Please Help Quantify X-Rays

This area is for discussions involving any fusion related radiation metrology issues. Neutrons are the key signature of fusion, but other radiations are of interest to the amateur fusioneer as well.
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Sam_Pasmann
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Please Help Quantify X-Rays

Post by Sam_Pasmann » Mon Dec 03, 2018 11:19 pm

Hello All,

My name is Sam, I've been a lurker here for a couple of years, but this is my first true post (aside from Introduce Yourself). I am the team lead of the University of Portland IEC Fusor Capstone team on campus, a project I proposed. Our team consists of 4 senior Mechanical Engineering students and our Adviser,a PhD in Mechanical Engineering with expertise in thermodynamics and combustion. I preface this because so far as we know there is no one at our school with significant experience in nuclear fusion (or nuclear power/science).

Our fusor design consisted of:
- 20kV power supply at 35mA
- KF-50 S.S. 5-way cross (with one viewport)
- 1inch Dia. Tantalum grid
- Remote power control for emergency shut-off
- Vented exhaust from the mechanical and diffusion pump
- Operating distance of at least 15ft (could be increased)
- nuetron detector (either BD or GS-Neutron-150)
- GM dosimeter (although we had not identified a specific one)

You may have critiques or questions of our design decisions, and I would love to hear them, but first... Initially, our project was supported and fully funded. However, some in our Engineering Department learned that fusors produce x-rays and "nuclear waste" (Tritium) and our project was put on hard stop (know we never tried to hide any of these things). Our team has been working very hard to dispel rumors everything from "cold fusion", "radioactive deuterium", "nuclear waste", "radiated chamber", and more. It is clear that fearful decision making took the place of logical scientific discussion.

Despite our efforts, our school decided to dispose of our deuterium lecture bottle, and has said we may proceed with construction but will not fuse. This has been very disheartening for our team. Regardless of whether or not our fusor is ever turned on, I would like to prove in our project reports and presentations that x-rays and other forms of radiation would not have been a serious safety risk. My teammate and I have been working hard on this, and based off data take from Stano, Michal and Raèko, Michal [1] were able to estimate our total tritium production. But we've had a much slower time trying to approximate x-rays. I have scoured Google Scholar for academic information on x-rays emitted from IEC machines and only find very generic info like "not enough to be a concern". The only hard evidence we have found has been MATLAB code developed by the Eindhoven University of Technology [2] to determine the x-ray spectrum, intensity, penetration depth, and total energy. We have been slowly adapting the code as we attempt to teach ourselves radiation science.

With all of that, would anyone be able to offer help in proving that x-rays are not a concern? Maybe I'm wrong, maybe at the power we planned (we've also now lowered our power to 13kV 30mA from a neon sign transformer) they would be a health risk, but all that I've read (which has been a lot) from here and all the scholarly articles on IEC machines I can find say they would not. But how can we provide our administration with reassurance without holding a dosimeter to a working machine? Would any of you have dosimetry data from some of your runs? Any data, resources, ideas, you can provide would be extremely appreciated.

One of the reasons we started this project was to help educate people to fight the stigma against nuclear power, now that stigma, not scientific discussions that are holding us back.

Thanks for all your help,
Sam

[1] Stano, M., & Raèko, M. (2016). Experiments on D-D Fusion Using Inertial Electrostatic Confinement ( IEC ) Device in the Laboratory Exercises on
Plasma Physics at the Comenius University *. Acta Physica Universitatis Comenianae, LIII, 71–81. https://doi.org/10.1037/0278-6133.10.2.80

[2] Minderhout, V. (n.d.). Photon radiation produced by the fusor theoretical model and measurements. Retrieved from
https://pure.tue.nl/ws/files/67736677/850820-1.pdf

EDIT 1: Spelling

John Futter
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Re: Please Help Quantify X-Rays

Post by John Futter » Tue Dec 04, 2018 2:58 am

With your power supply the only point that x-rays can leave is through the view port.
If the view port is covered with lead glass than then this escape route is closed.

As to the production of tritiumin a fusor
so little is made that it is almost impossible to measure with extremely sensitive equipment.
In fact it is far more likely that you will measure the fraction that is made in the upper atmosphere. It is this source that is used to age date ground water.
It is a pity that your school got rid of your deuterium --maybe one of you talked up your system and they have certainly overeacted.
My opion is that the most dangerous thing you have is your high voltage power supply. not x-ray production as I have shown you how to mitigate this and certainly not Tritium radioactive decay.

Sam_Pasmann
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Re: Please Help Quantify X-Rays

Post by Sam_Pasmann » Tue Dec 04, 2018 3:29 am

Thanks for the reply John.

This is what we told them, that high voltage should be the main concern. Below is the calculation we ran for tritium production, maybe you or someone else can review it and give feedback. As for x-rays, they don't want to take the risk of 'not knowing'. Is there any academic source, or calculations I could reference to prove this?

