Wikipedia:Reference desk/Archives/Science/2022 December 14

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December 14

Gamma decay.

So the shortest wavelength in the EM spectrum are gamma rays, then x-rays. It appears to me that gamma rays are called gamma rays because they have only been gamma rays emitted. If they can emit wavelength in the x-ray range, then they can get a name change. Have scientists been working on finding gamma decays to emit in the x-ray range? Also, if I look at gamma decay, and sort the shortest gamma ray, to the longest gamma ray, what is the pattern, from the decaying point of view? Nucleus mass? Do scientists predict they can 1 day have decay emit x-rays? And maybe win a Nobel prize if someone discovered a way. 67.165.185.178 (talk) 01:25, 14 December 2022 (UTC).

The total energy released in radioactive decay is the energy equivalent of the difference in mass (by ⁠$E=mc^{2}$⁠) between the parent nuclide and daugher nuclide(s). The energy of a photon is given by the Planck relation, ⁠$E=hf={\frac {hc}{\lambda }}$⁠, which implies that longer gamma rays carry less energy and shorter gamma rays carry more energy. Indeed, very low energy decays can produce x-rays or even ultraviolet rays in the case of the remarkably low-energy nuclear isomer thorium-229m (Sources: [1] [2]). ^Complex/_Rational 01:56, 14 December 2022 (UTC)

Excellent. And all these gamma rays, are ionizing. Can this thorium-229 or so, release the radiation that are non-ionizing? 67.165.185.178 (talk) 03:42, 14 December 2022 (UTC).

The excitation energy of Th-229m is less than 10 eV, which is commonly used as a threshold for ionising radiation. So, yes, it would emit non-ionising radiation by this definition. Though usually the gamma vs X-ray (or in this case UV!) distinction is by origin rather than wavelength. Double sharp (talk) 03:47, 14 December 2022 (UTC)

Double sharp's last sentence is important. An alternate and fairly common distinction between the two types of radiation is for "X-rays" to be the result of electronic reactions vs "gamma rays" coming from nuclear reactions, rather than a bright-line (ha!) delineation of wavelengths. X-ray#Energy ranges has a discussion. DMacks (talk) 03:58, 14 December 2022 (UTC)

It depends on whom you ask. The people who generate their own radiation (like radiologists) discriminate between X-rays and gamma rays by source, i.e., the apparatus they need to generate it. The people who only observe the radiation (like astrophysicists) discriminate only on energy, putting the threshold at something like 100 keV. PiusImpavidus (talk) 09:54, 14 December 2022 (UTC)

Yeah, I'm used to the nuclear-physics convention that anything coming out of a nucleus is gamma (even if by wavelength it's UV in the case of Th-229m), but indeed definitions vary between fields. Double sharp (talk) 14:54, 14 December 2022 (UTC)

Oh, and what does the m symbolize, in thorium-229m? 67.165.185.178 (talk) 04:01, 14 December 2022 (UTC).

What did you learn when you clicked on the thorium-229m link? DMacks (talk) 04:03, 14 December 2022 (UTC)

Oh okay, it stands for metastable. 67.165.185.178 (talk) 04:08, 14 December 2022 (UTC).

I want to underline something that several commenters here have said from different points of view:

Gamma rays and X-rays are the same thing. They're both just photons. Classifying photons by wavelength, energy, or source can be very useful for a number of reasons, but it's important to remember that these are still just sub-categories (with somewhat conflicting definitions) of the same fundamental thing. PianoDan (talk) 16:45, 14 December 2022 (UTC)

Just to really drive home the point that PianoDan is making above, the different "kinds" of electromagnetic radiation (gamma rays, X-rays, UV, light, IR, microwaves, radio waves) are all the same thing. There is no difference between any of them on a fundamental level except the wavelength, but in every other way, they are exactly the same phenomenon. When we use words like "gamma rays" or "X-rays" or "visible light" to describe certain ranges of wavelengths, we're largely doing so to make it convenient for us to explain how we use those forms of EM radiation, and in some cases are really just historical artifacts to a time when we didn't understand this stuff as well as we do now. When we named, for example, X-rays and gamma rays, we didn't really know what they were. X-rays have that "X" at the front because because Wilhelm Conrad Röntgen, when he first described them, didn't know what they were, so he used the standard placeholder "X" meaning "unknown" for the name, and it kinda just stuck. When gamma radiation was named, it was named because it was the third time of nuclear radiation (which is to say, radiation given off during nuclear decay discovered. No one really knew what it was, but since alpha radiation (the first so discovered) and beta radiation (the second so discovered) already had names, Paul Ulrich Villard, who discovered this third type, just kept the pattern going. Notice, however, that none of these names has anything to do with what the radiation actually was. It turned out that X-rays and gamma radiation were basically the exact same thing, so for mostly historical reasons, we differentiate the name by the process that produces it, rather than by any fundamental difference in the particles themselves. You see the same thing all the time; for example alpha particles are just helium 4, beta particles are just electrons. It's certainly no different than you calling your mother "Mom", but her brother calling her "Susan" or whatever. Different names in different contexts don't mean they are different things. The same thing can have multiple names. --Jayron32 18:11, 14 December 2022 (UTC)

