Alexey's fusor progress

[Rich Gorski]

Fusion rate is near linear with current but exponential with energy (voltage). So I think you would generate more neutrons with 45kV at 20mA... same 900 Watts of power.
Rich G.

[Cinar Kagan]

Isn't the D-D cross section logarithmic (at least to 1MeV)?

Cinar Kagan

[Rich Gorski]

If we look at the fusion cross section curve say for the DD reaction it appears to be exponential in nature at least up to 1 MeV energy.
For example:

<sv> at E = 10KeV ~ 10^-18 cm^3/s
<sv> at E = 30KeV ~ 10^-17 cm^3/s

A 10X increase in reaction rate for a 3X increase in energy. Exponential growth.

However the growth slows as energy approaches the peak and then starts to diminish beyond the peak. So, the fusion reaction rate as a function of energy really depends on where we are at on the energy curve. In terms of fusor type energy we are on the quickly rising part of the curve.

Rich G.

[Dennis P Brown]

You would think but I could not detect any increase in counts on the GM. And I used a large silver foil. My He-3 certainly was buzzing with counts.

[Alexey Khrushchev]

I'm sure you've checked all the components of the system. The only thing that comes to mind is insufficient silver purity. Could it be a low-grade alloy? I would try dissolving a piece of foil in nitric acid first and then adding sodium chloride, the white precipitate will prove the authenticity of the silver. You could try treating the foil with hydrochloric acid or alkali, the release of gas will prove the presence of other metals in the alloy. Silver forms alloys with a high content of tin, zinc, aluminum, cadmium, copper.

[Richard Hull]

Many here use coin silver (90% AG 10% Cu) This fouls their results. Pure silver foil is readily available from the jewelry supplier Rio Grande in the US.
pure 1 troy ounce bullion coins are often used, but pure silver foil is ideal.

Richard Hull

[Dennis P Brown]

The silver is supposed to be 99.999% but you know, could be the case. A coin, as Richard suggests is fool proof.

[Richard Hull]

5 nines silver, 99.999% is hyper expensive if you can even find it. The term fine silver is taken to be 3n0 99.9% or 999 and is common in pure bullion ingots and bullion coins.

5n0 or 99999 is a virtual impossible dream! 999 bullion coins are not ideal. Foil is the ideal as betas can escape back to detection, while a thick coin will produce activation deep into the coin that the betas can't get out of. If however you are looking at moderately high energy gamma rays due to activation as seen by a good gamma ray spectrometer, then a coin would be fine.

Activation in the big boy world is typically done with foils or small amounts of a chemical only. Why? well, the big boys use fluxes of 10e10 n/sqcm or greater and you don't need to create a huge multi-curie source in a large volume like a coin. We do not have such flux levels so a coin is acceptable. Purity beyond 4n0, 9999 is just overkill

Richard Hull

[Dennis P Brown]

Got some for a special ultra-pure Ag for an experiment from a company that sells many types of high purity and low materials (the experiment was a failure, of course.) So I decided to try that with neutrons since the money was spent. Its possible I got the wrong order - no way I could test it. It was stored with a lot of junk from years ago - so, maybe it wasn't my original silver foil, either. Labeling items would be a good pratice.

[Alexey Khrushchev]

For the activation experiments, I decided to make a more sensitive detector. For this purpose, I connected two SBT10A Geiger counters to the RadiationD-v1.1 board. Data transmission to the computer was done via serial port using Arduino Uno. I configured pulse accumulation at each point for 2s. I plan to place a silver plate between the two counters so that I can capture the maximum number of pulses. However, I noticed that using two counters doubles the number of background pulses, but the RSD remained at the same level as it was for one counter (about 50% for 25 points). Then I placed a vial of KOH between the counters, this doubled the number of pulses and the RSD was reduced by a factor of 1.5-2 compared to a single counter (also in the presence of KOH). Thus the device allows to increase the signal-to-noise ratio, but only with a slightly higher background.

[Cinar Kagan]

I'd like to share my own thoughts about your new activation setup.

I see that they are mica-windowed. I believe that that will increase detection by a large margin, especially with the two of them. Maybe you can try modifying your lead/shielding setup for your gamma spectrometer for the geiger tubes.

Also if you are not doing this, I recommend cleaning your chamber with solvents like isopropyl alcohol (This is optional and I am not sure which solvents to use anyway). When you open your chamber you can use gloves to prevent organic contamination. This will help the neutron rate increase with a shorther pre-run to burn out the organics and other contaminants. There is a risk of the solvents reacting with Titanium, be sure to check that before using them.

A silver coin sandwiched between two polyethelyne bricks (a few cm thick each?) might get closer to the chamber and might get more properly moderated.