Below is a sample calculation to determine the approximated run time of the M. Stano, M. Racko fusor to reach the maximum derived air concentration (DAC is the air concentration of tritium per volume) for the work place:
Tritium (T)
Given:
Estimated neutron production rate for fusor, running at 32kV and 2.5mA, to be 23200 neutrons per second
Atomic Mass (T) = 3.0160492 u = 5.0082670843x10(-24) g
T Production = 23200 T/s
T Specific Activity = 9650 Ci/g
Legal DAC (T) = 2x10(-11) Ci/mL

Activity per Tritium=9650 Ci/g (5.0082670843×〖10〗^(-24) g/T)≈4.833×〖10〗^(-20) Ci/T
Activity per second= 4.833×〖10〗^(-20) Ci/T ×23200 T/s=1.121×〖10〗^(-15) Ci/s

Assuming all tritium atoms were collected, not released or diluted (despite real conditions where tritium will be continuously exhausted outdoors), the continuous run time to reach the legal working air concentration:

Time to Legal Concentration=(2×〖10〗^(-11) Ci/mL)/(1.121×〖10〗^(-15) Ci/s)=17837 seconds/mL= 4.95 hours/mL

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Re: Please Help Quantify X-Rays

Post by John Futter » Tue Dec 04, 2018 9:30 am

sam
only a few dd's result in tritium
most result He4 so your calcs are overly generous in T^3 production

Bruce Meagher
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Re: Please Help Quantify X-Rays

Post by Bruce Meagher » Tue Dec 04, 2018 12:23 pm

To get the expected X-ray exposure rate of your fusor you might consider running a Monto Carlo radiation transport simulation with programs such as GEANT4, Gate, MCNP, etc. These programs have fairly steep learning curves, but should provide the results you’re after.

Another method would be to hand calculate the expected output with some simplifying assumptions. I’d suggest getting a copy of “Introduction to Radiological Physics and Radiation Dosimetry” by Attix to understand what’s required to make this calculation. I’d treat the fusor as a simple X-ray tube with the grid as the cathode and the chamber walls as the anode. You know the voltage and the current. The radiation yield of iron for 30 keV electrons looks to be about 0.1% (from the NIST ESTAR tables). Calculate the fluence rate at the inside surface, make some assumptions about the shape of the X-ray spectrum (or use a single energy as a simplification), calculate the attenuation through the thinest part for your stainless chamber and through the viewport window (they just appear like filters), then calculate the beam intensity at the outside surface. Finally calculate the exposure rate at the distance of interest.

Others have indicated that only the non-leaded glass viewport pass any measurable X-rays at 20 keV. Your calculations should confirm this.

I found this presentation < https://humanhealth.iaea.org/HHW/Medic ... ter_05.pdf> to be a good high level overview of x-ray production.

Bruce

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Re: Please Help Quantify X-Rays

Post by Sam_Pasmann » Tue Dec 04, 2018 6:47 pm

John, what is the ratio of T^3 to He4? From the reactions possible of dd, I assumed they both had a 50% chance of occurring.
2D + 2D -> 3He (0.8 MeV) + 1n (2.5 MeV)
2D + 2D -> 3T (1.0 MeV) + 1p (3.0 MeV)

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Richard Hull
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Re: Please Help Quantify X-Rays

Post by Richard Hull » Tue Dec 04, 2018 8:32 pm

4He is the rarest of all D-D fusions. About 1 in 10,000 D-D fusions result in a 4He.

At 20kv, as noted, virtually zero electron induced X-rays leave the SS fusor except via a view port. (99.9999% of all x-ray flux produced in the fusor is due to the "electron current") A true nervous Nelly issue at voltages under 25kv in a normal SS chambered fusor.

A virtual 50:50 production of 3He and T are the main output of fusion in D-D. Equally, at the same instant, there is a 50:50 production of protons and neutrons. (As we have pointed out and posted here constantly since 1998.) I remain stunned by those who do not know, intimately, this main and only reaction in our fusors.

20,000 neutrons/sec means 20,000 Tritons/sec from a net fusion rate of 40,000 fusions per second. Maybe, just maybe, 4 (4He) atoms will be produced.

Worrying about X-rays and T production from a 20kv fusor, is like being highly concerned about 4He production.

Tritium, in molecular form, pumped out the vacuum pump exhaust is a true non-issue, but a nervous Nelly can ship that outdoors where it will make a bee-line for the stratosphere where it can become "triter" (DTO, HTO or T2O) and rain back down on the earth to wind up in some child's drinking water in parts per quintillion. It remains much-ado about nothing and always will be. As for those radioactive tritons, we are all suffering under a "dilution".

Here! .....Wait!... We're not done yet!.... Let me add to the dread and doom. (I love it!)