Collisions at railroad crossings

Statistically, does California experience a disproportionately high number of collisions between trains and pedestrians and/or road vehicles at level crossings (when compared to other states)? If so, does the number remain disproportionate if corrected for the main confounding factors (namely, (1) the amount of population living in communities with active railroad tracks running through them, (2) the number of trains operating daily within the state and (3) the number of ungated railroad crossings and/or the mileage of street running)? If so, what are the possible reasons why the number is so high? (Because it certainly seems that way -- a person I know who rides Caltrain regularly told me that he experienced delays almost every week on average (!!!) due to either his train or another train ahead of him hitting someone or something on the tracks, and when I rode the Coast Starlight up to Salem a couple months ago, I experienced these delays personally -- the northbound train pulled into San Jose a full 4 hours late due to having run over some stupid hobo in Salinas, whereas the southbound train got to Salem exactly on time and kept going as far as Oakland without delay, but between Emeryville and Jack London Square we had an emergency stop due to some idiot driver pulling onto the tracks right in front of the train without looking (fortunately we were going dead-slow and therefore didn't collide, so we were only delayed 10 minutes or so). So, is California really that bad in terms of collisions at railroad crossings, and if so, why might that be? 2601:646:8A81:6070:8D7A:87F9:2C1B:94A0 (talk) 08:03, 14 December 2022 (UTC)

According to Operation Lifesaver which exists to prevent these types of collisions, Texas is #1 in the number of collisions and California is #1 in deaths caused by such collisions. This is not surprising since those are the two most populous states with California being most populous. The death rate in California per 100,000 residents is close to the national average. This is a nationwide problem although 234 deaths a year in a country of 332 million people is not a major cause of death. Pancreatic cancer, for example, kills about 50,000 Americans each year. As a long term resident of the Bay Area, I am well aware that Caltrain has a bad reputation for this type of disaster, since it is a heavily used commuter rail line between San Francisco and San Jose, with plenty of grade crossings and ample opportunities for pedestrians to engage in dangerous behavior. This article from 2000 reports 90 deaths in the previous eight years, which would be less than one a month but would certainly have an impact on daily commuting. Many of those deaths were suicides. Talking about "stupid hoboes" is pretty much guaranteed not to be useful. There are obvious safety improvements that should be made, such as eliminating grade crossings, but that would cost many billions of dollars and take decades. That is part of the California High-Speed Rail program, which is behind schedule and over budget. Cullen328 (talk) 10:17, 14 December 2022 (UTC)

For comparison, 5 people were killed at UK level crossings in 2020/21, [3] 2 in 2019/20 and 2 in 2018/19. [4] The population of the UK is 67 million, nearly double that of California, with a much denser rail network. Alansplodge (talk) 15:04, 14 December 2022 (UTC)

But California has over 10,000 level crossings, almost twice as many as the UK. To compare them properly you'd need to analyze both places in terms of the number of road vehicles and the number of trains that use the crossings daily. I'm not searching, but I doubt that those statistics will be easily found. --174.89.144.126 (talk) 15:32, 14 December 2022 (UTC)

Good point. The UK deaths were all pedestrians, mostly using rural footpath crossings. I suspect that the safety infrastucture of British vehicle crossings is rather better - crossings without automated barriers and/or warning lights are very rare and only in remote areas. Alansplodge (talk) 12:06, 15 December 2022 (UTC)

UK level crossings appear pretty safe then. In the Netherlands, we have about 12 accidental deaths among road users on level crossings per year (in addition to about 200 suicides), which amounts to one accidental death per level crossing per 200 years. That's about 98% of all accidental rail fatalities and 2% of all accidental road fatalities. Assuming the average level crossing sees about 6 trains per hour during the day (most see 4 or 8 per hour, some over 20 per hour, some only 2 per week), that's one accidental death per 8 million train passages. That may be a more useful statistic, but you still have to compensate for road traffic density and that the rush hour on road traffic may or may not coincide with peaks in rail traffic. Ideally, you take the number of trains at a level crossing in an hour, multiply with the number of road users at that crossing during that hour, integrate over a year, sum over all level crossings and then divide the number of accidental deaths or the number of collisions by that number. It's still not a fair number: as the most heavily used level crossings, with the most elaborate warning signals, get replaced by grade separated crossings, accident rate drops, but the average safety of the remaining level crossings drops too. PiusImpavidus (talk) 12:48, 15 December 2022 (UTC)

wormholes

hello i would like to ask if resonant tunneling antenna diodes can generate wormholes. thanks very much. 2607:FEA8:BCE0:D500:75E8:5E73:E7C8:DE4 (talk) 15:38, 14 December 2022 (UTC)

