WikiProject Physics (Rated C-class, High-importance)
This article is within the scope of WikiProject Physics, a collaborative effort to improve the coverage of Physics on Wikipedia. If you would like to participate, please visit the project page, where you can join the discussion and see a list of open tasks.
C  This article has been rated as C-Class on the project's quality scale.
High  This article has been rated as High-importance on the project's importance scale.

## Introduction has grown too long

The introductory paragraph is entirely too detailed and much of the material therein needs to be moved to later paragraphs and trimmed out of the intro. — Preceding unsigned comment added by Zedshort (talkcontribs) 20:38, 1 April 2012 (UTC)

Says you, after adding positron capture back into the lede, when it is a hypothetic process never yet seen, and only possible in complex-nuclei antimatter (maybe Captain Kirk and Spock see it in their engines). That's pretty hypocritical. There are NOT "five" processes of radioactive decay, but as many or more as appear in the table, and these don't count hypothetical ones. Just because you count five in a set of college class notes (your reference) [1] doesn't mean five is the number. Moreover, Internal conversion is a far more common process in nature than spontaneous fission, so if you're going to mention these in the lede in order of importance, try following your own rules and suggestions. SBHarris 20:48, 1 April 2012 (UTC)
My attempts are only constructive and not to insult. The illustration in the body of the text suggests and most any reference would mention five methods. While positron capture has not yet been witnessed experimentally that does not make it of no interest. As far as anti-matter reactions go, I am sure you know there is positron emission from nuclei. Which process is most common is interesting and I suppose the order in which they are listed might reflect that. Once again the lede is entirely too long. Please try to stay on subject and to not try to smear me by using pejorative references to Star Trek it sounds adolescent. No one of us owns this article.
• Please sign your edits. Use four tildes like this: ~~~~. You've been here since October and it's high time you learned the basics of editing.
• I'm sure your edits were good faith and meant as constructive. However, they were not, as you are adding false information and promoting things of little interest (positron capature) to the lede.
• This lede is indeed too long, but the way to cut a lede is to avoid mentioning trivia. A process that has never been detected (positron capture) is trivia. You can mention it farther down in the article.
• Positron capture is not positron emission. The latter happens commonly, and might be mentioned in the lede as a type of beta decay (technically it is beta-plus decay).
• There are no illustrations "in the body of the text" that show five types of radioactive decay and it would not matter even if there were. There are not 5 types and anybody illustating five types would just show themselves as an ignorant illustator. No, "most any reference" at the college or grad or research level would mention far more than 5 types types of decay, including internal conversion and emission of protons and neutrons.
• References to Star Trek are to point out that science fiction processes like positron capture should be discussed as hypotheticals (since SF does come true, as in the moon landing). We have seen antimatter, but never the complex higher atomic number type we would need to see, in order to see positron capture. One would need at least anti-beryllium-7 (complete with at least one positron in an atomic orbital) to see it. However, such hypotheticals are not lede material, in a lede that is already too long.
• Of course nobody WP:OWNs this article, and I welcome comments from people who actually know enough about radioactive decay to know that there are not "five types" of it, as you keep insisting. That makes me think you haven't even read the article you're editing. Could you please do that? SBHarris 23:37, 1 April 2012 (UTC)

>Actually, I have read the entire article and like most articles on wikipedia it is cluttered, poorly phrased and needs reorganizing, hence my attempts. I am sorry if I gave offense by adding the hypothetical process of positron capture but I find the potential of that process interesting and like to include it just for the sake of completeness. If there are more than five processes of radioactive decay I think they should all be added. Perhaps a table of those dozen or more methods would be the best format with all the products included. But from most of the sources I have read typically only three or five are listed. I wonder, have we had a dispute somewhere in the past as you seem to have taken offense at my being here and making these changes? I think I remember you adding to the article on the Energy-Catalyzer. Sincerely — Preceding unsigned comment added by Zedshort (talkcontribs) 00:40, 2 April 2012 (UTC)

You say you've read the article? So how is it that you somehow missed seeing the very table that you ask for? I guess you didn't read it very carefully, eh? And you're still not signing your messages; I suppose you prefer not to learn? And no, I've never edited Energy Catalyzer. SBHarris 00:52, 2 April 2012 (UTC)

## The general solution to the recursive problem are given by Bateman's equations

Hi,

the general solution to the recursive problem by Bateman's equations does not seem to be correct. The correct equation is shown at http://www.physicsforums.com/showthread.php?t=452474

may be someone can change this, with best wishes Wolfgang — Preceding unsigned comment added by 212.95.7.181 (talk) 12:58, 12 April 2012 (UTC)

