3037: Radon

Radon

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Title text: A good ²³⁸Umbrella policy should cover it.

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Explanation

This comic was the first in a series (of at least two comics) about absurd results of home inspections. The second, 3059: Water Damage came out less than two months after this one.

In this comic, Ponytail approaches Cueball about the concentration of radon in his basement. This refers to a common phenomenon where the levels of radon gases can build up in enclosed spaces over time; they form out of traces of uranium embedded in the surrounding bedrock/soils of most basements, and in the silicate minerals used in the concrete of the foundation. This uranium (over time, and in most cases via the midpoint of thorium) releases radon as a gas whilst experiencing alpha decay, although the time in which this occurs is noticeably long. Uranium-238 (²³⁸U or U-238), the isotope mentioned in the title text, has a half-life of 4.5 billion years, which is about the age of the Earth. Over the whole Earth, roughly 2.8 ppm of the planet is made of uranium; this is about 0.00028% of the planet, which weighs about 5.9722×10²⁴ kilograms. Even so, if uranium existed in the Earth's crust alone - about 1% of the Earth's total mass itself - this would imply that there is 1.67×10¹⁹ kilograms of uranium across the entire planet. Thus, radon gas is a relatively commonplace phenomenon, and radon mitigation techniques are frequently employed to keep the air safe and breathable. Basements, in particular, are known to accumulate radon gas if they are kept sealed over a long enough time, that is, with the windows and doors closed. Small cracks in the house's foundation may allow some radon gas to seep inside, which can be cleared if the basement is properly ventilated. Radon is denser than air, but this isn't why it accumulates in basements; it mixes completely with air, and does not "settle out" because of its atomic weight or density. Rather, its concentrations are higher in the basement than elsewhere in a building because the basement is adjacent to rock and the house foundation where it is generated, and because of the relatively poor air circulation usual in basements. Undisturbed, the concentration of radon reaches a steady state in a given area, between accumulation from being generated, and removal by air circulation and by radioactive decay.

In the comic Cueball is getting his house inspected; this is common in preparation for selling the home. Inspector Ponytail finds an excessive level of radon in the basement. Often when problems are found in a home, it's due to the age of the building, since technology has improved over time and building codes have added requirements in parallel.

But rather than inquire about the age of the home, Ponytail asks about the age of the planet on which it was built. The answer would be the same for all houses on Earth. Apparently she's an interstellar inspector, testing properties on many different planets in different star systems with different levels of radon - since most planets in a given system form within a few million years of each other and would have similar levels of radon. Earth's age of 4.5 billion years is about the same as the half-life of U-238, so radon levels are high because much of the original uranium is still in the process of decaying. She recommends waiting 100 billion years - much longer than the expected lifetime of Cueball,^{[citation needed]} the building, and the Sun as we know it - enough to cause U-238 to decay to a trivial amount, not factoring in other daughter nuclides due to their comparatively shorter half-life.

The Sun is an example of a G-type main sequence star, also known as a yellow dwarf, which the inspector notes is a short-lived star. In the next 1 billion years the Sun will become more luminous and end life on Earth, and in 4 to 7 billion years the Sun's outer layers will expand, turning it into a red giant that will likely engulf the Earth. If we'd 'built' around an M-type red dwarf we could have comfortably waited for the uranium to fully decay, though being in the habitable zone of a red dwarf has its own difficulties.

The title text for this comic mentions an umbrella policy, a type of insurance policy that covers damages beyond those covered by another, primary policy. It makes a joke with the isotope representation of uranium-238 being ²³⁸U, and is something that Cueball might need to consult with after handling the issue of radon gas in his home; most states in the United States, for instance, require property disclosure forms to be filled out if radon levels surpass a certain threshold. This text may also be an oblique reference to the concept of a nuclear umbrella, an altogether different kind of "insurance".

Transcript

[Cueball is on the left and is approached by Ponytail, who is reading a Geiger counter in her hand and holding a toolbox in her other hand.]

Ponytail: Radon levels in your basement are pretty high.

Ponytail: When was the planet under this house built?

[Ponytail stops walking and lowers the Geiger counter.]

Cueball: Uhh, about 4½ billion years ago, I think?

Ponytail: Oof. I was afraid of that.

[A frameless panel:]

Ponytail: This planet was contaminated with uranium when it formed. You really should have let it fully decay before building.

