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Re: FAQ - D-D fusion - Energy - Flux - Dose

Posted: Wed May 21, 2008 10:30 pm
by Wilfried Heil
The field of radiation measurement has been particularly beaten by multiple definitions and redefinitions of the same units. This can make it difficult for someone just getting started in this area. The particular system is not important, but one has to know which is which - a dose, a rate or an equivalent dose and so on.

You will notice that I'm only using the units "mrem" and for pressures "mbar" here, for consistency and because I don't find most of the SI units well adapted for our purposes. I grew up with pressures in bar, activities in Curie and cars with horsepower "HP" or rather "PS".

If someone should come to the point where we measure exposures in Sievert he'll be in trouble anyway.

One Pascal for pressure would fit nicely (run the fusor at about 1 Pa = 10E-3 mbar and it'll be in the operating range) but this is still a rather odd unit for the weather forecast. Who on earth would measure pressures in Pascal? An ant maybe, or a plasma physicist.

Re: FAQ - D-D fusion - Energy - Flux - Dose

Posted: Thu May 22, 2008 2:25 pm
by Richard Hull
This discussion is drifting and needs a new thread if what you have to say is not directly related to the above titled posted FAQ.

The efficiency part of my original posting was posed as an exercise, a mathematical problem to solve and not a lead in to a discussion.

Thanks all.

Richard Hull

Re: FAQ - D-D fusion - Energy - Flux - Dose

Posted: Thu May 22, 2008 9:15 pm
by Carl Willis

A search on "shielding" or "x-rays" in the Radiation Detection and Measurement forum is likely to provide the answers you seek.


Re: tritium dose.

Posted: Sat Aug 16, 2008 6:37 pm
by Frank Sanns
I don't think you have to worry about T in any of our fusors or even one producing 10E10 n/s for two reasons.

First, 10E10 sounds like a huge quantity but when you consider 3 grams of T is 6e23 atoms, then that is only 3E-13 atoms of T/sec. One curie of T is around 2e19 atoms so 10E10n/second translates to tens of microcuries/sec. This is not trivial but it is not a raging quantity and it assumed 10E10 n/sec and nobody here is within 3 orders of magnitude of that.

Secondly, T will not stick around. It is light and at RT it will have a velocity that will keep it escaping every but a sealed vessle. The reason there is no H or Helium on the earth is because it will reach escape velocity just from themal surroundings and it will be lost to space.

Frank S.

Re: tritium dose.

Posted: Sat Aug 16, 2008 10:31 pm
by Steven Sesselmann

I am with Frank on this one, Tritium is a hydrogen gas and will quickly float up to your ceiling and escape.

A much more serious helth hazard are the oil vapors from the roughing pump, wich typically runs all day when you are in your lab. I have solved this problem by connecting a plastic hose to the pump exhaust, and feeding it out through a hole in the wall, incidentally this would solve the trituim problem too (if there ever was one).

Tritium is a problem when it is in the form of tritiated water or "Tritium Oxide", tritiated water can hang around in the air as water vapour and it can also be absorbed by the skin and become an internal radiation hazard.

Heavy water (D2O) becomes tritiated when it is used as a neutron moderator around the neutron emitting cores in nuclear reactors, needless to say this tritiated water also becomes hot and steamy, so I imagine that special ventilation is needed in these reactor buildings.

In a full scale energy producing fusion reactor of the future, one would probably want to try and keep the valuable tritium and Helium3 fusion products, so there is an opportunity for someone to invent a way to separate these gases from the vacuum exhaust.

Further down the track...


PS: Chris, it is generally not a good idea to rename the subject line of an old thread, better to start a new one. It confuses everyone.

Re: tritium dose.

Posted: Mon Aug 18, 2008 4:32 pm
by Richard Hull
Frank re-iterated math already done on all three of our websites over the past decade by myself and others on this subject. Tritium, at even 10e6 neutrons/sec, is a total non-issue. Only two here have verified claims of such emissions and on short runs only. I know we would all like 10e9 n/sec, but it is safe to rule this out of our range, completely.

