Way to make Gamma Ray flashes

[Martin]

http://www.aip.org/pnu/2006/split/789-2.html?source=rsspnu

 

http://scitation.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=APPLAB000089000002021113000001&idtype=cvips&gifs=yes

 

it takes a beam of electrons

you scatter laser light off the beam, and the light picks up a lot of energy from the beam

 

the resulting gamma can be used to create electron-positron pairs

and supply useful amounts of positrons for other purposes

[YT2095]

Cool!

 

anymore data on Laser power and Freq, and the electrical charge used?

I wouldn`t mind trying this setup in the lab myself

[Martin]

Cool!

 

anymore data on Laser power and Freq' date=' and the electrical charge used?

I wouldn`t mind trying this setup in the lab myself [/quote']

 

that is all the information I have.

I was hoping swansont might comment, since I believe laser physics is one of his professional interests.

[[Tycho?]]

That is neat.

 

How does it work though, how does the electron beam transfer energy into the laser light?

[insane_alien]

tycho, i may be wrong(probably am), but the electrons could add energy to the laser light by relativistic effects. if the electron beam can reflect the laser light to some extent(this happens doesn't it?) then the electrons will transfer momentum to the photons resulting in a higher frequency and energy. blue-shifting in effect. the same could be done by firing a laser at a mirror coming at you near c. mirror would probably hurt more though.

[Martin]

tycho, i may be wrong(probably am), but the electrons could add energy to the laser light by relativistic effects. if the electron beam can reflect the laser light to some extent(this happens doesn't it?) then the electrons will transfer momentum to the photons resulting in a higher frequency and energy. blue-shifting in effect. the same could be done by firing a laser at a mirror coming at you near c. mirror would probably hurt more though.

 

this seems like good intuition to me.

 

just for "liberal arts education" or general knowledge

http://en.wikipedia.org/wiki/Compton_scattering

 

this is about the "reflection" or scattering of Xrays by a STATIONARY electron. which was observed by John Holly Compton around 1923.

 

for ordinary mild visible light, and electron doesnt have much "cross section" or chance of scattering, but with shorter wavelength higher energy light it is more apt to scatter the light. And Compton observed this in lab and quickly got the Nobel for it, in 1927.

 

Now if you understand the case with a STANDING STILL electron, and want to extend that to the case of a moving electron it is kind of a change of perspective or frame. You put yourself in the shoes of an electron in a BEAM going some goodly fraction of c. If you shine even ordinary visible light in his eyes then HE is going to perceive it as Xray (because of doppler shortening of wavelength), so he is going to be able to scatter some of it

 

and some he may even scatter SOME part of it roughly back in the direction it came from,

that is roughly in the direction he is going

 

so by reflecting the light in a speeding mirror you do a kind of alchemy like turning straw into gold-----you take ordinary visible light and turn it into very short wavelength Xray light----much higher photon energy.

 

the extra energy comes out of the electron, just as it would out of a moving mirror-----the electron is slowed down by the collision with the photon.

 

there is more to say about this. Alien already said the main idea. I was hoping swansont would comment, or give a reference, and he may yet do so.

 

=============

 

tycho, think about the example of a solar sail

when a photon hits a mirror and is reflected back there is conservation of momentum and if the mirror is free to move (not bolted to the table) it will acquire a microscopic bit of momentum

 

so you can bleed momentum out of light and give it to a mirror (the solar sail)

and the reaction is reversible----you can slow down (even stop) an oncoming mirror by bouncing light off it---which bleeds momentum out of the mirror and transfers it to the reflected light

 

the momentum of a photon is just E/c where E is the energy

so increasing a photon's momentum automatically increases its energy----the two are proportional

[Martin]

in that Wikipedia on COMPTON SCATTERING there was this short bit about INVERSE Compton scatter

 

===quote===

Inverse Compton scattering

Inverse Compton scattering is important in astrophysics. In X-ray astronomy, the accretion disk surrounding a black hole is believed to produce a thermal spectrum. The lower energy photons produced from this spectrum are scattered to higher energies by relativistic electrons in the surrounding corona. This is believed to cause the power law component in the X-ray spectra (0.2-10 keV) of accreting black holes.

The effect is also observed when photons from the Cosmic microwave background move through the hot gas surrounding a galaxy cluster. The CMB photons are scattered to higher energies by the electrons in this gas, resulting in the Sunyaev-Zel'dovich effect.

===endquote---

 

this is what we are talking about

 

CMB photons are very tame, but they can be turned into more energetic ones by collision with hot electrons, that is called SZ effect

 

so in connection with this gammaray thing, remember "inverse Compton scattering"

 

here is Wiki about the SZ effect

http://en.wikipedia.org/wiki/Sunyaev-Zel%27dovich_effect

 

===================

 

another "liberal arts" thing to know about is GZK

http://en.wikipedia.org/wiki/GZK_cutoff

 

our universe is being gradually figured out by detectivework using clues like this SZ and GZK business

it is another case where a particle, if it is going really fast, can have a significant larger "cross-section" for interacting with even a CMB photon (a microwave photon, really weak from our perspective),

[timo]

I might be missing the point but for me it seems that from the point of view of physics, there is nothing spectacular going on. Photons are scattered on electrons.