I see that Bateman's equations for the general case have now been placed in this article. Should we also note that Bateman's equation for the two-decay case is in the article on Transient equilibrium? I am not certain whether it is the same Bateman's equation. Dirac66 (talk) 16:28, 12 April 2012 (UTC)

Hello all. The formula for Bateman's equations given in the physics forum link above and now on the wikipedia page does not agree with that given in Kenneth S Krane's Introductory Nuclear Physics (Unit II Nuclear Decay and Radioactivity, Chapter 6 Radioactive Decay, Page 173 in my copy). Krane doesn't have the decay constant after the sum term in the Nd formula. If someone could confirm and change I'd be much obliged. [This comment by 86.177.136.35, 24 June 2012]

Strange. If we take the equation now in the article and omit the λi after the sum as you suggest, then the units come out wrong. There will be a λD with units of reciprocal time in the denominator which does not cancel, so ND will have units of time. I don't have Krane's book, but it would seem that either he has erred or you have read him wrong. Perhaps someone can check Ref.8, the article by Cetnar. Dirac66 (talk) 23:04, 24 June 2012 (UTC)
Ah, that may be because of a disagreement between this article and Krane for the Ci equation. In this article there is only one product symbol. Krane has separate product symbols for the numerator and denominator and only the denominator is neglected for i=j. I think this would lead to dimensions T^D on the numerator and T^D-1 on the denominator? Edit: A possible test presents itself: the Bateman equation for the case where D=2 is widely quoted. Derive the Bateman equation for D=2 using the method given here and the method in Krane and compare against another reference source? [This comment also by 86.177.136.35, 24 June 2012]
Aha. The extra factor in Krane's numerator is the λi which the formula now in the article (which cites Cetnar's paper) places before the one product symbol. So the two formulas are equivalent, and the only question is which is the clearer presentation for this article. I vote for the one now in the article since it shows the λi explicitly. (And to sign your posts, click on the four ~ below, 4 lines under the Save page button on the right.) Dirac66 (talk) 01:40, 25 June 2012 (UTC)
Of course! My apologies for being so dense. Thank you for clearing that up. 86.148.86.94 (talk) 22:25, 25 June 2012 (UTC)

## Spontaneous burst

To say that spontaneous radioactive decay occurs in a truly random fashion says nothing. Since science argues that all atoms of a particular element and isotope are truly identical and lack a unique "serial number", all should decay at the very same time or never, for they have no inherent difference that could differentiate among them!

This is in contrast with what we observe. Therefore, there must be a mechanism that individually identifies atoms and "draws lots" from the configuration space of the information universe, to find out which single atom should "spontaneously" decay at any given time and somehow individually "pings" the unlucky one to induce the decay.

Yet, this WP article says nothing about science's effort to find out, how and where the "NIC addresses" of individul atoms are stored in nature, as well as the search to identify the "CAT5 cable" that connects individual atoms to the configuration space, so that they can be pinged to decay if the "Ultimate Dice-thrower" decides its game over for that atom.

Indeed, one can write pretty math equations for truly random spontaneous decay, but that does not explain the physical mechanism by which such is induced to effect. Contrary to the currently fashionable notion that Universe = Mathemathical Information, there are many trans-computable processes, from 3-body problem to turbulent flows, that show matter and energy are more existant than maths!

This mandates a big change in the tone of this article. In fact, treatise on "spontaneous radioactive decay" should become a separate article, because of its deep philosophical, theophysical and experimental implications! 82.131.210.163 (talk) 12:11, 20 April 2012 (UTC)

I was responsible for the mathematics section, and have trimmed it to the more essential content. Hope it is ok. Maschen (talk) 10:53, 15 September 2012 (UTC)
"Random" means unpredictable. We say that radioactive decay is "random" because it is practically unpredictable. That is, We have no scientific theory that predicts when a given nucleus will decay. That does not mean that there is no reason why a nucleus decays: It only means that we don't know the reason.
When you say, "there must be a mechanism that individually identifies atoms and..." That is a theory---your theory. Until your theory is backed up by published, and widely accepted scientific research, it does not belong in a Wikipedia article. 129.42.208.183 (talk) 23:21, 30 January 2014 (UTC)
I frown upon the fact that a small company website which only mentions this issue in passing, without justification or considerations of any kind, is passed off as an authoritative source on the metaphysical interpretation of quantum theory. (See the current 1st citation: http://www.iem-inc.com/information/radioactivity-basics/decay-half-life). 141.39.226.227 (talk) 19:47, 25 April 2015 (UTC)

