Refracting gamma rays

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DeltaV
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Refracting gamma rays

Postby DeltaV » Wed May 09, 2012 4:07 pm

Gamma ray optics

D. Habs, M. M. Günther, M. Jentschel, and W. Urban, Refractive Index of Silicon at γ Ray Energies, Phys. Rev. Lett. 108, 184802 (2012)
For x rays the real part of the refractive index, dominated by Rayleigh scattering, is negative and converges to zero for higher energies. For γ rays a positive component, related to Delbrück scattering, increases with energy and becomes dominating. The deflection of a monochromatic γ beam due to refraction was measured by placing a Si wedge into a flat double crystal spectrometer. Data were obtained in an energy range from 0.18 MeV to 2 MeV. The data are compared to theory, taking into account elastic and inelastic Delbrück scattering as well as recent results on the energy dependence of the pair creation cross section. Probably a new field of γ optics with many new applications opens up.

krenshala
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Postby krenshala » Wed May 09, 2012 4:18 pm

Very interesting.

Isn't this the first step toward being able to collimate the beam? Perhaps GRASERs aren't that far into the future after all.

DeltaV
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Postby DeltaV » Wed May 09, 2012 4:23 pm

That's the scary part.

I'm thinking deflection of p11B gammas (if they occur) to minimize lead shield mass. Force them parallel to the thickest lead dimension.

vernes
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Postby vernes » Wed May 09, 2012 8:27 pm

With grasers, you get a way to make a holographic scan of anything it can pass through, with a resolution that goes with that wavelength.

I think Joe Strout will like to hear about this new technology.

Tom Ligon
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Postby Tom Ligon » Thu May 10, 2012 5:31 pm

Learning some years back about x-ray optics was an eye-opener for me. I'd never considered anything more sophisticated than pinhole collimation for them.

Then they came up with x-ray lasers ... basically a carbon or metal rod exposed to x-rays!

krenshala
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Postby krenshala » Thu May 10, 2012 6:13 pm

I've always thought it was really neat that granite makes an excellent lens material for microwave frequencies. ;)

Tom Ligon
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Postby Tom Ligon » Tue May 15, 2012 6:35 pm

I once had a character beam lethal microwaves from a maser thru a granite wall to take out a bad guy. The editor is a physicist and made me go back and do some checking on power loss, with the comment "there's dielectrics in them thar rocks."

So off to the U of Md library, where I got deep into the physics. Bottom line for my story, dielectric constant won't make the microwaves be lost, although any boundary will reflect some. Volume resistivity is what soaks up power, and microwaves will carry thru granite just fine.

But the more interesting observation is that the symbol for dielectric constant in the papers I checked used the same as the symbol for index of refraction in glass! Not only may it use the same symbol, but it works almost the same for wavelengths where the material is transparent. Yeah, granite can make a microwave lens.

Per Wikipedia: http://en.wikipedia.org/wiki/Refractive_index

And then look for the section on dielectric constant.

krenshala
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Postby krenshala » Tue May 15, 2012 6:47 pm

Tom Ligon wrote:I once had a character beam lethal microwaves from a maser thru a granite wall to take out a bad guy. The editor is a physicist and made me go back and do some checking on power loss, with the comment "there's dielectrics in them thar rocks."

So off to the U of Md library, where I got deep into the physics. Bottom line for my story, dielectric constant won't make the microwaves be lost, although any boundary will reflect some. Volume resistivity is what soaks up power, and microwaves will carry thru granite just fine.

But the more interesting observation is that the symbol for dielectric constant in the papers I checked used the same as the symbol for index of refraction in glass! Not only may it use the same symbol, but it works almost the same for wavelengths where the material is transparent. Yeah, granite can make a microwave lens.

Per Wikipedia: http://en.wikipedia.org/wiki/Refractive_index

And then look for the section on dielectric constant.

Every time you post stuff like this, Tom, it makes me want to go out and find some of your stories to add to my (ever growing) book queue. ;)

Tom Ligon
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Postby Tom Ligon » Tue May 15, 2012 6:53 pm

PM your e-mail and I'll see if I can send a .pdf.

Be warned, there was also a sequel, and I might send both.


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