FAQ - Bubble Fast Neutron Detector

If you have a question about this topic, the answer is probably in here!
User avatar
Richard Hull
Site Admin
Posts: 10911
Joined: Fri Jun 15, 2001 1:44 pm
Real name: Richard Hull

FAQ - Bubble Fast Neutron Detector

Post by Richard Hull » Tue Sep 28, 2004 7:39 pm

admin note 160322: the previous link to bubbletech.ca has been 404'd. Search http://bubbletech.ca to see if you can find what you're looking for.



I include images of the device below.......

These are FLAT RESPONSE, FAST NEUTRON DETECTORS
200KEV - 15 MEV

I just checked with these folks, by calling and chatting with one of their physicists on staff, and the BD100R of the highest sensitivity is $75.00 . These produce 33 bubbles/mrem. (You MUST specify "33 bubbles/mrem", as they have these in graded sensitivities) This seems pretty cool. The stated accuracy for absolute integrated flux is +/-20% which is really very good.

Not so good is the "no-way-out" shelf life of 9-12 months, max. Also very bad, is the fact that this is a Canuck product and they hose you for an additional $30.00 U.S. for handling all the border/entry paperwork for a single dosimeter and an additional $30.00 Fed EX shipping fee. CAN YOU SAY OUCH! I also had to give our federal ID number here where I work. Probably helps grease the rails for entry and tax purposes. What the hell ever happened to NAFTA!!!

I had to check this item out myself, so I fell on my sword and ordered one!

The shelf life is due to the drying out of the water based hydrogel polymer inside the tube. The unit is reset, (bubbles erased), by simple compression supplied by a screw mechanism on every tube. when not in immediate use, the device must be returned to its aluminum, cigar tube, storage device or the thing will not last even 9 months. (helps prevent dehydration.)

The unit is activated by removing from its storage tube and unscrewing the compressor mechanism. Measurement is made and the device read. Tightening down on the screw pops the bubbles and turns the tube off. The bubbles need about 10-30 minutes to go away, depending on age. This time increases with age, but not use. The tube ultimately fails when bubbles won't all go away, but can still be used for a while by just logging the bubbles present at start and counting the bubbles at end and subtracting. Ultimately, the bubbles will merge into big bubbles and the sensisitivity is blown.

Another final "gotcha" is that the temp range is narrow. A warranted 10-30 deg C window is it for measurement and storage.

There is a no limit on the number of count runs during the shelf life. It is age, and age alone, that kills this puppy.

Lets do some figuring.

1mrem absorbed dose of 2.4 mev fast neutrons is created by an hourly passage of about 8n/sqcm/sec or about 2.8X10e4 neutrons through that square cm. This is 1 mrem for 33 bubbles. This means, on average, one bubble will be generated for every 872 neutrons impacting the tube/sqcm of surface, at range.

For a high sensitivity tube placed 20cm from the poissor outside a fusor producing 50,000 n/sec isotropic, one bubble would be created every 88 seconds. (someone check the math here).

The rate of production would go up linearly with emission rate, ie., 100,000 n/s would produce one bubble every 44 seconds @20cm, but vary as the square of the distance, ie, one bubble every 352 seconds for 50,000n/s at 40cm, etc.

This is pretty good for only 75 bucks + the outrageous shipping and handling. This would still beat most any other method except for a good BF3 or He3 setup. All peaks and valleys in production would be lost and smoothed out via the integrating nature of this dosimeter.


I could see these being a great check for fast neutrons provided there were enough of them around for a period of time. They could complement a counter. Still, there is nothing like the satisfying chirp of a counter when in a neutron field.

These would be THE ULTIMATE AND MOST FANTASTIC TEST FOR A RUNAWAY FUSOR. No bubbles - no runaway - your counter went screwy, instead...........lotsa' bubbles, you've got something going on................just a foam in the tube, kiss th' wife goodbye, but remember to post here about the experience and parameters before going off to die.

I was informed that the low end resolution (few bubbles) will blow the statistics by proportional amounts. ie, one bubble will not even be the 872 neutrons calc'd above but could be 2080 or 410. Two bubbles would narrow this error a bit and three or four would have much more meaning. (follows 1/n rule in statistics) Regardless, NO ORDER OF MAGNITUDE ERROR IS POSSIBLE.

Given a 10 minute run at the moderate rate of 50,000n/s that would load this puppy up to about 6 or 7 bubbles and I was told this is OK to within 35% absolute flux.

Another great thing is that with a one time purchase, you could develop a fixed indium foil activation scenario for your specific fusor and transfer cal so that one of these "bubble bottles" would be all you would ever need.

