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I What is inverse kinematics?

  1. Apr 12, 2016 #1
    My question is what inverse kinematics is.
    Many scientists are using inverse kinematics for measuring cross-section or something.
    For example, suppose that we measure cross section of 14N+p->n+14O.
    We can use N14 for beam and p for target. But, we can also do the other way.
    When they use inverse kinematics, what advantages can they have?
  2. jcsd
  3. Apr 12, 2016 #2


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    There are a few reasons to do an experiment in inverse kinematics.

    The first is beam/target availability. Some nuclei are more appropriate to use as targets than as beams, or vice-versa. A good example is if one of the nuclei are radioactive - then generally that must be the beam.

    The second reason is that of kinematics. If you have a heavy beam on a light target, everything is going to be forward focused, which can be beneficial for efficiency purposes, for example, if you want to wack everything into a mass spectrometer. Also, at high energies, doing an experiment in inverse kinematics ensures that all the products will leave the target, so you have a lower threshold.
  4. Apr 12, 2016 #3
    Thank you for answering my question.
    But, I wonder again that at high energies, all the products will leave the target, so you have a lower threshold.
    I wonder how it can be done and why we can have a lower threshold.
  5. Apr 12, 2016 #4


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    Imagine you want to study the reaction at an energy of e.g. 100 keV, and for simplification let's assume the reaction does not need or release energy.
    You can shoot a proton with an energy of 100 keV on nitrogen, then you get (typically) a neutron with about 5 keV and oxygen with 95 keV. At those energies both get stopped really fast, so you need an extremely thin target, and even then most of your products will lose some notable energy in the material.
    You can also shoot nitrogen with an energy of 1.4 MeV on a proton, then you typically get a neutron with an energy of 100 keV and oxygen with an energy of about 1.3 MeV. That allows them to get out of the target much more easily.

    At tens of GeV, everything will leave the target, sure, but the point of measuring the threshold energy is to have energies as low as possible.
  6. Apr 12, 2016 #5
    Thank you for answering my question.
    I can understand it. Thanks
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