2568: Spinthariscope

Explain xkcd: It's 'cause you're dumb.
Revision as of 15:27, 10 May 2023 by FaviFake (talk | contribs) (Moved the "This was the Nth comic after countdown in header text" notice into the more appropriate Trivia section)
Jump to: navigation, search
Other high scorers are melt-in-your-hand aluminum-destroying gallium and tritium-powered glowsticks. Lawn darts are toward the other end.
Title text: Other high scorers are melt-in-your-hand aluminum-destroying gallium and tritium-powered glowsticks. Lawn darts are toward the other end.


This is another comic with one of Randall's fun facts.

As stated in the comic, a spinthariscope is a device with a small amount of radioactive material (americium or thorium) and a screen. When one of the radioactive atoms decays, it emits an alpha particle, which strikes the screen, which emits a small flash of light. You can see these flashes by looking through a lens.

It was invented in 1903 initially as a scientific instrument, but was soon replaced by more accurate and quantitative devices. But the original device was still popular for some time as an educational toy for children, and you can still get them today in some places.

The joke in the comic is that most people have little understanding of radiation, and overreact to any mention that something is radioactive. So when Cueball tells Megan, White Hat, and Ponytail that the toy contains radioactive material, they're shocked and scared. But the amount of radioactive material in the toy is very tiny and the radiation is itself so trivially contained that there's practically no risk from it. The short-ranged alpha particles are likely stopped by the lens through which the harmless flashes of light (from particles that instead hit and neutralise in the internal screen element) are seen. Alpha decay always leads to an unstable decay product, which results in further decay (always gamma decay, and sometimes beta decay as well) which are less easily blocked, but the amount of such radiation from these decay products is negligible.

The fun fact in the caption says that Spinthariscopes have the highest ratio of "that can't possibly be safe and legal" to actual safety and legality of any known toy. When people hear about Spinthariscopes for the first time, they often assume, due to the radioactive material inside, that they must be very dangerous. They thus also question if such a toy is at all legal to make or own in the first place. But the fact is that Spinthariscopes are both safe and legal to make, sell and own in the United States. So, the perceived danger and presumption that it must be illegal is at a very high number, and the actual danger and the actual illegality results in a very low number on the same scale. It is this ratio between perceived and actual danger and illegality that are the highest for Spinthariscopes, higher than for any other known toy.

The formulation, however, causes some confusion, because the caption uses actual safety and legality (high) instead of actual danger and illegality (low). Instead of a high ratio between perceived danger and actual danger, the result is an even ratio between perceived danger and actual safety, which are both high. The ratios for the other mentioned toys would also be even, as they have low perceived danger and low actual safety. This is obviously not the intended meaning, as the other toys are said to be toward the other end of the scale.

The title text mentions some other materials/toys that sound dangerous but aren't. Gallium is a metallic element with a low melting point of 29.76°C (85.568°F) so it will melt in your hand. Additionally, gallium has strange properties when it interacts with aluminum, causing aluminum to "melt" or become brittle. Tritium is a radioactive isotope of hydrogen, but can be used to create glowsticks and other lighted objects. Though these two toys might seem dangerous, they are actually typically used perfectly safely.

At the opposite end of the spectrum is lawn darts, a toy containing large darts that are thrown into the air to fall back down onto a target that's placed or marked upon the ground quite near the players' positions. Unlike the spinthariscope, which sounds dangerous but is actually harmless, lawn darts sound relatively innocent but can cause severe injury if you accidentally hit a person (and a few children were even killed), so they were banned in the US and Canada in the 1980s. When sharpened, these toys even compare quite favorably to antique weapons of war.

Today many houses have smoke detectors using ionization caused by radioactive decay of Americium-241 to detect the smoke. So having something with radioactive material in your house is quite common, and in this case increases the safety level for those houses.


[Cueball is holding a small item up in on hand in front of his three friends. Megan has her arms lifted and bent in front of her, White Hat has his arms raised over his head and Ponytail is pointing at Cueball while her other hand, held down behind her, is balled into a fist.]
Cueball: It's a spinthariscope, a 1940s toy with a radioactive isotope inside. If you let your eyes adjust to total darkness and look into the lens, you can see the flashes of individual atoms decaying.
Megan: What??
White Hat: Aaaaa!
Ponytail: Get it away!
[Caption below the panel:]
Fun fact: Spinthariscopes have the highest ratio of "that can't possibly be safe and legal" to actual safety and legality of any known toy.


comment.png add a comment! ⋅ comment.png add a topic (use sparingly)! ⋅ Icons-mini-action refresh blue.gif refresh comments!


Someone has already updated the Wikipedia page to mention this comic reference, before anyone here has gotten around to writing the explanation Barmar (talk) 19:56, 14 January 2022 (UTC)

But that was not welcome so it has been removed again. But here is the version with the update which has sparked no less than 26 other edits of the page in less than two days, after no one had made a change to the page since October last year... But at this moment there is no reference to the comic. --Kynde (talk) 14:21, 15 January 2022 (UTC)

I added an initial explanation, but I don't recognize the references to gallium and tritium (although I know what glowsticks are), so someone else should fill in about that. Barmar (talk) 20:13, 14 January 2022 (UTC)

Seems like there's something off with how the "ratio" is worded. It is a safe and legal toy, so the "actual safety and legality" is actually high-ish, right? 20:44, 14 January 2022 (UTC)

- If "actual safety" is a large number and "apparent safety" is a small number, then their ratio (actual divided by apparent) is a large number. If "sctual safety" is a small number and "apparent safety" is a large number, then their ratio is a small number. So the comic's wording is perfectly fine and logical, and the paragraph about products in the explanation is not needed. (It's also kind of, um, **untrue**, but I'm trying to be kind to whoever wrote it.) 21:44, 14 January 2022 (UTC)

