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Particle Physics and Pony Fiction Experimentalist

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Rainbow Arc Welders and Radioactivity · 9:37pm Jul 14th, 2019

They may live in a small town in a remote part of rural Equestria, yet the ponies of Hope Hollow are an innovative lot. We saw in Rainbow Roadtrip that while ‘hopeless magic’ made them see themselves as an impoverished colourless backwater, they could actually play a full part in Equestrian culture with their well-stocked library, high-tech cottage industries, and rainbow festivals.

One question which came to my mind while watching the episode: is this the first time we have seen a pony with a welding mask?

I know Sunset Shimmer showed us her formidable metalworking skills in an Equestria Girls short, but has this been seen in the pony kingdom? We would expect the Cutie Mark Crusaders have tried it at some point, but I can’t actually remember such a scene.

What is the specific metal-joining technology needed to make a rainbow generator? It’s not obvious what type of welding they are doing. Torque Wrench and Sunny Skies are seen with a small hoofheld device like a simple gas torch, but wearing the kind of face protection required for arc welding.

Welding is the art of joining metal components by heating them above their melting point allowing the separate pieces to fuse together. For light work you can generate enough heat by burning a liquid or gas fuel. However to reach the higher temperatures needed to join bigger sheets of steel or other metals you need an arc welder. Connect a big enough power supply to an electrode and hold it close to a base metal and you create an electric arc as electrons are stripped off atoms and the normally insulating air turns to plasma. A high electric current then flows between the electrode and metal creating intense heat and light.

Such a magic trick comes with significant safety risks. A welder must protect their eyes against the intense ultraviolet light. The same protection is needed for anypony else present, unless the welder is working behind heavy PVC curtains. Which does raise the question of why Sunny Skies was not wearing eye protection in this scene?

It may or may not be apparent to the reader at this point that I am sort of bluffing, and actually don’t know much about welding at all. A point which I can make further clearer with a story about gadgets I know rather more about - particle detectors.

One of the best tabletop particle physics demos is a Cloud Chamber. This was one of the first particle detectors, invented by Scottish physicist CTR Wilson, who was trying to study cloud formation in his lab. You take a glass or plastic tank, with a bit of foam wetted with alcohol at the top, and a metal plate at the bottom sitting on dry ice (solid CO2) or some other cooler. The alcohol vapour falls to the bottom of the tank and forms a supersaturated vapour layer, just at the point of its gas-liquid transition. When a particle passes through, it ionizes the gas, and that is the trigger for the vapour to condense to liquid, with the result being a line of tiny droplets forming along the track of the particle.

I think a picture of Derpy is appropriate here.

While this is now old technology, it is much more impressive to look at than a laptop screen showing the data from a silicon detector. Hence cloud chambers are one of my display pieces at the science stalls I run. When I was introduced to the latest model (shown above) by a colleague, I was told it was necessary to place a small metal rod in the centre of the plate (you can just see this although it is out of focus)

They thought this had something to do with directing the thermal currents in the vapour, although nobody seemed to be clear why that was necessary. After watching it in operation, in particular the way most particle tracks appeared near the rod, we came to realise that this was actually a radioactive source. Eventually someone learned that we had a thoriated welding electrode. Thorium is radioactive. A quick search revealed you can buy these things at hardware stores, making it a cheap and easy source of radiation for such a demonstration. It seems the manufacturer neglected to mention this fact in the instructions, or maybe they did, but someone accidentally threw out the instructions when unpacking.

When running such science demonstrations, you often find yourself explaining things on the spot to answer all the audience's questions. Demonstrators repeat things they hear from other demonstrators and this way you sometimes end up repeating mistakes until someone thinks to check. This way we somehow ended up telling a story that the radioactive element on the welding rod was an essential component of an arc welding system. It makes sense, right? To start an arc you need to ionize the air so the current can flow, so that must be what it's for.

It’s a plausible narrative, but when I sat down and tried to research it, I found no evidence at all to support it. It seems that this story is just a myth created by overzealous science communicators. Thorium is used for welding electrodes due to its high melting point and suitable chemical properties. The radioactivity is just a side effect, and as it does have potential health risks (if welders breath in thorium dust released when electrodes are ground), there are efforts to identify alternative materials.

Particle physicists may know about radioactivity, but we are not generally so hot at welding.

Comments ( 10 )

How often would one expect to see a track without the rod?

Typically one every five to ten seconds, but it depends on how supersaturated the vapour is.

So... are we just going to ignore the casual confirmation that the main timeline also has fully-functional prostheses? Or do we just have trouble saying the name "Kerfuffle" without giggling uncontrollably?

It’s quite possible that it’s simply a cultural thing based on how large pony’s eyes are, the welder wears a mask...

My question is who’s making bank by selling unicorns a different mask instead of standardizing all of them to have a removable cover?

You can still get Thoriated Gas Mantles?

Then theres the picosecond pulse laser welders that let you weld glass to steel?

Then theres cold plasmas using high frequency charge seperation? But couldnt those give high localised inductive currents, and so welding?

