Fusor Forums

This paper was written for another purpose, but I place it here for reference. My original bubble detector FAQ still remains a good quick rinse for bubble detector use.

Original FAQ
viewtopic.php?f=13&t=5728#p34172
Richard Hull

FYI - Dead Link

The link is restored as a PDF file. So much was lost in the move to our new Go Daddy platform. The paper was written a while back. (2008) I was lucky to find it on an old win 98 computer.
Thanks Joe for alerting me.

Richard Hull

One important factoid about Bubble Detector's.... they register false bubbles when exposed to high intensity UV flashes from high amperage spark gap or linear / toroidal pinch tube discharges. If used in a pulse type system, keep them in the light proof cigar tubes during operation.

And lastly, heat will cause false readings as well.

As you pointed out Richard, activation is the ultimate proof of neutron production.

Mark Rowley

All,

The current datasheet:

http://bubbletech.ca/wp-content/uploads ... 720091.pdf

Claims automatic temperature compensation between 20°C to 37°C


Since I am considering to place an order: am I pointing towards the wrong detector?


Cheers, Finn Hammer

Finn, from my experience so long as they are operated in their specified acceptable temperature range there is no problem for either pulsed or steady state systems. As for UV, Stainless steel from the fusor shell should block any UV. I think they are good detector for time-averaged neutrons/sec measurements on a fusor or other source and would compliment your other detectors well. With some assumptions about the energy spectrum of the neutrons I think you could a decent calibration factor for your activation counts and other measurements.

I did this way back when hector was a pup and it worked great for years. The key is planting your neutron detection/counting system's moderator and enclosed detector at a fixing position. Never move it, once calibrated, relative to your fixed fusor!

I had a water moderator and due to evaporation occurring between long inactivity spells, I had to add water to the "calibration level" in the moderator to maintain the calibration factor that was derived from averaged 2 month operational level results of bubble dose readings and digital counts from my 3He system. It sat fixed and never moved 2003-2019 when fusor IV was dismantled. Fusor V is now stabilized over the last wo years and with a new HDPE moderator that is never to be moved, the new calibration has been going on and being adjusted from 2020 to date, (2022). I have reported on this new calibration factor for my system in past posts.

I took a lot of run readings over those two months and threw out the top and bottom single "flyers", then did a good job of averaging the results. I realized due to assumptions and natural neutron counting slop that my 21.63 calibration figure was more or less a reductio ad absurdum fallacy so I rounded down to 20 and lived with it for those 16 years, never looking back and maintaining those original system constants.

Richard Hull

I have found that as long as you do not change the moderator type or dimensions, nor the detector you can move the assembly to a different place if need be, measuring the old and new distance between the detector assembly and the fusor main grid and use inverse square law to calculate the new calibration. But for convenience, I mark the location of the REM ball, so that after doing work that involves removal, I can return it to the exact same spot so I don't have to recalculate.