Had a Doctor of plasma physics who works with the Max Planck Tokamak in Germany for about half of his working year check over some numbers I had come up with and provide some calculations. Maybe it'll help - results pasted below.
Tom
The max. 60kV operating voltage puts an upper limit on the X-ray energy of 60keV. The NIST graph and table of photon mass attenuation coefficients for iron (close enough to steel) at:
http://physics.nist.gov/PhysRefData/Xra ... b/z26.html
shows that for E < 60 keV, the mass attenuation coefficient is > 1.2 cm^2/gm. It is 8.2 cm^2/gm for 30 keV and rises steeply to 170 cm^2/gm for 10 keV.
The calculation of penetrating flux follows de Beer's law of exponential attenuation :
I(x) = Io exp(-m x) where the thickness x is expressed as mass per unit area (gm/cm^2) and m is the mass attn. coefficient. For your chamber, x = rho_m * t where rho_m, the mass density is 8.0 gm.cm^2 for steel and t is the thickness in cm. My own plasma chamber is 4mm stainless steel, so taking that as an example, one gets
x = 8 x .4 = 3.2 gm/cm^2 and hence the attenuation of 60 keV X-rays is exp(- 1.2 x 3.2) = 0.021, i.e. only 2.1% of 60 keV X-days will penetrate. For 30 keV this is much smaller: exp(-8.2 x 3.2) = 4 E-12, already negligible.
The results are obviously high dependent on your chamber thickness. They are even more highly dependent on the
X-ray energy. Actually, since the inner shell binding energy of electrons in iron is (from recall) > 5 keV this already makes a big (positive) difference since from the above table, m would be about 1.55 giving 0.7% instead of 2% (for a thickness of 4mm).
The publication Kwon et al. Journal of the Korean Nuclear Society, Vol.12 (1980) p.171 et seq.
http://www.kns.org/jknsfile/v12/A048032 ... f91bb5a89f
gives convenient factors converting neutron flux rates to neutron dose rates. For 2.5 MeV neutrons, the calculation is: dose rate (REM/hour) = 1.24 x 10-4 x flux (neutrons per cm2 per sec). For your numbers, this gives, for a maximum flux of 7 neutrons/cm2/s , a maximum dose rate of 0.875 mrem/hour which is very close to your quoted does rate!
Thus I can verify that your calculation is correct. You could also quote it in terms of the radius from the centre of the vessel, when (replacing (1/1.5 m) 2 by 1/r2) it becomes (based on your 0.833 mrem/hour): maximum dose rate = 1.874/ r2 mrem/hour (r in metres). The Environmental Protection Agency states that the average radiation dose per year to Irish people is 4037 microSieverts:
http://www.epa.ie/radiation/radexp/expo ... EbFT0voF38
A Sievert is 100 Rem hence this average annual dose corresponds to 403.7 mrem/yr. I can’t find a recommended maximum annual dose on the epa site, but I would guess that the Office of Radiation Protection
would be concerned if the likely additional dose from the fusor were comparable to or in excess of the average dose. Thus it would be quite important to state how many hours you envisage operating the fusor, and hence
the expected annual dose. At 1 mrem/hour (to use a round number), you would equal the average Irish annual dose in 400 hours – admittedly a lot of operation time, and I’m sure you wouldn’t be planning to run it for anything like as long as this cumulative period over a year. You should, however, specify how long you do intend to run it (and I am assuming that you will be present when it is running).