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Why is Technetium unstable?

  1. Jul 25, 2013 #1
    I've viewed lots of questions on the internet of this nature and almost all of them dodged the question or simply gave an answer tantamount to "because it is".

    I already know that Technetium is unstable and radioactive.

    What exactly on an atomic level prevents Technetium from being stable when all of the other adjacent nearby elements are just fine. What makes 43 protons unstable, but 44 and 42 protons perfectly fine?
     
  2. jcsd
  3. Jul 25, 2013 #2
    Well, I barely know any chemistry, but I can say that 44 and 42 protons are perfectly fine likely because they are even numbers.

    There seems to be a very prevailant trend that even numbered atomic numbers have more stable isotopes. I have no idea why, sorry. It suggests that only some "special" number of neutrons makes an odd numbered element fit together in a way that makes it stable, and maybe that special number for the technetium nucleus either can't exist, or is just crazy rare, or that possibility would be unstable anyway for other reasons (like the ratio of protons to neutrons, since that is a factor.)

    Instead of looking at in terms of technetium being unstable, I view it as only having one less stable isotope than most other odds. It seems a little less weird that way.

    Sorry I can't give you an answer, I can just offer some "connections." I too am interested in an answer on this.
     
    Last edited: Jul 25, 2013
  4. Jul 25, 2013 #3

    mfb

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    Staff: Mentor

    Wikipedia has a good overview.

    The reason for the odd/even difference:
    Protons and neutrons have spin 1/2, each energy level can be occupied by two of them (one with "spin up", one with "spin down"). Therefore, even numbers of protons (or neutrons) fit nicely into low energy levels, while the next proton (or neutron) has to go to the next higher energy level. This makes it easier to undergo beta decay - the nucleus gets rid of the additional proton (or neutron).
    Therefore, elements with an odd number of protons have less stable isotopes. Technetium is just a fluctuation where "barely stable" becomes "not stable any more".
     
  5. Jul 26, 2013 #4
    Technetium is an odd element.

    For an odd element, mostly odd isotopes are stable. For an element, both even and odd isotopes are stable. Also odd isobars rarely have more than one of them stable while even isobars often have several.
    Listing elements by the number and specifics of their odd isotopes - omitting the even:
    1: 1 - 1
    2: 1 - 3
    (All 5 isobars are unvound)
    3: 1 - 7
    4: 1 - 9
    5: 1 - 11
    6: 1 - 13
    7: 1 - 15
    8: 1 - 17
    9: 1 - 19
    10: 1 - 21
    11: 1 - 23
    12: 1 - 25
    13: 1 - 27
    14: 1 - 19
    15: 1 - 31
    16: 1 - 33
    17: 2 - 35 and 37
    18: 0
    19: 2 - 39 and 41
    20: 1 - 43
    21: 1 - 45
    22: 2 - 47 and 49
    23: 1 - 51
    24: 1 - 53
    25: 1 - 55
    26: 1 - 57
    27: 1 - 59
    28: 1 - 61
    29: 2 - 63 and 65
    30: 1 - 67
    31: 2 - 69 and 71
    32: 1 - 73
    33: 1 - 75
    34: 1 - 77
    35: 2 - 79 and 81
    36: 1 - 83
    37: 1 - 85
    38: 1 - 87
    39: 1 - 89
    40: 1 - 91
    41: 1 - 93
    42: 2 - 95 and 97
    43: 0
    44: 2 - 99 and 101
    45: 1 - 103

    So, does the pattern of the number of stable odd isotopes reveal any shell effects? Element 43 is like 18 in being between 2 elements with 2 stable odd isotopes each and not having any itself. But 30 is the same position does have 1 stable odd isotope.
     
  6. Nov 15, 2016 #5
    All these still don't answer the question
     
  7. Nov 15, 2016 #6
    As mfb said, Wiki has the answer. Specifically:

    "...for every number of nucleons from 95 to 102, there is already at least one stable nuclide of either molybdenum (Z=42) or ruthenium (Z=44). For the isotopes with odd numbers of nucleons, this immediately rules out a stable isotope of technetium, since there can be only one stable nuclide with a fixed odd number of nucleons. For the isotopes with an even number of nucleons, since technetium has an odd number of protons, any isotope must also have an odd number of neutrons. In such a case, the presence of a stable nuclide having the same number of nucleons and an even number of protons rules out the possibility of a stable nucleus."
     
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