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A Linear enercy transform (LET) and momentum

  1. Dec 13, 2016 #1
    I have some understanding of Liner Energy Transfrom (LET), but when I compare it with other terminologies such as momentum, then it gets little contradicting.
    For example, I know that if talk about particles and ions, then a gold ion (AU) has much higher LET than an Iron particle (Fe). And therefore AU has a much shorter penetration distance than Fe. AU gives up much of its energy in a short distance.
    But what is confusing to me is that "AU" is a much heavier particle than "Fe", and when I think about this subject in terms of momentum, then AU has a higher momentum than Fe, since it is heavier.
    So, in terms of classical physics and the subject of momentum, then AU, should travel a higher distance than Fe, since it has higher momentum!!!
    Can someone please explain the flaw in my explanation, and what is it that I am not understanding correctly?

  2. jcsd
  3. Dec 14, 2016 #2


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    Hello Rudy, :welcome:

    Can't find Liner Energy Transfrom and can't find Linear enercy Transform either. Can find linear energy transfer and it has to do with "energy loss of the charged particle due to electronic collisions".
    So it applies to Au ions and to Fe ions (not to Fe particles -- !?).
    If you have a reference we might be able to comment. There are more factors than just the atomic mass that influence interaction cross section.
  4. Dec 14, 2016 #3
    I am sorry, I had misspelled it. Yes, I was talking about Linear Energy Transfer. Please look at the table below that I have included.


    I am not sure but I believe that "Range" is inversely proportional to the square of atomic number (Z^2), correct me if I am wrong please.
    I understand that an ion with higher LET will have a shorter range, since it will give off more energy per unit of length. But the part that doesn't make much intuitive sense is when I start thinking about this in terms of classical physics 101 (e.g. momentum).
    If we have two objects at the same speed, but one weighs more, then it will travel a longer distance. And this make intuitive sense, because it is heavier.
    Now, isn't it that Au ion is heavier than Fe ion, so shouldn't we expect for Au to travel a longer distance?! Because to me Au has higher momentum.
    This is the part that I get confused. I would appreciate if I get a clarification to my confusion.

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  5. Dec 14, 2016 #4


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    What about the second column in your (?) table ? Is that MeV/nucleon ? Or per neutron ? Is there a reference for the table ?
  6. Dec 15, 2016 #5
    I really think my question is very standard question. The specific really doesn't matter....
    Look at this for example:

    You can find a similar plot in almost any reference material. So, the general rule is that the heavier the ion, then its LET is higher.....
    So, I don't understand why this is the case?! Can you explain please?
    Because as I said, to my understanding, I think that the heavier the ion is then the more momentum it has, therefore I am expecting for it to travel farther, before coming to stop, which would imply that it should have a lower LET....!!!!
    But I know this is not the case, and in reality it is the opposite..... The heavier the ION, then higher the LET... Why?
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