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: Well armed Fusioneer
Date: Jul 21, 12:41 pm
Poster: Richard Hull

On Jul 21, 12:41 pm, Richard Hull wrote:

On the topic of what radiation instruments to acquire..........

Starting out with a demo device you should have a geiger counter. (mica windowed preferably) This is for QUALTITATIVE X-ray announcement. ( I got X-rays...I don't got no X-rays) You can't do effective dosimetry or advanced X-ray metrology with a geiger counter beyond maping out an X-ray field, finding and fixing X-ray leaks, etc. Demo devices under 10kv don't even need this.

With advanced or large demo devices using voltages over about 12kv, the gegier counter is a must have minimal safety item.

With a fusor or demo system in regular operation some form of useful and calibrated X-ray dosimetry is going to be desirable.

The second instrument you should acquire is a "cutie pie" ionization chamber calibrated from milli-roentgens to a few roentgens. Barring the acquistion of this superlative real time tool, a good set of 3-5 dosimeter pens with charger would be needed. These are QUANTITATIVE X-ray dosimetry instruments.

The cutie pie is a real time instrument reading actual x-ray dosage. The pens, I jokingly call post-mortem dosimetry. (After the danger is past you can check to see how parboiled you are and if you need to be turned over to cook evenly on the other side.)

X-rays are certainly no joke at 20kv and at higher levels can produce severe burns or other medical bothers. At almost any conceivable level of operation, the neutron hazard will never rise to the level of the x-ray hazard. This, inspite of the fact that 2.45mev fusion neutrons are the most nasty form of harmful radiation known to man, having and RBE (relative biological effectiveness) of 10 on a scale of 0 to 10.)
Finally comes the neutron counter should be acquire, built, begged or borrowed only after the first two groups are in hand. This instrument is not needed for any form of dosimetry or protection and is therfore medically optional under 40 kilovolt system voltages. However, it is a must have item if you are interested at all in how your actual fusion is going, (if at all).



The key shielding will be for x-rays. Light lead sheeting (1/16th inch) can easily be wrapped around leaky openings at ports, etc. This will suffice up to about 25kv. Heavier cast lead plates or blocks will be needed above 30kv.


Parafin blocks, polyethylene or tanks of water are fine here and act to thermalize the neutrons (they are never really stopped per se.) Thermal neuts are very low in RBE. So we just need to put the brakes on and scatter those pesky fast neuts.

You needn't wring your hands over this until you record over 10e7 n/sec isotropic emission. Still, at 10e5 I err on the side of caution. I have borated parafin. (Made by melting borax into the parafin and casing as needed.)

The key point in shielding is obvious.............
use a small, low cost effective shield jammed hard up against the offending source area and it will shade a large included angle and keep costs way down.

Richard Hull