The mechanism for alpha decay is pretty well understood. Quantum mechanically, you can consider the nucleus as made up of alpha particles, plus an additional odd neutron and/or proton. The alpha particles move at the fermi velocity, trying to escape, but are held back by the nuclear binding (strong) force when they hit the surface. Each time, there is some probability of Quantum tunnelling through the barrier. Statistically, it is many many trials with very low odds, until it escapes. Statistical randomness is a fundamental part of quantum mechanics. Gah4 (talk) 00:42, 13 October 2016 (UTC)

The statistics name for this is memorylessness. That atom doesn't remember how long, it just keeps trying to decay. Gah4 (talk) 08:15, 13 October 2016 (UTC)

## Changing decay rates

Otto Reifenschweiler also observed changes in decay rates in Tritium Reduced radioactivity of tritium in small titanium particles (published in Physics Letters A.)

Claus Rolfs has performed experiments in which he accelerated radioactive decay Half-life heresy: Accelerating radioactive decay

Should these two also be mentioned in the section ? --POVbrigand (talk) 14:13, 7 May 2012 (UTC)

### Evidence against correlations... NOT

Looking to the 3 figures on the reference nr. 29, "Evidence against correlations..." one has to conclude that their claim is not substantiated because a synchronous variation will not show on the graphs. On what basis they assume very unlikely ? quoting: "If the Jenkins proposal were correct, it is very unlikely that the alpha, beta-minus, beta-plus, and electron-capture decays of all radioactive isotopes would be affected in quantitatively the same way. Thus the ratios of counts observed from two different isotopes would also be expected to show annual variations."

79.168.86.244 (talk) 18:14, 10 May 2015 (UTC)

## Rate of radioactive decay influenced by "the Sun".

The theory as I read it was that the rate at which neutrinos pass through a body can influence the rate of radioactive decay of that body. Since the overwhelming proportion of neutrinos passing through the earth (or indeed our easily accessive solar system) is from the sun (an "almost" point source of neutrinos at planetary distances), then obviously any change in the neutrino-producing component of solar activity will change the neutrino flux and hence the radioactive decay rate, as will the distance from the Sun. But to repeat, I have no reference for it, so I'm only including it here as an anecdote.

The other significant part of this is that IF it is true, then with neutrinos passing through solid matter so easily, their effect on radioactive decay will be felt equally on the surface of the earth as it would be inside the earth, and at any depth. 124.184.13.246 (talk) 08:56, 31 August 2012 (UTC)

If you search manganese + radioactive + neutrino on your favorite search engine, you will find many results. There is no theory here. The physicists (Fischbach and Jenkins) who published that took a guess that it might be because of neutrinos. They also took into consideration 30 year old data and considered equipment related anomalies, but how can you do that if you don't have the equipment. The isotope they talk about is Mn 56. They also talk about a solar flare in Dec 13, 2006. Does a solar flare emit neutrinos? I though you get neutrinos when you have beta decay. Anyway, what is so special about a solar flare? Vmelkon (talk) 07:00, 13 October 2013 (UTC)
Radioactive decay, as describe in this article, is without any outside influence, such as shooting particles at the nucleus. Hitting a nucleus with a neutrino counts as an outside influence, though the interaction rate is very low. Gah4 (talk) 00:46, 13 October 2016 (UTC)

## "inaccurate constants"

"Although these are constants, they are associated with statistically random behaviour of populations of atoms. In consequence, predictions using these constants are less accurate for small number of atoms."

I changed this to be somewhat *less* misleading (current edit):

"Although these are constants, they are associated with the statistical behavior of populations of atoms. In consequence, predictions using these constants are less accurate for individual atoms."

- Because deleting it yielded a reversion from another user. The original statement was patently misleading. The problem with small numbers of atoms is not with constants or statistical behavior, but rather with analytical techniques. Except in a few cases where half lives are too long to be very well constrained. So...it really is wrong/misleading. My best guess is that it was put in by a creationist type to cast doubt on the veracity of radioisotopic dating. Geochem. PhD here. I apologize if the format of this talk page edit is not perfect; I do not edit wikipedia with any regularity. Saw this error while perusing the page. Can someone with more clout on here delete the phrase and keep it that way? — Preceding unsigned comment added by Meteoritekid (talkcontribs) 09:21, 12 June 2015 (UTC)

It's a bit clumsily worded, but all the original statement is trying to say is that smaller samples give rise to greater uncertainties and why this is (= the mean of a stochastic process). I don't see the connection to creationist twaddle. As for "individual atoms", that makes it plain wrong - you shouldn't ever use half-lives for individual atoms. Kolbasz (talk) 19:46, 18 June 2015 (UTC)