Cinar Kagan

[Alexey Khrushchev]

Unfortunately the sandwich of two detectors didn't fit in my lead house. So I plan to install them in a polyethylene sphere (25cm diameter) which is a moderator. The walls are about 3cm thick, plus I'll put a couple of pieces of paraffin in there. I am now in the process of planning and assembling an Arduino based detector. At first I wanted to connect the counters to the HV source via a 3m shielded cable, to be able to trigger the measurement without leaving the fusor control panel. However, it turned out that a long cable reduces the counting speed by half. I don't know what's wrong, I used a thick TV cable and soldered everything carefully.... Anyway I had to redo everything , now the length of all HV wires is minimized and the control panel will only have a 5V power supply which will be connected via a 3m cable to the HV source of the dosimeter. Thus the long cable will not carry the high voltage (400V) as I had originally planned, but 5V. In order to make everything neat and reliable I am modeling and 3D printing the device case and auxiliary elements. Eventually I want to make a device that will measure the induced radioactivity of the silver plate 1s after the HV fusor is turned off.

Thanks for the recommendation to clean the chamber with isopropanol. I will definitely try it!

[Alexey Khrushchev]

I want to make a new moderator from ultra-high molecular weight polyethylene. I wondered what size it should be. Let's assume that the optimal thickness of the front wall (the one closer to the chamber) should be about 2 inches. Then, for geometrical reasons, in order to collect and slow down more neutrons, the size of the moderator should be at least 2 times larger than the chamber diameter (see figure) - i.e. the front wall in my case should be 200*200mm and 50mm thick. It would be even better to surround the chamber from all sides with polyethylene, but considering its price it seems to me to be a redundant solution.

[Richard Hull]

UHMW polyethylene is not good! Use only High density. Carl Willis warned all of us against this many years ago. I think there was another element like chlorine or something like that in the UHMW which might foul the moderation.

Richard Hull

[Alexey Khrushchev]

I'm surprised by this. There are many examples on the forum of UHMW polyethylene being used as a moderator. It is not very clear to me how it can contain significant amounts of chlorine. To check this I will take an IR and Raman spectrum of my UHMW sample, if there is chlorine there I will see it.

[Jim Kovalchick]

UHMW does not contain chlorine and should be a decent moderator. Be wary of colorants that may contain neutron absorbers like chlorine. Black colored plastics are usually okay because they contain just carbon.

I made a silver activation cell that does relatively well by covering the front of a 1" thin window geiger with sterling foil. I placed it in a section of 4" corrugated hdpe drain hose you can find at builders stores. I filled it with white hdpe granules. I start counting as soon as I kill the high voltage. I sample count rate in short increments and then plot it. My setup is far from optimum but it works to see activation starting around 30 kV.

Jim Kovalchick

[Alexey Khrushchev]

After studying the forum I came to the conclusion that for activation of silver twice as high as background at 30 kV a current of 10 to 20 mA is required. What was the current in your case?

[Rich Gorski]

Alexey,

In my Ag activation experiment I placed the detector between the fusor and the silver due to the 1/4” thick silver ingot that I used. With that thickness it seems obvious that most of the beta/gamma emission from 108Cd and 110Cd would be heavily attenuated in the ingot so I placed the detector on the side facing the fusor (active side). In my opinion when using a thin silver foil the it probably doesn’t matter much which side you put the detector on but the thicker the silver gets I believe there is an advantage to place the detector on the side facing the neutron source.

I also noticed that you have increased the voltage from 24kV to 30kV. That will help to increase neutron production rate since the DD fusion cross section increases exponentially with ion energy below around 100 KeV.

Rich G.

[Alexey Khrushchev]

Rich,

It is also possible that neutrons reflected from the second wall of the moderator (the one farther away from the chamber) will have a lower temperature, and thus are more likely to be absorbed by the silver. In any case I wanted to use two GM counters on either side of the silver.

[Alexey Khrushchev]

Today I finished assembling my beta meter containing two SBT-10A counters. I decided to power the high voltage power supply (400V) directly from the arduino (pin 5V) this will reduce the time to start the measurement, now I just need to plug the usb cable into my computer to initiate the real time countdown. At the same time I will be at a safe distance from the fusor.

The circuitry for connecting the meters to the arduino is not exactly conventional. I didn't use a divider capacitor, instead the microcontroller is connected on the cathode side of the counter , through a 1k ohm resistor. Essentially I measure the change in current flowing through the meter. This circuit works well and I don't see the point in complicating it.

I also got a plate of ultra-high molecular weight polyethylene, and if it weren't for a cold, I'd have made a good neutron moderator by now.....