|WikiProject Elements / Isotopes||(Rated Start-class, Low-importance)|
- This table isn't labelled very well; it shows a number of fission products, elements which come into existence as a result of nuclear fission reactions. In nuclear fission reactions the center, or nucleus of a fissionable atom splits into two or three parts. Years of very patient and cautious observation and experimentation allow scientists to predict which isotopes of which elements result from the fission of a given isotope of a given element, or to state which possible isotopes of which elements can result from the fission of a given isotope of a given element, and the probable proportions in which these fission products will be produced.
- This table is in this article because it shows that Plutonium-244 is a primordial isotope of plutonium occurring naturally as an actinide. The text of the article elaborates that the neutron capture required to produce plutonium-244 in natural ores is highly unlikely given the very low neutron flux in the vast majority of uranium deposits in the Earth, so that a process called r-process nucleosynthesis in supernovae is the only plausible way for most of the plutonium-244 on Earth to have been made. loupgarous (talk) 09:20, 20 March 2013 (UTC)
Could something be done about the veeery thin column at the top of this page? The table thing-ie on the right crowds the text down to just 2-3 words per line. I'd fix it myself -- alas I don't know how.
Hoffman et al. estimation of Pu-244 content in the rare-earth mineral bastnasite
It says that the they detected Pu-244 with a concentration of c244 = 0.15×10−18 g/g in bastnasite, making its concentration 4.5 billion years ago in similar minerals 255 times larger or 3.6×10-2 g/g, almost 5 times the pre-solar nebula abundance, relative to U-238, mentioned above. This seems erroneous and the differences in these estimates isn't explained. I sugest removing at least one of them. Crackhorace (talk) 17 November 2016
@Double sharp: I notice you edited in a mention of Sm-146 being primordial, but I don't see a source for it and can't find one myself. Could you enlighten me? Magic9mushroom (talk) 14:45, 24 August 2017 (UTC)
- @Magic9mushroom: I think that was fairly old, before the half-life of 146Sm was more accurately determined to be lower than that of 244Pu. I'll remove it; thanks for alerting me! Double sharp (talk) 14:50, 24 August 2017 (UTC)
@Double sharp: So you're saying Sm-146 is not in fact primordial? I mean, certainly if Sm-146 is primordial Pu-244 would be the second-shortest-lived primordial; I'm more concerned with whether Sm-146 has or hasn't been confirmed to be primordial. Back-of-the-envelope calculations suggest there should be about 4 mg left in the entire Earth, so it's in the weird limbo where there is some but no conceivable experiment could detect it (a kilogram of natural samarium should contain about 9 atoms of Sm-246 and have about one decay every 10 million years). Magic9mushroom (talk) 02:44, 25 August 2017 (UTC)
- @Magic9mushroom: Well, Pu-244 and Sm-146 probably are primordial in the abstract sense. However, I don't think we should list them without some confirmatory experiments. There may have been citations for Sm-146 being primordial here at some point; I really don't remember. Perhaps isotopes of samarium has it. Double sharp (talk) 03:11, 25 August 2017 (UTC)
@Magic9mushroom: Ah, I found a source (doi 10.1039/B608157F). It says that 146Sm should be primordial, as you note, but it should not be easy to find, especially because mass spectrometry is going to get swamped by the stable isobar 146Nd. So they propose here a method to effectively separate Nd from Sm and pin it down; but since even the detection of 244Pu is unconfirmed, we may have to wait a while to find 146Sm. They also suggest that a similar Hf–W separation should help to find 182Hf, which may be around from more recent nearby supernovae like 60Fe. So, perhaps we may finally get rid of these two borderline cases in the future, though I am not inclined to be as hopeful given that this paper is from 2006. Double sharp (talk) 03:40, 25 August 2017 (UTC)
@Double sharp: That paper still assumes a 100-million-year half-life, which means it's probably overestimating the abundance of Sm-146 in the present day.
I'm going to remove the mention of Sm-146 being detected from the Isotopes of niobium article, because it's not sourced there either and was edited by an IP from a sentence originally talking about Pu-244. I think this article could do with some cleanup as well; there's one paragraph stating unambiguously that Pu-244 is primordial and a second saying that it's disputed, which frankly stinks. And lastly, I think Isotopes of samarium should probably have the bit saying Sm-146 definitively isn't primordial reworded. Your thoughts on the latter two? Magic9mushroom (talk) 06:35, 25 August 2017 (UTC)
- @Magic9mushroom: I would suggest that we start, for both Pu-244 and Sm-146, by stating how much of these isotopes we should expect to have left today, and thus noting that they should be primordial. Then we can talk about the reports (or lack thereof) of their primordialness, and whether or not they have been confirmed. Do you think that would be a better approach?
- As for general coverage that is not specifically about Pu-244 and Sm-146 and simply discusses primordial nuclides and gives an offhand number, I would stick to the status quo and simply consider U-235 the shortest-lived primordial for those purposes until we have some experimental confirmation of these two. Double sharp (talk) 07:14, 25 August 2017 (UTC)
- @Double sharp: Well, I don't have a source for how much 146Sm is expected to be on Earth; the paper issuing a revised half-life for 146Sm gives a half-life, an age of the Earth and an initial solar ratio of 146Sm/144Sm, but to get an estimate from that involves synthesis with samarium elemental abundance and 144Sm isotopic abundance from other sources. That's why I said it's back-of-the-envelope. For 244Pu I'm not even sure it can be theoretically calculated at this time; 244Pu doesn't produce detectable isotopic-abundance anomalies (it's 4n, so it decays to 232Th... which is mononuclidic), and our theoretical understanding of the r-process is limited in the actinide region, so there's no way to calculate how much 244Pu was there at Sol's formation absent direct observation of how much is here now.
- With respect to the broader articles, I agree with listing 235U as the shortest-lived in tables, since it's both the shortest-lived confirmed primordial and the shortest-lived primordial existing in useful quantities (billions of tonnes compared to maybe grams for 244Pu and milligrams for 146Sm), but I don't think e.g. the note about 244Pu and 146Sm in the Primordial nuclide article itself needs removing entirely. Magic9mushroom (talk) 08:36, 25 August 2017 (UTC)
- @Magic9mushroom: Well, at the very least, we can say that some minute quantities of Pu-244 and Sm-146 should persist today, citing that 2006 paper, and continue as before. In your example, the primordial nuclides are the subject of discussion, so these two borderline cases are certainly on-topic. Double sharp (talk) 09:00, 25 August 2017 (UTC)