 

 

A little cooking-recipe:

If one is only interested in the possible energies and momenta of the scattered photon, calculating this is not too hard:

 

0) Given is an initial photon and an initial electron with four-momenta p1 and p2, respectively. They scatter. What one is interested in is the momenta of the scattered particles as a function of some parameters. I´ll denote the momenta of the scattered particles by k1 and k2. Quick note on my notation: [math] p_1 = (E_1, \vec p_1) [/math].

 

1) Do a Lorentz Transformation T to a system in whcih p1+p2 = (Ecms, 0, 0, 0). Ecms is the energy in that system. Its value doesn´t matter here.

 

2) In that frame of reference (the so-called center of mass system), [math] \vec p_1 = -\vec p_2 [/math] and due to conservation of momentum and energy also [math] \vec k_1 = -\vec k_2, |\vec k_1| = |\vec p_1| [/math].

 

3) All possible k1 and k2 can be obtained by rotating [math] \vec p_1, \ \vec p_2 [/math] by an arbitrary degree around an arbitrary axis. The energy entries are fixed by [math] \vec k_1, \ \vec k_2[/math] and the particle masses. The degrees of freedom for a rotation in 3D is two, so I´ll assume the rotation is described by two angles A and B for the following.

 

4) Determine k1 and k2 as a fucntion of A and B.

 

5) Apply the inverse Lorentz transformation T^-1 on k1 and k2 to get back to the original frame of reference (lab system).

 

6) The back-transformed k1(A,B) and k2(A,B) are all possible energies and momenta for the scattered particles. Investigate them for whatever property you´re interested in.

 

Note: Above is rather generic and can be substantially simplified for the given case. The key point only is that you do a Lorentz Transformation to a system where the scattering process looks simple.

 

 

@YT: In theory, the properties of the laser do not matter. You just need photons. Practical applications in which you might want to have a controlled and measurable flux of high-energetic photons are a different issue, of course. Charge used is the elementary charge, of course (electrons).

@[Thyco?]: It´s a normal scattering process.

@insane_alien: The explanations seems ok but the increased energy of the photons imho is not really a relativistic effect. You can also increase the energy of an incoming tennis ball by hitting it hard with your racket.

[insane_alien]

yeah i probably could have worded it better.

[YT2095]

the only thing I can envisage as something that would work would be using a laser to create an ionised path that electrons could flow along.

is that even close to what they`re doing?

[timo]

As I understood it they simply let a beam of light and a beam of electrons collide/cross. I am not really getting your question. Are you asking how to create an electron beam? There´s probably a lot of possibilities doing so. One that comes to my mind is heating a cathode, accelerating the emitted electrons in a constant electric field and focus the mess with magnetic lenses. That´s done in electron microscopes, for example.

If you really want to produce high-energetic gamma rays out of a laser<->electron collision you´ll probably need a very high-energetic electron beam. The threshold value for a gamma to undergo pair production is in the order of 1 MeV. Let´s assume the electrons in your beam would need roughly the same energy as kinetic energy (you can perform the calculation I sketched in above to get a better value), then I´d think you can forget any hope to get that energy form a constant electric field: The voltage needed is 1 million volt.

There are other ways to get high-energy electron beams but I´d have to read up on that, too.

[YT2095]

cheerz, and you`re right, I have no chance of that power range, certainly not at a Constant either.

oh well, nice idea while it lasted

[insane_alien]

YT giving up? or is it a ploy to throw any goverment agents off my making them believe that you can't generate that much power.

[[Tycho?]]

this seems like good intuition to me.

 

just for "liberal arts education" or general knowledge

http://en.wikipedia.org/wiki/Compton_scattering

 

this is about the "reflection" or scattering of Xrays by a STATIONARY electron. which was observed by John Holly Compton around 1923.

 

for ordinary mild visible light' date=' and electron doesnt have much "cross section" or chance of scattering, but with shorter wavelength higher energy light it is more apt to scatter the light. And Compton observed this in lab and quickly got the Nobel for it, in 1927.

 

Now if you understand the case with a STANDING STILL electron, and want to extend that to the case of a moving electron it is kind of a change of perspective or frame. You put yourself in the shoes of an electron in a BEAM going some goodly fraction of c. If you shine even ordinary visible light in his eyes then HE is going to perceive it as Xray (because of doppler shortening of wavelength), so he is going to be able to scatter some of it

 

and some he may even scatter SOME part of it roughly back in the direction it came from,

that is roughly in the direction he is going

 

so by reflecting the light in a speeding mirror you do a kind of alchemy like turning straw into gold-----you take ordinary visible light and turn it into very short wavelength Xray light----much higher photon energy.

 

the extra energy comes out of the electron, just as it would out of a moving mirror-----the electron is slowed down by the collision with the photon.

 

there is more to say about this. Alien already said the main idea. I was hoping swansont would comment, or give a reference, and he may yet do so.

 

=============

 

tycho, think about the example of a solar sail

when a photon hits a mirror and is reflected back there is conservation of momentum and if the mirror is free to move (not bolted to the table) it will acquire a microscopic bit of momentum

 

so you can bleed momentum out of light and give it to a mirror (the solar sail)

and the reaction is reversible----you can slow down (even stop) an oncoming mirror by bouncing light off it---which bleeds momentum out of the mirror and transfers it to the reflected light

 

the momentum of a photon is just E/c where E is the energy

so increasing a photon's momentum automatically increases its energy----the two are proportional[/quote']

 

Thats pretty neat, I wouldn't have thought of the blue shifting part of it. Good explanation by the way.