5088918 I'll admit to having done that.

Welding is one of those "It looks simple until you do it" things. Now it's been 45 years since I've struck an arc, but I'll toss out a few things.
1. Don't look at the arc welding point unless you're wearing the dark-type welding goggles/face shield. You can still be in the vicinity, see it off to the side, etc.... but looking *right* at it focuses that intense light on the most sensitive part of your eye.
2. You *can* look at a oxy-acetylene torch tip without welding goggles/face shield and not be damaged. Oxy welding/cutting uses a less bright light, so the darkness of the goggles/face shield is lighter. Wear the lighter goggles anyway. Wear the darker goggles for arc welding. You only have two eyes. See 3 below.
3. Both types of welding/cutting splatter molten metal. Full face protection keeps you from having interesting scars that interfere with shaving. Women with low-cut blouses should go right back into the locker room and put on something decent. Cotton, not nylon/rayon. Chunks of melty metal and hot shell casings are attracted to exposed boobs. Wear your stupid welding gloves no matter how hot it is out there. Wear real shoes, not plastic ones, with toes on them unless you want to limp the rest of your life. Don't roll up your cuffs. Buy pants the right length. Chunks of metal drop into those rolled-up cuffs and set your pants on fire. Literally. Point of note: Our VoTech class managed to hit *every* one of these points at some time during my four years in high school, plus the idiot who nearly got a thumb pulled off when he got his welding gloves caught in the high-speed wire brush while polishing a weld. Just polish-polish-polish-WHUMP! (loud human curse words) His thumbnail eventually grew back. Careless people can not only get themselves killed around the equipment, but careful people too.
4. The electrical part of arc welding is not *as* dangerous, much like a six foot shark is less dangerous than a twenty foot one. No welding in puddles, on gas tanks, propane tanks, anywhere you're not (censored) certain that you're safe and then check again.
5. In the 80s, Stick Welding was the most common. The 'stick' is a thick rigid wire made of melty stuff with an insulating fluffy stuff surrounding it. Put the stick in the welding jaws, turn on the welder electricity, touch the stick to the surface (try not to wince at the electrical flare, and remember you're doing this with a piece of dark glass in the way so you're nearly blind), and run the arc *slowly* along the weld so it melts the stick, the weld surface, and leaves a trail that looks like ( ==*))))))))) going that <- way ) with crusty junk on top from the insulating fluffy stuff (it keeps the metal from oxidizing during the weld, which is critical) Then take a hammer/wire brush and knock off the 'cruft' that the insulating stuff left behind, revealing just how badly you did it and where you need to re-weld/cut/curse. Turn the voltage too high, you cut through the metal instead of welding. Too low, nothing melts. Move too slow, you still melt a hole in your work. Too fast, it doesn't melt deep enough to hold.

As a farmer, my dad was an artist with the stick welder and the oxy-acetylene torch. Every piece of farm equipment winds up breaking and needing fixed, or totally rebuilt, or turned into something else. He built stalls for the dairy barn, field equipment, haying equipment, tractor modifications, combine parts, you name it. I did some, but the absolute best weld I ever did was an oxy-acetylene weld on the luggage rack of my motorcycle back then. The thing was just absolutely perfect, and I still have no idea how I managed it.

(Modern welding is almost all Metal-Inert-Gas but I've hogged enough blog space)


So... are we just going to ignore the casual confirmation that the main timeline also has fully-functional prostheses?

Well the great thing is that we don't have to make a big thing about it. Just nodd in approval at the normalisation of disability in the show. Just as it should be.

Or do we just have trouble saying the name "Kerfuffle" without giggling uncontrollably?

Can't you handle the double f for the fuff?


who’s making bank by selling unicorns a different mask instead of standardizing all of them

Kerfuffle of course, each one appropriately colour matched.


You can still get Thoriated Gas Mantles?

Yes. Have a look on ebay. Easier to buy than picosecond pulse lasers.

Thanks for all the details. Now you mention it, it brings back vague memories of a general workshop skills course I did years ago.

I used an oxy-acetylene torch for a project in middle school shop class; I have the utmost respect for people that can use one well :facehoof:.

In college I was required to take a metal shop class, and discovered that the metal shavings from a just-used drill press can be both hot and crazy-sharp: gently brushing a few shavings aside with my hand cut into my fingernail. I didn't even realize I'd been hurt until I saw some blood.

I still remember the professor pointing to a hole in the ceiling above one of the metal lathes and explaining how the person responsible for that little mishap was lucky to be alive.

Man that was a fun class…

So what is the rod for? A source of loosely bound electrons?

Also, because I somehow did not know about this:
...You can get picosecond pulse lasers commercially? What's the energy output on those? I wonder if I could figure out a way to write a grant around those... Less you ask for, the more likely you are to get it.

I think they just need an electrode with a high melting point and chemically inert so it doesn't contaminate the weld. There may be some more complicated chemistry going on.

You'll have to ask 5088961 where to get the picosecond lasers

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