## Prediction of very long decay rates.

For example, the article on Cadmium states that: "The two natural radioactive isotopes are 113Cd (beta decay, half-life is 7.7 × 10^15 years) and 116Cd (two-neutrino double beta decay, half-life is 2.9 × 10^19 years)." How is such an extraordinarily long decay rate calculated/predicted? 124.184.13.246 (talk) 09:01, 31 August 2012 (UTC)

Try asking the reference desk. Wikipedia:Reference desk/Science --Klausok (talk) 11:20, 31 August 2012 (UTC)

The values are calculated for exponential decay using the measured decay rate -dN/dt = λN, where λ = 1/τ = decay constant. Then λ = -(1/N)dN/dt, and the half-life t1/2 = τ ln 2 = (ln 2)/λ = (N ln 2)/(dN/dt). Dirac66 (talk) 20:08, 15 September 2012 (UTC)

Look for 'isomeric' instead of 'isometric' and if doing this myself is not illegal please reply telling me that i should have done then and thereKhpatil (talk) 14:54, 7 December 2012 (UTC)

Isomeric occurs 3 times in the article, and it is the correct spelling in the context of radioactivity. An isomeric transition in nuclear physics involves the decay of a nuclear isomer with emission of a gamma-ray. Isometric on the other hand has no meaning in radioactivity or nuclear physics which I know of. Dirac66 (talk) 19:15, 7 December 2012 (UTC)

## Are you CRAZY??

Quote: "Primordial nuclides found in the earth are residues from ancient supernova explosions which occurred before the formation of the solar system."

EVIDENCE for this? ANY? EVIDENCE? AT ALL? — Preceding unsigned comment added by 78.156.126.230 (talk) 15:36, 20 December 2012 (UTC)

The Nucleosynthesis article seems reasonably cited. DMacks (talk) 16:08, 20 December 2012 (UTC)
Wikipedia articles should not cite each other (see WP:CIRCULAR), so I will remove the cite of nucleosynthesis. Also, the statement is inaccurate. The lighter nuclides come mostly from big bang synthesis and ordinary steller synthesis. RockMagnetist (talk) 17:02, 20 December 2012 (UTC)
Keep panties on. This is an article on radioactive decay and the statement above clearly was meant to refer to radioactive primordial nuclides, of which there are 34 (Te-130 was erroneously reported radioactive but this was retracted). The lightest of these is K-40 so (with that possible exception, and we don't know the ratio) all are comfortably supernova products not AGB or Big Bang material. That was the point of the initial statement above, which I've now qualified so there can be no misunderstanding. I can't tell if our incredulous IP objector is a red giant star fan or a creationist or what. Finally, referring to another article which is well-referenced from without is hardly a violation of WP:circular. Somebody needs to read WP:SS. The conclusion here isn't central to this article subject and we don't need the burden of refs for it. If you must have one or two, fine, but it's not controversial and is a waste of space. SBHarris 20:41, 20 December 2012 (UTC)
The numbered editor was certainly overexcited, but s/he did point out that this article gave insufficient guidance as to where to find evidence for the statement about supernovae. In my teaching experience, one student who asks a question (even rudely) usually represents a number of others who wonder the same thing. So I thought it best to include a pointer to the more detailed discussion which DMacks had suggested above, in order to help future readers who may ask themselves the same question (hopefully more politely). I thought of a footnote first, but I accept RockMagnetist's correction to a Main article link, which is Wiki style for pointing to more detailed discussion of a (sub)section topic.
As for the restriction to radioactive primordial nuclei, we could say instead (or also) that all primordial nuclei heavier than iron (or nickel?) are from supernova explosions. This would go slightly outside the article topic, but also give more information very concisely.
Sorry, forgot to sign previous comment. Dirac66 (talk) 21:54, 20 December 2012 (UTC)
Thanks for the clarification. It never hurts to be clear. Sbharris, it's ironic you point to WP:SS because in Wikipedia:SS#References it says "Each article on Wikipedia must be able to stand alone as a self-contained unit (exceptions noted herein)." (I don't know what exceptions they are referring to.) It makes sense for each article to have its own citations because other articles can change - and actually Nucleosynthesis isn't particularly well provided with citations. I have never seen an inline citation described as a "waste of space" before. RockMagnetist (talk) 22:54, 20 December 2012 (UTC)
Come to think of it, an external citation doesn't even take up more space than the internal citation that I removed. RockMagnetist (talk) 23:00, 20 December 2012 (UTC)
I was thinking of internal space (what you see in edit mode) but never the less I'll admit you're right that cites are needed everyplace. Even summary sections with main articles need a cite or two. In an article like the United States (summarized by section as heavily as any you'll see) the standard seems to be about one cite per paragraph. So knock yourself out here, but it shouldn't take more than one or two on this particular point.

