Radiation Safety Questions

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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Anze A Ursic
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Radiation Safety Questions

Post by Anze A Ursic »

Hello everyone,

as I get closer to actually trying fusion with my device, I keep getting asked to provide assurance about radiation safety to my university. I have a simple cylindrical-style fusor in a relatively large vacuum chamber and we intend to go up to fusion voltages, so I suppose anywhere from 30-40kV at 10mA and it can be controlled remotely via a LabView GUI I built. I have read through the relevant FAQs, which have greatly helped me calculate X-ray attenuation and neutron radiation shielding requirements. However, I figured I'd post my setup here to crudely show how my lab is looking at this point and ask for any final pointers. The worst part about this is that this will be done in a lab surrounded with other equipment that is completely irrelevant to this project, but is too large or too heavy to move. This is causing concern as some think we may activate some of this surrounding equipment (it's mostly metal equipment with plastic handles and whatnot). However, from my understanding, the relatively low neutron rates (<10^6 n/s) and short exposure time (<2 min) would yield no such problem. But to appease the safety folks, I figured a few bags of Borax or maybe a few cases of water with some Borax dissolved in them surrounding this thing may not be a bad idea, but again, any input is great.

The other thing, of course, is X-rays. I have done the relevant calculations and per the picture below, we will be separated from the fusor by about ~3.4m (11ft) of air, ~6mm of steel (our chamber is roughly 0.25" thick) and about ~0.3m (1 ft) of reinforced concrete. Again, based on the calculations I have done, with the Intensity = Intensity_0 * exp(-(mu/rho)*distance) approximation, I found that the steel and concrete alone would shield >99% of the produced X-rays at 40kV and even the 11ft or so of air separation is more than many others have in their setup from what I have read. The only issue I see from the setup is the viewport, which will be pointed towards the wall behind which there is nothing (just the outdoors, and this place it restricted access, so no random people walking around). The other problem may be the HV feedthrough, which is ceramic and does not shield as well as steel, which will be pointed in the opposite direction, also towards the wall behind which there is a storage unit with no people. Another issue i thought of is that the x-rays may "bounce" off the walls and while the door is in a pretty neat position, not directly in front of the fusor, I am thinking of shielding the air-gap between it and its frame. The actual door is one of those steel heavy duty doors, so apart from the gap, it should be good.

Anyway, the calculations look good on paper but nothing beats experience, which I know people here have a lot of and of which I have none, so if anyone here would like to chime in for any pointers or comments, I'd greatly appreciate it! Thanks!

AAU
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Rich Feldman
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Re: Radiation Safety Questions

Post by Rich Feldman »

This is not from personal experience.

Plan for x-ray dosimeters, approved by your radiation safety jurisdiction.
How could anyone sign off without such a plan?

Looks like in your case, dosimeters are a trivial detail compared to the
planned investment in shielded enclosure etc. For which you want trustworthy advice before construction.
All models are wrong; some models are useful. -- George Box
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Anze A Ursic
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Re: Radiation Safety Questions

Post by Anze A Ursic »

Oh yeah, sorry, we will have X-ray dosimeters and Geiger counters as well as a neutron counter.

Anze
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Liam David
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Re: Radiation Safety Questions

Post by Liam David »

For typical neutron rates, and given the relative ease of shielding x-rays with lead sheet, your plan is very much overkill. Activation of surrounding equipment will also be a non-issue. However, it's no surprise that your university is concerned.

To determine what level of shielding is required, you should set (or ask someone from the university) the maximum allowable dose rate for personnel, both at the operator station and for any potential passerbys. For example, a device emitting 1e6 n/s will give an unshielded flux of 1e6/(4pi*(3.4*100)^2) = 0.69 n/s/cm^2 at 3.4m. Given the dose conversion factor of 28000 n/cm^2/mrem for 2.45 MeV neutrons, this translates to 0.09 mrem/hr. For short runs, this is not a concern. If you want to get an idea of how a setup actually performs short of building and measuring it, neutron transport simulations are indispensable (https://docs.openmc.org/en/stable/).

