risk assessment

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frostyk72
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risk assessment

Post by frostyk72 » Fri Apr 23, 2010 4:20 am


hey guys

i have to write a risk assessment for doing fusor experiment at tafe.
so what kind of risks are involved?

i know there are x-rays at 5kv+
with a fuel source at about 10kv - 15kv there will be fast neutrons.
possibility of vacuum chamber breaking and possibly causing damage if not made strong enough to handle low pressures.
risk of electrocution working with high voltage and amps

have i got everything to write a report from?
any safety tips for overcoming these problems.

have thought of a wall of bricks 2 bricks thick around chamber to stop neutrons, possibly some containers of water with some sort of cooling to prevent it heating up to much. still got to find out how thick i will need chamber to stop x-rays.

any help would be great.
thanks in advance.

steven w

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Steven Sesselmann
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Re: risk assessment

Post by Steven Sesselmann » Fri Apr 23, 2010 5:12 am

Steven W.

In order of priority, your risks are..

Electrocution
X-rays
Gas explosion (Hydrogen)
Vacuum Implosion
Gamma rays
Bankrubtcy
Neutrons

Take care, be pedantic with all electrical wiring, always use the same colour cable for your earth and HV if possible, and double check everything before you turn the power on.

Use a small sheet of lead plumbers flashing, between you and any x-ray source (under 50 kv), X-rays under 20 kv are really only a problem where they can shine through glass. A geiger counter or ion chamber proportional counter is absolutely essential.

Don't forget that Deuterium if you get some, is really just another Isotope of Hydrogen, and reacts violently if ignited in the atmosphere.

Shield against implosion of glass vacuum chambers if you use one, polycarbonate would be the material of choice

Gamma rays can be an issue if you are successfully achieving high fusion rates.

Personal bankruptcy while chasing illusive neutrons can be a significant risk.

Neutrons are highly unlikely to be a risk, even the most successful fusors running at high volts and amps, only put out around 10^6 neutrons per second, which are unlikely to harm you unless you sit on top of the fusor for a long time.

Your educational institution would rather not know about neutrons, as the word will almost certainly result in a big NO.

Steven S.
http://www.gammaspectacular.com - Gamma Spectrometry Systems
https://www.researchgate.net/profile/Steven_Sesselmann - Various papers and patents on RG

frostyk72
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Re: risk assessment

Post by frostyk72 » Fri Apr 23, 2010 6:25 am


thanks for reply steven

well i dont know how far will be able to push it.
i'm sure if we are under the threshold for neutrons we should be fine. to fiddle.
aim is to just to get a little glow happening for starters.
what is the voltage threshold for fusion in a fusor?

vacuum chamber will probably be steel. with a small view port for camera.

what sort of gas would you recommend for least explosive, and good to make a good glow for starters.
maybe good fusion later if i am allowed.

shielding against gamma rays?
what would you recommend?

bankruptcy, well havent got much money to start with so thats fine.

and yeah will be double checking everything and i'm sure teacher who helping me will do the same.
vacuum pump and diffusion pump should get here next week.
all i need now is vacuum chamber, dad said he will build me one , will be small but should work

thanks again

steven w

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Re: risk assessment

Post by Tyler Christensen » Fri Apr 23, 2010 6:31 am

The voltage level necessary to actually hit fusion is not a hard number, I've detected trace fusion as low as 15kV with extremely sensitive neutron detection equipment (2 foot 3He tube), however odds are you'll needs 25kV+ unless you start out with large 3He tubes.

For just plasma, you can use any gas really, most people in a demo fusor just run atmospheric air in which works fine. You can also use any inert gas which will not be flammable, such as argon. To actually perform fusion, the only fuel is deuterium which can be treated as hydrogen as far as flammability goes (aka very explosive in an oxygen mixture).

I don't think gamma shielding is a big deal especially if you're at a bit of a distance, but if you were concerned about it, thick lead shielding should suffice.

