Science desk
< December 26	<< Nov \| December \| Jan >>	December 28 >

Welcome to the Wikipedia Science Reference Desk Archives
The page you are currently viewing is a transcluded archive page. While you can leave answers for any questions shown below, please ask new questions on one of the current reference desk pages.

December 27

Is it possible that europium is more unstable than bismuth?

The only natural occurring isotope of bismuth, Bi209, has a half-life of 2.01*10^19 years, and for europium, Eu151 has a half-life of 5*10^18 years, and the lower bound of the half-life of Eu153 is 5.5*10^17 years, so is it possible that europium is more unstable than bismuth? And hence europium will be the most unstable natural occurring element besides thorium and uranium? 111.253.202.97 (talk) 02:15, 27 December 2023 (UTC)[reply]

Probably not. According to this paper, all theoretical predictions for the alpha half-life of ¹⁵³Eu are over 10¹⁴⁰ years, and no other decay modes (besides spontaneous fission) are possible. Double sharp (talk) 03:26, 27 December 2023 (UTC)[reply]

So what element will be the next "unstable" natural occurring element after uranium, thorium, and bismuth? 2402:7500:944:2AC:45B9:41E0:7299:F0CC (talk) 03:59, 27 December 2023 (UTC)[reply]

Based on the tables in that paper, perhaps rhenium? ¹⁸⁷Re is already known to be beta-unstable with a half-life of about 4×10¹⁰ years, and ¹⁸⁵Re is expected to be alpha-unstable with a half-life on the order of 10²⁴–10²⁵ years. Though I note that the tables don't consider double beta decay (relevant for other elements), so this should be taken as just a guess. Double sharp (talk) 04:07, 27 December 2023 (UTC)[reply]

The longest known half-life of a nuclide is 2.2*10^24 years for Te128, thus maybe the half-life of Re185 is shorter than Te128? (Although their decay modes are different: Re185 is alpha decay while Te128 is double beta decay) 2402:7500:944:2AC:E564:A5C5:C845:76AC (talk) 04:57, 27 December 2023 (UTC)[reply]

Since predictions aren't perfect, it may indeed be that this is the case. (Predictions slightly overestimated the half-life of nearby ¹⁸⁴Os.) Double sharp (talk) 05:53, 27 December 2023 (UTC)[reply]

OK, it is for the proton number, the proton numbers with primordial nuclides are 1~83 except 43 and 61, together with 90 and 92, besides, 83, 90, 92 are the proton numbers among them which have no stable nuclides, and perhaps 75 is the next "unstable" proton number after 92, 90, 83. But what is the answer for the neutron number? The neutron numbers with primordial nuclides are 0~126 except 19, 35, 39, 45, 61, 89, 115, 123, together with 142, 143, 146, besides, 21, 142, 143, 146 are the neutron numbers among them which have no stable nuclides, and the next "unstable" neutron number after 143, 21, 146, 142 may be 71 (corresponding to Te123)? If so, what number will be the next "unstable" neutron number after 143, 21, 146, 142, 71? 2402:7500:942:3D81:695F:5302:9A90:FEE6 (talk) 07:47, 27 December 2023 (UTC)[reply]

Probably either 87 (¹⁴⁹Sm should be alpha-unstable at 10¹⁷–10¹⁸ years) or 111 (¹⁸⁷Os should be alpha-unstable at 10¹⁶–10¹⁹ years). Either of these might come before 71, actually. Double sharp (talk) 08:08, 27 December 2023 (UTC)[reply]

I should note, though, that we ought to distinguish proton or neutron numbers with no beta-stable nuclides from those having beta-stable nuclides which are unstable to alpha decay. Atomic numbers 43 and 61 are instances of the former (all isotopes of Tc and Pm are susceptible to beta decay), whereas if the alpha decay of ¹⁸⁵Re (beta-stable) is observed, for instance, it would only be reclassified from stable to primordial radioactive.

