2860: Decay Modes

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Decay Modes
Unlike an Iron Age collapse, a Bronze Age collapse releases energy, since copper and tin are past the iron peak on the curve of binding energy.
Title text: Unlike an Iron Age collapse, a Bronze Age collapse releases energy, since copper and tin are past the iron peak on the curve of binding energy.


Decay modes refer to the different ways in which unstable atomic nuclei transform into more stable ones, typically by emitting particles or radiation. The process of decay is a natural phenomenon that occurs in radioactive substances. There are several types of decay mode each characterized by the particles emitted or the energy released during the process. In the comic's diagram, protons are white and neutrons are gray.

The first six modes are real, and most occur relatively frequently:

In alpha decay, an unstable nucleus emits an alpha particle, composed of two protons and two neutrons. Alpha decay is the primary source of helium on Earth, as alpha particles are 4He nuclei. This decay mode is most commonly seen in proton-rich / neutron-deficient heavy nuclei, which normally have many more neutrons than protons. By reducing the numbers of protons and neutrons by 2 apiece, the product nucleus has a higher ratio of neutrons to protons.

In beta decay (more properly beta-minus decay), a neutron-rich nucleus emits a W⁻ boson, converting one neutron into a proton, as shown in the supplementary diagram. The boson, in turn, decays into an electron (the titular beta (minus) particle) and an electron antineutrino. The main diagram shows only the release of the beta particle, which was the only thing expelled from the nucleus that could be observed directly when the types of nuclear decay were first described and enumerated.

In gamma decay, an unstable nucleus (represented by the lumpy, prolate nucleus in the diagram – representing a high-energy nuclear isomer) emits a high-energy photon known as a gamma ray and settles into a stabler, lower-energy state.

In electron capture, a proton-rich atom captures an electron from the K or L electron shell. This converts a proton into a neutron and emits an electron neutrino. Randall adds a 'slurp' written sound effect in the comic to make the effect more clear; in real life no sound is actually present in an electron capture event. [citation needed]

In positron emission, or beta plus decay, a proton-rich nucleus emits a W⁺ boson, converting one proton into a neutron. The boson, in turn, decays into a positron (the beta plus particle) and an electron neutrino. Again, the main diagram shows only the beta particle, presumably for simplicity, the nucleon conversion being shown separately. This is much rarer than beta minus decay.

In neutron emission, a neutron-rich/proton-deficient unstable nucleus emits a neutron (which then goes on to decay into further daughter particles).

The other six modes are fictional:

Baryon panic: In this mode, all the subatomic particles flee the atom simultaneously, similar to a crowd fleeing a building during a fire alarm, or other similar states of panic in people. In reality, this mode of decay would require an incredible amount of energy. The like charges of protons do repel each other, but they are held together more tightly by the residual nuclear force in the presence of neutrons.

Omega decay: The atom has decayed and left behind a skull in its wake, leaving cracks in the area surrounding it and sending neutrons and protons flying everywhere. Whereas alpha, beta and gamma are the first three letters of the Greek alphabet, omega is the last, so the name omega might suggest the ultimate, final decay. The skull presumably represents the finality of such a decay given that the end stage of human decay leaves behind a skeleton, something that does not exist in nucleons.[citation needed] Many works of science fiction propose forms of radiation and/or particles with further letters in the Greek alphabet, such as The Omega Directive in Star Trek. In real life, the omega baryon was predicted to exist by Murray Gell-Mann's early quark theory, and then discovered several years later with the properties he had predicted. This mode may also represent the atom becoming the origin of a false vacuum decay, a theoretical decay of space itself, which would indeed spread outward and be very final and lethal.

Electron wilt: The electrons surrounding the atom fall to the ground. Some plants are subject to diseases that cause this kind of wilting of their leaves. Electrons will attempt to settle into a 'ground state' but this does not involve them literally slumping to the ground, rather they will be as close as possible to the nucleus subject to the limitations of energy levels and the Pauli exclusion principle. In addition, since the ground is made of atoms, there would be no flat surface for the electrons to fall onto.