The majority of the x-ray hazard at 30-40 kV can be mitigated by shielding just the viewport and any flange connections with o-ring seals with lead. Backscatter from the storage unit will likely be a non-issue, but if there's no one on floors above, I would suggest having the HV feedthrough on top of the chamber and just letting it irradiate the planes flying overhead. A simple cinder block wall between the chamber and operators that puts everyone within its "shadow" would all but eliminate concerns, including from scattering. There is certainly no need to build a whole room.
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Anze A Ursic
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Re: Radiation Safety Questions

Post by Anze A Ursic »

Thanks, Liam! That's great info!

We are aware the plan is somewhat overkill, but this room we will be performing the experiment in is actually approved for radiation producing equipment. There is no way we could do it in the current lab, since it is not approved for any sort of radiation (except some lasers, I think). It's easier to just move it to a pre-approved location, rather than get our current lab approved for anything, which would likely not happen anyway because it's close to classrooms.

Anze
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Liam David
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Re: Radiation Safety Questions

Post by Liam David »

If it's already built, then there's really no reason not to move it in there. It'll give you a lot of flexibility for experiments without having to wrangle and reconfigure shielding all the time. Hopefully the safety folks give you the green light.
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Richard Hull
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Re: Radiation Safety Questions

Post by Richard Hull »

If your chamber is .25-inches thick you will have no issues with x-rays at 30kv they will not make it out of that steel. Most 304 SS chambers are no more than .0625 thick and at 40 kv, in my fusor I get no more than 6mrem/hr rate (Victoreen ion chamber) at the shell itself! (shell contact rate running at 40kv)....However at my 1" diameter viewport with no shielding at the glass I get a 50mr/hr rate!! Shield any glass view port! I use .125-inches of lead and this drops the viewport rate down to under 1mrem/hr at the viewport in contact with the lead. I do not shield myself at all for the 6mrem/hr rate of x-rays at my operator's station 6 feet distant. (inverse square law safety.) I use to wear a 0-100mrem dosimeter at the operators station but I could never read any dose on it after 1.5 hours of run time. I no longer use the dosimeters.

Neutrons, at contact with the shell of the fusor while applying 42kv@12ma will rise to between 6-8mrem/hr of fast neutrons. At the operators station, six feet distant, this amounts to about a barely readable 5 counts per minute on my Eberline PSC-1 neutron counter with a conversion factor for fast neutrons of .0062 mrem/hr rate per count, this equals, 5 x .0062 = .031 mrem/hr rate absolute maximum at this full-on fusion rate. Therefore I do not, nor have a ever, shielded my fusor at 6 feet for x-rays or neutrons.

Make of this what you will, as these are real readings taken over my operational rate on my fusor for 20 years of near 10e6n/sec isotropic emission of fast neutrons at peak operation.

I shield only the view port with .125-inches of lead and that is it. I might run my fusor at these rates no more than 30 times per year with 6 of those runs taking place over 2.5 hours each run on the first Friday and Saturday of October each year. (HEAS gathering here where 30-50 people will want to see it run.) Check images in various Octobers in the Image Du jour forum of the big event.

I attach the URL of last years event. this was the 32nd consecutive year this event was held. Many photos taken by others are missing due to recent sadness in backup

viewtopic.php?p=92879#p92879

And the year before in 2020

viewtopic.php?t=13666

Richard Hull
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Fusion is the energy of the future....and it always will be
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
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Anze A Ursic
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Re: Radiation Safety Questions

Post by Anze A Ursic »

Thank you, everyone! I was told today the radiation safety people will get back to me by thursday with follow-ups. They are somewhat confused because nobody has ever attempted to build a fusor here. They deal with high-power X-ray tubes and other X-ray producing equipment as well as high-yield neutron sources, but never something like this. I will keep you posted!
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Richard Hull
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Re: Radiation Safety Questions

Post by Richard Hull »

Compared to what they are familiar with the fusor is a non-radiation source. They have to be hype careful around what they work with. It is only natural that they are concerned. About a dual emissive device...(neutrons and X-rays). They will find it quite benign compared to anything in their experience.

