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: Re:Demo Fusor
Date: Feb 09, 09:22 am
Poster: Richard Hull

On Feb 09, 09:22 am, Richard Hull wrote:

>To: Richard Hull
> I have a few questions on the demo fusor.
>Would making the grids from larger wire be of
>any great value?
> This sounds dumb, but how can I tell the number
>of neutrons/sec. and can I tell the differance
>between X-rays and neutrons, all I have is a
>good geiger counter and a shoestring budget!!
> Is Deuterium gas government controlled?
> Has anyone used a cylindercal anode and cathode
>perhaps with ion guns at opposed sides of the
> Thanks Bob


The idea is to make the inner grid as invisible as possible to high speed matter, but look like a solid charged sphere for electrostatic purposes.

Heavy wire will most definitely work, but limit neutron production in proportion to its "transpareny" to ion entry and recirculation.

In short, the thinner and fewer the inner grid wires can be made in keeping with the establishment of a smooth, spherical, electric field, the better.

Neutron counting is where the early cold fusion folks went adrift in the rush for confirmation.
Neutrons are not easy to measure. A gieger counter can't directly detect neutral particles.

There are three ways of counting neutrons. The first and most modern is the counting of fast neutrons directly in a single setup. This utilizes a nice calibrated scintillator such as Bicron's 720 fast neutron detector. (this is my choice). The scintillator with coupled photo multiplier tube costs about $1500.00 and this includes zero electronics (power supplies, amps, etc.) and no counter. I have just received the raw scintillator after an 8 week wait (custom made) and paid $325.00. I have my own bi-alkali S-22 blue sensitive PMT which I will couple up to it and build all my electronics from scratch by my own design. (pretty much a snap with my scrap bin.) This detector works off proton recoil from fast neutrons, and scintilates off of the silver activated zinc sulfide inclusions in the anthracene loaded styrene plastic scintillator.

The second way is to thermalize the fast neutrons with a moderator. This can be a large tank of water, blocks of paraffin, or more modern, a slab of UHMW polyethylene. Once the neutrons are thermalized a boron trifloride counter tube (like a huge geiger tube will detect them. (this is usually by alpha particle emission from instantaneous decay products of interaction with the BF3) These tubes can be had from O.E. Technologies used for $150.00. They still net power supplies and electronics. Also, these systems need careful calibration. This method is the one most often used by the pros in the past. I have a Reuter and Stokes BF3 counter tube and will calibrate it with my Bicron setup.

The third and easiest way to count neutrons is to neutron activiate Indium foil and then count the beta particles with a gieger counter. This method is very crude, but effective if +/- 10% accuracy is acceptable. It is self calibrating providing all the math is done correctly. A good book to check out for details on neutron activation measurements is the older reference "Neutron Physics" by Wurtz I think this is a 60s publication. I also plan to check this method out as a check against other methods.

I don't think I have mentined this before, but there are "neutons per second" (total production from an idealized point source) and "neutron flux" (neutrons per unit area). Most of the Farnsworth team's specs were in neutrons per second. This has to be figured out going backwards based on surface area of a sphere at the detector's range from the source.

Richard Hull