to match the observed 50-minute half-life.
To determine which atoms are giving off gamma rays, the group has set
up a high-resolution detector to measure the energies of the rays and
see whether they match the signature of argon-39. To make such
sensitive measurements, the detectors must be within a few hundred
meters of the source of the gamma rays. For now, they're sitting on a
rooftop, waiting for lightning to strike.

[dlsworks]

Yes,....I read that lightning can move electrons at relatavistic speeds. Amoungst that X-rays were reported in >80% of studied strikes with energies in the 10's of MeV.
Darius