[ RadSafe ] News: Thundercloud "accelerator" fires gamma-ray beam

[Peter Bossew]

Interesting article. Thanks for the reference.
Similar findings in

Dwyer et al. (2004): Measurements of x-ray emission from 
rocket-triggered lightning
GEOPHYSICAL RESEARCH LETTERS, VOL. 31, L05118, doi:10.1029/2003GL018770, 
2004

Abstract

We report measurements of the x-ray emission from rocket-triggered 
lightning, made during the summer of 2003, using four instruments placed 
between 15 and 40 m from the lightning channels. X-rays were measured 
0–80 ?s just prior to and at the beginning of 73% of the 26 return 
strokes observed. The emission was composed of multiple, very brief 
bursts of x-rays in the 30–250 keV range, with each burst typically 
lasting less than 1 ?s. The x-rays were primarily observed to be 
spatially and temporally associated with the dart leaders with a 
possible contribution from the beginning of the return strokes, with the 
most intense x-ray bursts coming from the part of the lightning channel 
within ?50 m of the ground. Because triggered lightning strokes are 
similar to subsequent strokes in natural lightning, it is likely that 
x-ray emission is a common property of natural lightning.


and in an internal document of the German Bundesamt für Strahlenschutz 
(federal radioprotection agency),
Stöhlker et al.: Fachliche Weiterbildung des 
BfS-Radioaktivitätsmessnetezes etc., 2006, which discusses effects of 
lightnings as short gamma pulses recorded by the German early warning 
system., see att. graph. (The increase og the GDR for about 4 hours is 
due to Rn progeny washout).

Also an event recorded by the EURDEP system (http://eurdep.jrc.it/), 
station LU0077, 27 Feb 2007, has been interpreted by the operator as 
lightning induced gamma flash. (discussed in the AIRDOS report, AIRDOS 
(2007): Bossew, P, De Cort, M., Dubois, G., Stöhlker, U., Tollefsen, T., 
Wätjen, U.: AIRDOS, Evaluation of existing standards of measurement of 
ambient dose rate; and of sampling, sample preparation and measurement 
for estimating radioactivity levels in air. AA N° TREN/NUCL/S12.378241, 
JRC ref. N° 21894-2004-04 A1CO ISP BE. (to be published))

Peter Bossew



John Jacobus wrote:
> >From 
> http://physicsworld.com/cws/article/news/31092
>
> Thundercloud "accelerator" fires gamma-ray beam
>
> Physicists in Japan claim to have the best evidence
> yet that thunderclouds can act as high-energy particle
> accelerators for seconds or even minutes at a time.
> Using an array of radiation detectors installed at a
> nuclear reactor, the team recorded a 40-second burst
> of gamma radiation during a severe thunderstorm.
> According to the researchers, the energy distribution
> of the pulse suggests that the radiation is produced
> by electrons that have been accelerated by the high
> voltages present in a thundercloud (arXiv:0708.2947).
>
> Physicists have known for over a decade that 10 - 20
> MeV gamma rays are produced in millisecond bursts
> during electrical storms. These bursts are believed to
> occur when high voltages in a thundercloud accelerate
> electrons to energies up to about 35 MeV. These
> electrons are slowed down by colliding with atoms in
> the air and as a result give off bremsstrahlung --
> gamma rays that are created when an electron is
> deflected off its course by an atom. 
>
> Much longer bursts lasting up to several minutes have
> also been seen, but these events seem to be much rarer
> than their shorter counterparts. Physicists have yet
> to work out where in the sky the longer pulses are
> coming from – if they are indeed coming from the sky.
> The energy distribution of the pulses and whether the
> pulses contain any other types of radiation such as
> charged particles was also unclear. 
>
> Now Harafumi Tsuchiya of the Cosmic Ray Laboratory of
> Japan’s RIKEN research institute and colleagues have
> used a new bank of direction-sensitive detectors they
> installed at a nuclear power plant to detect a 40-s
> gamma ray burst during a very intense thunderstorm on
> 6 January, 2007. Their system at the
> Kashiwazaki-Kariwa plant on the coast of the Sea of
> Japan was designed to measure the energy distribution,
> composition and source of thundercloud pulses. 
>
> By analysing the energy distribution of the pulse, the
> team was able to say that the pulse was made of
> bremsstrahlung gamma rays. The directionality of their
> detectors allowed the team to confirm that the pulse
> came from the storm and because such gamma rays can
> only travel short distances in the atmosphere, the
> team could also conclude that the pulse was created a
> kilometre or less from the detectors. 
>
> Since the gamma rays arrived about a minute before the
> first lightning strike, Tsuchiya believes that the
> pulse was probably created while electrical energy was
> building up in the thundercloud, rather than when
> energy is being discharged as lightning. He adds that
> the process is likely to begin with a cosmic ray
> passing through the cloud and ionizing the air to
> produce electrons, which are accelerated to towards
> the bottom of the cloud, which has a positive charge.
> These electrons ionize other atoms on the way,
> creating a stream of high-energy electrons. 
>
> Tsuchiya says that bremsstrahlung at MeV energies
> would be focused into a beam that only illuminates a
> small area on the ground, which could explain why so
> few long-duration pulses have been seen. The team plan
> to verify this by placing many radiation detectors
> over a wider area. 
>
> David Smith, a physicist at the University of
> California at Santa Clara and an expert on atmospheric
> gamma ray pulses, agrees that the pulse was made in a
> thundercloud accelerator. “The spectrum looks just
> right for bremsstrahlung”, he says. According to
> Smith, the millions of volts required to produce MeV
> electrons could be sustained in a cloud for seconds or
> even minutes as long as the stream of electrons does
> not become so intense that it causes an avalanche-like
> electric breakdown of the type that could lead to
> lightning. Smith is now designing an airborne
> experiment to test whether lightning flashes are
> preceded by gamma-ray pulses.
>
> +++++++++++++++++++
> "If you guard your toothbrushes and diamonds with equal zeal, you'll probably lose fewer toothbrushes and more diamonds."
> - Former national security advised McGeorge Bundy
> -- John
> John Jacobus, MS
> Certified Health Physicist
> e-mail:  crispy_bird at yahoo.com
>
>
>   

-----------------------------------------------------
Peter Bossew 

European Commission (EC) 
Joint Research Centre (JRC) 
Institute for Environment and Sustainability (IES) 

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