Track detectors

This area is for discussions involving any fusion related radiation metrology issues. Neutrons are the key signature of fusion, but other radiations are of interest to the amateur fusioneer as well.
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Mark Rowley
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Re: Track detectors

Post by Mark Rowley » Sat May 15, 2021 4:58 pm

Maciek,
I’d be willing to give it a go. I just reverified calibration with a bubble dosimeter a couple weeks ago.

Mark Rowley

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Maciek Szymanski
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Re: Track detectors

Post by Maciek Szymanski » Mon May 17, 2021 8:03 pm

Great! My plan is to use two sets of three dosimeters irradiated in two sessions plus a reference one which will be not exposed, but otherwise identical and sent together with the rest both ways to compensate for factors like cosmic rays in the airplane, xray inspection and overall history of the CR-39 batch used. I'll prepare the drawing of the complete dosimeter and post it on the forum, so you can check how to fix it on the fusor.
“Begin at the beginning," the King said, very gravely, "and go on till you come to the end: then stop.” ― Lewis Carroll, Alice in Wonderland

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Maciek Szymanski
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Re: Track detectors

Post by Maciek Szymanski » Mon May 17, 2021 8:34 pm

Regarding Lexan as the track detector. According to Solid State Nuclear Track Detection:Theory and Application by A. M. Bhagwat energy wise the detection threshold of Lexan is 80 times higher than for CR-39:


D410388A-F5B6-44AB-B87F-0153A8AD483E.jpeg

It is also worth noting that the cellulose nitrate has 4 times lower threshold than Lexan (but still 20 times higher than CR-39).
“Begin at the beginning," the King said, very gravely, "and go on till you come to the end: then stop.” ― Lewis Carroll, Alice in Wonderland

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Mark Rowley
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Re: Track detectors

Post by Mark Rowley » Tue May 18, 2021 1:45 am

Sounds good Maciek. Send me a PM when you’re ready for the specifics.

Mark Rowley

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Maciek Szymanski
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Re: Track detectors

Post by Maciek Szymanski » Fri May 21, 2021 8:36 pm

Here is a quick design of the neutron detector:


BDFBC352-35D8-4B7B-995D-758CA6760106.jpeg
The detector should be placed as close as possible to the fusor to increase the count number. It would be nice if one would be positioned at the viewport, to see if the increased x-ray exposure will make any difference. If it is needed one or both screws can be longer and provided with an extra M3 nut for fixing the detector.
“Begin at the beginning," the King said, very gravely, "and go on till you come to the end: then stop.” ― Lewis Carroll, Alice in Wonderland

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Mark Rowley
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Re: Track detectors

Post by Mark Rowley » Fri May 21, 2021 10:42 pm

Viewport or any distance is workable. My calibration is at 17cm distance at the same height as the grid. Not sure if that’s important for your end goal.

The brackets look good. Much better than a bare piece of plastic.

Mark Rowley

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Maciek Szymanski
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Re: Track detectors

Post by Maciek Szymanski » Sat May 22, 2021 4:20 pm

Ok, so I'm ordering the aluminum flat bar and 2mm PE sheet. I should have the dosimeters ready for dispatch at the end of the next week.

In the meantime I've got some data regarding the "dead counts" of the CR-39. The four pieces of 10 years old CR-39 sheet were exposed for the alpha particles form the radioactive source for 30, 60 and 120 minutes in vacuum. After etching the samples were photographed under the microscope (6 images for each sample) and the tracks counted with the ImageJ program.

After averaging the results the track density for each sample are:

Sample 1 (30 min exposure) - 4092 mm^-2
Sample 2 (60 min exposure) - 5731 mm^-2
Sample 3 (120 min exposure) - 8932 mm^-2

As it can be seen on the following chart the 3 points are perfectly collinear:

8371894D-7F12-4E0B-BEED-F909B5640BEC.jpeg

The extrapolated count of 2450 mm^-2 for the 0 time exposure can be accounted for the accumulated damage during the storage time. As it was earlier mentioned it is best to obtain a fresh detector plastic, but nevertheless some means of determining the "dead count" for the particular batch is rather unavoidable. And after another 5 years of storage this number can't be trusted anymore. Personally I think it is best to include the "dead count" procedure for each measurement session.
“Begin at the beginning," the King said, very gravely, "and go on till you come to the end: then stop.” ― Lewis Carroll, Alice in Wonderland

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