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Offline thedoc

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How can fusion occur in a classroom?
« on: 13/03/2014 10:42:27 »
This week a 13-year-old British schoolboy has become the world’s youngest person to carry out nuclear fusion...
Read a transcript of the interview by clicking here
or Listen to it now or [download as MP3]
« Last Edit: 13/03/2014 10:42:27 by _system »


 

Offline syhprum

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Re: How can fusion occur in a classroom?
« Reply #1 on: 13/03/2014 21:02:40 »
Fusion only occurs at high temperatures and densities these various cold fusion scams have frequently been demonstrated to be false.
 

Offline evan_au

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Re: How can fusion occur in a classroom?
« Reply #2 on: 14/03/2014 09:52:52 »
Accelerating ions using electric fields in a vacuum chamber can impart significant energy to the particles - enough to generate X-Rays.  But it's quite a challenge to get beams of ionised deuterium and tritium to collide with each other, instead of the electrodes.

There is one known method for creating fusion at relatively low temperatures and pressures: Muon-Catalysed Fusion.

However, like all public, verified claims of controlled fusion to date, you have to put in far more energy when creating the fusion conditions than the usable power you get out (despite recent announcements from the National Ignition Facility).
 

Offline CliffordK

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Re: How can fusion occur in a classroom?
« Reply #3 on: 15/03/2014 06:25:35 »
Quote from: From Story
Fused together then you got a helium atom. But this helium atoms, it’s very, very energetic. Instead of releasing the energy as heat, it sends out a high energy neutron. So, you can just get a neutron detector, then you can prove that you've done nuclear fusion.

I would ask which reaction occurred:

2H ==> 1H + Neutron
OR
2(2H) ==> 4He ==> 3He + Neutron

How are they ruling out simple fission (which would be endothermic)?

In the first reaction, some simple hydrogen would be formed.  In the second, very rare 3He.  If enough atoms were formed, they should be relatively easy to separate.
 

Offline Bored chemist

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Re: How can fusion occur in a classroom?
« Reply #4 on: 15/03/2014 13:07:35 »
Fusion only occurs at high temperatures and densities these various cold fusion scams have frequently been demonstrated to be false.
LOL
This is fusion at energies around 30KeV
you just called 340 million degrees "cold".



And re
"2H ==> 1H + Neutron"
"Stripping is the immediate and casual explanation of so many ignorant physicists who really think that we are not doing fusion at all in our systems and think all of our neutrons are just knock offs.
I further realize that it is THEIR problem and not ours, but we have to note to them that stripping reactions of the sort they are referring to don't begin anywhere near our level of operation in the fusors. "
from
http://www.fusor.net/board/viewtopic.php?f=14&t=6577&p=44549&hilit=spallation#p44549


« Last Edit: 15/03/2014 13:28:10 by Bored chemist »
 

Offline syhprum

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Re: How can fusion occur in a classroom?
« Reply #5 on: 15/03/2014 16:44:18 »
If producing fusion was only a matter of producing the required high temperature it would be easy peasy presumably it would be happening all the time within the CRT of my old TV.
What is required is a product of temperature and density for a sufficient time.
Modern Uranium 235 Bombs use a similar device to increase the speed of ignition instead of the vastly expensive and difficult control polonium 210 that was used in the first one, in fact the first drawings of atom bombs published in 1946 showed an Xray tube like device as the use of Polonium 210 was still considered secret. 
« Last Edit: 15/03/2014 16:58:51 by syhprum »
 

Offline Bored chemist

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Re: How can fusion occur in a classroom?
« Reply #6 on: 15/03/2014 16:58:56 »
" it would be happening all the time within the CRT of my old TV."
To exactly the extent that your old telly is full of deuterium- i.e. not at all.

"What is required is a product of temperature and density for a sufficient time."
And, with this sort of fusor the time is essentially unlimited and the density is quite high.

Have actually you read how they did it?
Are you aware that this neutron emitter tubes are reasonably readily available?
http://en.wikipedia.org/wiki/Neutron_generator

Are you just saying this is impossible because you don't understand how it's done?
 

Offline syhprum

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Re: How can fusion occur in a classroom?
« Reply #7 on: 15/03/2014 20:39:01 »
Stung by your criticism I carefully re-read the original article although I don't think I missed any thing the first time.
What the school seems to have constructed seems to be an unsophisticated unsealed Neutron generator (I am of course familiar with the commercially available devices), in as much as such devices work by a fusion process they can be said to have constructed a nuclear fusion device but it is not what most people think of as nuclear fusion.
My old TV has an amateur rebuilt CRT which is not as well pumped as the commercial production and in all likelihood contains a small amount of H20 and D2O. 
« Last Edit: 15/03/2014 20:43:05 by syhprum »
 

Offline Bored chemist

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Re: How can fusion occur in a classroom?
« Reply #8 on: 15/03/2014 21:38:14 »
I understand that the mathematicians' definition of "very" is that if a is a small number and b is a small number then a times b is a very small number.
There will be a small number of deuterium atoms in your friend's tube.
And they will probably get ionised and attracted to the cathode but they are vastly more likely to hit almost anything but another deuterium atom because the fraction of other atoms that are deuterium is small. So the likelihood of fusion is very small.

Unsurprisingly that's different from the state of affairs in a fusor where foreign gases are excluded as far as possible and deuterium is plentiful of the order of ten  or a hundred microns of mercury pressure about 10^-4 atmospheres. You might want to compare that with about 10^-9 torr in a CRT (about 10^-12 atm). the difference is so vast it doesn't matter if I'm out by a couple of orders of magnitude here or there.

So previously you said "these various cold fusion scams have frequently been demonstrated to be false."
and I pointed out that 300,000,000K isn't cold.
You said "If producing fusion was only a matter of producing the required high temperature it would be easy peasy presumably it would be happening all the time within the CRT of my old TV."
and that was wrong too.
And you said"What is required is a product of temperature and density for a sufficient time."
so I pointed out that it has plenty of time (unlike an A bomb) and quite a high density.

So, the last thing to address is where you say
"but it is not what most people think of as nuclear fusion. "
Well, it does do nuclear fusion.
It's difficult to see why "most people" wouldn't think of that as nuclear fusion.
 

Offline syhprum

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Re: How can fusion occur in a classroom?
« Reply #9 on: 16/03/2014 09:00:00 »
I suppose I am the only person who when they hear nuclear fusion referred to think of devices like the ITER or Nuclear bombs while most people think of neutron generating tubes. 
 

Offline Bored chemist

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Re: How can fusion occur in a classroom?
« Reply #10 on: 16/03/2014 09:44:43 »
I rather suspect that most people have never heard of ITER.
The fusion reactor that most people know of is the Sun, and I doubt many people think of that as a fusion reactor very often.
An H bomb does fusion. so does ITER. So does the Sun. So does the item in the OP.

At best you have pointed out that most people have a poor understanding of nuclear fusion.
Most people have no sensible idea of, for example, how a mass spectrometer works.
This makes no difference to the fact that mass specs exist, and do mass spectroscopy.




 

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Re: How can fusion occur in a classroom?
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