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: clarification
Date: Aug 11, 9:06 am
Poster: Jones Beene

On Aug 11, 9:06 am, Jones Beene wrote:

Let me add the following, which is just from my recollections of prior posts that I can't find at the moment and from personal experience with a BF3 tube.

>>However, in followup, it was later determined that Miley did not, in fact , even look for thermal neutrons and has no capability for doing so, but only that the high energy neutrons he found did scale with voltage.

>The last sentence above is a stunning statement! A lose, plain, naked, BF3 tube is a very efficient detector of ONLY thermal neutrons. You have to put up a parafin or PE wall to thermalize 1-5mev fast neuts to even get the BF3 to count! If miley uses any BF3 counters, and I assume he does, thermal counting would be a snap!!! Fast neuts in a BF3 tube have a nearly zero cross section whereas true thermals have thousands of barns cross section!

Let me rephrase the "has no capability" comment from the above. I believe he was using a 3He detector. When I asked his lab assistant why they didn't shield with a moderator and look for lower energy neutrons, I was told that when using parafin with a Fusor the scattering would be so great that you would essentially get zero hits even if a decent flux of mixed energy neuts from the fusor was present.

Richard, have you found the BF3 tube to be that efficient? I have an Amperex type 75 (900 volt) BF3 that I have tried on numerous occaioions without success (used with a Bicron analyst detector) in situations where a small thermal flux was present. I have never been able to get adequate readings with it. Perhaps it is defective or more likelyt is from my lack of skill with configuring a good setup.

I am convinced that the only real test to find the extent of stripping vis-a-vis real D-D fusion in a Fusor or any plasma device would be to use a mass spectrograph. Since most of us don't have one sitting around in the garage, it would involve the following.

First, you would have to be very certain that your fill was nearly 100% D, i.e. mass 4
Second, you would need to do a very long run with the fusor to get enough ash to reliably test
Third, you would need to evaucate and carefully capture the ash after the long run with no contamination and get it over to a university or testing lab.

If there is substantial mass 3 relative to 5 then you know you are getting a lot of stripping. If there is any 2 at all I would suspect that you are getting major stripping. If there is any 6 and little 3 you are probably getiing little stripping.

Can anyon comment on this? or has anybody tried it?