As to the more interesting question of where heavier-than-iron nuclides come from, it's complicated. About half of the nuclei heavier than iron are s-process nuclei that required some slow cooking somewhere (like AGB stars where free neutrons come from alpha reactions on C-13 and Ne-22) and the rest are r-process nuclides that require a truly titantic neutron flux from some fusion bomb event (like the first H-bombs making Es and Cf out of U and Pu). The sites for this are probably high mass supernovae that aren't quite large enough to make black holes, but have as many free neutrons at the end as possible. Certainly U and Th were made that way, and I'll have to go through the tables to see about the other 30-odd primordial radioactives. Some may be s-process nuclides that haven't been (or at least were not REQUIRED to have been) put through a genuine supernova or even nova, so we'd be liars if we said that all such nuclides heavier than iron had. Apparently red giants make some really heavy nuclides by the s-process, dreging them up and saute-ing them, then eventually puffing them gently out into space to make later generation solar systems like ours. SBHarris 06:02, 21 December 2012 (UTC)

## Diagram Problem

The diagram that shows all the isotopes possible plotted on N vs Z is cool. The diagram just below it that shows how various decay modes transition within the former diagram is cool. what's not cool is that they have contradictory axes; the top diagram has N vertically while the bottom one has Z vertically. The two could make beautiful harmony, if only they could agree. Also, in the result transition diagram, there is a small epsilon associated with beta+, a positron. I've never seen that convention before. Am I just behind the nuclear physics joke curve?  :) SkoreKeep (talk) 06:31, 3 January 2013 (UTC)

Oops, pardon me. The transition diagram is just above, not below, the N/Z plot. — Preceding unsigned comment added by SkoreKeep (talkcontribs) 06:35, 3 January 2013 (UTC)

The lower complicated one is standard. It would be nice if somebody would make a version of the upper one showing transmutations, that had its axes flipped in the same direction. Perhaps you could write a note to the original maker?

The epsilon stands for a a separate process called electron capture that always competes with positron decay, requires less energy, and produces the same transmutation. SBHarris 08:35, 3 January 2013 (UTC)

I could do it (and notify the author)... M∧Ŝc2ħεИτlk 08:39, 3 January 2013 (UTC)
Done, any better? M∧Ŝc2ħεИτlk 08:46, 3 January 2013 (UTC)
I don't see it. Post it here, why don't you ? SBHarris 09:21, 3 January 2013 (UTC)

It was in the article and you only had to refresh, but here it is anyway:

Different types of decay of a radionuclide. Vertical: atomic number Z, Horizontal: neutron number N

M∧Ŝc2ħεИτlk 09:26, 3 January 2013 (UTC)

Wow I cannot get my browser to refresh. Do you know how without logging out? I even see the old version here on the talk page. I DO see the new one when clicking the photo itself and (yes) that's exactly what was needed. Thanks! SBHarris 19:25, 3 January 2013 (UTC)
...No problem, sorry about that. It should be possible to refresh anytime by clicking veiw -> refresh in the menu of the browser or ctrl+r (assuming Windows... not sure on Mac/Linux etc.) M∧Ŝc2ħεИτlk 20:14, 3 January 2013 (UTC)

### Obscure symbol

Is the symbol ε standard? I have never seen it used to mean electron capture before and am more familiar with EC. Anyway ε is not defined in this article, neither in the caption to the figure discussed above, nor in the accompanying text, nor in the tables of different types of decay. Nor is it defined in the article on Electron capture. If we are going to use this symbol in the figure we must define it, but I think it would be simpler to just write out electron capture in the figure itself. Dirac66 (talk) 20:03, 3 January 2013 (UTC)

If it's ok I tweaked the caption of the image, I've never come across the epsilon notation for electron capture either... M∧Ŝc2ħεИτlk 20:14, 3 January 2013 (UTC)
I went ahead and changed "ε" to "EC" for short. Better? M∧Ŝc2ħεИτlk 20:25, 3 January 2013 (UTC)
Yes, EC is better, thank you. The only trouble is that like SBHarris, I only see the new image by clicking on the photo itself to go to the image file. In the article itself I still see the 2009 version with Z on the vertical axis and N horizontal, and refreshing my browser (IE8) does not seem to help. And I also tried Mozilla Firefox and still saw the 2009 version. Can there be a bug in the Wikipedia system for this image?? Dirac66 (talk) 21:58, 3 January 2013 (UTC)
That's really strange... I can see it perfectly... There can't be any internal bugs with the image (else it would not have uploaded). M∧Ŝc2ħεИτlk 22:06, 3 January 2013 (UTC)
I've notified the issue here, comments are welcome. Apologies, M∧Ŝc2ħεИτlk 22:23, 3 January 2013 (UTC)
Actually it depends where I look. I do see the new 2013 version at the top of the image file page File:Radioactive decay modes.svg, but on the article page Radioactive decay, I see the old 2009 version. And I have a PC, but I just got the same results on a Mac belonging to someone who would not have this image cached (because she never looks at physics articles). Dirac66 (talk) 22:45, 3 January 2013 (UTC)

