Talk:Decay chain

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[edit] A table

In rewriting Radioactive decay, I found the following table, reproduced here complete with plaintext label. Being of rather limited knowledge about radioactive decay, I have a few questions to ask.

The three such naturally occurring series are shown in the following table:

Natural radioactive elements
Series Starting Isotope Half-life (years) Stable end-product
Radium U-238 4.47×109 Pb-206
Actinium U-235 7.04×108 Pb-207
Thorium Th-232 1.41×1010 Pb-208
  • I see that the decay chains listed are those with nucleon numbers congruent to 0, 2, and 3 mod 4. Where's the series congruent to 1?
  • In the same vein, why are only heavy-element chains listed?
  • How are the "starting isotopes" determined? I see that these three isotopes have very long half-lives, but surely they must be, for their part, decay products of some other nuclides.

--Smack 19:47, 22 Dec 2004 (UTC)

I don't claim any expertise in the area, however, I'm not sure I understand your question.
  • What do you mean when you say a nuclean number is "congruent"?
  • All radioactive isotopes will have a decay chain. For lighter elements, the decay chain is typically short; a single beta emission would result in a stable product
  • All radioative isotopes have decay chains. A comprehensive table to decay chains would list them all. If you're asking how any radioactive isotopes came to be radioactive in the first place, that's a separate question.  :-) Samw 04:03, 29 Dec 2004 (UTC)
  • Congruence of integers is defined in Modular arithmetic. An alpha decay reduces the nucleon count by 4, and a beta decay leaves it unchanged. Hence along a decay chain all nucleon counts are "congruent to each other modulo 4". What Smack is asking is why there is no chain listed with nucleon number 237/233/229/...
  •  
  • What he is asking is e.g. how we know U-238 starts the series. That U-238 could itself be a product of <something>-242 (which could be a product of <something else>-242 or <some other thing>-246), which could have such a short half-life that in the final mixture it cannot be detected. -- Paddu 04:38, 29 Dec 2004 (UTC)
  • There are <X>-242 that decays into <X>-238: Americium-242 and Plutonium-242. Pu-242 has a long half-life in human terms, but in geological terms, there's none left naturally. So, like the answer to the first question, these 3 are considered the start of the decay chains because these 3 have very long half-lives.Samw 18:22, 29 Dec 2004 (UTC)
  • BTW, there's already an article on Nucleosynthesis describing how all elements, including radioactive ones, come to be. Samw 21:26, 31 Dec 2004 (UTC)
I think I understand now. A decay chain is considered important only if it contains a very long-lived nuclide, which (once produced by some process) can act as a continuous source of nuclides farther down the chain. Since neither light-element decay chains nor the U-237 chain contain such a nuclide, they're not listed.
That said, it seems unnatural to name a sequence of unstable nuclides after its least unstable nuclide. Furthermore, IMHO, this whole notion of nucleon-number preservation is unscientific. It smells like it was thought up by engineers rather than physicists. They (we?) often give too little thought to scientific generality and consistency. --Smack (talk) 17:13, 6 Jan 2005 (UTC)
http://members.tripod.com/vzajic/1stchapter.html suggests you're right and that the "actinium series" name was chosen for practical reasons to avoid calling it U-235 series to distinguish it from the U-238 series. Samw 02:19, 7 Jan 2005 (UTC)

Here's a reference that shows all 4 decay chains: http://www.amazon.com/gp/reader/047180553X/ref=sib_vae_pg_179/102-8556324-8260101?%5Fencoding=UTF8&keywords=decay%20chain&p=S05J&twc=24&checkSum=0J4LnZVge9osi%2BmMweCi%2BMsMqE6XDZCnQP3F%2FiebUWE%3D#reader-page Samw 01:17, 19 Feb 2005 (UTC)


[edit] Neptunium series

What about the Neptunium series that describes the decay chain of the transuranic elements?--ragesoss 17:21, 22 January 2006 (UTC)

[edit] Half-life of Thorium-232

Why is the half-life of Thorium-232 written as 1.405·10^6 a, meaning 1.4 million years? Since this is dramitically less than the age of the planet, shouldn't this be more like 1.405·10^10 a (this is the number claimed in the Thorium article). Since I'm no nuclear physicist, I'd rather point this out in the discussion before I tamper with the article. Felix Dance 15:52, 14 April 2006 (UTC)

Thanks, I've corrected. Samw 19:24, 14 April 2006 (UTC)

[edit] Merge from Radioactive decay path

It was suggested that Radioactive decay path be deleted and anything salvagable be merged here. I thought I would dump it here so It wouldn't be lost until I get around to adding it here, or you can add it here ;). The only reason I learned this was to understand how scientists date materials and why no reputable scientist believes the earth is only 6000 years old, as opposed to about 4.5 billion years. I think this is important considering the increasing attacks that pure science has come under from religious and political factions lately in America.

  • Radioactive decay paths are an integral part in dating materials. By comparing the relative abundance of various elements in a sample one can estimate its age based on the decay path and half lifes of those elements. Analysis of various Uranium containing Zircon crystals (along with other data) puts the age of the earth at aboout 4.5 billion years. Decay paths are also important in reactor experiments where the elements produced are so short lived that their existence can only be infered by the abundance and type of their decay products.
  • Radioactive decay paths are also important in less than geologic scales such as with Carbon 14 which is used in Radiocarbon dating of organic materials. (yet more testable proof that the earth is more than 6000 years old)
  • Age of the Earth 4.55 Billion (4.55×109) Years
  • Age of the Universe 13.5 Billion (1.34×1010) Years
  • Nuclear Theory : Island of Stability
  • Nuclear Theory : Shell Model
Tiki God 14:08, 28 July 2006 (UTC)

[edit] Diagram

I added the decay chains diagram -- what do you think? Opinions welcome. — Johan the Ghost seance 13:03, 25 November 2006 (UTC)

The labels are all messed up -- though it looks OK on my system... :-( So I guess I have to fix it. — Johan the Ghost seance 13:10, 25 November 2006 (UTC)
OK, fixed. (It seems to be really hard to make an SVG that displays the same in Inkscape and in MediaWiki... :-/ — Johan the Ghost seance 13:19, 25 November 2006 (UTC)

[edit] a vs y?

I know it's a nit, but is it now standard practice in nuclear physics to use the letter 'a' to mean 'years' instead of 'y'? Obviously 'a' comes from the Latin 'annus' ('year'), but a lot of English-speaking Wikipedia readers might not know that.

Karn 23:39, 25 November 2006 (UTC)

It's kind of sucky, but after much searching, there does seem to be a real basis for this use in science: see year#Julian year. Maybe make the "a" a link to this? — Johan the Ghost seance 22:14, 27 November 2006 (UTC)
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