Skin Effect VS Gamma Ray

  • #1
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Skin Effect:

93c6c445aefed3e6d8f6c8f6c4e779e1.png
. where
f7f177957cf064a93e9811df8fe65ed1.png
= resistivity of the conductor
4d1b7b74aba3cfabd624e898d86b4602.png
= angular frequency of current = 2π × frequency
661cb9a9fadf9b56a1d176ec19e7212d.png
= relative magnetic permeability of the conductor
9d7d948f0c85e55e1c799c1b3087b7be.png
= the permeability of free space ------------------------------ From Wiki

According to Skin Effect, the higher the frequency, the less that a EM wave can penetrate an conductor.
Since Gamma Ray is 300EHz (E = 10^18), it should be relatively easier to be stopped, but that doesn't seem true.

Why is the high frequency Gamma Ray cannot be relatively easy attenuated?
 

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  • #2
davenn
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Hi there
welcome to PF :)

Skin effect is referring to an RF current flowing in a conductor

I have never heard of it as an effect when a metallic object is irradiated from an external source
I suspect skin effect in the way you were thinking isn't applicable in this situation

Dave
 
  • #3
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Why is the high frequency Gamma Ray cannot be relatively easy attenuated?
Wavelenght so short and energy so high that It penetrates most metals like knife penetrates hot butter
 
  • #4
Baluncore
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The skin effect gives the effective depth of current flow in the surface of a conductor when an EM field propagates across that surface at close to the speed of light.

Holes in conductors that are smaller than about one quarter wavelength do not effect EM waves. The holes between metal atoms are big compared with the wavelength of a gamma ray. The ray would pass through the holes in the conductive surface without being reflected by the surface or inducing any regular current in the metal surface.

The arrangement of atoms in a metal crystal will diffract X-rays. Gamma rays have shorter wavelength than the size of an atom. Gamma rays may be absorbed or diffracted by the neutrons in the metal atom nucleus.
 
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  • #6
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Penetration depth is a measure of how deep light or any electromagnetic radiation can penetrate into a material. It is defined as the depth at which the intensity of the radiation inside the material falls to 1/e (about 37%) of its original value at (or more properly, just beneath) the surface.

"Penetration depth" is a term that describes the decay of electromagnetic waves inside a material. The above definition refers to the depth
338c3e57104bf9520bd1e4ce1070fc90.png
at which the intensity or power of the field decays to 1/e of its surface value. In many contexts one is concentrating on the field quantities themselves: the electric and magnetic fields in the case of electromagnetic waves. Since the power of a wave in a particular medium is proportional to the square of a field quantity, one may speak of a penetration depth at which the magnitude of the electric (or magnetic) field has decayed to 1/e of its surface value, and at which point the power of the wave has thereby decreased to
d080a120896852f103978593719f9a33.png
or about 13% of its surface value:

[PLAIN]http://upload.wikimedia.org/math/8/f/5/8f5eccd8722c4b4216fe06e6583cbc8e.png, [Broken]
7ce27f3e4d8902d814f8c4506cc4340c.png
denoted the skin depth,
93c6c445aefed3e6d8f6c8f6c4e779e1.png

338c3e57104bf9520bd1e4ce1070fc90.png
denotes the penetration depth -------------- Wiki: http://en.wikipedia.org/wiki/Penetration_depth



So the Penetration Depth as a function of frequency
upload_2014-10-6_10-27-17.png
Which is still saying the higher the frequency, the less it penetrates.



As I tried to relate skin depth and energy, skin depth is defined as the depth that renders the energy decays to 1/e^2. Could it be that the Gamma Ray is so energetic, so that even at 1/e^2, it is still very powerful?
 

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  • #7
Baluncore
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Very big fish swim along a net. Middle sized fish get caught in the holes of the net. Small fish swim through the net as if it was not there.
You should not apply mathematics from one field of physics to another without understanding the similarity of the physics behind the two situations.

Skin effect is a macroscopic property that is quite irrelevant to microscopic wavelength gamma rays. Skin effect requires there to be a conductive mesh surface, encountered by an EM wave with wavelength significantly longer than the size and spacing of the holes in the conductive mesh surface.

No matter how much you quote wikipedia and apply wishful thinking, you will not change the fundamentals of physics.
 
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  • #8
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Skin effect is a macroscopic property that is quite irrelevant to microscopic wavelength gamma rays. Skin effect requires there to be a conductive mesh surface, encountered by an EM wave with wavelength significantly longer than the size and spacing of the holes in the conductive mesh surface.
This is what helps me to understand the physics. Thanks

I know from facts that my proposition is wrong, that's why I am here trying to understand why it
is wrong :D
 
  • #9
analogdesign
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Hugo,

Baluncore gave you the answer. Your equation does not apply for gamma rays because of the reason Baluncore stated below.

The skin effect gives the effective depth of current flow in the surface of a conductor when an EM field propagates across that surface at close to the speed of light.

Holes in conductors that are smaller than about one quarter wavelength do not effect EM waves. The holes between metal atoms are big compared with the wavelength of a gamma ray. The ray would pass through the holes in the conductive surface without being reflected by the surface or inducing any regular current in the metal surface.

The arrangement of atoms in a metal crystal will diffract X-rays. Gamma rays have shorter wavelength than the size of an atom. Gamma rays may be absorbed or diffracted by the neutrons in the metal atom nucleus.
 
  • #10
sophiecentaur
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This is what helps me to understand the physics. Thanks

I know from facts that my proposition is wrong, that's why I am here trying to understand why it
is wrong :D
Reflection at the surface of a metal (RF frequencies) can be considered as the effect of currents induced in the surface (i.e. skin effect). However, when the energy of the photons is high enough, the photons will pass through without disturbing more than a small percentage of the electrons. There is an intermediate case (photoelectric effect) where the electrons are so wildly excited by the incident photons (visible and UV) that they can be ejected from the surface.
 
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  • #11
dlgoff
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However, when the energy of the photons is high enough, the photons will pass through without disturbing more than a small percentage of the electrons.
When the frequency (energy) is high enough, the optical properties of solids comes into play.
The velocity of propagation of a electromagnetic wave through a solid is given by the frequency-dependent complex refractive index N = n - ik where the real part, n is related to the velocity, and k, the extinction coefficient is related to the decay, or damping of the oscillation amplitude of the incident electric field. The optical properties of the solid are therefore governed by the interaction between the solid and the electric field of the electromagnetic wave.
Absorption and extinction coefficient theory
 

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