Fusor progress, Finn Hammer

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Finn Hammer
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Re: Fusor progress, Finn Hammer

Post by Finn Hammer » Mon Nov 20, 2017 8:32 pm

First Neutrons!!

Noooo, not produced, but measured!, I think.

It all started like this:
IMG_20171117_145419.jpg
And if you can guess what it is, then you are good. It is the first pour of paraffin into a HDPE container made from surplus pipe I found in the Water departments Dumpster. Polyethylene is getting awfully expensive these days, and this is what they got. Food grade HDPE, nothing less, doesn't get any better than that.

Outside 8 inches. hole 2, so all in all 3 good inches of moderator. Made it 450mm long for a total of 14kg.

Looks like this with both endcaps welded on, hope it doesn't explode one day:
IMG_20171120_203933.jpg
I couldn't help myself, had to jerry rig a detector harness, and test if it is able to detect some maverick cosmic neutrons, now moderated to thermal velocities, and this is the setup. Not pretty, I admit, and a lot of humm radiated into that setup, definately room for improvements on that account, but anyway, this is what it looks like in the business end:
IMG_20171120_203707.jpg
It cannot get much worse than this, really.

But hey! It seems to work.
I buried my best СИ-19Н tube deep in the gut of that mother of all moderators, and sure enough, before a half a minute, this is what I saw:
DS1104Z_20171120-203822.png
Arrh, sorry, nudge nudge, gotta zoom in a bit:
DS1104Z_20171120-203911.png
That's more like it, looks just like a neutron hit to me, as from what I read around the forum these days.

One more:
DS1104Z_20171120-090114.png
And another one:
DS1104Z_20171120-085601.png
100Mohm series resistor and all in all the same setup that Bob Higgins has proposed. On a 5 minutes run I counted 15 hits, but half of those were perhaps weak enough to get buried in gamma noise. I have 1900V on the hot side of those 100M.
Shouldn't be to hard to detect with a comparator, and an arduino could count these hits via an interrupt pin, display totals and even calculate averages on the fly too.

So this is it for today, I am happy, nothing beats progressing, and I have been looking forward to being able to detect neutrons for a while now.


I wish I had a strong source to help discriminate Gamma ray induced noise, but the best I can manage at the time is a piece of fiestaware, and it does not induce any change to the output of the tube, so hopefully that dial off a MIG2 oxygen indicator gauge which I've got coming will prove hot enough.

The smooth curves you see up ahead are the ones grabbed at 500ms per div. In the case I grab them real time, with 1ms per div, it looks like this:
DS1104Z_20171120-212337.png
But who cares? It is that sweet clean front edge we are going to trigger on anyway.

(But honestly, I am going to clean that PSU up real good as a first priority.)



Cheers, Finn Hammer
Last edited by Finn Hammer on Mon Nov 20, 2017 8:51 pm, edited 1 time in total.

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Richard Hull
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Re: Fusor progress, Finn Hammer

Post by Richard Hull » Mon Nov 20, 2017 8:49 pm

You will not see...or...should not see a neutron pulse at 100 milliseconds, (100ms/div). I hope you mean 100 microseconds/div (100us/div).

If the latter is the case then.....Yes!!....You are seeing cosmic ray based neutron events, probably neutrons surviving the plunge from 11 miles up where neutrons abound from starring cosmic events. Most are absorbed/scattered in the water in the lower amosphere. Some fast neuts are created at lower levels by starring events with cosmic rays that make it through the upper atmosphere.

I get 5-8 neturons per minute here in may lab on a regular basis with my super 3He 4 atmosphere detector. Thus, your smaller volume detector seems to be perfect and right on the money. It appears that inspite of you kludged up mess of connections you are, indeed, counting neutrons!

All the best making this real pretty and clening up the mess. Do not mess up in clenaing up. You have a working system here.

To all else reading this..........If your, supposed, electronic neutron counter, regardless of type, and, you are located at or near sea level, you had better not measure over 10 cpm neutron background. The foregoing assumes your counter system is not better and more sensitive than mine or Finn's.

If you read much more than 10 CPM you are counting noise of NORM. (Naturally Occuring Radioactive Material)

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
Retired now...Doing only what I want and not what I should...every day is a saturday.

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Finn Hammer
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Re: Fusor progress, Finn Hammer

Post by Finn Hammer » Mon Nov 20, 2017 8:57 pm

Richard,

You are right.

The division is 1mS per div, and the pulses settle in at 500µS

Cheers, Finn Hammer

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Richard Hull
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Re: Fusor progress, Finn Hammer

Post by Richard Hull » Mon Nov 20, 2017 9:05 pm

My professional preamp gives me neutron pulse widths of about 4-20us, depending. I am not familiar with the Russian tube's time constants. I bet that nasty old 100meg resistor is the culprit! This is a function of and demand made upon the user of the Russian tube. I have commented on this before.
That resistor forces the giant pulse widths. Still, a fine and suitable neutron detection though. However, the count rate is severly limited by this fact. I have further noted that this count rate limitation might not impact the average fusioneer for a number of reasons which I have enumerated.

Again, it sounds like you have a good counter there and, based on your background report, it is working fine.

It is nice you scoped the output. This is the first report I have seen from a Russian tube, operating properly, that has forever informed me that all using such a tube will experience rather long pulse widths. For me, this is a real eye opener and important data for all who are wise enough to see its implications.