If you take the amount of screaming in terror (high for the spin-thingie) and DIVIDE by the actual danger (low for the spin-thingie), then you get a ratio that in a rational world would always be close to 1 - the worse something is, the more (rational) people would want it banned. I think his point is that the ho-hum factor, the LACK of protests, for throwing a sharp heavy object high in the air toward a group of other children, divided by the actual danger from said sharp heavy object thrown high toward other children, results in a value on the opposite end of the spectrum. I was one of the kids who threw these things around without thinking, and nobody ever objected. Fortunately, I never saw any kid get killed by them, but that was pure luck. Point being, I don’t think the wording in the comic is wrong; the ‘correction’ is. 22:35, 14 January 2022 (UTC)
On second thought, there is something confusing about the wording of the comic: it conflates safety and legality as if they were the same thing, but the fact that they are NOT the same is the problem. 22:49, 14 January 2022 (UTC)
They're not the same, but they're correlated. While the government hasn't always been very dilligent about it, these days dangerous toys usually get banned. Barmar (talk) 22:57, 14 January 2022 (UTC)
But the comic don’t divide the large/low amount of screaming by the low/large amount of danger, but by the large/low amount of safety for spinthariscope/darts. Hence the formula of the comic results in a number close to 1 for both toys, and a regular toy (low amount of screaming divided by large amount of safety) results in a number closer to zero.
While False (talk) 22:57, 14 January 2022 (UTC)
You’re right. The comic is misworded, but not by saying “ratio” instead of “product” - it’s misworded by saying “actual safety” when it means “actual danger” thus giving the ratio a backward meaning. 23:17, 14 January 2022 (UTC)
I believe the problem is commenters are confusing a description of level of risk with the name of the scale. Apparent (level of risk) : actual (level of risk). Low level of risk = safe. High level = dangerous. So “apparent (high risk)” is naturally and obviously written as “apparent danger” while “actual (low risk)” is just as obviously “actual safety.” It is (or ought to be) as simple as somebody describing a mirage in the Sahara as having a very high “apparent wetness to actual dryness” ratio. 09:01, 28 June 2024 (UTC)
Just so!
While False (talk) 23:28, 14 January 2022 (UTC)
I believe the ratio is apparent danger vs actual danger. So spinthariscope would be 10 apparent danger / 1 actual danger. And the lawn darts would be the opposite end of the spectrum: 1 apparent danger / 10 actual danger. 22:40, 14 January 2022 (UTC)
To me it appears that you are describing the “perceived danger to actual danger” ratio, while the comic mentions the “perceived danger to actual safety” ratio, which would be of no extreme value (high number divided by high number) for a spinthariscope. So I think that the current explanation, while cumbersome and against the convention of use of ratios, is mathematically true.
While False (talk) 22:57, 14 January 2022 (UTC)
I think it is perfectly clear what Randall intended to say. And even if it can be misunderstood I think there is no need to make a very big fuss out of that. I have tried to reword the explanation so it begins with stating the obvious intention, and then mentions at the end that it could be misunderstood. Feel free to improve my wording. --Kynde (talk) 14:13, 15 January 2022 (UTC)

Make your own Spinthariscope kiddies https://www.instructables.com/Pocket-Size-Spinthariscope/. Steve (talk) 21:05, 14 January 2022 (UTC)

The Gilbert U-238 Atomic Energy Laboratory, which was marketed in the early 1950s & contains more energetic radioactive sources (i.e. uranium ores), might possibly be more dangerous. 21:28, 14 January 2022 (UTC)

The talk page for the Wikipedia article has an interesting exposition by an IP in 2010 of why these aren't dangerous and the various isotopes used. Yngvadottir (talk) 21:49, 14 January 2022 (UTC)

And with that simple strip, all existing spinthariscopes sold out. 01:01, 15 January 2022 (UTC)

I remember the (pre-'80s) lawn-darts in the 'leisure equipment box' that our Cub/Scout unit took to every annual camp and other suitable weekend activities (here in the UK). High-density plastic (possibly with a metal slug enclosed within the 'point', to add to the flights' directional stablisation, but maybe just plastic) and all points and edges rounded. Probably still dangerous if inadvertently thrown straight-enough upwards with enough force that gravity eventually brings it straight back down upon the unwary head of the thrower (or that of a fellow participant awaiting their turn), but we seemed to avoid that predicament. Things like the hefty hockey-sticks (field-hockey), cricket bats and even threadbare boxing gloves probably caused more injuries that needed treatment. But probably more by good luck than any legitimate physical reason. 03:09, 15 January 2022 (UTC)

I've just added info about decay chains, that there is beta and gamma radiation as well but at negligible doses. I wanted to give more information, but although I know some spinthariscopes use americium-241, I don't know the isotope of thorium used in others. Does anybody else know? Cosmogoblin (talk) 10:15, 15 January 2022 (UTC)

There's an error in this section - it states that alpha decay always leads to an unstable decay product, but in the case of Polonium 210 (which was used in some spinthariscopes), it decays by alpha emission directly into stable Lead 12:59, 3 February 2022 (UTC)

Even though I know what he's trying to say, it's seriously bothering me how he worded it. NoriMori (talk) 08:03, 17 January 2022 (UTC)

Re: the removed "US Logic" section, I disagree about it being off-topic, but mostly I think there was no reason to remove. If it were disconnected spam/advertising/vandalism, maybe. It was longer than necessary, but an honest commentary even if drifting a bit. 00:23, 21 January 2022 (UTC)

Anybody know how much you can buy a spinthariscope for?New editor (talk) 19:05, 25 January 2022 (UTC)