One Big Nucleon: The protons and neutrons combine to form a single huge baryon. Exotic baryons with more than the usual three quarks, such as pentaquarks, have been created in the lab but are not known to exist in nature. String theorists propose that black holes are actually fuzzballs, single "subatomic" particles which are macroscopic in size (namely that of their event horizon) formed by the fusion of the strings of in-falling matter under extreme gravitational conditions. This is a also a joking reference to the concept of One Big Union, a goal promoted by some trade unionists since the late 19th and early 20th centuries, according to which all individual and national trade unions should gradually amalgamate into one single economy-wide trade union — the notional One Big Union — in order to organise and fight for workers across all industries and professions, rather than only within each union's specifically organised job sites. Prominent early proponents of the idea include the Industrial Workers of the World and Canada's One Big Union. The joke is that this is a kind of radioactive decay caused by revolutionary class consciousness shared between nucleons in different atoms.

Fungal decay: The nucleus rots, and fungal fruiting bodies (toadstools and mushrooms) grow around it. This plays on the meaning of "decay".

Collapse due to invasion by the Sea Peoples: The atom floats in water, with boats on either side full of Cueballs shooting arrows at it, and the atom is breaking up. The Sea Peoples are a somewhat mysterious group that attacked Egypt and other regions of the eastern Mediterranean in the late Bronze Age (1200-900 BCE). Due to a combination of factors, such as climate change, mass migration and invasions (including from the Sea Peoples), several nations around the central and eastern Mediterranean underwent societal decline or outright collapse, an occurrence known as the Late Bronze Age collapse. Randall has mentioned the Sea Peoples previously in 1732: Earth Temperature Timeline.

Bronze/Iron Age Collapse (Title text): Continuing from the last panel of the comic, and making a pun on the Iron Age of civilization with the properties of iron atoms. Nuclear fusion – the merging of small light elements – expels energy, powering stars and creating increasingly heavier elements which also fuse until the process reaches iron, predominantly 56Fe. Fusing iron nuclei does not release energy, so the previous cycle of fusion abruptly stops and the star contracts under gravity (whereupon it can now create the different conditions from which small amounts of heavier nuclei do form, and disperse to be discovered in later star systems). In contrast, nuclear fission – where atoms spontaneously split into lighter elements, releasing the energy ultimately imbued into them during their synthesis – applies increasingly so to the heavier nuclei with increasing instabilities as they 'collapse' out into their various fission products. The atomic components of bronze, tin and copper, could potentially release energy, in the right conditions. Tin's main isotopes (114Sn across to 124Sn, with more than two-thirds weight 116, 118 or 120) are considered stable, as are the two for copper (63Cu and 65Cu, being practically all that is naturally present), but trace/synthesized isotopes beyond that range (e.g., actively induced by initiating a neutron bombardment) are known to, eventually, beta(±) decay/'collapse' to forms of antimony (from the tin) or nickel/zinc (from the copper).


Ambox notice.png This transcript is incomplete. Please help editing it! Thanks.

Radioactive Decay Modes

[A 6x2 table of illustrations of atoms, depicting types of atomic decay, with a label underneath.]

[First row]
[A small group of 2 protons and 2 neutrons are shown leaving a larger nucleus.]
Alpha decay
[A small particle is ejected from the nucleus while a neutron is shown converting to a proton as indicated by a shaded circle becoming white.]
Beta decay
[A nucleus emits a wavy arrow representing a wave, while a diagram shows the nucleus changing from a ellipsoid shape to a more spherical one.]
Gamma decay
[A nucleus absorbs one of its electrons along with a small sound effect.]
Electron capture
Nucleus: Slurp
[A small particle is ejected from the nucleus while a proton is shown converting to a neutron as indicated by a white circle becoming shaded.]
Positron emission
[A shaded particle is ejected from the nucleus.]
Neutron emission
[Second row]
[All protons and neutrons are ejected from the nucleus, leaving behind an empty space.]
Baryonic panic
[A few protons and neutrons are floating around a black "hole", with branching cracks coming out from it. Inside the hole is a stylized skull.]
Omega decay
[The nucleus and all the atoms has fallen to the floor, with one still falling and another bouncing off.]
Electron wilt
[A normal nucleus has an arrow pointing from it to a large, light grey sphere with dark grey patches.]
One big nucleon
[The nucleus has six white mushrooms of various sizes growing out of it, with some of the protons and neutrons being black and rotted.]
Fungal decay
[The nucleus is shown being attacked on both sides by Cueballs in boats, holding spears and firing arrows. They are all floating in water, as well as a few fallen protons and neutrons, one with an arrow sticking out of it.]
Collapse due to invasion by sea peoples.