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
Retired now...Doing only what I want and not what I should...every day is a saturday.

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Finn Hammer
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Re: Fusor progress, Finn Hammer

Post by Finn Hammer » Mon Nov 20, 2017 9:11 pm

Richard,

Ok, cool. I will try to reduce the value of that resistor, along with the supply voltage to see if it makes any difference. Obviously there is a nasty time constant in there somewhere.

I was reading about pulse pile up in one of the publications that Carl Willis pointed out, and there are preamplifiers that can pick up a pulse from a whole chain of piled up pulses. I will have to dig it out and reread it. Something about current sensing amplifiers or something like that.

Cheers, Finn Hammer

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Richard Hull
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Re: Fusor progress, Finn Hammer

Post by Richard Hull » Mon Nov 20, 2017 9:17 pm

I am more than ready to believe the high value resistor is a demanded function of the Russian tube type to work as a quencher. If so, it is not a real issue as the tube seems fully functional and detecting real neutron events with it in circuit.

It is nice that you are willing to experiment with it. However the minute your count goes up, such as to 10 CPM, you might just accept the 100 meg resistor as a given to the tube type.

"Pile-up" is not a real issue in my system with it's short pulses. This is probably the difference in a $2000.00 detection tube and pre-amp and the in-expensive Russian tube's normal operational characteristics. It is just that the Russian tube might suffer plie-up at very high count rates, rates that the average fusioneer may never see or approach. I have used a rule of thumb of 10 to 1 ratio. If your pulse count rate time frame is 10 times the pulse width, pile-up will not be significant. A 500us width would allow a 5ms rate or 200 cps/12,000cpm count rate before pile-up is an issue.

You and I are currently on line and this is good as you are reponding more or less in real time.

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
Retired now...Doing only what I want and not what I should...every day is a saturday.

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Finn Hammer
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Re: Fusor progress, Finn Hammer

Post by Finn Hammer » Mon Nov 20, 2017 9:27 pm

edit: It is late, getting units all mixed up, gotta go to bed

But my goal would not be to increase counts per minute, it would be to shorten the pulsewidth. 500µS pulsewidth would allow (edit: 12000) counts per minute, and since they probably will not come flowing like off a clock generator, fewer.



I am not at this point able to know what that means, I am only just starting to work this aspect of fusor work, and the calculations related to neutron per minute out of a fusor is still black magic. But I will get there eventually.

Cheers, Finn Hammer
Last edited by Finn Hammer on Mon Nov 20, 2017 9:31 pm, edited 1 time in total.

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Re: Fusor progress, Finn Hammer

Post by Richard Hull » Mon Nov 20, 2017 9:30 pm

I updated, edited my last post. I do this a lot as I think. check it out. I figured on 12,000 cpm as the max count for a 500us pulse width based on my self-arrived ratio of 10 to 1.

Pile-up is a big issue with GM counters or any detection method where the pulse width approaches the width, in time, between real detection event occurances. This ties into the physical "dead time" of the device quite outside of the time constants of the counting electronics.

As an example, you can theoretically change the input capacitance and resistance to a GM tube such that a scope will show a pulse width of 20us. However, even a super well quenched GM tube has a physically determined "dead time" of 60-100us. during this tuime period a second pulse will not be detected! Thus, in this case the dead time rules and the maximun count rate is dead time limited and not pulse time limited.

I am unaware of a published dead time spec on these Russian tubes. As such, a quest for shorting the electronic pulse width might mean nothing at all

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
Retired now...Doing only what I want and not what I should...every day is a saturday.

Silviu Tamasdan
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Re: Fusor progress, Finn Hammer

Post by Silviu Tamasdan » Tue Nov 21, 2017 12:51 am

As an anecdotal fact, the pulses I see with my corona tubes setup are 30-40us.

As for moderator, yes I noticed HDPE tends to be expensive. I have cut mine from restaurant-grade cutting boards bought from Amazon (look for the 1" thick ones) as they have tended to be the best bang for the buck I found. Then I discovered that motor oil works well as a moderator, and since I always have quite a bit of it around I have added that to my moderator stack. It works because it's composed of carbon and hydrogen same as HDPE, parrafin etc.
There _is_ madness to my method.

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Finn Hammer
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Re: Fusor progress, Finn Hammer

Post by Finn Hammer » Tue Nov 21, 2017 9:37 pm

Richard, Silvio

Thanks for your usefull input, it helps me to focus on what is possible and desirable, and to spot it on sight.

I lowered the voltage to 1600V and suddenly the counts changed to this much more desirable profile:

Notice the setting: 2µS / division.
2µs.png
Much like the difference between hitting the gong with a sledge hammer instead of tapping it with a teaspoon.

The sensitivity dropped to 1-2 pulses per minute.

I am still struggeling to get the supply to remain stable and ripple free, and don't see this as the final word, so I will remain quiet for a while untill I have some conclusive data to show.

Sitting in front of the scope, counting to between 30 and 55 seconds to time the cosmic hits (will they still come with this setting, how is it going to look?) reminds me of an old Zen story:
A grain of salt wanted to know how salty the oceams were, so it jumped in, and became one with the water of the ocean. That way the grain of salt gained perfect understanding.

Cheers, Finn Hammer

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