FAQ - Flux versus TIER... an example

[Richard Hull]

One, especially newbies, must never confuse "neutron numbers or TIER" as we use the term, (total isotropic emission of radiation per second) with the term neutron flux! The fusor only emits neutron particle radiation due to fusion. For our purposes, we quote the sum total of all neutrons emitted from our fusor per second. The term "neutron flux" is something we amateurs virtually never use.

Neutron flux is the number of neutrons found at any range from the source, passing through one square centimeter of area per second. A 1e8 flux field of fast neutrons you could not survive. 1e8 TIER from a fusor at the closest range (shell or chamber wall) has not been reported here. (1E7 TIER is the max) This is not dangerous for short periods of fusor operation and is a near impossibility to achieve for the casual fusioneer.

Finally, the TIER figure for a fusor is a difficult calculation fraught with inaccuracies in the hands of all but the more advanced amateur fusioneers with the best neutron detection gear in hand. TIER is derived from an accurate neutron count of slow neutrons over some stated period of time taken at a fixed and stated range. From here calculations based on numbers of neutrons counted over the area of the detectors moderator at range versus the interception cone area at range from the fusor, all back related to time in seconds to obtain TIER. Lots of errors, mistakes and fudge factors for the simple algebraically challenged fusioneer who loses track of units in the effort. Even if performed flawlessly the result must never be assumed to be factually isotropic. In short, the effort is a good stab at TIER neutron numbers.

Thus, we never tend to use the term "flux" as related to a fusor since it is derived from a TIER figure as you will see below..

example: A flux of one fast neutron per square cm (1e0) at the shell of a spherical fusor of radius 7.5cm would be a TIER of...about

4(pi)r^2 = 4 X 3.14 X 56.25 or a TIER of 706 n/s.
from here is is easy to expand...

A flux of 1E1 or ten = 7,060 n/s TIER...Flux of 1E2 would be a TIER of 70,600 n/s....Flux of 1E3 would be a TIER of 706,000 n/s...etc., etc..

Thus a flux of 1E3 or 1000 neutrons per square cm/sec at the shell of a 6-inch diameter spherical is just short of what we call a mega mark TIER fusor. This is rare number for over 95% of all folks who ever made the neutron club!! This means the typical claimant to the neutron club never hit a neutron flux of 1eE3.

A flux of 1E8 would be a TIER of 100,000,000 or 100 million n/square cm/sec.

Richard Hull