Many thanks to Sasha W. whose original URL posting spawned an expanded reply which morphed into this FAQ

******************* UPDATE 10/04/04 **************************

As promised, I am updating this post!! I have received my BRD-100R (33 bubble/mrem) detector and have attached two images.

The first shows the overall detector AFTER A RUN.
The second image shows a closup of the device and bubbles.

I set the device in contact with the weak source from the college and it gathered 38 bubbles in 3 hours. That is a total of 38/33 or 1.15 mrem dose. This makes the source a particularly weak 0.38 mrem/hr fast neutron source. Based on the fact that there are 8 neutrons per second per second passing through a 1 sqcm area per single millirem/hour This makes this source a 3 neutron/sec/sqcm source and the center to center separation of 2 cm would lead to a 4 pi rate of about 300 n/sec. (this is figuring in the tube geometry, etc.

Using the detector.................

Upon arrival, I freaked out as the device was filled with thousands of tiny bubbles and I couldn't get rid of them!!! A call to BTI confirmed that these are normal in the sensitive units and that upon exposure to fast neutrons, the real bubbles were massive by comparision and this turns out to be the case. (see the second photo to see the fine and the real counting bubble differential). Upon recompression following the above counting, the device cleared itself in under 20 minutes and was ready for another run.

**************************** UPDATE 10/06/04 **********************

Regarding Background:

A fantastic discovery is that there is no need to take a background reading with this detector!!!! I took the BTI detector to my upstairs lab, activated it and read the background for 5 hours. Not one single bubble appeared! This is fantastic news. Most high end fusor neutron data collection runs never last over ten minutes, at most! Thus there is no background detection check required with these devices. They must truly be in a neutron field of fast neutrons to even start to detect!

To those so disposed as to take in the full ramifications here, it means that by using this detector, you have a nearly perfect piece of neutron metrology, provided your fusor is really doing fusion! No electronic snafus, no batteries, no electronic noise issues, no false runaways, no background gamma, or cosmic issues. These things will not even detect thermal or epithermal neutrons common to all fast neutron fields provided those neutrons reflected or moderated are under about 50kev!!!

All of this was confirmed with another call to BTI and further discussions with a physicist there. He noted that these just WILL NOT count thermal or epithermal neuts!! FANTASTIC!!

Temperature effects:

There is a full temperature adjustment chart avaialable. At 41 deg F you are only reading at 1/2 the rate specified. At 68 deg F you are right on calibration. At 90 deg F you are reading two times higher than rating. Restated, for a 33 bubble /mrem BTI detector that would mean one millirem would be represented by 16 bubbles at 41 deg F, 33 bubbles at 68 deg F and 66 bubbles at 90 deg F. So, you must mind your temperature at time of data collection and put in the appropriate correction factor.

***************************************************************

I am now clearly recommending the BTI bubble detector as THE ONLY neutron detection method for fusor work that is totally bullet proof. Bottom line.......if you SEE bubbles you HAD fast and ONLY fast neutrons present. For $75.00 + about $50.00 worth of postage and entry paper hassles, you have your detector. This is especially nice if you are just going to kiss fusion and not take her all the way to the alter for life. BF3 units, etc. are hundreds of dollars for a known good unit. If you fuse and then move on, you have a device that might never be used again!

This bubble detector is the only suitable device for counting pulsed systems net or integrated activities.

More data will be placed in new posts later on this detector.

Data for those interested can be found at the URL above.

*******************************************************************************************
update: 3/3/17

IMPORTANT! Due to the rather short lifetime of these devices and their relative expense for the average amateur scientist and would-be fusioneer, it is highly recommended that no one here purchase the BTI dosimeter until they are actually finished with their fusor and have it working to some degree. (producing a plasma in a metal chamber at voltages in excess of 20kv and currents over 10ma in a deuterium atmosphere of 5 microns or greater.)

If you purchase before you have a, more or less, functional fusion device, you might just fail to do fusion, and while struggling to get the device updated to really do fusion, the BTI might go bad. Never, ever, start your fusion quest by purchasing a BTI bubble detector! It might be best to make it your last purchase.

Richard Hull
Attachments
MVC-004F.JPG
MVC-004F.JPG (61.18 KiB) Viewed 3370 times
MVC-005F.JPG
MVC-005F.JPG (73.57 KiB) Viewed 3370 times
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.

