Dr Who Posted June 11, 2012 Share Posted June 11, 2012 Why is it that some radioactive decay trees go through stable isotopes? For example manganese-54 can beta-negative decay to iron-54 (a stable isotope), which then double beta-positives to chromium-54. The same thing occurs with potassium-40, which beta-negative decays to calcium-40 (a stable isotope), which then double beta-positives to argon-40. Moreover, I would have expected calcium-40 to be very stable since it is doubly magic. Link to comment Share on other sites More sharing options...
swansont Posted June 11, 2012 Share Posted June 11, 2012 Fe-54 and Ca-40 are listed as stable and neither are listed as known double-beta-decay nuclei. Where are you finding this information that they decay? Link to comment Share on other sites More sharing options...
imatfaal Posted June 11, 2012 Share Posted June 11, 2012 The decay tree for Manganese 54 is widely reported as Electron Capture to Chromium 54 (plus an electron neutrino) - wiki does list Beta minus and Beta plus but note the very low percentages; such that most datasheets list the EC decay route a 100%. The decay to Iron54 is .0003% and the decay of Iron 54 to Chromium 54 is very very slow, to an extent that it can almost be ignored (especially as only theoretical possibility at present). 54Fe is observationally stable, with a branching theory that it decays to 54Cr, with a half-life of more than 3.1x1022 years via double electron capture (2β+) I guess you are reading from periodictable.com I am not sure I would completely trust a site that has any percentage adding to more than 100! 1. Stanford datasheet 2. Isotopes of Manganese 3. Isotopes of Iron 4. Periodictable.com Link to comment Share on other sites More sharing options...
Dr Who Posted June 12, 2012 Author Share Posted June 12, 2012 Fe-54 and Ca-40 are listed as stable and neither are listed as known double-beta-decay nuclei. Where are you finding this information that they decay? The decay tree for Manganese 54 is widely reported as Electron Capture to Chromium 54 (plus an electron neutrino) - wiki does list Beta minus and Beta plus but note the very low percentages; such that most datasheets list the EC decay route a 100%. The decay to Iron54 is .0003% and the decay of Iron 54 to Chromium 54 is very very slow, to an extent that it can almost be ignored (especially as only theoretical possibility at present). I guess you are reading from periodictable.com I am not sure I would completely trust a site that has any percentage adding to more than 100! 1. Stanford datasheet 2. Isotopes of Manganese 3. Isotopes of Iron 4. Periodictable.com I am getting the information from "The NUBASE evaluation of nuclear and decay properties" (which was published in Nuclear Physics A and according to google has been cited 602 times). I have also used periodictable.com as it gives the same information, just in a graphical format. In terms of the values being more than 100%, I assumed this was for presentation, since 100% looks significantly better than 99.9997%. Also, I know we are talking very low percentages here, but from this paper, it implied that these radioactive decays do occur and thus I was wondering how come they are able to go through, what is referred to as a stable isotope. Link to comment Share on other sites More sharing options...
swansont Posted June 12, 2012 Share Posted June 12, 2012 Also, I know we are talking very low percentages here, but from this paper, it implied that these radioactive decays do occur and thus I was wondering how come they are able to go through, what is referred to as a stable isotope. Perhaps some people are interpreting a decay probability in the life of the universe of 1 - e^-(10^-12) or so as being essentially zero. Link to comment Share on other sites More sharing options...
Dr Who Posted June 13, 2012 Author Share Posted June 13, 2012 Perhaps some people are interpreting a decay probability in the life of the universe of 1 - e^-(10^-12) or so as being essentially zero. Are you saying that these decays have never been observed, i.e. they are only theoretically possible? If so, why have they been included in what appears to be an experimental paper? Link to comment Share on other sites More sharing options...
swansont Posted June 13, 2012 Share Posted June 13, 2012 Are you saying that these decays have never been observed, i.e. they are only theoretically possible? If so, why have they been included in what appears to be an experimental paper? 40Ca −34846.27 0.21 STABLE (>5.9 Zy) 0+ 01 99Be64 T IS=96.941 156; 2β + ? … 54Fe −56252.5 0.7 STABLE 0+ 01 IS=5.845 35; 2β + ? I'd say that question mark is an indication that it's only theoretical. Another clue is the listing of > 5.9 Zy for the half-life of Ca-40. Z = Zetta = 10^21 Link to comment Share on other sites More sharing options...
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