Ponytail: Wait another 100 billion years and these rocks will be fine.

[Zoom in on Cueball's head.]

Cueball: But the Sun will burn out in 5 billion years.

Ponytail (off-panel): Yikes, you built around a short-lived yellow star? What a mess.

Ponytail (off-panel): Hope you have good insurance.

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Discussion

The sun is a white star. It looks yellow from within the atmosphere because blue light is scattered out of it, the same reason the sky is blue. How did physicist Randall not know that? Nitpicking (talk) 20:26, 13 January 2025 (UTC)

Randall is almost certainly a Superman fan, and we all know that Kryptonians get their powers from yellow suns. Barmar (talk) 21:07, 13 January 2025 (UTC)

Wikipedia disagrees; The Sun is a G-type main-sequence star (G2V), informally called a yellow dwarf, though its light is actually white. It formed approximately 4.6 billion years ago from the gravitational collapse of matter within a region of a large molecular cloud. 172.71.23.87 20:43, 13 January 2025 (UTC)

Your quote agrees with me. As @Starstar says below, it might be intentional on his part. Nitpicking (talk) 20:53, 13 January 2025 (UTC)

No "his quote" doesn't?? (Unless I'm understanding your meaning with "his quote") Yes the sun is White. HOWEVER, it is NOT called a "white star". Stars aren't categorized by color but by tempeture. Which I mean I guess it sorta means their catagorized by color but thats being nitpicky. Our sun is 5,772 K, which according to wikipedia means its a class-G star which is known by the not nerds as a yellow dwarf. Being a physicist means Randell is VERY aware of the category of our Sun. Repeat, the Sun is called a "yellow dwarf", therefore is Ponytail said "white star", she'd be talking about a star that is 9000 K and therfor NOT our Sun. Seriously this was like a 5 minute google search. Apollo11 (talk) 21:01, 13 January 2025 (UTC)

At any rate, I believe it plays into Ponytail just goofing around more than being precise Starstar (talk) 22:12, 13 January 2025 (UTC)

Perhaps it is intentional? Starstar (talk) 20:36, 13 January 2025 (UTC)

Possible trivia: The effect used in the title text for "²³⁸Umbrella" does NOT use html formatting. It uses unicode for the almost-but-not-technically superscripted "238" before "Umbrella." On some systems, this renders with the "23" being larger than and slightly below the level of the "8". Whether Randall knew of this effect or not is a mystery. If he did know, his motivations are a mystery. Maybe the 8 is radioactive and emitted a non-massless particle, thereby making it smaller (less mass != less volume, but go with it here) and more buoyant (less weight) in the presence of the adjacent characters. 198.41.227.105 21:19, 13 January 2025 (UTC)

You can't use HTML markup in the title attribute, so there's no other way to do super/sub-scripting there. He could have used JavaScript to emulate the title attribute, though. Barmar (talk) 21:38, 13 January 2025 (UTC)

I see no issue with the title text's 238 when on a PC neither on xkcd or here. The numbers are all similar. --Kynde (talk) 12:22, 14 January 2025 (UTC)

What do people think of Hairstylist Wannabe's near-total rewrite of the explanation? While they added lots of technical details about radon, I think they missed much of the humor. Ponytail's comments are typical of the kind of things a home inspector or repair person will say to the owner, not really "flippant". Barmar (talk) 21:48, 13 January 2025 (UTC)

I like the facts but i changed the joke explantion back. Apollo11 (talk) 22:07, 13 January 2025 (UTC)

The rewrite has waaaaay too much detail. This site is for explaining what's going on in a comic, not repeating everything you know that's related, however remotely, to the comic. Just add wikilinks to things! Like, do we really need to have repeated here how much ²³⁸U the Earth contains? How much radiation one experiences from uranium? I vote to remove a lot of the detail and just explain the comic. DKMell (talk) 23:45, 13 January 2025 (UTC)

Possible trivia: 238 Umbrella is a common weight for a patio umbrella stand. -- TallJason (talk) 22:53, 13 January 2025 (please sign your comments with ~~~~)

I started to write another paragraph:

The primary reason why the radon is considered more deadly than the original uranium (and thorium) is its nature as a heavy gas; the earlier states of decay remain stuck in the original rock, interstitially, whereas radon more freely leaches out. This quickly disperses to extremely diluted levels in the open air but, being a gas that is denser than air, it can accumulate to low (but potentially significant) levels in a cellar or basement, having few natural air-currents to drive the heavier gas atoms out of the sump in which the radon sits. Although each atom does not last long in this state, the resulting polonium, bismuth or lead atoms (all being isotopes that are themselves radioactive) can find themselves drifting as dust particles initially (and, after settling, easily disturbed), with the potential