The list of beta-stable isobars also shows where these "unstable numbers" are, and continues into the region of non-primordial nuclides, where we see that there are no beta-stable isobars with neutron number 147. ^Complex/_Rational 15:19, 27 December 2023 (UTC)[reply]

Or probably 84? Ce142 is double-beta-unstable. Also, could someone search the decay of Re185, Sm149, Os187, just like Os184 and Xe124 (whose decay are found recently)? I saw the article, maybe someone can search the decay of the nuclides whose theoretical half-lives are shorter than 2.2*10^24 years (which is the half-live of Te128)? This includes Nd145, Sm149, Dy156 (a little longer), Yb168 (a little longer), Hf176, Hf177, Hf178, Ta180m (maybe someone can search its isomeric transition), Re185 (a little longer), Os187, Pt192. 210.243.206.107 (talk) 02:35, 28 December 2023 (UTC)[reply]

Decays of ¹⁴⁵Nd, ¹⁴⁹Sm, ¹⁵⁶Dy, ¹⁶⁸Yb, ^180mTa, and ¹⁹²Pt have been searched for, so far without success. Double sharp (talk) 03:37, 28 December 2023 (UTC)[reply]

I know, and I also want someone to search the decay of Re185 and Os187, maybe this search can make (proton number 75) or (neutron number 111) be an "unstable" number (so far there is still no single "unstable" number for proton <= 82 or neutron <= 126 (they are the limit of observationally stable nuclides) which have a primordial nuclide except the neutron number 21 (which corresponding to potassium-40, which has a half-life less than the age of the universe, and is the only one primordial nuclide with proton number <= 82 and neutron number <= 126 with half-life less than the age of the universe, thus this search may broke the record, in the past the nuclide Te123 is wrongly found to be radioactive, but now it remains (observationally) stable, thus the neutron number 71 is not an "unstable" number. 118.170.53.246 (talk) 05:12, 28 December 2023 (UTC)[reply]

There is also ₇₈Pt. Ruslik_Zero 20:35, 27 December 2023 (UTC)[reply]

It seems that the largest proton number with a really stable isotope is ₆₆Dy, though magic ₈₂Pb has theoretical lifetimes in excess of 10⁶⁰ years. Ruslik_Zero 20:53, 27 December 2023 (UTC)[reply]

Well, the proton numbers with a theoretically stable nuclide are 1~66 except 43, 61, 62, 63, and the neutron numbers with a theoretically stable nuclide are 0~98 except 19, 21, 35, 39, 45, 61, 71, 83~91, 95, 96, also in theory, no two stable nuclides have the same mass number, and the mass numbers with a theoretically stable nuclide are 1~164 except 5, 8, 143~155, 160~162. 210.243.206.107 (talk) 02:50, 28 December 2023 (UTC)[reply]

Electron capture vs. beta plus decay

Is there a reference I can use to distinguish between electron capture and β⁺ decay? While writing about isotopes of bromine, I encountered a reference describing the isotope ⁷⁷Br as primarily undergoing electron capture rather than β⁺,^[1] but NUBASE2020 lists only β⁺ for most nuclei capable of β⁺ decay, inluding ⁷⁷Br.^[2] –LaundryPizza03 (d c̄) 08:19, 27 December 2023 (UTC)[reply]

Perhaps both decay modes are known for ⁷⁷Br. The energy difference between ⁷⁷Br and ⁷⁷Se is large enough for positron emission to occur (greater than ⁠

2m_{e}c^{2}~=1.022~{\text{MeV}}

⁠), but a number of sources specifically describe electron capture and the Auger effect and do not classify ⁷⁷Br alongside other positron emitters (such as ⁷⁶Br). As such, EC should definitely be included, but I wouldn't include a branching ratio unless a source specifically describes one. ^Complex/_Rational 15:33, 27 December 2023 (UTC)[reply]

References

^ Kassis, A. I.; Adelstein, S. J.; Haydock, C.; Sastry, K. S. R.; McElvany, K. D.; Welch, M. J. (May 1982). "Lethality of Auger Electrons from the Decay of Bromine-77 in the DNA of Mammalian Cells" (PDF). Radiation Research. 90 (2): 362. doi:10.2307/3575714. ISSN 0033-7587.
^ Kondev, F. G.; Wang, M.; Huang, W. J.; Naimi, S.; Audi, G. (2021). "The NUBASE2020 evaluation of nuclear properties" (PDF). Chinese Physics C. 45 (3): 030001. doi:10.1088/1674-1137/abddae.