No. --Wrongfilter (talk) 15:44, 14 December 2022 (UTC)

More specifically, quantum tunnelling and wormholes are not the same thing. --OuroborosCobra (talk) 16:02, 14 December 2022 (UTC)

from internet searches i found macroscopic and electromagnetic quantum tunneling can generate wormholes. is that this correct. 2607:FEA8:BCE0:D500:D9DA:4F2F:3CE:E4B6 (talk) 17:42, 14 December 2022 (UTC)

Please read the Wikipedia articles you have been sent to read. Wormholes and quantum tunnelling are entirely unrelated phenomena, and have nothing to do with each other. Wormholes are a consequence of gravity, and are thus explained by general relativity. Quantum tunnelling, as the name implies, is a result of quantum mechanics. It is not an electromagnetic effect, per se, but rather due to the way that all elementary particles behave. The quantum tunnelling article actually has a nice, lay-person level explanation in the "Introduction to the concept" section.--Jayron32 17:59, 14 December 2022 (UTC)

Water's boiling point

One of the things that allow life to exist on Earth is that liquid water is available in large numbers. This is because of the distance to the sun, but also because of our atmosphere and its pressure, that allow a wide temperature range for liquid water (from 0º to 100º). If Earth was in the same orbit but had a lower atmospheric pressure, that range would be way more limited. And IIRC, with no atmosphere water would sublimate from ice to vapor directly.

This is something I simply know, but I would need a proper source for it. I'm listing in a sandbox all the reasons that allow life to exist on Earth, from an astronomical perspective, but all the sources I find that explain our liquid water attribute it only to the goldilocks zone, making no mention to the atmospheric pressure. Cambalachero (talk) 19:06, 14 December 2022 (UTC)

What you're looking for is a phase diagram of water, or even more simply the triple point of water. The pressure at the triple point is the lowest pressure at which a liquid could exist, so any pressure less than about 0.006 atm (0.6% of the earth's atmospheric pressure) would not be able to support liquid water. The relationship between pressure and boiling point is seen on any phase diagram as the liquid-solid line on the graph. If you want a text description, it's really basic stuff taught in any first-year chemistry class. Here it is in LibreText Chemistry and Here it is on OpenStax Chemistry, for two free entry-level chemistry textbooks. I can't imagine that literally every entry-level chemistry text book doesn't discuss the relationship between pressure and phase changes. It's REALLY basic stuff. --Jayron32 19:49, 14 December 2022 (UTC)

If the motivation here is to explore limits of alternative "Goldilocks zones," we might need to freeze the discussion (sorry, bad pun) and revisit exactly what that zone is.

If we're reducing it to a few words of sound-bite, we might say that a planet is in the Zone if liquid water exists on that planet.

But hang on - we also want to say, "... and we're looking for liquid water because..." ... it's an important part of every form of plausible biochemistry that we're interested in - even the plausible alternative xenobiology that borders on the speculative!

At the same time, the so-called "habitable zone" also has other requirements. If the liquid water is in equilibrium at an ambient temperature that is so hot that it's denaturing proteins, then protein-based biology won't work: that's "not the habitable zone." If it's so cold that metabolism is chemically unsustainable, that's also "not the habitable zone." We can imagine biochemistries that are very different from our fundamental earth-like biochemistries - and we can even test some of this in a lab - but there are still limits! And so we can traverse down the speculative, alternative, plausible sorts of "habitable" zones for speculative, alternative, plausible sorts of non-Earth-like life forms, ... just bear in mind that as you stray farther afield, even the requirement for liquid water will also evaporate (sorry, bad pun).

Here's a NASA website that talks about the Kepler Occurrence Rate, and here's the SETI study that goes into the boring details; and if I may editorialize a bit - NASA had to make some "clarifying editorial updates" to their press release in order to keep things more science-y and less fiction-y.

Real scientists do care about this stuff, but they have to mince words, define terms, and tread very carefully. Speculation is fine as long as we are still making meaningful scientific statements - which fundamentally boils (sorry) down to falsifiability and testability.

Nimur (talk) 21:12, 14 December 2022 (UTC)

Just as (relatively analogous to water) examples of plausible alternative biochemistry: ammonia has long been suggested as a possible water substitute, being another 2p element hydride with hydrogen-bonding benefits and a good solvent. I've similarly wondered about hydrogen fluoride for some years, and that possibility is explored in this paper. Going much farther afield, some early transition metals form some intricate structures and make a plausible high-temperature biochemistry (at which point we've left analogies to water very far behind). Double sharp (talk) 03:01, 15 December 2022 (UTC)

@Cambalachero, this is somewhat addressed at Rare Earth hypothesis#Requirements for complex life, specifically in the subsection A terrestrial planet of the right size (which is tied to atmospheric pressure, as well as longevity of that atmosphere). You could check out the references there for more. 199.208.172.35 (talk) 21:15, 14 December 2022 (UTC)