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Posted: Mon Nov 24, 2008 8:47 pm
by gary_f
Frustrations with Bubble Tech led me to a conversation with a health physicist where I work. He suggested loaning me a Landauer CR-39 based dosimeter. The Neutrak 144 is a little chip of plastic, sensitive only to fast neutrons, and inexpensive. The downside is that you have to send it away to get it "developed" and counted. But a representative at Landauer said the cost would be on the order of $50 or so, including processing. He also said it's been used in a vacuum, specifically by shuttle astronauts working in space, so it might be used directly in the fusor chamber.

This seems like a good way to certify fusion, although not the real time feedback we prefer.

Gary Foss

Re: CR-39

Posted: Mon Nov 24, 2008 9:30 pm
by Richard Hull
That is $50 for a one shot!!! Ouch! What is its baseline sensitivity?

What if you run your machine and the thing comes back zero or unmeasurable exposure. You make changes in the fusor, run it again and pay another $50.00?...,etc, etc.

I would imagine inside the fusor might present a problem based on temperature and ion bombardment.

At least The BTI device is good for over one year and you read it immediately.

Still, give it a shot and report back to us.

Richard Hull

Re: CR-39

Posted: Wed Nov 26, 2008 12:17 am
by gary_f
20 mrem to 25 rem is the claimed dose range. The spec sheet is here: ... .en-US.pdf

The process is actually pretty simple, you soak it in sodium hydroxide which etches out the pits, and then you count them under a microscope. The technical support guy said it's about 30% efficient on a particle basis.

Re: CR-39

Posted: Thu Dec 04, 2008 5:39 am
by Dan Tibbets
I have seen mention of CR-39 dosimeters in various contexts. ... act/1/1/61
Aparently polycarbonate and othe clear plastics work almost as well. If you have a microscope (I dought it would have to be high quality) and are willing to do the labor , I suspect it could be used as a cheep detecter. Using Sodium hydroxide or potassium hydroxide from the hardware store to etch (enlarge the pits to light microscopic size), and cut up clear polycarbinate plastic sections from somewhere. I'm uncertain of a good source of polycarbinate. If nothing else you could cut up some protective eye goggles. For counting you could use a graded glass slide, or just count a fixed number of random 100x to 400x magnified fields. I'm uncertain what magnification is needed to see the pits. The longer the exposed plastic is in the etching bath, the larger the pits become. With matched controls , known etching times, temperature and concentrations, you should have a fairly accurate capacity, perhaps more sensitive than most electronic detecters. While less convient than a bubble detecter, it would give you a perminate record. Also, if the size of the pits are representative of the energy of the original neutron, you could have a very course idea of the neutron spectrum (?). The major problem would be calibrating the setup initially. You would need access to a known neutron isotope or working fusor with alternatly determined neutron output. Possibly a collaberation with others would help.

Another laborious method of 'shoestring' neutron detection might be a cloud chamber.

Dan Tibbets

Re: cloud chambers

Posted: Thu Dec 04, 2008 6:05 am
by Nanos
Talking of cloud chambers, I remember seeing a demo of one on television when I was younger, the BBC2 Royal Institution Christmas Lectures in 1993, which via a quick search of the internet, is now available to watch: