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Beta Decay Question

  1. Aug 30, 2009 #1

    AFJ

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    Hello everyone,

    Newbie here. I am student/enthusiast of science but tend to stay away from physics.
    This excerpt is written by creationist John Woodmorappe concerning accelerated nuclear decay done in the lab, and I was wondering if there was anyone here would like to critique it. I'm not here to debate, but to ask physics questions from you guys.

    "Experimental demonstration of the actual existence of bb decay, however, did not occur until the 1990s. 163Dy, a stable nuclide under normal-Earth conditions, was found to decay to 163Ho, with t½ = 47 days, under the bare-nucleus conditions of the completely ionized state.4 More recently, bb decay has been experimentally demonstrated in the rhenium-osmium (187Re-187Os) system. (The Re-Os method is one of the isotopic ‘clocks’ used by uniformitarian geologists5 to supposedly date rocks.) The experiment involved the circulation of fully-ionized 187Re in a storage ring. The 187Re ions were found to decay to a measurable extent in only several hours, amounting to a half-life of only 33 years.6 This represents a staggering billion-fold increase over the conventional half-life, which is 42 Ga! (Ga = giga-annum = a billion (109) years)."
     
    Last edited by a moderator: Aug 30, 2009
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  3. Aug 30, 2009 #2

    Vanadium 50

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    What's happened in the lab is not exactly "accelerated nuclear decay". They look at a bare nucleus, rather than a nucleus in an atom. The 163Dy atom is stable, because it's energetically unfavorable for it to produce a free electron, becoming a 163Ho nucleus as it does so. However, if I completely strip the nucleus of its electrons, a process that takes several MeV of energy, then the 163Dy nucleus can decay into a 163Ho+66 ion - i.e. it would have one bound electron. This electron is bound quite deeply - the binding energy is about one-eighths of an electron mass.

    The point isn't that rates of nuclear processes can't be changed. They can. The point is that it takes energies comparable to these nuclear processes to do it. Except in certain unusual environments, like exploding stars, these energies aren't available.
     
  4. Sep 1, 2009 #3

    AFJ

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    Yes, thank you. I have gotten that before, so you have helped to confirm it. Okay I wonder if you might help me in half-lives. I looked up the equation one time and it's like no-way dude. I'm into cytology, biology, chemistry and stuff like that, so really it's kind of like a hidden mystery to us physics and mathematics peasants (lol). But no one disputes half lives--not even creationists.

    So, I'm thinking philosophically today and in algebra. If x is all the uranium 238 in the world right now, and z is all the lead 206, and y is all U238 decay to lead 206. Then x-y=z.

    But then that would mean there was U238 in the Hadean period when the earth was formed but no lead 206. Now please hear me out.

    Then this would be quite strange for the pattern in the elemental table which increases in relative increments in atomic number and weight. We would have to treat the entire quantity of the respective elements as is treated in each dated rock--that all the lead 206 in the rock is a result of U238 decay.

    According to this inductive assumption (because really we don't know) we must then accept ultimately that all lead 206 is a result of nuclear decay. This I would find far too coincidental that the only incremental increase that was skipped in the elemental table was the one that came by only nuclear decay, along with rubidium and argon (and the other dating elements), while the rest were formed in space after the big bang.

    Now, my question--how DO they figure the actual half-life of U238. This is someone who is stupid asking okay. Do they measure it with a geiger counter then multiply? Is there some sure undisputed law of physics which governs half-life calculation of U238? I have'nt been able to find the answer in physics layman's terms.
     
    Last edited: Sep 1, 2009
  5. Sep 4, 2009 #4

    PeterDonis

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    That's not quite how rocks are dated; the procedure is more complex, precisely in order to avoid having to assume that all the lead-206 (or whatever other final isotope is involved) is the product of radioactive decay.

    Check out the http://www.talkorigins.org/faqs/isochron-dating.html" [Broken] on the talk.origins site for a good explanation of how it's actually done. Your further question is actually independent of this, but I wanted to mention it.

    Basically, yes; you take a known mass of some radioactive isotope (i.e., a known number of atoms to start with), and count how many decays there are in a given period of time (i.e., how many atoms out of the original total decay). Because there are such a huge number of atoms in a macroscopically sized sample (on the order of 10^24 of them in a kilogram of U-238), even a very short period of time compared to the half-life is enough to get a large number of decay counts and, with an accurate enough counter, to show a change in the count rate (for example, the half-life of U-238 is about 10^17 seconds, so in one second we would expect about 10^7 counts from a kilogram of U-238; after a few minutes we would have more than 10^9 counts, and the number of counts per second would have decreased by about 10^2, enough to detect the change in rate). Then you can do a curve fit and show (1) that the decay curve is exponential (within the limits of measurement accuracy), and (2) what the time constant (half-life) is.
     
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  6. Nov 14, 2011 #5

    AFJ

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    Thanks Peter,
    I know it's been a while. I saw I might have gotten a warning. I appreciate your help on how they actually do the counts. I'm not trying to debate, because I am really not a physics student. I do like chemistry though, so I do understand a little in that area. But particle physics is a little past me.

    I had another question. I was reading something from Ernest Rutherford the other night. http://web.lemoyne.edu/~giunta/ruthsod.html#IV I was interested in the half life graph on a residue that was a filtrate from thorium, which he called ThX. It actually had a positive Y axis curve. He called this curve a "recovery" curve. He compared this curve to a "decay" curve in another sample of thorium hydroxide. It was curving down in a negative axis direction. You can find the graph in the section entitled, "IV. The Rates of Recovery and Decay of Thorium Radioactivity."

    Question #1. Does anyone know what Rutherford's ThX turned out to be (you might know this as early 1900's research)? It was obviously something he isolated from thorium.

    Question #2. Why is there a positive y axis curve that follows a "recovery half life?" This "ThX" actually increased radioactive activity over time. While the thorium hydroxide slowed down.
     
  7. Nov 14, 2011 #6

    Astronuc

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    Thorium decay series here:
    http://hyperphysics.phy-astr.gsu.edu/hbase/nuclear/radser.html#c2

    See also this classic:
    The chemistry of the radio-elements, Volume 1, Issue 2 by Frederick Soddy

    Thorium X = Ra-224, according to the half-life of 3.7 days,

    http://www.nndc.bnl.gov/chart/reCenter.jsp?z=88&n=136 (try zoom 2, then zoom 1)

    Radiothorium = Th-228
    UX1 = Th-234, the daugher of U-238 by alpha decay.
    UX2 = Pa-234, from beta decay of Th-234
    UY = Th-231, the daughter of U-235 by alpha decay
    Mesothorium I = Ra-228
    Mesothorium II = Ac-228

    Ref: An. N. Nesmeyanov, Radiochemistry, Mir Publishers, 1974
    and, Radioactivity, Van Nostrand's Scientific Encyclopedia, 5th Edition, Van Nostrand Reinhold Co., 1976


    See the old names here - http://web.lemoyne.edu/~giunta/isotopes.html - which once can confirm with the above references.


    When a short-half life nuclide has a longer-lived decay product, then the short-lived nuclide will decay while the decay product will increase in activity, until the short-lived parent decays so much that the activity of the longer-lived decay product decreases.
     
  8. Nov 17, 2011 #7

    AFJ

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    Thanks Astronuc,
    I was wondering about that possibility. The only problem I'm having is, if the theory prediction is 100% correct, Rutherford should have seen a decay curve first, then a recovery, because the curve he would have seen was being affected by the radioactivity of the new daughter isotope(s). Do they see a decay and recovery curve from one sample at times?

    I will read Soddy. Kind of been in the organic chemistry thing, and running a business. Wished I could gulp it all down, but there's only 24 hours in a day lol. Thanks.

    One other observation--if you look at Rutherford's graph, you see little day long curves that go in the opposite direction, in both the thorium hydroxide (which decayed) and the thorium nitrate precipitate, "ThX," (which increased). These curves resemble transition curves in chemistry, which could indicate the radioactivity is exicted or diminished by chemical reactions. Rutherford was doing all kinds of different experimentation, including shaking the thorium in ammonia, ignition, etc.

    The little curves are removed in the second graph to show "syncronizing" decay and recovery half lives. This might sound crazy, but since I'm not a professional, I can say this. I still suspect things such as pressure (i.e. fission is initiated by an implosion in atom bomb/ cavitation) and certain chemical reactions may affect the decay rate, but it's just a hypothesis I will have to research more.
     
    Last edited: Nov 18, 2011
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