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Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
Uzzors wrote ...
Using the above formula I got a dose rate of 2,88mGy/hr, or roughly a whole year's dose per hour. The assumptions I used are listed below. Shield attenuation was calculated using tables from The dose rate formula assumes you're standing in the main x-ray beam, unless I'm mistaken.
X-ray tube output fluence (1mm Be)
Target Atomic Number 74 Tube Voltage 50 kV Tube current 4 mA distance 1000 mm
Dose rate 9,92 mGy/sec
Attenuation of Pyrex (5mm, 50kV) 7,41E-001 Attenuation of lead (1mm, 50kV) 1,09E-004
Total dose rate 0,8 µGy/sec 2,88 mGy/hr
Radpro gives a dose rate of 13 mGy/sec with these numbers, compared with the 9.92 mGy/sec using the Glasgow equation, which I don't think to be significant given the very approximate nature of these calculations, and Radpro's inclusion of so-called build-up factor.
But as Anders has said, the 1 mm lead shielding attenuation figure produced by Radpro certainly does look wrong, even allowing for very conservative 'over-shielding.'
Serves me right for using someone's java calculator instead of working it all out in longhand!:-D
Registered Member #95
Joined: Thu Feb 09 2006, 04:57PM
Location: Norway
Posts: 1308
I don't consider those numbers anything other than a worst case scenario to have as a guideline. If I can reduce the calculated radiation levels to an acceptable level using the math above, then I assume my setup will not be worse than that. There's still the issue of other effects like x-ray scatter however. Part of the reason I accept higher than realistic figures is because I can pretend all the "unaccounted for effects" are lumped in with it.
Registered Member #1134
Joined: Tue Nov 20 2007, 04:39PM
Location: Bonnie Scotland
Posts: 351
Proud Mary wrote ...
Radpro gives a dose rate of 13 mGy/sec with these numbers, compared with the 9.92 mGy/sec using the Glasgow equation, which I don't think to be significant given the very approximate nature of these calculations, and Radpro's inclusion of so-called build-up factor.
But as Anders has said, the 1 mm lead shielding attenuation figure produced by Radpro certainly does look wrong, even allowing for very conservative 'over-shielding.'
Serves me right for using someone's java calculator instead of working it all out in longhand!:-D
Ultimately Radpro, and even plain Math, will just ballpark your figures.
There are so many variations in tube design that even accurately calculating a tubes output is well nigh impossible, and that is before you factor in ageing and warm up.
Actual measurement is the way to go.
James wrote ...
Below 50kV you are unlikely to get much penetration,
Don't be so sure!
This image was taken at 50kVp:
It demonstrates the effective penetration through steel, you can expect to achieve at 50kVp.
And as Proud Mary says, there is a LOT of exploration to be done at sub 10keV. This is in fact where my work is at now, since everyone seems to have done to death the 50-150keV range!
To the original poster, find a decent sturdy steel box in which to house your tube, and line it with at least 3mm of lead, and operate the tube at no more than 50kV.
Registered Member #3610
Joined: Thu Jan 13 2011, 03:29AM
Location: Seattle, WA
Posts: 506
Or just find an old dental x-ray head and wire up a controller for it. That gives you a nice complete well shielded unit that is relatively safe to use.
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Homemade X-ray machine question