Different types of decay of a radionuclide. Vertical: atomic number Z, Horizontal: neutron number N
Different types of decay of a radionuclide. Vertical: atomic number Z, Horizontal: neutron number N
LOL. Dirac66 has applied ye olde scientific method by using another computer and discovering that image cache-ing is indeed not the problem. I found that the image shows the newer version when simply displayed without the thumb box. From then on, it was a matter of applying controls to isolate the variables one-at-a-time. So, all you science dudes, what is the difference between the two images left and right? Don't look below, it's a puzzle.
An old name for K-capture is epsilon decay (which redirects to electron capture on WP), and if you google "electron capture epsilon" you get some interesting cases where the epsilon is used as a symbol for this decay. The German WP article on electron capture mentions this, but the English one does not.
Interactive Chart of Nuclides uses epsilon, and that is the way I always knew it.Gah4 (talk) 16:45, 3 June 2016 (UTC)
Anyway, size matters. If your thumb box is just an episilon too small for the new fancy image, the computer will find an older version of the same image that WILL fit it. Apparently. That's my hypothesis, and I'm stickin' to it. SBHarris 03:31, 4 January 2013 (UTC)
Well, as long as its visible in the main article to everyone there's no problem. Thanks for clearing that up! M∧Ŝc2ħεИτlk 08:58, 4 January 2013 (UTC)
Yes, it works for me too now. Very good, and I will remember your hypothesis if I ever see the problem in another article. As for epsilon decay, I would guess this name was proposed after Thomson's delta rays, and that physicists later abandoned both letters for the more descriptive modern terms. Dirac66 (talk) 12:27, 4 January 2013 (UTC)
All the table of the nuclides that I know of have Z on the y-axis, and N on the x-axis. That conveniently allows different isotopes of an element to be read in the natural (for most of us) horizontal direction. Both diagrams in 'types of decay' don't work this way. It seems from the description above that this should have been fixed by now. Gah4 (talk) 15:57, 3 June 2016 (UTC)

## 6He and 8He

Look at Isotopes of helium #Table: these isotopes appear to be able simultaneously emit a β and split to two nuclei: 6
2
He
→ 4
2
He
+ 2
1
D
+
e
+
ν
e
. This article does not know such type of decay. Incnis Mrsi (talk) 18:21, 1 February 2013 (UTC)

Could be, but many unusual things happen at the low N, Z end of the table. Gah4 (talk) 00:26, 13 October 2016 (UTC)

## Exact probability distribution of N(t) when it is not assumed continuous

The article says:

"[...] Although the parent decay distribution follows an exponential, observations of decay times will be limited by a finite integer number of N atoms and follow Poisson statistics as a consequence of the random nature of the process. [...]"

I'm pretty sure that the exact distribution is not Poisson's; it is Binomial with parameters ${\displaystyle N_{0}}$ and ${\displaystyle e^{-\lambda \cdot t}}$. I have done the math derivation myself.

GNU/Octave code to simulate problem: http://pastebin.com/UHsrfXu0 (comments in Spanish)

Generated image: http://postimg.org/image/dqe92tzkn/

(In the background you can see a 3D plot (with color) of the Binomial probability function (of N(t)) evolving with time)

 — Preceding unsigned comment added by Francisco Albani (talk • contribs) 08:02, 19 June 2013 (UTC)

The discussion of Poisson statistics was confused. I have corrected it and added a citation. I think your calculation is reproducing the usual derivation of the exponential decay law by considering finite time intervals. RockMagnetist (talk) 14:23, 19 June 2013 (UTC)

## Chain of two decays: 'the equation is not"

From the article:

${\displaystyle {\frac {\mathrm {d} N_{B}}{\mathrm {d} t}}=-\lambda _{B}N_{B},}$
adding the increasing (and correcting) term obtains the law for a decay chain for two nuclides:
${\displaystyle {\frac {\mathrm {d} N_{B}}{\mathrm {d} t}}=-\lambda _{B}N_{B}+\lambda _{A}N_{A}.}$
The equation is not
${\displaystyle {\frac {\mathrm {d} N_{B}}{\mathrm {d} t}}=-\left(\lambda _{B}N_{B}+\lambda _{A}N_{A}\right),}$
since this implies the number of atoms of B is only decreasing as time increases, which is not the case.