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
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
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Anze A Ursic
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Re: Radiation Safety Questions

Post by Anze A Ursic »

Yeah when I was writing that report they wanted on potential radiation hazards, I realized there really are none if you are proactive. Some lead shielding and some parafin wax / borax combo and you've eliminated 99.9% of radiation. Moving this thing would be time consuming, I'll talk to them about trying to run it in the current room. Hell, we could do it at 1am when nobody is there. We're practically ready to go apart from some power supply problems...
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Richard Hull
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Re: Radiation Safety Questions

Post by Richard Hull »

That is the real solution. Run the thing with folks in the know manning the instruments. No test like a hot test.

Take readings at the running device and then at 6 feet. At that range, the needles will rest pretty much at zero with a 30-40kv fusor running. You must put a 1/8 - 1/4-inch thick lead shield over the viewport if you have one.

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
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
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Anze A Ursic
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Re: Radiation Safety Questions

Post by Anze A Ursic »

You won't believe this but I just got a 2000 word response email from the environmental safety folks detailing what all I have to do. Apparently, I have to meet up with them, go infront of a panel of an "Isotope Committee", talk to radiation officers, have my entire lab measured for background radiation several times by approved agents with approved equipment, review the entire university's radiation safety policy and highlight where and what is pertinent to our application, not to mention a bunch of other stuff.

Furthermore, they won't allow me to be exposed to any greater dose of radiation than 2mR/hr and they're saying that they estimate that my device, which I have never run and is probably incredibly inefficient even for fusor standards, would produce up to 10^7 neutrons / s, which is ridiculous.

So now I have until the 19th to show, point by point, how I will rectify non-existent problems and I can bring to the committee anyone I'd like or who's advising me, although I am working on this alone...

But hey, this is on ZOOM, so if anyone here would like to volunteer to swing by and convince them otherwise, I'd be eternally grateful! haha! I'm sure there's folks here who'd like to raise the black flag to bureaucracy!
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Richard Hull
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Re: Radiation Safety Questions

Post by Richard Hull »

Typically ridiculous assertions by folks using math who have never done anything in the real world. Bureaucracy?...No!... idiocy.

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
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
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Re: Radiation Safety Questions

Post by Rex Allers »

Depressing to hear that.

They give you a series of challenging tasks that must be performed, some of which require you to find and schedule other unknown people to complete, and then require it in an unrealistically short period of time.

Perhaps a bureaucratic way to say no without having to just say no.

Seems nothing can be done these days without first appeasing some overblown flavor of nanny state.

I have no advice to offer, but wish you the best.

Maybe you could claim it has potential military value. That seems to be an area that can progress without needing to worry about collateral damage and can get resources without having to justify much.
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Anze A Ursic
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Re: Radiation Safety Questions

Post by Anze A Ursic »

I've been working on this thing since late 2017, I am not giving up now. If they want a fight, I'll at least fight back.
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Re: Radiation Safety Questions

Post by Dennis P Brown »

Try to involve someone in safety directly - that often enables you to explain things and get them on your side. Remember, their job is to protect other students besides you but they get no credit for being right and risk their job if in any way they are wrong - even in the slightest.

For instance, you know it is essentially impossible to prove ahead of time that the fusor will never achieve or exceed 10^+7 neutrons (so true for most places that also have dangerous experiments); however, you can prove, via a slow ramp up with an absolute measurement (bubble detector), that you can stay under some arbitrary dose that is well under what they accept and in total neutrons. Just create a SOP that guarantee's this and will always be followed. That is how it is often done in most labs (Gov., commercial, schools, universities) that require radiation safety.

Don't alienate them - they have final say and can't be side stepped. Try not to talk down to them and do make them feel that you are including them and want to work with them for a safe lab/experiment.

I've gotten around many safety people (and failed with others) so I know something about this subject. Still, back in the 70's it was allowed for Prof's to build a full blown nuclear reactor (based on fuel that was highly enriched with 235) simply on a lab bench in a class building. Glad those days are over!

