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: More on Mass Spec Analysis
Date: Aug 26, 0:26 am
Poster: Dave Cooper

On Aug 26, 0:26 am, Dave Cooper wrote:

Thanks to Ben, Jim and Richard...excellent comments! Of course, you're right, we are in the molecular flow regime. The implications of this are that mass detector location doesn't matter as far as general gas sampling is concerned.

What I was exploring was whether it would be reasonable to expect that fusion reaction gas products would be at higher concentrations in certain locations within the fusor. Why I was thinking this is based on the following.

Within the small, high voltage E Beam vacuum tubes that the I work for makes, even at pressures below 10E-8 torr, we often observe localized transient pressure rises in the vicinity of thermally heated and electron beam irradiated metal and glass surfaces.

When you think about it, in a high vacuum, a cluster of gas molecules is not too far fetched.. at least on time scales of a few tens of microseconds.

So the issue is whether the rate of generation of fusion products is high enough to produce localized concentrations. From Richard's comment, it would appear the answer to this question is no. The concentration is relatively uniform within the fusor.

Also re: Richard's observation about the energy of the electron beams (rays), I agree, you don't want them in ionization chamber of your mass spec.

Regarding the concentration of reactants relative to residual atmospheric gases, that Ben asked about, a very rough estimate would be the following:

A spherical 25 cm diameter fusor chamber -
Volume = (pi/6)(25^3) = 8.18 liters or about 0.365 Gram Molecular Volumes. (Avogadro's number of molecules). At 1E-6 Torr, or 1E-9 atmospheres approximately, this would make about 2.2E14 molecules of gases. If the neutron counts of 1E5 to 1E7/sec are indicative of a similar amount of fusion events, then about 1/2 ppb to 1/20 ppm concentration occurs per second of fusion activity... (if I didn't get lost in the numbers, there.)

So exact concentrations would depend on the size of the fusor, background pressure, and run time, but it looks like ppm or better concentrations would be reasonable expectations.

These concentrations, while challenging to resolve in the presence of large concentrations of similar AMU background gasses, probably.... could be detected. A Gas Chromatograph preceeding the MS (GC-MS) could improve detectability, but we are now talking about fairly expensive equipment, not likely to be in the amateur's lab.

Okay... so we will think some more...
thanks everybody for good comments and ideas.