I don't think having incorrect equations in an article is a good idea: when people are looking for the formula, they won't pay much attention to the text, and even when they know the last one is wrong, they may accidentally copy it (easy mistake to make: you look up from your paper, see a line that begins with what you just wrote, so you assume that's the one you were copying). I doubt that people who know differential equations would need to be told explicitly why the two terms don't have the same sign, and you certainly don't need an incorrect formula to explain the correct one. Ssscienccce (talk) 19:14, 20 January 2014 (UTC)

I agree that incorrect equations are undesirable and can lead to confusion, so I will now remove the first of the above three equations (with one term only) and the third (with the wrong sign). The correct second equation is still explained very adequately. Dirac66 (talk) 23:58, 20 January 2014 (UTC)

This text, which appears under the "Discovery and History" heading, should be moved to the "Occurrence and applications" section:

The discovery of radioactive elements in the 1890s opened the way for new dating techniques that suggested an age for Earth of several billion years.

That is, assuming it belongs in the article at all. There are numerous applications of radioactivity that are not listed anywhere in this article; Food irradiation, cancer treatment, tracing underground pipes, labeling chemicals for biological experiments, smoke detectors, radio-thermal generators,... That's just scratching the surface. There's no scientific reason why dating rocks and fossils is any more special than any of those. 129.42.208.183 (talk) 23:10, 30 January 2014 (UTC)

## Concerning all the changes I made to the article

You are welcome. Zedshort (talk) 01:37, 30 September 2014 (UTC)

## wikidata

This article just links to a few items on wikidata, I don't know why. Please make attention.--171.232.148.168 (talk) 15:09, 15 June 2015 (UTC)

## Tough LaTeX

The last part of the "half-life" subsection contains a bit of LaTeX {{math|''t'' = ''T''{{sub|1/''n''}}}} that comes out nonsense (as {{{1}}} on all my browsers), and which needs to be fixed. But I don't see anything obviously wrong with it. Can somebody figure out what the second expression needs to be?

Here it is:

Mathematically, the nth life for the above situation would be found in the same way as above—by setting N = N0/n, {{{1}}} and substituting into the decay solution to obtain

Thanks! SBHarris 00:29, 30 September 2015 (UTC)

Is this what you're after? t = T1/n It is HTML, not LaTeX. 00:36, 30 September 2015 (UTC)
I think that's what I'm after indeed, but can you change it the same form as the previous equation N = N0/n? Yes I recognize wiki-markup and HTML whenever I see chevron brackets <>,</>, but the previous expression doesn't use any. So what is it, then? SBHarris 00:45, 30 September 2015 (UTC)
Good catch! The problem was the equality sign. Kolbasz (talk) 07:44, 30 September 2015 (UTC)
Aha, it's a wiki math template thing (the curly brackets suggested a template thing). In this case a wiki-template for texhtml. Bizarre. You had to add a 1= ? Why does WP keep fooling with other systems that work fine? Do they think physicists and mathematicians use wiki-templates? SBHarris 19:45, 30 September 2015 (UTC)
There are good technical reasons to do stuff like embedded equations via templates. But because of the way templates work, certain characters are going to be interpreted as control characters by the template parser - this is pretty much unavoidable. Unfortunately for mathematics though, the syntax for named arguments in MediaWiki happens to be |[name]=[value]. So in the original markup, {{math|''t'' = ''T''{{sub|1/''n''}}}}, the {{math}} template sees that as "do my template magic with the argument ''t'' set to ''T''{{sub|1/''n''}}" because of the equality sign. Since the template doesn't have an argument ''t'', you get a null result of {{{1}}} instead. Adding the 1= makes it interpret it as "do my template magic with argument number 1 set to ''t'' = ''T''{{sub|1/''n''}}" instead, which is what we want ({{foo|bar}} and {{foo|1=bar}} mean the same thing - invoke the template "foo" with the first argument as "bar"). The alternative fix is to escape the offending characters with {{}} instead. Kolbasz (talk) 21:25, 30 September 2015 (UTC)

## Vector version available on Periodic Table Stability & Radioactivity image

Just thought I'd let you know so you can see if it works for you. If there's something that can be improved, please let me know. Thanks, Morgan Phoenix (talk) 04:33, 19 January 2016 (UTC)

## Orders of magnitude

Hello all. There is a quote:

       and range over 55 orders of magnitude in time


In the interest of engaging and exciting those who may not understand what even 7 orders of magnitude of seconds means (human lifetime), perhaps some sort of comparison would drive home the magnitude (ha!) of the 55 orders of magnitude quote? Buzzm (talk) 00:48, 25 January 2016 (UTC)