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Steven Sesselmann
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Re: risk assessment

Post by Steven Sesselmann » Fri Apr 23, 2010 6:33 am

Steven

For a nice glow discharge, and to study plasma through your viewport, air vacuum will do just fine, no need to introduce any special gas.

Allthough for most of us Air is a pretty special gas

Steven S.
http://www.gammaspectacular.com - Gamma Spectrometry Systems
https://www.researchgate.net/profile/Steven_Sesselmann - Various papers and patents on RG

frostyk72
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Re: risk assessment

Post by frostyk72 » Fri Apr 23, 2010 7:04 am


well if i can get plasma in air will just do that for starters.
that will lower risk alot

bk8509a
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Re: risk assessment

Post by bk8509a » Fri Apr 23, 2010 12:56 pm

It will lower risk, and money.

Check out number 6 on that list: "Bankruptcy".

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Doug Coulter
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Re: risk assessment

Post by Doug Coulter » Sat Apr 24, 2010 6:30 pm

Yes, I was rolling on the floor over that number 6 one....this is a hobby for the rich or the very resourceful, or both, for sure.

You don't need real thick lead to stop power supply energy photons (X rays), here a couple mm does that just fine. If you get to copious fusion, you'll just want to stand back farther, as the amount of lead needed to stop the really hot gamma rays from the rare (1:10,000) DD->He reaction is in the inches range.

Here's a guide the radiologists use for shielding.
Attachments
XRayShielding.gif
Why guess when you can know? Measure!

bk8509a
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Re: risk assessment

Post by bk8509a » Sat Apr 24, 2010 7:03 pm

Steve,

I don't know how good you are at math, but here's ALL you need to calculate x ray safety from THE most reliable source when it comes to standards: NIST.

http://www.nist.gov/physlab/data/xraycoef/index.cfm

Everything you need is there. I have a paper on X ray shielding that I gave to my school in order to use the fusor, which I can give to you, but it's much more important that you do these calcs yourself, if you have the know-how.

You just need to understand
N0=NI e^-x

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Doug Coulter
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Re: risk assessment

Post by Doug Coulter » Sun Apr 25, 2010 4:51 pm

Well, that's interesting indeed and does describe how to attenuate X rays by some factor.

But it has nothing whatever to do with getting them to a safe level for humans -- that level (which is variable vs energy) isn't even mentioned.

Nice to know how to attenuate by factor 100, for example. But if your source is say, 10,000 times what's good for a human -- does that do you enough good? Not mentioned at the above source, which is why I quoted from a source of *human health* radiology that also figures in what's required to keep you healthy. According to radiation doctors anyway -- they may or may not know something about X ray effects on human health. NIST simply does not address that at all.

Not as informative on pure attenuation, but it's what it takes in an average hospital X ray room (which runs a lot more power than we do for a lot more hours per day, and generally at higher voltages), for people exposed day in and day out, and so is pretty conservative. In practice, the table I quoted above is what we use, and is what it takes to make my survey meter read as though the fusor wasn't on even right at the shield. A lower threshold scintillator detector still can see if the fusor is on, meaning some low (sub 5kv) x rays still get out. As the NIST source indicates (and so do all the physics books) X ray absorption is not a one-shot and a certain thickness of substance X won't stop them all, but tends to down-scatter X rays in energy and finally stop some, but not all completely, no matter how thick, in theory.

I half expected Richard to jump in here and say something along the lines of "don't worry, be happy, below about 30-40kv the fusor shell gets them all" which would also be more or less correct. Since he didn't, I am.


Sorry Brian ;~) The NIST source is definitive, but not fully useful unless you take human dose tolerances into account. In practice -- we don't run like a hospital in any of power, voltage, or duration, so we in general are safer and their safety procedures are fine for us. The attenuation ratio is of interest, but incomplete where human exposure is involved....
Why guess when you can know? Measure!

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