User avatar
Adam Szendrey
Posts: 1333
Joined: Fri Mar 29, 2002 10:36 pm
Real name: Adam Szendrey
Location: Budapest, Hungary

Re: FAQ - Bubble Fast Neutron Detector

Post by Adam Szendrey » Tue Sep 28, 2004 8:38 pm

Hi Richard,

Thanks for the FAQ on this "bubble meter".
Is there any possible way to rehydrate the hydrogel inside the tube? Or to refill it? Can such a gel be purchased separately?
Well i guess most of the cost of this tube is the gel inside.
If there would be a way to extend it's useful life it would be a fantastic ultra cheap fast neutron detector! Well even for a year it still is cheap :).

Adam

User avatar
Richard Hull
Site Admin
Posts: 10911
Joined: Fri Jun 15, 2001 1:44 pm
Real name: Richard Hull

Re: FAQ - Bubble Fast Neutron Detector

Post by Richard Hull » Tue Sep 28, 2004 9:13 pm

The answers are no, no and no. The mix is their secret. Carl Willis opined that it may be part of a planned death to keep selling the detectors, but I guess it is a natural chemical separation of the gel and a drying out of the polymer used. If it performs to half of their promises and one quarter of my expectations, it will be nothing short of incredible!

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.

Jon Rosenstiel
Posts: 1345
Joined: Thu Jun 28, 2001 5:30 am
Real name: Jon Rosenstiel
Location: Southern California

Re: FAQ - Bubble Fast Neutron Detector

Post by Jon Rosenstiel » Wed Sep 29, 2004 1:24 am

For a detailed description of the bubble detector see:

Knowles (Radiation Detection and Measurement, third edition). He devotes three pages to the "Superheated Drop Detector". (Bubble detector).

Jon Rosenstiel

User avatar
Richard Hull
Site Admin
Posts: 10911
Joined: Fri Jun 15, 2001 1:44 pm
Real name: Richard Hull

Re: FAQ - Bubble Fast Neutron Detector

Post by Richard Hull » Wed Sep 29, 2004 1:55 pm

New materials come on the scene constantly and the bubble detector has been around for years as a gross exposure dosimeter. However, it has never had the sensitivity of these new devices. New polymer? New superheated vapor? Who knows? They are not telling deep specifics regarding materials or processes.

I seem to remember at least 4 years ago, on the old "songs" list, going over a bit of this in a thread. I called another organization and got pricing, but the sensitivity was not all that impressive.

I am certainly eager to get my hands on Chalk River's best bubble detector.

As an aside, I was told that they can make 100 bubble/mrem units to special order with very special pricing to match. However, they have found a considerable variation in these .01 mrem/bubble units and note that their 33 bubble unit is the point where repeatable, consistent, recording is possible without heroics. I think 0.033rem/bubble is fine with me.

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.

User avatar
Richard Hull
Site Admin
Posts: 10911
Joined: Fri Jun 15, 2001 1:44 pm
Real name: Richard Hull

Re: FAQ - Bubble Fast Neutron Detector

Post by Richard Hull » Wed Oct 06, 2004 3:35 am

I just updated the original post 10/06/04 with Fantastic background detection news. You must check this out!

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.

3l
Posts: 1867
Joined: Sat Jul 07, 2001 7:51 pm
Real name:

Re: FAQ - Bubble Fast Neutron Detector

Post by 3l » Wed Oct 06, 2004 5:59 pm

Hi Richard:

Would this bubble system work well on pulsed fusion devices?
Could it be used in one place?
If so I will probably get one.

Happy Fusoring!
Larry Leins
Fusor Tech

User avatar
Richard Hull
Site Admin
Posts: 10911
Joined: Fri Jun 15, 2001 1:44 pm
Real name: Richard Hull

Re: FAQ - Bubble Fast Neutron Detector

Post by Richard Hull » Wed Oct 06, 2004 6:10 pm

Re-read the original post. (near the bottom) I note specifically that this is the ONLY detector that will give a fully creditable neutron report on a pulsed device.

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.

3l
Posts: 1867
Joined: Sat Jul 07, 2001 7:51 pm
Real name:

Re: FAQ - Bubble Fast Neutron Detector

Post by 3l » Wed Oct 06, 2004 6:44 pm

Hi Richard:

I see it now.
Cool.
When you talked with the Canadian firm would they only deal with companies?
I have a company but it would be nice to order as an individual too.

Happy Fusoring!
Larry Leins
Fusor Tech

User avatar
Richard Hull
Site Admin
Posts: 10911
Joined: Fri Jun 15, 2001 1:44 pm
Real name: Richard Hull

Re: FAQ - Bubble Fast Neutron Detector

Post by Richard Hull » Wed Oct 06, 2004 7:53 pm

They should certainly sell to an individual.

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.

Post Reply