Step 6: Setup Neutron Detection

The proof of fusion (and a quantitative analysis of how much fusion) is obtained through detecting neutron radiation, the byproduct of a D-D fusion reaction. There are three options which will be described. They are in order of descending ease of setup.

-A Neutron Bubble Dosimeter
A bubble dosimeter is a small unit with a gel in it that forms bubbles when ionized by neutron radiation. This is the easiest form of neutron detection available since all you have to do is unscrew the top and set it next to the fusor. Some of the drawbacks are that it is an integrative detector which means all you get is a total neutron emission number over the time that it was used, rather than an instantaneous neutron rate. Additionally, they are somewhat hard to get since the only company to make them is Bubbletech in Canada, which has a minimum order of 3 with steep shipping and handling (expect to spend $700+ if ordering directly from them not in a group buy). Additionally, they tend to be fairly worn out after a year of shelf life (although I've kept mine in a refrigerated storage container at 50*F and it seems to be like new after I think more than a year). The advantage is that calibration data is provided with purchase and of course it is easy.

-Silver Activation
When silver is placed near the reactor (with a moderator [paraffin wax, water, HDPE, etc] between it and the neutron source, since only thermal neutrons will activate the material) it becomes slightly radioactive with decent neutron fluxes. It has a short half life of only a few minutes, but if you quickly put a geiger counter next to the silver, counts can be detected. In my best runs, I have gotten a piece of silver to about 250CPM over background on a CDV-700 geiger-counter. The disadvantages of this are that it requires a decent neutron flux (at least about 100,000 neutrons/s) which is above the average "beginner's first run" neutron rate. Also, it is somewhat difficult to calibrate, and the counts can't be taken until after the fusor has been shut off.

-A Proportional Tube
Tubes can be purchased which are filled with either BF3 or Helium-3 (some very old tubes are Boron-10 lined inert gas tubes). These tubes, similar to a geiger counter, can be used with a counting device to detect electrical pulses when neutrons pass through the tube. Either an all-in-one counter can be used, often made by a company called Ludlum, or a modular counting system can be made using NIM modules. The tube is surrounded by about 2 inches of moderating material such as wax or water. This is by far the most accurate and useful form of neutron detection, however the cost of a new tube is prohibitive to most people, and they are extremely rare on the surplus market. Also, counting equipment can become quite costly.

NIM Configuration: If you chose to make a NIM setup as I have, the typical layout is a charge sensitive pre-amplifier at the head of the proportional tube, which is plugged into both a high voltage power supply generating positive polarity voltage appropriate for the tube (in the range of 800V-2kV generally). The amplifier also hooks into a shaping amplifier, which is followed by a Single Channel Analyzer (for setting the detection discrimination level), followed by a pulse counter and/or rate meter.

