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I Stopping Power and Range units for charged particles

  1. Feb 13, 2018 #1
    Dear members,

    The unit of stopping power is given as Mev/cm in many sources. It is easy to comprehend this unit.The mass stopping power, which is the total energy lost per path length by a charged particle, is defined as the division of MeV/cm to the density of investigated material, g/cm3, and unit of mass stopping power is MeVcm2/g. This unit is also logic due to the addition of the density parameter of the material.

    The range of a charged particle is obtained by an integration operation related to the stopping power so the unit of range will be cm when MeV/cm is adopted, and will be g/cm2 when MeVcm2/g is adopted.

    I am trying to compare the calculation results of stopping power and range data obtained for a number of elements and composites where I got the results in both unit sets as;

    i. Mev/cm for the stopping power and cm for the range
    ii. MeVcm2/g for the stopping power and g/cm2 for the range

    I would like to express the stopping power in the units of MeVcm2/g since the density effect is important regarding the materials studies and the range in the units of cm since I would like to express this phenomena as lenght to make it more understandable.

    The problem arise here. The high stopping power should result less particle range and vice versa. If the unit of MeVcm2/g is used for the stopping power, which takes account the density of the material, and cm for the range, which does not takes account the density of the material, "high stopping power should result less particle range and vice versa" situation is disappearing. Also, due to the density effect I suppose, the material with the highest stopping power and the particle with the highest range differs when using different unit sets.

    So, what are your comments? Which unit set is more useful, sensitive and logic when comparing different charged particle ranges in various materials and those materials stopping power? What should I do?

    Please do add your valuable comments and share your knowledge.

    Best regards,
  2. jcsd
  3. Feb 13, 2018 #2


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    I got a case of MEGO while reading your post. However the stopping power of any material is obviously affected by the density of the material. Usually this is presented as Mev/cm for the given material, with density built into the calculation.
  4. Feb 13, 2018 #3


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    It does not disappear, it is shifted to a later step.

    A range of 20 g/cm2 gives you 20 cm in water, but tens to hundreds of meters in water vapor.
  5. Feb 13, 2018 #4
    Thanks for your reply and yea, I should not have lost myself while writing.

    If MeV/cm has built in density affect then why there exist another unit obtained by dividing MeV/cm with density ?
  6. Feb 13, 2018 #5
    I understand that situation yet representing the range in cm unit while using MeVcm2/g for stopping power will not result in the mentioned relationship. I need to use g/cm2 for range.

    So, you suggest me to use the unit set ii and give the metric range when asked or what is your suggestion? Please explain.
  7. Feb 14, 2018 #6


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    I don't understand what you are asking in your last post.

    You have two different options.
    • Give the stopping power and range in a density-independent way (MeV cm2/g and g/2), then you can use the same formula for gases and liquids, and it will often apply as approximation to a wide range of materials.
    • Give the stopping power and range in a density-dependent way (MeV/cm and cm), then this number is valid for a specific material in a specific form only, but it is easier to use if you happen to have this material.
    Both options have advantages and disadvantages, and both options are used due to that.
  8. Feb 15, 2018 #7
    Thanks a lot for your kind and patient behavior.
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