Archived - Neutrons v. Potential curve

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Carl Willis
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Archived - Neutrons v. Potential curve

Post by Carl Willis »

Here's a neutron CPM vs. potential curve generated by running my fusor at low power, over a range of voltages. Pressure was relatively steady at 8.7 mtorr throughout for the data used. Note, however, that current was not held constant--it rises with potential as shown in the curve in the "HV and Fusor Input Power" forum. So my curve shown here does not imply that the gains of raising voltage are independent from those caused by raising current. Really, I think this plot just states the obvious (crank the juice up if you want more neutrons) and does not work towards solving the questions about where we are on the cross-section curve. Anyway, here it is:
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Carl Willis
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Carl Willis
Posts: 2841
Joined: Thu Jul 26, 2001 7:33 pm
Real name: Carl Willis
Location: Albuquerque, New Mexico, USA
Contact:

Re: Neutrons v. Potential curve

Post by Carl Willis »

Hi Allen,

The detector is a Ludlum 12-4 in which I have linked some of the innards to a computer serial port for data gathering. The moderator is the standard HDPE "Bonner ball" that, I am told, is cadmium loaded. The actual neutron counter used in this model is the G-5-1 BF3 tube sold by N. Wood.

In all my measurements the center of the counter is 9.5" from the center of the fusor.

Altitude at the GSO airport (about a mile from here) is 926 ft msl. The counter is probably a good 30 ft higher because it resides on the second floor of a building.

Background readings are ~10 cpm. I'll update this post after looking at my background collection data again so that I get the exact numbers. Yes, it's somewhat high, and it IS the counter's / my fault. After I had the unit calibrated by a technician at Duke using a PuBe source last year, I asked him about the high background, and he said the discriminator could use some tweaking but that he didn't see any reason to mess with it. I subsequently tweaked the pot to get a count only every couple minutes, but I later set it back to its original value so that I would not distort the calibration when it came time to make measurements. The background is stable and since it is only a small fraction of my readings when fusing (~40 mrem / hr), I have opted to live with it. NOTE: I have NOT subtracted background from this graph.

Hope this helps.
Carl
Carl Willis
http://carlwillis.wordpress.com/
TEL: +1-505-412-3277
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