UK metric system (update)

The UK government has announced plans to make it legal to sell wine by the pint. No more messing about with those fiddly little wineglasses, then. -- Verbarson ^talk_edits 11:58, 27 December 2023 (UTC)[reply]

Also note that "98.7% of respondents to a consultation favoured using metric as the main measurement unit for sales, as now, or as the only unit" (from the same BBC report). Mikenorton (talk) 12:54, 27 December 2023 (UTC)[reply]

Last passenger

After pulling the emergency brake in a train (and in particular a British one), is there any way to release the brakes without recharging the brake pipe? I think not (based on what I know of trains), feel free to correct me if I'm wrong! 2601:646:8080:FC40:7042:7EFC:5F93:408A (talk) 12:01, 27 December 2023 (UTC)[reply]

Typically, you can release it. I don't know the specifics of British passenger trains and there's quite a bit of variation, but I'd expect a manual release valve, typically accessible on the outside of the vehicle. See the image on the right. This is a goods wagon (Swiss, I think). The yellow handle on the top is to switch between fast and slow application. Slow application (left, G for Güter=goods) prevents large differences in braking force throughout the length of the train and is useful on long goods trains. Passenger carriages normally only have the fast setting (right, P for Personen=people), so the lever would be absent. The red handle on the left is to disable the brake on this wagon entirely, useful if the brake is broken. It's safe to run a train with the brakes disabled on a small fraction of the wagons. The red handle on the right is to adjust the braking force to the weight of the wagon, so that it brakes harder when loaded. In this case, set it to the left to pretend that the wagon weighs 13 tonnes, to the right for 26 tonnes, and one should switch when the weight exceeds 27 tonnes. As the weight of passenger carriages doesn't change much with load, such handles aren't used on passenger carriages. Finally, the yellow thing on the bottom is the manual release. Pull it to release the air brake. It's convenient to have when you want to shunt and don't have time to connect the brake hose and recharge the brakes. It's also used when transferring a wagon to a locomotive that uses a lower brake pipe pressure than the old locomotive. PiusImpavidus (talk) 21:57, 27 December 2023 (UTC)[reply]

I see! So it is plausible, if the passenger in question was able to go outside the train and pull the release valves without anyone noticing? (FYI, as you might be able to tell from the title, my question had to do with a Christmas disaster movie I watched -- I don't want to give too much away, but the gist of it is, there was a psycho on a train who murdered the conductor, pulled the emergency brake from the conductor's cab, murdered the engineer when he came out to inspect the train, and then released the brakes without recharging the brake pipe, and took off in the train without brakes in order to crash it at the end of the line!) 2601:646:8080:FC40:7042:7EFC:5F93:408A (talk) 03:09, 28 December 2023 (UTC)[reply]

Yes, that part is plausible. Using the manual release will make some hissing noise, but trains are usually sufficiently soundproof not to notice that on the inside. PiusImpavidus (talk) 16:15, 28 December 2023 (UTC)[reply]

And more to the point, even if anyone hears it, they'll probably think it's just the normal sounds of brakes releasing after an emergency stop! (And in this particular scenario, the engineer and the conductor won't notice anything because they're both dead!) 2601:646:8080:FC40:7042:7EFC:5F93:408A (talk) 02:22, 29 December 2023 (UTC)[reply]

Where was the camera on the Apollo lunar lander?

I'm trying to better understand how NASA filmed the Apollo 11 lunar landing considering obviously there was no one on the Moon to film it. I found this picture which is supposed to show the camera on the lander but I am not seeing it. Nothing that resembles a traditional camera is in the image as far as I can see. Can someone point out where in the image is the camera? A Quest For Knowledge (talk) 12:09, 27 December 2023 (UTC)[reply]

See Apollo TV camera, which has another image of the camera's stowed location on the lander. Mikenorton (talk) 12:37, 27 December 2023 (UTC)[reply]

(edit conflict)Also a video explaining the Lunar Module 2 MESA (Modularized Equipment Stowage Assembly) which contained the camera. This image shows the MESA and its camera in the deployed position. Alansplodge (talk) 13:04, 27 December 2023 (UTC)[reply]

See the landing film on Apollo 11, the only film of the Apollo 11 lunar landing was taken from the LEM as it came down. Martin of Sheffield (talk) 12:54, 27 December 2023 (UTC)[reply]

I think the OP might be asking about the famous blurry images of Armstrong's feet coming down the ladder onto the lunar surface. Alansplodge (talk) 13:04, 27 December 2023 (UTC)[reply]

[kassis1982-1] Kassis, A. I.; Adelstein, S. J.; Haydock, C.; Sastry, K. S. R.; McElvany, K. D.; Welch, M. J. (May 1982). "Lethality of Auger Electrons from the Decay of Bromine-77 in the DNA of Mammalian Cells" (PDF). Radiation Research. 90 (2): 362. doi:10.2307/3575714. ISSN 0033-7587.

[2] Kondev, F. G.; Wang, M.; Huang, W. J.; Naimi, S.; Audi, G. (2021). "The NUBASE2020 evaluation of nuclear properties" (PDF). Chinese Physics C. 45 (3): 030001. doi:10.1088/1674-1137/abddae.

[1]

[2]