Steven is right, also. Please don't rename a reply's subject line. If your question is that big a deal and not immediately related to the topic to the point of forcing you to consider renaming the subject line, start a new thread.

Tritiated water can be in the form of HTO or DTO but only very rarely T2O. T tends to replace only one molecule of liquid water. Such contaminants, we need not worry about either.

There are plenty of things to "nervous nelly" about around a fusor, Neutron radiation or nuclear waste gases are not among them.

In operation, only electrocution should be considered a prime and ever present danger. In the highest end operation, above 30 KV, x-rays might be addressed as a weaker secondary consideration. X-rays only become a major issue above 50kv at which point, the shell goes rather transparent to the pesky rays.

Richard Hull

Re: tritium dose.

Posted: Mon Aug 18, 2008 5:33 pm
by Chris Bradley
Sure. I hear what you're saying but it wasn't really the maths of the tritium that I was thinking about, but if there were any physical reasons it might 'linger'. The second maths question is different and is clearly a matter of academic interest wrt fusor technology - at what point would it become an issue?

Re: FAQ - D-D fusion - Energy - Flux - Dose

Posted: Mon Aug 18, 2008 8:37 pm
by Jboily

Thank you for the information and corrections.

There is something I do not understand in your calculation. The 500 W DD fusion would produce 168 watts of neutron. At 1 meter distance, somebody would absorb at the most 1.34 mRad per sec. (that is if the the energy absorbed within the first cm cube of Skin, less if the energy is distributed across a deper region). This would be 1.07 mRad in 8 a seconds exposure, similar to the exposure from a medical XRay.

How would a 500 watts reactor produce 800-2000 rem (a letal dose)! Unless it was overloaded in the 10 MW range.

What is the conversion ratio for Rad to Rem at 2.45 MeV?


Re: FAQ - D-D fusion - Energy - Flux - Dose

Posted: Mon Aug 18, 2008 9:29 pm
by Jboily
I just answered my question, a RAD is 100000 J/gram, a factor of 10^5. Then you multiply by a Q of about 10 to get to Rem.

Everything then seem to fit. Sorry for the confusion.

Re: tritium dose.

Posted: Tue Aug 19, 2008 2:43 pm
by Richard Hull
The answer to your question is simply tritium production and environmental contamination about a fusor occurs at a point so distant that none of us could ever reach it. Period.

We talk in isiotopic emission of n/sec. The big boys talk in flux of n/sqcm/sec

I doubt if 10e12 n/sec, isotropic, from a fusor would produce a tritium level that would be worrisome based on our operational times. Again, the x-rays and neuts, themselves, would be the major worry at this level. (Which we could never attain)

Based on Frank's 10e19 atoms per curie, the fusor at 10e12 n/sec would produce only 0.1uCi per second. Not to worry.

The body sheds T quickly, again, a big plus.

Unless you stick your pump's exhaust pipe in your mouth at 10e12n/sec you need fear naught.

I don't know about others, but I vent my pump system to the great out of doors. This is mostly to avoid oil mists. T outside is a non issue, of course.

Dearest creator, will we ever be free of tritium issues constantly popping up as being useful fuel in a running fusor, (which it is not), or creating an imminent danger to ourselves and our beloved pets? (which it is not) Alas, I fear we shall forever be lashed to the wheel of both false joy and false fear due to the tritium issue.

Mathematical machinations will tell the tale, but many would rather cry and wail. For numbers great and small are oft something heard as a distant call. Reason and logic are hoped to abound, but alas, they are rarely found.

Radiation, asbestos and lead are the current demons in our head. To rid them of our space we toil with the result, our lives we foil.

Richard Hull

I'm a poet and don't know it, but my feet show it....They are Longfellows.