[ RadSafe ] Article: Sparks made in the lab are found to emit X rays like lightning

[John Jacobus]

>From Nature.
Published online: 28 October 2005
(Original link is listed at the bottom)

Small sparks pack a big punch

Sparks made in the lab are found to emit X rays like
lightning.
Philip Ball
 
Lightning might not be so different from the less
spectacular indoor version.
 
Studying lightning in the lab could be much easier
than previously thought. You don't need to make huge
sparks to get the same kinds of effects seen with
lightning bolts, researchers report: a simple
electrical discharge in the lab can do the trick. 

That's good news for researchers still puzzling over
how lightning works.

Lightning bolts are thought to trigger a process
called 'runaway breakdown'. As the surge of electric
charge passes through the air, it ionizes atoms and
accelerates electrons to speeds that approach the
speed of light, leading to the emission of X-rays and
gamma rays. 

"It is like what happens in a particle accelerator, or
in the X-ray machine at the doctor's surgery," says
Joseph Dwyer, a physicist at the Florida Institute of
Technology in Melbourne, Florida. Sparks generated in
laboratories were thought to involve 'conventional'
breakdown, in which the air is still ionized but the
electrons don't get accelerated to such high speeds.
 
Charged up

"People assumed that conventional electrical
discharges weren't like lightning," says Dwyer. "It
turns out we were wrong." There is a striking
similarity between the two, he says. 

He and his colleagues generated sparks in the
laboratories of Lightning Technologies in Pittsfield,
Massachusetts. This involved charging up a bank of
capacitors to about 100,000 volts each, and then
allowing them to discharge between two metal spheres
held 10 centimetres apart.

In every case, Dwyer and his colleagues detected
X-rays emitted by the spark that resulted. They report
their results in the journal Geophysical Research
Letters1.

Dwyer says that the X-ray intensities he has seen
aren't sufficient to pose a health hazard. But the
findings could help unravel what lightning actually
is.

Enlightening rays

"Lightning remains a mystery," says Dwyer. It doesn't
travel from cloud to ground in one step, but advances
in a series of hops. Each hop produces X-rays. "So
understanding the production of X-rays can tell us
about how lightning propagates," Dwyer says. 
 
Now it seems that researchers may be able to do that
with simple lab equipment. But, he adds, not every
electrical spark is a source of X-rays. He and his
colleagues took their X-ray detectors to the Boston
Science Museum in Massachusetts, where an immense van
der Graaf generator produces a simulated lightning
display for visitors every day. They couldn't detect
any X-rays at all from these artificial blasts,
implying that the museum's 'lightning show' isn't so
realistic after all. 

References
Dwyer J. R. et al. Geophys. Res. Lett., 32. L20809
(2005). | ChemPort |

Story from news at nature.com:
http://news.nature.com//news/2005/051024/051024-12.html

 
  © 2004 Nature Publishing Group | Privacy policy 

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On Oct. 5, 1947, in the first televised White House address, President Truman asked Americans to refrain from eating meat on Tuesdays and poultry on Thursdays to help stockpile grain for starving people in Europe. 

-- John
John Jacobus, MS
Certified Health Physicist
e-mail:  crispy_bird at yahoo.com


	
		
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