Perhaps we could compare to the known range of distances. The radius of an atomic nucleus is about 10-13 m, and the radius of the observable universe is about 1011 light-years x 1016 m / light-year = 1027 m, or 40 orders of magnitude larger.Dirac66 (talk) 01:05, 25 January 2016 (UTC)
Well, there is the article Time (Orders of magnitude), which I took the liberty of wikilinking in the lead. You might be able to pull some copy out of that. Kolbasz (talk) 08:32, 25 January 2016 (UTC)

## Nuclear decay

I would like to propose that this article be renamed to Nuclear decay. There is already an article for Particle decay, which can be "radioactive" as well, so I don't feel the title is very accurate, or at least is not very clear as to the distinction between Radioactive decay and Particle decay. I feel it would be cleaner to name this article Nuclear decay, and have Radioactive decay link to it, as that is usually what is meant. — Preceding unsigned comment added by 70.247.169.219 (talk) 18:46, 26 March 2016 (UTC)

Since there is a redirect for it, there doesn't seem to be a big reason for the change. As well as I know it, "radioactive" normally describes atoms, and is also better known to the general public. (That is, muons decay but aren't considered radioactive.) The name could be changed, and the redirect reversed, but that seems to me to be more work than it is worth. Gah4 (talk) 15:51, 3 June 2016 (UTC)

but the mean life and half-life t1/2 have been adopted as standard times associated with exponential decay. Just about everywhere except nuclear decay, 1/e life is used. One exception is optics, where optical absorption is exponential base 10. (Or log base 10 if you do it the other way around.) Gah4 (talk) 00:32, 13 October 2016 (UTC)

## law of small numbers

I tried a link to statistical significance for Although these are constants, they are associated with the statistical behavior of populations of atoms. In consequence, predictions using these constants are less accurate for minuscule samples of atoms. but it was reverted. I had thought about law of small numbers, but that is a disambiguation page, and none of the choices are close at all. There are other ways to lose statistical significance, but not having enough data points is the usual way. Any other suggestions? Gah4 (talk) 06:08, 13 October 2016 (UTC)

## A radioactive source emits its decay products isotropically

A radioactive source emits its decay products isotropically As noted with the recent change, this isn't, in general, true. Assuming that the nuclear orientation in space is isotropic, (that is, statistically independent) then it is naturally true. I suppose it should also be for spin zero nuclides. But nuclides with spin are not isotropic, and when spin aligned, the decay products likely aren't, either. Gah4 (talk) 09:08, 13 October 2016 (UTC)

## Niépce's discovery

It is unclear from the articles on Abel Niépce de Saint-Victor and Henri Becquerel what exactly is Becquerel's discovery with respect to Niépce's work, or indeed if Becquerel deserves credit for the discovery of radioactivity. The current state of the Intro to the History section seems especially inappropriate because Becquerel seems to have had prior contact with Niépce's work.

Somebody should volunteer a bit of research and improve these 3 articles ;) 213.149.51.245 (talk) 07:46, 17 March 2017 (UTC)

Looking at Abel Niépce de Saint-Victor, it mentions uranium salts, but not uranium metal. Looks to me that Henri Becquerel figured out that it was an elemental property. With the advancements in chemistry and physics over those years, it would have been pretty surprising that much earlier. Also, Becquerel used dry plates exposed over days. In the days of wet plate photography, that would have been much more difficult to do. It is easy to look back now, and figure out that with a little more work, Niépce would have discovered radioactivity, but harder to do it from the viewpoint of the day. Gah4 (talk) 19:02, 17 March 2017 (UTC)

Hello fellow Wikipedians,

I have just modified one external link on Radioactive decay. Please take a moment to review my edit. If you have any questions, or need the bot to ignore the links, or the page altogether, please visit this simple FaQ for additional information. I made the following changes:

When you have finished reviewing my changes, you may follow the instructions on the template below to fix any issues with the URLs.

You may set the |checked=, on this template, to true or failed to let other editors know you reviewed the change. If you find any errors, please use the tools below to fix them or call an editor by setting |needhelp= to your help request.

• If you have discovered URLs which were erroneously considered dead by the bot, you can report them with this tool.
• If you found an error with any archives or the URLs themselves, you can fix them with this tool.

If you are unable to use these tools, you may set |needhelp=<your help request> on this template to request help from an experienced user. Please include details about your problem, to help other editors.

Cheers.—InternetArchiveBot 22:46, 12 June 2017 (UTC)