Lightning and Gamma Rays

[Enthalpy]

The following idea is wild speculation because I know little about lightning, so it probably deserves its legitimate place in the crank ideas subforum. You have been warned.

 

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In the past years, bursts of X and gamma rays were observed during lightning strikes. This is a surprise and explanations are difficult because energy in a bolt isn't concentrated enough, so to say, to produce such photons: the temperature in the bolt is too low for thermal radiation of X and gamma, and the energy of electrons is too small as well - even if air gets a smaller density in the bolt, even if some electrons travel over a longer distance than the average between collisions.

 

Several explanation attemps are under way, invoking very dynamic processes, and none has yet succeeded as far as I ignore.

 

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My proposal is that the lightning path and the gammas both result from a cosmic ray.

 

Cosmic rays are abundent: at ground level, a wire chamber detector of 2m*1m*0.5m sees over one per second. Over its length, a lightning strike crosses the paths of several cosmic rays, which conduct electricity better than unexcited air does, and since the lightning voltage builds up slowly, the bolt can await a favourable triggering by a set of cosmic rays paths. This isn't new:

http://en.wikipedia....le_in_lightning

 

And then, the X and gamma detectors would just catch the photons produced by the cosmic ray nearest to the ground, on the path created for the bolt.

 

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How to test it? For instance, put several X or gamma detectors on the ground, check if the detector nearest to the impact gets photons. Then, attract the bolt with a vertical fast jet of hot or ionized air for instance, check which detector on the ground gets photons: the one near the jet or the one aligned with the direction of the bolt's previous segment.

 

Marc Schaefer, aka Enthalpy

 

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The test with the direction of the gamma won't be easy because a cosmic ray shower is very broad when it reaches the ground...

 

But since a bolt is rather slow for our present technology, we could check if the gamma rays precede the bolt. Or if other particles from a shower are present.

Edited August 13, 2012 by Enthalpy

[CaptainPanic]

A lightning bolt is a rather narrow phenomenon. It's typically just a few cm in diameter. Cosmic radiation is everywhere. I find it a little weird to suggest that such radiation would cause such a local phenomenon. Also, why would lightning sometimes have a preference for cloud-cloud, and sometimes for cloud-ground discharge if caused by such radiation?

 

If you get something like 1 high-energy particle per m3 per second, and each high energy particle can ionize even multiple molecules, you get just a handful of ions along the entire length of the lightning bolt. It sounds a little too insignificant... Although I have to admit that there are reasons why lightning does not travel in a straight line. It does search for a path of lowest resistance.

 

Btw, I do not pretend that I understand the current popular explanation of why gamma radiation occurs in/near thunderstorms. The text used on that wiki page suggests that the scientists aren't entirely certain about it either.

[Enthalpy]

Within the broad ionization provided by a cosmic ray, the bolt finds its narrow way. A discharge concentrates naturally, unless a very low gas pressure prevents it. And as cosmic rays have all directions (except through Earth) they can seed a horizontal bolt as well.

 

Cosmic rays need over a few GeV to reach the ground; at 10eV per carrier pair, it makes several 100 million carriers on the track.

 

I saw only one ray per second in a detector at the Expo'92 but Wiki suggests 10,000/m²/s at 1GeV which looks enough to build a path.

 

I mistrust the linked explanation where the electric field accelerates lucky electrons. While electrons at 100MeV (since such gamma energies are observed) lose about 0.5MeV/m in air hence can accelerate in a 2MV/m breakdown field, they would still require 100m straight path to get 200MeV. As well, the seeds for hot electrons would need to have >10keV to accelerate further, or >5mm without a collision, and both are impossible from luck at normal pressure and temperature.

 

Electron stopping power of air:

http://physics.nist....Text/ESTAR.html

[Enthalpy]

Changed my mind - on nearly everything...

 

Relativistic electrons can already propagate where the field is insufficient for usual breakdown. So if cosmic rays were the feeds for relativistic electrons, X and gamma rays would be diffuse around a thunder cloud and not synchronized with lightning.

 

Then, the tip of a bolt's leader concentrates a huge field, because the tip is narrow and the propagating bolt brings the high potentials nearer to an other through its short-circuit. Though, normal avalanche electrons (20eV) are slow, and these corresponds to the propagation speed of the leader.

 

The huge field suffices (from 20MeV up), and the locally available voltage as well, to let normal electrons jump into the relativistic valley and propagate away. So, the bolt's leader is a perfect source for these electrons.

 

Relativistic electrons won't multiply much. Over 1MeV their collisional friction is only 0.2MeV/m, which creates electrons of varied energies, while 0.1MeV in the proper direction would be necessary for a new relativistic electron in a runaway (the rest of friction produces photons).

 

 

Even if they multiply a bit, as they propagate in one direction, they would need other particles to propagate backwards to sustain an own discharge path. Positrons can't multiply by impact ionization of atoms and are likely to disappear before having travelled kilometres back, so they're bad candidates.

 

In short: the normal bolt's tip produces relativistic electrons, these don't multiply much, can't sustain an own discharge path, and create energetic photons.

 

This view resembles what Wiki and a paper from 2010 claim:

http://en.wikipedia....ctron_avalanche

I'll reference the paper when I find it.