A few years back, someone in a related group 'cooked' themselves with a radar unit (died in three days) and many years back, ditto with an x-ray unit (died slowly over months a few weeks after the exposure.) Radiation can be dangerous and these safety people often only read about the failures and so don't understand that most people do know what they are doing to be safe.
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Re: Radiation Safety Questions

Post by Anze A Ursic »

Could someone kindly help me out with some of the points they made? I'm not trying to obfuscate responsibility here, but I'm going to need some help with some of this stuff if I'll ever wanna answer all their stuff as well as do all the 30 trainings I have to apparently take before even trying fusion. I'm also 25 and finishing up my MS degree in electrical engineering so while I know a decent amount about radiation attenuation and shielding, it is far from being my forte or something, so forgive the possibly simple questions. Also it would be a shame if this experiment did not come to fruition, seeing as how we have everything ready, the power supply, deuterium hooked up, etc. Here are some of the points that confused me most:


They are comparing X-ray dose rates of my device to that of an X-ray tube with similar power. "Another model estimates a dose rate for a 3 phase x-ray tube of the same current and voltage as 43,000 R/hr at 1 m." I'm sure inside the chamber that might be the case but we have a 316 SS chamber that's 0.25" thick (I just remeasured today, it may be even a bit thicker, but I'm doing worst case scenario here). That 43,000 R/hr goes to practically zero, or at least a negligible amount, with a 0.25" thick steel shield, right? In fact, my calculations showed a decay of ~10^{-8} from the original intensity. I get the viewport is a different issue but we are just gonna shield that with lead anyway. Further, I built a remote-controlled system that allows us to be in another room doing this, so we'd be separated from this thing by 5-7m including a 15cm of a concrete wall

They also wanted me to account for "build-up factor" from scattered photons and said that this could result in me getting 330% higher dosage than initially expected if there is 30cm of concrete between us and the fusor. Although that calculation was done for 40keV photons, where 40kV is the maximum voltage I anticipate to go to, so in reality the average photon would have an energy of ~20-25keV, if we assume something approximating a Maxwellian distribution.

Also, I understand that neutrons can be shielded / captured by a combo of a few inches of paraffin wax and Borax, but is there an analytical method to show them that this is actually a viable shielding mechanism?

I guess my problem here is that while being separated from this fusor by a quarter inch of steel and a minimum of 5 meters, us folks here on the fusor forums know intuitively that for the typical 30-40kV 10mA fusor, that's enough shielding and separation for the quick 5-10 minute runs people do. And we know neutrons also don't present a massive activation or radiation threat when treated with ample distance and some home-made shielding, but if anyone could help me translate some of this intuition into an actual numerical proof, I'd greatly appreciate it. Like I said, I'm only 25 and I know many people here have more experience in this field that I have years of my life.

Anze
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Liam David
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Re: Radiation Safety Questions

Post by Liam David »

Short of measurement, about as close as you'll get to a "numerical proof" for geometry-dependent calculations is simulations.
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Anze A Ursic
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Re: Radiation Safety Questions

Post by Anze A Ursic »

Yeah I figured. I'm curious if they'd allow me to shield it properly, based on similar methods used here and let me run the thing with several dosimeters. Then, if any of them go past an arbitrary amount, just kill the run. I have an emergency shut-off for my power supply. A hot run is a best run!
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Re: Radiation Safety Questions

Post by Dennis P Brown »

I have addressed similar issues with various health and safety departments/people and have been successful most times.

Get a radiation safety book (I have one and used it to enabled me to model many types of radiation and situations for human exposure.) An excellent one is "Introduction to Health Physics" by H. Cember and T. Johnson; they have a solutions manual too. This text will provide everything you need to know on all types of radiation, biological exposure issues, and how to do proper safety calculations. Your education level is far more then sufficient to understand and master those calculations. The required calculations for that room and a 'worse case' fusor can be done on paper - no computer needed.

In any case, I'd suspect that such detailed work would be essential in order to demonstrate to your safety people that you know what you are talking about and have proven it. It is not something anyone else can really do here since this is literally a legal issue.

Without a proper SOP (standard operating procedure; a paper that outlines the step by step procedure on how the fusor will be operated each and every time) nor design parameters with proper estimates on radiation types and exposure (as you and others have mentioned), I'd suspect it is unlikely they will let you build and irradiate yourself and the area to prove it is safe. Do ask them but I highly doubt it (The "good old days" of build it, get irradiated, and then test are apparently over at most places - no more putting plutonium in children's cereal* anymore, I guess.)

