By the time I got around to trying this, my bubble detector had worn out. I bought a REM ball from Ebay. The previous user had already determined the voltage setting and had noted it on a label attached to the REM ball, but I had to use the calibration factor in the manual. So measurements made with the REM ball may not agree with my earlier runs with the bubble detector, but I could still compare the standard grid vs pointed electrodes by using the REM ball for both measurements. The center of the REM ball is 26.67 cm from the center axis of the chamber.
Best run with "standard grid" using REM ball.
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Eg 40 KV
Ig 7 mA
Pressure 15.0 microns
Flow rate 4.0 sccm
4.8 mREM/h
calculated isotropic neutron emission 334,000 n/s
I have no idea why I could not make 500,000 n/s unless the calibration of the REM ball is off. But in any case, I can still compare.
Picture of pointed electrodes in operation.
Best run with pointed electrodes.
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E in 40 KV
I in 5 ma (the pointed electrodes did not want to draw as much current as the grid)
Pressure 20 microns
Flow Rate 5.0 sccm
5 mREM/h
calculated isotropic neutron emission 348,000 n/s isotropic.
As can be seen there was no real improvement, although one could argue that I'm getting the same amount of neutrons for less input power, but in any case I will try something else.