 

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An experiment reproducing 60kA*1µs from the first strike in a bolt but reduced to 1MV needs only 30kJ. An assembly of commercial capacitors can store this energy, for instance:

http://highenergycor...|1002|1013|1017

50 of these fit in 1.7m * 1.3m * 0.5m. This particular capacitor model or an other may deliver the 60kA, depending on its internal gathering electrodes.

 

A diode-capacitor pump to charge them can use rectifiers and a few transformers made for CRT screens. The slow charge is meant to reproduce the lightning conditions; a Marx generator would apply the voltage brutally on the air, different choice.

 

I imagine the gamma source in a tube with an integral bottom and a removable cap (possibly remote-controlled), a layer of ⁹⁰Sr at the bottom, covered by a layer of 40µm of aluminium (for instance) to stop betas below 100keV, then a fine-meshed honeycomb in the tube to select the desired beta direction over a short distance.

 

The discharge tube must be corrugated as insulators are, but internally as well. The anode must be hollow and deep to brake the electrons in air. One mobile electrode would be nice. The tube contains the X-ray detector and can be submerged in transformer oil or surrounded by concrete.

 

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The Z-machine is said to produce more X-rays than expected from striction; maybe relativistic electrons in the discharge contribute. To enhance this effect, replace the thin wires of tungsten or steel by a light element like lithium or deuterium, and add an anode of a heavy element like tungsten.

 

Marc Schaefer, aka Enthalpy

[EMField]

Because lightning is plasma. Plasma is an electrified medium, not a "hot" gas. And the natural consequence of z-pinches is radiation:

http://www.plasma-universe.com/Pinch

 

Of course the sun is plama, has a magnetic field and emits the same radiation as a z-pinch, but it just has to be fusion, lol, you guys kill me!

Edited September 12, 2012 by EMField

[Enthalpy]

How to decide whether lightning is triggered by cosmic rays or produces X and gamma rays?
wikipedia
versus other processes, for instance
wikipedia
already discussed here
scienceforums

A laser beam, shooting concentrated and in brief pulses from the ground to the clouds, could already trigger lightning. A brilliant mind nicknamed Sapo proposed to install X- and gamma-ray detectors around the laser:

• If ionizing rays are detected, they are produced by the jolt.
• If none is detected, then they usually result from cosmic rays that trigger the jolt.
• Unless theories propose the production of gamma rays only if the jolt progresses slowly, or a similar subtlety.

The original place of this proposal is inaccessible now, and I feel the idea shouldn't get lost.

[swansont]

On 8/13/2012 at 8:36 AM, Enthalpy said:

In the past years, bursts of X and gamma rays were observed during lightning strikes. This is a surprise and explanations are difficult because energy in a bolt isn't concentrated enough, so to say, to produce such photons: the temperature in the bolt is too low for thermal radiation of X and gamma, and the energy of electrons is too small as well - even if air gets a smaller density in the bolt, even if some electrons travel over a longer distance than the average between collisions.

Gammas come from nuclear interactions, so no, you don't get gamma rays.

X-rays, sure. Bremsstrahlung. Or possibly the acceleration of the electrons along the way. For the former you just need to have a few kV of potential, and lightning can have much higher values.

[Sensei]

8 minutes ago, swansont said:

Gammas come from nuclear interactions, so no, you don't get gamma rays.

Electrons with high kinetic energy (>1.022 MeV) during collision with matter will create pair of yet another electron-positron, or during collision will emit high energy photon, which will pair-produce them. Annihilating electron-positron pair will make new gamma photons.

You can make them even in Van de Graaff generator. 20 MV the largest generator was used to fuse couple atoms. Newly produced atom can be excited and emit gamma rays.

 

Edited January 5, 2019 by Sensei

[swansont]

35 minutes ago, Sensei said:

Electrons with high kinetic energy (>1.022 MeV) during collision with matter will create pair of yet another electron-positron, or during collision will emit high energy photon, which will pair-produce them. Annihilating electron-positron pair will make new gamma photons.

What is your evidence that such collisions take place in lightning? Or that there are electrons with an energy difference large enough to do this in the lightning? 

Quote

You can make them even in Van de Graaff generator. 20 MV the largest generator was used to fuse couple atoms. Newly produced atom can be excited and emit gamma rays.

Were these electrons striking a target, or were they striking each other?

[Sensei]

27 minutes ago, swansont said:

What is your evidence that such collisions take place in lightning? Or that there are electrons with an energy difference large enough to do this in the lightning? 

https://en.wikipedia.org/wiki/Terrestrial_gamma-ray_flash

"In 2009, the Fermi Gamma-ray Space Telescope in Earth orbit observed intense burst of gamma rays corresponding to positron annihilations coming out of a storm formation. Scientists wouldn't have been surprised to see a few positrons accompanying any intense gamma ray burst, but the lightning flash detected by Fermi appeared to have produced about 100 trillion positrons. This was reported by news media in January 2011, and had never been previously observed.[27][28]"

..also search for "positron" and "annihilation" in the above article references..

 

[swansont]

That’s not lightning, though.

[Sensei]

1 hour ago, swansont said:

That’s not lightning, though.

You wanted reference, I gave you..

Edited January 5, 2019 by Sensei

[Enthalpy]

"Gamma" is often used for "energy higher than X-rays", but "originating from nuclei" is more correct, sure.

However, cosmic rays make nuclear reactions easily.

If lightning electrons, rather than cosmic rays, create the MeV rays by some process to be determined, then they do have the energy to excite nuclei. One excited state of ⁴⁰Ar is just 1.46MeV above the ground state.