Fusion Message Board

In this space, visitors are invited to post any comments, questions, or skeptical observations about Philo T. Farnsworth's contributions to the field of Nuclear Fusion research.

Subject: Re: Neutron Counter interface
Date: Oct 29, 7:58 pm
Poster: Richard Hull

On Oct 29, 7:58 pm, Richard Hull wrote:


>Finally, here's a question for down the road a bit. What is the proper approach to finding the solid angle the detector occupies? (in order to calculate total fusor neutron yield) I have been thinking that the angle occupied by the BF3 tube itself is all that is needed. But perhaps there is significant scattering in the PE ball and a larger angle should be used. Any help would be appreciated!


I would retain calibration if possible for health safety reasons. I am glad you plan on having it calibrated. Ostensibly, you are correct on the counts, but precise data on the counter efficiency is not available and the data supplied by the manufacturer assumes a very uniform neutron flux over the entire ball volume. Due to the nature of the beast and our nearness to the fusor, this is not the case. However it is as close as we have information for extrapolation.

Because of the above, the normal diffusion and scattering of neuts in the poly moderator is not "as designed".

I place the tube's axis pointing at the inner grid. I refigure the area of the end of the tube as the sensitive region, but double that figure to account for a few diffused neutrons in the sides from off axis entries. I have discussed this with the staff at eberline and two health physicists freinds and they argree that barring a heavy known source calibration, this, and the manufacture's data can be massaged into the fusor scenario.

The distance for the 4 pi r squared solid angle calcs is that from the center of the tube to the inner grid's center. For most of my measurements this is 25-30cm.

Richard Hull

As to the last question