Talk:Isotopes of francium

Stability
If elements after lead are gradually losing stability, then why are thorium and uranium suddenly so stable(relative for such big bulky nuclei)? and how can CURIUM have such a long half life-almost primordial?32ieww (talk) 00:22, 19 February 2017 (UTC)
 * It's not so simple. Even-numbered elements are generally stabler than odd-numbered elements (even beyond lead), and there is the concept of magic numbers and nucleon shells (there's a reason why technetium is unstable but everything immediately around it is).--Jasper Deng (talk) 02:22, 1 March 2017 (UTC)

Uranium has a semi-closed shell (ending a proton orbital). Also it's probably not best to extrapolate from the Po-Ac region; those elements are less stable than one would expect purely from the liquid drop model, because they are just above the "energy well" at Pb and Bi and don't have much of a barrier to falling down the well. The elements from Th to Lr have the stability that you would expect. From Rf onwards the elements are more stable than the liquid drop model predicts, because the shell effects protect the nuclei effectively from spontaneous fission. When we are far from the closed or semi-closed shells (e.g. N = 162 or 184), such as at N = 170, the nuclei tend to undergo SF instead of alpha decay (e.g. 280Ds, 281Rg, 282Cn, 283Nh, 284Fl; the even ones undergo quick SF, while the odd ones, though protected by the odd proton which hinders SF, still have a prominent SF branch for 281Rg). Double sharp (talk) 05:08, 15 April 2017 (UTC)

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Fr-221: natural?
This article says Fr-221 is present naturally as a daughter of Np-237. However, Np-237 is considered extinct (over 1000 half-lives have elapsed since the Earth's formation; it is ludicrously unlikely that even one atom persists) and therefore should not be generating any decay products in the modern era (and indeed, the other isotopes in the 4n+1 decay chain are not marked as naturally existent).

Am I missing something? I suppose spontaneous fission in a thorium ore and subsequent neutron capture by Th-232 would naturally produce a miniscule quantity of radiogenic 4n+1 nuclides (Th-233 -> Pa-233 -> U-233 -> Th-229 -> Ra-225 -> Ac-225 -> Fr-221 -> At-217 -> Bi-213 -> Po-213 -> Pb-209 -> Bi-209), but that's not the etiology claimed in this article and if that is deemed significant (we'd need a source for that) it would apply to all of the isotopes listed and not just Fr-221.

If no-one objects, I'll remove the mention of natural Fr-221 to fit with the rest of the extinct 4n+1 chain. Magic9mushroom (talk) 07:33, 6 June 2017 (UTC)
 * It is from neutron capture by natural uranium, forming 237U (knockout) which then beta decays to 237Np and travels down that path. If thorium is also present, it can similarly capture a neutron and form 233Th, as you say. In concentrated pitchblende deposits from the Congo 237Np occurs in high enough amounts (though still tiny traces) that already in 1952 (paper) its daughters 233U, 229Th, and 225Ac could be identified. 221Fr is the daughter of 225Ac and hence must also be present, but I don't know of any source that specifically mentions having detected it – which would be no mean feat, given its minuscule half-life. For this reason I am equally uncertain about whether it should be included, but I can see arguments on both sides. What do you think? ^_^ Double sharp (talk) 12:06, 6 August 2017 (UTC)

Well, now, that's a can of worms. I suppose, given that we list cosmogenic isotopes as "trace", and that's also natural transmutation, that the products of transmutation in actinide ores should be mentioned. That would include, what? Np-237, Th-233, the rest of the 4n+1 chain descending from those, and Pu-239? The complicating factor in the cases of Po/At/Rn/Fr/Ra/Ac is that since every isotope of those is listed as "trace", it might mislead people into thinking the "traces" are remotely similar instead of differing by a factor of >10 billion (in the case of Np it's no issue because Np-237 is the only natural isotope, and in the case of Pu Pu-238 from β−β− decay of U-238 is also miniscule). Certainly, the note should be different than the ones in the main decay chains; I'm thinking something along the lines of "Product of transmutation in actinide ores".

Thoughts on the balancing act between technical accuracy and potential for misunderstanding? Other possible solutions? Magic9mushroom (talk) 22:42, 7 August 2017 (UTC)
 * I would think that we still have to call these trace radioisotopes, albeit with a note about it. A bright line between products of the three extant decay chains and those of the 237Np series seems unworkable given that many of the rare side-chain products of the former would be just as rare as the latter: I'm thinking of cases like 219At, 218Rn, 206Hg, and suchlike. At the most, therefore, I think we should just leave it to the notes to explain the origin of each trace radioisotope. Double sharp (talk) 23:04, 7 August 2017 (UTC)

221Fr and 221Rn are the lightest known nuclide to undergo cluster decay
According to Cluster decay#Experiments, 221Fr and 221Rn are the nuclides with the lowest mass number that are known to undergo cluster decay (the page Isotopes of barium says that 114Ba is predicted to undergo cluster decay, but this is not observed). So I think this "lightest nuclide" property should be noted for one of 221Fr and 221Rn or both of them in the table of isotopes, like what has been done for 242Cm. 129.104.241.214 (talk) 00:57, 4 December 2023 (UTC)

Possible alpha decay of 222Fr
Although not listed in, 222Fr should have an alpha decay partial half-life at the order of several days judging from the trend and the theoretical decay energy (222.017552 - 218.008694 - 4.002603254130)×931.4941 MeV = 5.8263 MeV. 129.104.241.214 (talk) 10:47, 28 December 2023 (UTC)