# The Naked Scientists Forum

### Author Topic: What is the formula for electron propagation distance  (Read 2502 times)

#### Breakable

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##### What is the formula for electron propagation distance
« on: 08/03/2010 22:40:51 »
Hi,
I am trying to calculate electron propagation distance (dose rate?) in a material.
Specifically my interest is to calculate how much of the beta radiation exits trough the front of CRT, because I cannot find any reliable source for this information.
The only information I was able to find to base my calculations on was
From which I was able to make some guesstimates, that most of the radiation should stop at 0.35mm in case of 25kev beam. The question is then why the CRT tube is so thick, and additionally shielded?
One of the interesting parts I was able to see in the graph, is that at the end of the x axis, the curves start to go perpendicular to the x axis, which would suggest there some sort of effect allows part of the radiation to pass (tunneling effect?).
Can somebody please help me find the correct formula in an understandable form? I am really afraid of getting lost inside "DIN 6800-2" or documents of similar complexity. I promise I will not abuse this dangerous information! ;)

#### Geezer

• Neilep Level Member
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• "Vive la résistance!"
##### What is the formula for electron propagation distance
« Reply #1 on: 08/03/2010 23:55:34 »
One piece of information:

I believe the face of the CRT is very thick for reasons of safety. People have been known to throw heavy objects at televisions. If the evacuated envelope is breached it tends to implode and there is some danger that the electron gun and tube neck will become a dangerous projectile. The reinforced face helps to prevent a breach and, in the event that one does occur, it acts as a high inertia shield.

I'm not sure which "shield" you are referring to. Do you mean the conductive coating (aquadag) on the outside of the tube? If so, I think it's main purpose is to act as the ground plate of a very high voltage capacitor to help smooth the EHT.

BTW, disconnected CRTs are quite capable of charging up this built in capacitance from just about anything. It's not a very large capacitance, but it can deliver quite a jolt and cause an unsuspecting technician to drop the CRT on the floor.

#### Breakable

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##### What is the formula for electron propagation distance
« Reply #2 on: 09/03/2010 13:53:06 »
Thank you for the information, but now I have even more questions, which is not what I want
Regarding the shield I was expecting that the mask is connected to the ground, to allow for electron flow. It seems Aquadag is used for this purpose (and other purposes).
Does that imply that the electrons that bounce of the phosphorus surface cannot escape the tube from in the front?
I still would love to get a propagation formula, and see what can the results be for electron beam vs glass, as there seems to be 0 information about it in popular sources:

#### Bored chemist

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##### What is the formula for electron propagation distance
« Reply #3 on: 09/03/2010 19:44:01 »
The electrons stop in a very short distance when they hit the screen.
But, when they do this they generate Xrays and those need more shielding- thick lead or barium filled glass is used.

#### Breakable

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##### What is the formula for electron propagation distance
« Reply #4 on: 10/03/2010 10:10:06 »
I think its a good idea to calculate the distance.
It is not scientific to say "short distance" without knowing what it is.

#### Bored chemist

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##### What is the formula for electron propagation distance
« Reply #5 on: 10/03/2010 22:01:12 »
"From which I was able to make some guesstimates"
"It is not scientific to say "short distance" without knowing what it is."

LOL.

#### Breakable

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##### What is the formula for electron propagation distance
« Reply #6 on: 11/03/2010 10:43:05 »
I am sorry if I made you angry, this was not what I was trying to achieve.

The original request was:
"Can somebody please help me find the correct formula in an understandable form?", this is why I am referring to my calculations as guesstimates.I was not saying I am right in my original post, I was saying that I am guessing, and I need to improve.
You were making a statement, and provided no proof. This is not good for me.

I was referred to some information at: