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: neutron measurement
Date: Feb 04, 10:53 am
Poster: Richarsd Hull

On Feb 04, 10:53 am, Richarsd Hull wrote:


It is enevitable that I forget something in every post. Scott's measurement of neutrons was with a He3 tube (seen on top of his fusor).

I am familiar with and have a boron trifloride detector tube (BF3). It measures slow neutrons. All neuts from fusors will be fast neuts. This means moderation or "thermalization" prior to hitting the detector. Scott might answer this..... is the He3 tube capable of detecting fast neutrons directly?

I went to a Bicron 720 fast neutron scintillation crystal and PMT detector to allow me to detect fast neuts directly and have not fully implimented my BF3 system due to the need for moderation. Moderation forces you to have a thick barrier of moderator between the chamber and the detector which reduces the solid angle of detection, thereby reducing the flux in the tube, making the signal in low level fusor neutron production near the noise floor.

Scott appears to have not been at a voltage where he should have measured any neutrons anyway.

Ideally, we want a good strong signal which is vivid and vibrant to herald neutron production and rule out errors due to x-rays or other photonic events in the PMT or detctor tube.

As an example, my detector is 1% efficient. (bicron spec). It offers a 2" window to detection. Background is typically ~8 events/minute in my system. At a range of only 12" from the interior of the central grid,(a realistic distance), I would have to have a neutron production of about 10,000/sec to just detect a simple doubling of the background signal! All of this assumes a perfect electronically discriminated system with no attendant x-ray production reaching the detector.

Richard Hull