How many hyper-energetic fusion tritons, protons and 3He atoms are going to immediately get pumped out of the fusor? The exact amount, due to my calculations, is 0.00000! No, they will all slam into the fusor shell creating multi-megavolt, killer x-radiation whistling through class rooms, the neighbor's dog, their children, you and into the parked cars all around..... Lions and tigers and bears, oh-my! The physics of nuclear things is fraught with dangers for the uninformed. Non-thinkers and nervous-Nellies beware. I have never mentioned the mev x-rays before now, figuring no one ever thought that far forward on the real, yet non-issue, mev x-rays coming out of a fusor. Fully 3/4 of all fusion debris will create x-rays of fearsome energies that virtually no shielding will stop! Naturally, as the multi-mev particles plow into the SS walls, few will produce a single multi-mev x-ray.....No! they will create a full spectrum of x-radiation with many x-rays coming of each Triton, proton, 3He nucleus. Most will be in the hundreds of thousands of eV. Oh god, the horror of it all. Gleefully, the x-rays from this plowing of fusion debris is incalculable.....Many x-rays from each... Put that in yer pipe and smoke it.

What few tritium containing molecules that are ultimately pumped are probably in the form of wall emitted HT, DT, in search of an oxygen partner wanting to end up as "triter" looking to undergo radioactive decay in the next few seconds or up to 100 years from now. (Remember....exponential decay) Yes Virginia 1 sec to 100 years of decay lay ahead for each little tritium atom.

Worry, worry, worry.....Woe betide us all...Ring-a-ring of neutrons, a pocket full of tritons, a-fusion, a-fusion, we all fall down. Phooey!

Richard Hull

P.S. trust me to tell the whole story and make it worse than you could have ever imagined.
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
Retired now...Doing only what I want and not what I should...every day is a saturday.

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Re: Please Help Quantify X-Rays

Post by Bruce Meagher » Wed Dec 05, 2018 5:51 am

My understanding is no MeV X-rays will be produced by heavy energetic charged particles (proton, triton, or He3 particles). Heavy charged particles don’t emit measurable bremsstrahlung radiation when slowing down in the stainless steel shell. Lots of characteristic X-rays from the iron and other elements, some bremsstrahlung from the ejected electrons (delta rays), but all so low in energy they will probabilistically never make it outside the chamber.

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Richard Hull
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Re: Please Help Quantify X-Rays

Post by Richard Hull » Wed Dec 05, 2018 7:43 am

When one has metals being hit by charged particles in the sub 100kev range. You will see the common K shell characteristic X rays,(XRF). However as the energies climb of the bombarding particles into the 400kev range you can have L and M shell x-rays in the 200kev+ range generated which will penetrate any fusor shell. Above 1mev, charged particles generate more of these M shell X-rays. As you go higher some nuclear excitation can occur with gamma possibilities, the gamma term is pretty much reserved for true inter-nuclear photon emission while classic X-rays are electron shell based x-rays.

So, there will not be just the classic K shell, x-ray fluorescent soft x-rays, but some very nasty M shell spectrum 100kev to 400kev x-rays until the photon's wavelength lengthens through interactions to be limited to the common XRF, K shell interaction range. It is true that the bulk of the x-radiation will be rather soft, but those M shell hot ones will be there.

Particle accelerators have big issues with such x-radiation if they try to "beam stop" or target materials. Tons of iron placed all around the "business end" of the accelerator is needed to stop lethal photonic radiation, be it x-ray or gamma photons.

Thus the "fusing fusor" does emit x-rays of prodigious energies. (fact).

Now, what about the x-ray flux?? The truly dangerous flux from any fusor is limited by it's electron current....How many milliamps are coming out of the supply into the fusor? This is the sole arbiter of any x-ray flux. A multi-milliampere flux of x-rays is always a nasty flux. How many electron current x-ray photons are produced at 10ma current?

One ampere is joule or watt second or 6.2 X 10e18 electrons/sec. Assuming every electron is accelerated and creates an x-ray photon, we might expect a maximum of 6.2X10e18 X 10e-2 = 6.2X10e16 x-ray photons to be produced in a fusor each second!! (That number in words is 62 quadrillion/sec)

Now, can that monstrous flux penetrate the shell? This is solely dependent on the accelerating voltage. A spectrum of x-radiation energies spreads from ultra soft to the hardest x-rays possible based on the voltage. The highest energy x-rays will represent only a small fraction of any x-ray flux. Thus, our fusors need only be x-ray shielded if the voltages climb beyond about 40kv applied when the hardest 35kev-40kev shell penetrating "shine through" x-rays become so numerous that their flux number fraction of that monstrous total flux creates a concern.

Now, what is the current or flux of the protons, tritons, and 3He nuclei in our fusors. Remember, these are charged particles and can represent a flow of current; let us run some current numbers. As all the particles are in the mev range and assuming 200,000 fusions per second. that makes a total of 300,000 charged particles capable of creating 1 or more shell penetrating x-radiation photons per second. The total charged particle current is 3X10e5/6.2X10e18 =r .48X10e-13 amp or in words, 48 femptoamps! A real current, but a pitiful one and no where near the electron x-ray flux from the power supply current. 100 billion times smaller particle and x-ray flux than the power supply electron flux. ( the 100 billion factor pretty closely mimes the ratio or COP, tiny fusion energy generated versus the electrical energy from our wall outlet.

Nasty x-ray stuff is shot out of the fusor but at levels too small to effectively even measure.

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
Retired now...Doing only what I want and not what I should...every day is a saturday.

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