Shown in the first picture is my NIM setup, the second picture is the pre-amplifier attached to a moderated helium-3 tube, the third picture is a bubble detector after being exposed to neutrons.
<p><em>I like what are doing making a fusion reactor maybe it will replace a nuclear fisison reactor one day. As long as you play safe with high voltage and radiaition I have no problems. Good luck.</em></p>
<p>Is this even legal since you are maxing radiation which requires a permit. </p>
<p>depens on the country you live in. In the US you need permession but that's just that no 12 year old's are going to try this</p>
<p>A late reply, I know and I'm trying to be Nice ... but Sorry, you are incorrect ... WE are Americans and we don't ever ask permission (especially from the Government) for ANYTHING (including building Nuclear Reactors) that we might wish to do. Also, one of the better designs WAS designed and built by a 12 year old ... American.</p>
<p>lol, I know. I am not even old enough to drive and am looking into building a fission generator for my science project since I really want to win and last years hydrogen battery only got me third place. Age is not even relevant.</p>
<p>Could you use a 2 3/4&quot; 6 way or 5 way vacuum chamber?</p>
Yes, it has been done. 2.75&quot; crosses are generally too small to handle the thermal load of a several hundred watt fusor, the grid will be tiny, and you'd be lucky to get more than 20-30kV in before something arcs over. But purely to achieve fusion, yes it can be done. A 6&quot; spherical chamber is hugely more effective and will result in much higher fusion rates.
<p>okay thanks, I'm not going to use a 2.75&quot;. I thinks it's too small too, but it's so much cheaper. Just wanted another opinion.</p>
<p>Where you by any chance on Mythbusters The Search?</p>
Not to my knowledge
Well.. this is embarrassing lol. One of the contestants had a picture the same as your profile picture in there audition video. They either made one of these or stole your picture lol.<br>
<p>Maybe I didn't read it thoroughly but how does it generate electricity or is it just as an experiment? Can I generate electricity with it? Maybe enough to power a small house?</p>
<p>It's working nuclear fusion, not fusion power. It takes more electricity than it generates.</p>
<p>Well, then what's the point of it? If it takes more power to run than it makes, why would i make one in the first place? It seems like a waste of resources to me. Maybe I'm missing something. </p>
<p>What's the point of 99% of things on this website? The point is to do it. If this is a waste of resources, it seems you're missing the whole point of the maker community.</p>
<p>how much is this gonna cost?</p>
Depends on your goals and schedule. Between 1k and 10k generally, with a very common spot in the 2-4k range.
How much did it cost you to make it?
<p>Per the original article you can put one together for $500. But the original articale was written in the 70's.</p>
<p>Can this be used for turning molybdenum-98 into molybdenum-99 and/or molybdenum-99 into technetium-99 ? Please??</p>
<p>Does Wattage for the reacotr matter? If so, what would you recomend?</p>
<p>Alot of comments unanswered here: </p><p>1.No machine will ever be 100% efficient. We can get closer and closer, but never to exactly 100%, because some energy will always be lost as heat.<br>2. Energy in &gt; Energy out. (look up gibbs free energy for more info). Since 100% efficiency is impossible, you will never get exactly, or more energy out of a reaction in you put in.<br>3. While im sure that this machine can produce small amounts of fusion reactions, almost all energy is lost to heat or radiation, don't plan on dumping a few thousand bucks into building one of these and having near perfect clean energy.</p><p>4. Basic nuclear chemistry. This machine uses incredibly high temperatures to overcome the positive to positive repulsion between deuterium nuclei. No, this will not work with H-1, H-3, or an radio-isotope of thorium. Only deuterium (an isotope of hydrogen with an atomic mass number of 2 AMUs.)</p>
<p>Getting more energy than you put in doesn't necessarily violate the laws of physics. Say you had an engine and some gasoline, if you poured the gas into the engine and turned it on, you'd get more energy out of it than what you personally put in. However, if you look at the energy it took to create the engine, the gas, and you, it WILL be a net loss. So, us building a fusion reactor and using it can generate more energy than it takes to build, operate, and fuel the reactor, but the energy that went into forming the dueterium (through whatever process dueterium is naturally formed) and other materials makes it a net negative reaction.</p>
not true especially with the engine scenario. yes you get lots of kinetic energy out. but a significant amount of energy is lost to heat, light, and sound. imagine it's a perfect world and 100% of the air fuel mixture is burned. you lose energy in the explosion as heat and light first of all the explosion also makes a great deal of noise. so yes all the energy put into the process can be accounted for but not all of it is going to the kinetic power generation of an engine ( turning the wheels). <br><br>in the real world we lose even more of that power to friction for in the moving engine components and the drive train on the way to the wheels. again all the the energy is accounted for but is not useful and we aren't gaining any extra. NASA's em drive is the only current known possibility of more energy being generated than I'd bring put in, and its still unknown how it works by the people that made it and whether or not it's just instrumentation error.
<p>A nuclear reaction is lots of energy at the cost of the original atoms. We get something but the universe lost atom #10^47753 which I really could have live without. He was talking bad about you.<br><br>There are lots of examples but this is the way of the future. You don't think we will still be driving combustion engines in a thousand years, do you?</p>
<p>Getting more energy that you put in is the entire point. A simple example is the car you run. You provide a spark and get motion, air conditional and the power for another spark. The only thing you need is more fuel.</p>
<p>It's just the smallest fusion reactor. Not meant to be super efficient. Just fun to build.</p>
<p>how did you go about calculating the intensity of x-ray emission? or did you just shield liberally?</p>
<p>It's minimal fusion. Liberal shielding I would think, but you can gauge it by testing the air between testing. The radiation exposure should be minimal.</p>
<p>How can I produce tritium with this? Also where would the tritium exit the reactor?</p>
<p>It would likely get sucked out with the rest of the gases. Some deuterium/tritium would stay to get fused again or failed and fizz.</p>
How old do u need to be to obtain a radiation maxing permit in Canada
<p>Is it possible to just use a geiger counter with the right GM tube instead of a Neutron Bubble Dosimeter?</p>
<p>also, have you figured out how to recompress a bubble dosimeter without their equipment? just high pressure, or is there more?</p>
<p>this wont work </p>
what diameter tungsten wire is appropriate for the grid?
<p>Hello. Could you also braze using silver and flux or could you soft solder using a silver bearing solder (one without lead and zinc)? Could one also weld only on the outside instead of the inside? Why or why not? Could a Cockroft Walton multiplier also be used for the power supply? Thank you in advance for any input.</p>
<p>could you use 2 or 3 neon sign transformers(10-13kv, 30ma) to get the desired voltage and current?</p>
<p>A Neon Sign Transformer is fine for a demo fusor. You'll be able to get a plasma ball in the center of your grid. But you will never get fusion. NST's are current limited and you cannot connect them in series to get the 35-40kv you will need for fusion. Stay away from Microwave Oven Transformers, too. You're looking for a big X-ray transformer for real fusion.</p><p>http://www.fusor.net/ is an excellent resource.</p>
<p>Well, I know what I'm working on next...</p>
<p>I have seen many things like this before.</p>
<p>I am really interested in this and would love to build it. Is it possible to hook this up with thorium instead of deuterium? How can I simplify this project? Is this fusion reactor hooked up to a capacitor or something of the like that it charges - how is the power harnessed?</p><p>Thanks,</p><p>Josh</p>
<p>How is the power harnessed?</p><p>The most likely way you would harness the power would be to use the heat coming off the reactor to drive a thermal process, probably with water becoming superheated steam to turn a generator turbine.</p>
<p>There is no power harnessed. You lose practically everything to radiation.</p>
<p>Fusion reactions convert some matter into energy which can heat water and thus spin a steam turbine.</p>
<p>I know, in theory. But there have been few instances where more energy came out than went in. Which means you 'd better use the energy you put into the fusor on an electric heater and heat the water directly. You'll be wasting less energy. Fusors, and fusion in general are/is not yet an energy source as much as an energy sink for the moment. </p>
Yeah, but we're working to change that. Have you been keeping up with the Wendlestein 7-X?
<p> Can you please explain what's the point? I don't think the efficiency of all this is 100%. So aren't we just using a lot of voltage to produce less voltage?</p>
<p>The points for building this sort of thing have already been described, I believe. If you would like to have a neutron source, then this could be a path to having one. Then, again, for most folk, the point would be merely to have built it and to have seen it working, and to consume extra time and money that you have. The second question you ask rather answers itself, I think.</p>

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