Short of building off site and proving your numbers to them (can you build off site?), a proper model with calculations to go with a solid SOP is your next best option to convince them - especially since you have a well shielded room to base you calculations upon.

*This really did occur here in the U.S. back in the 50's. And no, the children did not know nor were they asked for permission.
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Anze A Ursic
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Re: Radiation Safety Questions

Post by Anze A Ursic »

Dennis,

I actually wrote up a 10 page document outlining every single radiation hazard possible using the very book you mentioned. I did my X ray calculations by assuming my fusor X-ray production efficiency to be about 1% (so at 40kV 10mA which is 400W, 4W goes to X ray production). From there I calculated the number of photons created per second and so on and I analyzed their attenuation through steel, air and concrete using I = I_0 exp (-mu*d) and got results in R/hr and Gy/hr. I also used Table of Isotopes 6th edition to show that every element in the room around the fusor would have a low chance of getting activated knowing the thermal neutron capture cross section. Finally, I also showed the Tritium production would be insignificant compared to the allowable EPA values.

Before I even emailed them I talked to several Nuclear Engineering professors to make sure my numbers make sense and my document was reviewed by two of them.

The issue seems that these people are assuming my X ray and neutron numbers will be much, much higher because they're comparing my numbers to that of schools that have fusion programs. So they're saying "this school which has a fully functioning fusion reactor got a neutron rate 10x higher". On the other hand, if I just say that I'm a single student working on this thing unfunded and that we're just building an amateur fusor with questionable equipment, that'll also bury us. So as you can see, I'm in a bit of a gridlock. This is going to be tricky.
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Re: Radiation Safety Questions

Post by Dennis P Brown »

Your situation is classic of safety people; most are uneducated in any issues involving radiation (I know, not what one would expect.) You might try getting one person to focus on and try to educate them on a fusor. However, if they insist that your fusor will be an order of magnitude higher than what you (know) calculated, explain that you'll shield for that level by using x-centimeters of paraffin and for X-rays, x-millimeters of slate (cheap, non-conductive, and non-toxic) around the fusor. Then they boxed themselves in since you now have demonstrated that the radiation levels of external exposure are below what they set. Then you have them caught by their own conditions.
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Re: Radiation Safety Questions

Post by Anze A Ursic »

Dennis,

that's what I'm trying to do as we speak. I just sent them an email answering every single one of their points / concerns (mind you, there were about 25). The bigger issue I see is per some radiation policy we have in place a "equipment user / operator" is defined as a heavily-trained person, and the number of trainings I'd have to do is about 20. Everything from radiation basics to shielding, to units, application etc, etc...

But wait, it gets even better! At the end of the email it's mentioned that because our institution has never had a fusor, we have no training specific to the fusor, so they are considering sending me to AN EXTERNAL INSTITUTION to get proper training on that too! hahahaha! Brilliant!

I am happy I'm graduating in the next few months and getting a well-paying job so I can build stuff on my own. But until then, I have to run this thing at least once!
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Re: Radiation Safety Questions

Post by Richard Hull »

Graduation places you on a plane above many about you, but is no carte blanche. You must continue to learn and study. Learning and study that is self-directed is always to be preferred, coupled to a good bit of hands-on work to balance the theoretical study with the hand of experience. Real world experience and knowledge in the doing and experiencing will see you advance beyond anything any institution of higher learning might offer. Go out and live for further enrichment in search of goals you define for yourself. Do not let the thoughts of others prove a snare to your feet.

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
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
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Anze A Ursic
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Re: Radiation Safety Questions

Post by Anze A Ursic »

Thanks for the kind words, Richard.

I was a bit upset when I first read their entire response, but that's only because I've been working on this since 2018 and it's been one snag after the other (whether technical or bureaucratic), this seemingly being the final nail in the coffin for the project. But ultimately I get their concerns and I actually appreciate they gave me a dedicated person to talk to. I just have to show that a lot of thought has gone into this, including radiation safety.

They actually just responded saying that if proper measures are taken, I could run this device in the current lab. That is fantastic. Shielding it heavily, even based on their high expected values, is much easier that it is to move the entire vacuum chamber to a new lab.

Thank you all for your help. I will post when I have updates. Hopefully one of them being my application to the neutron club :-)

Anze
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