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radiation pressure

 
 
danika
 
Reply Fri 16 Oct, 2009 07:24 am
I have read, that in the termonuclear bomb the fusion of the D-T nucleus was started by the explosion of a normal fission atomic bomb, but not directly by its splitted particles but by its X-ray radiation. I cannot imagine, has the X-ray radiation a pressure enough to compress the D-T fuel particles to ignit a fusion procedure? The radiation pressure exists at all?
Regards
Tamás Pásztor
Hungary
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Type: Question • Score: 1 • Views: 1,368 • Replies: 6
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engineer
 
  1  
Reply Fri 16 Oct, 2009 08:40 am
@danika,
No, a fusion bomb (H-bomb) is set off with a fission reaction. The heat from the fission reaction is what starts the fusion reaction.
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DrewDad
 
  1  
Reply Fri 16 Oct, 2009 09:44 am
@danika,
http://en.wikipedia.org/wiki/Teller%E2%80%93Ulam_design

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

Quote:
Fission bomb radiation source

Most of the energy released by a fission bomb is in the form of x-rays. The spectrum is approximately that of a black body at a temperature of 50,000,000 kelvins. The amplitude can be modeled as a trapezoidal pulse with a one microsecond rise time, one microsecond plateau, and one microsecond fall time. For a 30 kiloton fission bomb, the total x-ray output would be 100 terajoules.

Radiation transport

In a Teller-Ulam bomb, the object to be imploded is called the "secondary". It contains fusion material, such as lithium deuteride, and its outer layers are a material which is opaque to x-rays, such as lead or uranium-238.

In order to get the x-rays from the surface of the primary, the fission bomb, to the surface of the secondary, a system of "x-ray reflectors" is used.

The reflector is typically a cylinder made of a material such as uranium. The primary is located at one end of the cylinder and the secondary is located at the other end. The interior of the cylinder is commonly filled with a foam which is mostly transparent to x-rays, such as polystyrene.

The term reflector is misleading, since it gives the reader an idea that the device works like a mirror. Some of the x-rays are diffused or scattered, but the majority of the energy transport happens by a two-step process: the x-ray reflector is heated to a high temperature by the flux from the primary, and then it emits x-rays which travel to the secondary. Various classified methods are used to improve the performance of the reflection process[citation needed].

The implosion process

The term "radiation implosion" suggests that the secondary is crushed by radiation pressure, and calculations show that this pressure is very large. In fact, what happens is that the outer layers of the secondary become so hot that they vaporize and fly off the surface at high speeds. The recoil from this surface layer ejection produces pressures which are an order of magnitude stronger than the simple radiation pressure. The so-called radiation implosion is therefore really a radiation-powered ablation-drive implosion.
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DrewDad
 
  1  
Reply Fri 16 Oct, 2009 09:47 am
@danika,
danika wrote:

I have read, that in the termonuclear bomb the fusion of the D-T nucleus was started by the explosion of a normal fission atomic bomb, but not directly by its splitted particles but by its X-ray radiation.

So it's not even directly by the X-ray radiation, but by the pressure created when the outer layer of material is vaporized by the X-rays.
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contrex
 
  1  
Reply Fri 16 Oct, 2009 10:43 am
This guy starts buying deuterium, we should maybe get alarmed?
DrewDad
 
  1  
Reply Fri 16 Oct, 2009 10:48 am
@contrex,
More likely to kill himself with radiation poisoning than to make a working bomb.

More likely by FAR.
farmerman
 
  1  
Reply Fri 16 Oct, 2009 10:59 am
@DrewDad,
The secret is a huge density of NEUTRONS. Think of the necessary amount like water in a cross section of a pipe. There is a valve at the end of the pipe that needs a certain pressure to open. By compressing the flow through a smaleer and smaller cross section, the water pressure builds up until its velocity and mass is great enough to open the valve. Same thing with a mass of neutrons needed to trigger the Fusion device. Its called Mass Flux or (so many neutrons per unit of cross section aimed at the target. (Looks like a soccer ball.

Youd use a standard TNT explosion to trigger the fission bomb by focusing neutrons into the U corewhich generates yet more neutrons and triggers the fusion bomb. Anything not in that order renders the bomb a big dud. Thats why, many years ago, an H bomb was lost in the swamps of South Carolina. The initial fission "reflectors" were not in the bomb cavity and it dropped from the plane like a 5 ton paperweight. AS far as I know theyre still looking for the damn thing, because it IS leaking alpha and gamma particles
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