...but it got out of hand. Was going to edit it down (and correct anything I'd accidentally mispoken/misedited/ispunctuated, in the initial fervour) when I'd finished, but I've got to go somewhere, so leaving it as possible inspiration for someone else to use/ignore/tear part/whatever. Have fun. 172.68.205.92 23:50, 13 January 2025 (UTC)

"possible inspiration for someone else" Good stuff, but surely it already exists (without xkcd context) many other places? Can be just linked? PRR (talk) 02:33, 14 January 2025 (UTC)

I thought, the title text was a reference to nuclear umbrella. 172.68.50.200 07:45, 14 January 2025 (UTC)

"This process will render the Earth uninhabitable for humans within approximately 5 billion years." That seems very optimistic. Isn't it more like 1 billion years? --Coconut Galaxy (talk) 10:05, 14 January 2025 (UTC)

Yes the Earth will become uninhabitable in close to but less than a billion years. But not because the sun is expanding at the end of it's life. But because it gets hotter and begins to strip the Earths atmosphere, and this also means the end of the oceans. When they are gone, complicated life forms should not be possible. Bacteria could live until the sun possibly engulfs the Earth (it is not certain if this will happen though.) --Kynde (talk) 12:22, 14 January 2025 (UTC)

This comic sparked a tangentially related discussion at Wikipedia talk:WikiProject Chemistry#Radon and Radium spectral lines, leading to the discovery that the spectra given on Wikipedia for multiple chemical elements (including Radon) had been wrong since 2013 -- the result of a bug in a 15-year-old Matlab plugin. Rexon Mobile (talk) 17:03, 14 January 2025 (UTC)

I'm removing th[e] paragraph [on radiation dose] entirely, since it's wildly incorrect and adding negative value; I may or may not have time to add a more accurate discussion later, if someone else hasn't done so first:

The actual amount of uranium experienced

You're actually talking about the total background radiation exposure, not specifically radiation from uranium (and one wouldn't normally describe exposure to radiation from uranium as "experiencing uranium" in any event).

in any given environment,

No, on average across all individuals, in all environments; the amount of background radiation exposure will be much higher in some environments than in others.

according to Randall's own Radiation chart, is 10 microsieverts worth of radiation, on average,

Across all individuals.

over a year

Over a day. It literally says that in the entry in the chart.

the amount in one's body,

The amount of radiation exposure due to potassium decay within one's body.

in contrast, is about 390 microsievert over that same timeframe,

No, that one actually is per year.

again on average. The lowest dose linked to any serious risk is in the millisievert range, over thousands of times stronger than any of these sources. Thus the radiation from radon buildup in a normal house is not of concern,

No, the average amount of radiation exposure per individual -- averaged across the entire population, who vary wildly in not only the uranium content of the local soil, but also the characteristics of their basements, and even in whether they have a basement at all -- is not a concern. There are plenty of "normal" houses in which the radiation from radon buildup is a concern; there are just also plenty of other "normal" houses in which it is not.

as long as it is properly managed in time. Instead it is radon's toxicity that is the problem, both from the radon itself and its "daughter" isotopes, that poses a danger to humans.

This is absolutely false. Radon and its daughter products are dangerous to humans precisely because of the ionizing radiation they emit, which has a tendency to produce lung cancer when decay occurs within the lungs (in the inhaled air for radon itself, or attached to floating dust particles for daughter isotopes). Radon itself isn't poisonous in a chemical sense at all -- as a noble gas, it doesn't react with other substances under normal conditions. Some of the daughter products are chemically poisonous, but are still far more dangerous for their radioactivity than for their chemical properties (e.g., lead-214 is far more dangerous than a similar quantity of any of the stable lead isotopes (206, 207, and 208)).172.70.127.191 20:35, 14 January 2025 (UTC)

I think the title text has umbrella and cover because umbrellas cover things. -- Awesome person (talk) 20:47, 15 January 2025 (please sign your comments with ~~~~)

mēëêèép -- Me a meep sheep (talk) 00:49, 27 August 2025 (please sign your comments with ~~~~)
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