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Omega Decay has a didtinctive Star Trek Voyager vibe, I believe... ;-) https://memory-alpha.fandom.com/wiki/Omega_molecule 23:03, 27 November 2023 (UTC)

There are a few things Omega could relate to: Rick and Morty Omega Device https://rickandmorty.fandom.com/wiki/Omega_Device, Galaxy Quest Omega 13 Device https://galaxyquest.fandom.com/wiki/The_Omega_13_Device 02:46, 28 November 2023 (UTC)
Omega voyager vibe? Nah, Voyager just used a cool sounding name. They share a root, but this isn't depending on ST:VOY 09:09, 28 November 2023 (UTC)

There appears to be an issue- the fungal decay and sea peoples are missing. I don't remember what they were! Help! 23:55, 27 November 2023 (UTC)Fizzgigg

"One big nucleon" looks a lot like a planet to me.Nitpicking (talk) 03:02, 28 November 2023 (UTC)

I was rather hoping that bismuth would appear as a product, even if entirely unintentional, but it's far too high up the chain to ever occur from "bronze decay"... 14:01, 28 November 2023 (UTC)

Protons shown in white, while the neutrons in black in the comic. Nothing wrong with this but if you visualize it the other way it makes this very confusing. (talk) 19:11, 28 November 2023 (please sign your comments with ~~~~)

The transcript might need some rearranging, because the labels are technically under the diagram? although that might make it confusing. or less confusing.--Mushrooms (talk) 18:01, 29 November 2023 (UTC)

Part of the explanation for alpha decay seems a bit mixed up: "...proton-rich / neutron-deficient heavy nuclei, which normally have many more neutrons than protons." Surely 'proton-rich' means more protons and 'neutron-deficient' means fewer neutrons, so such a nucleus would have many more protons than neutrons, wouldn't it? I hesitate to change the explanation because I'm more of a language expert than particle physicist. 00:26, 3 December 2023 (UTC)

Consider uranium 238, which has 92 protons and 146 neutrons. It decays by alpha radiation to thorium 234: 90 protons and 144 neutrons. In both cases, there are a lot more neutrons than protons, but the ratio of neutrons to protons is higher in the latter because if N > P, N/P < (N-2)/(P-2). Or polonium 210, with 84 protons and 126 neutrons, which decays by alpha (as the last step in the U-238 decay series) to stable lead 206, with 82 protons and 124 neutrons. With sufficient decrease in the number of protons and increase in the N/P ratio, the system becomes stable. All elements have multiple possible isotopes, and as the proton count increases, the number of neutrons needed for stability tends to increase a bit more quickly. If there aren't quite enough neutrons, a common decay mode is alpha, which decreases the proton count and "improves" the ratio. If the number of neutrons is a bit too high for stability, the most common decay mode is beta, increasing the number of protons and decreasing the number of neutrons, again "improving" the ratio. This is a gross oversimplification, of course. BunsenH (talk) 05:44, 3 December 2023 (UTC)
I read "...proton-rich / neutron-deficient heavy nuclei, which normally have many more neutrons than protons." as "This example has more protons and less neutrons than you'd expect for a nucleus of this weight. One with this many nucleons, in total, should consist of a greater proportion of neutrons"... But it does look a bit confusing. Definitely would be open to a rewrite (but not flipping the beginning, which'd only be rightly understood when wrongly comprehended, and vice-versa). 13:41, 3 December 2023 (UTC)

New Category: Fake Versions of a Real Thing?[edit]

I've noticed a recurring subject in xkcd where the comic lists versions of a real thing, the first of which are real, and the later ones fake joke versions. Examples are 2860: Decay Modes, 2924: Pendulum Types, 2719: Hydrogen Isotopes, and maybe 2614: 2. I think we should make a new category for it. PDesbeginner (talk) 02:08, 21 June 2024 (please sign your comments with ~~~~)

It's far more widespread than that, perhaps more a super-category given how it's practically a staple in every "several versions of things" comic. It might be nice to categorise them, but perhaps a better title for it? "Hyperbolic lists"? "Flights of fancy"? "Sublime extrapolations"? (No, I think all those suggestions have problems with them, but I have a basic idea of what kind of language I would use, just not the exact words.) Needs someone's better input, but I could see it being done. 12:55, 21 June 2024 (UTC)
Thanks for the feedback! PDesbeginner (talk) 14:54, 21 June 2024 (UTC)