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Attenuation Coefficient

  1. Apr 23, 2010 #1
    During my A level physics class we were discussing the attenuation coefficient of x-rays and a question arose that I can't find an answer to anywhere. If someone could help answer what effect physical state (ie gas/liquid/solid ect) has on the attenuation coefficient of x-rays it would be much appreciated? The only simplistic answer that arose was that perhaps because of the spacing difference between the molecules/atoms in other states this may cause "lesser" physical states to have lower attenuation coefficients. But then argueable to a certain extent this can be resolved by lowering the temperature, raising the pressure and keeping the volume constant to allow different states in the same area to exist.

    Any thoughts?
     
  2. jcsd
  3. Apr 23, 2010 #2
    I don't know the exact details of the radiation-matter interaction of x-rays so this is probably not accurate.

    But I would think there are two main considerations. Simplest is the absorber concentration, which should appear as a direct factor in the attenuation coefficient. Much more complex is the effect of chemical bonds on the electronic energy levels in the absorber, a mechanism which (I imagine) will strongly affect absorption and is dependant on the type of bonding and hence state of matter of the absorber.
     
  4. Apr 23, 2010 #3
    And since chemical bonding between different states varies with the particular substance a general trend can't be assessed. Or so I assume as I lack the relevant chemical knowledge. The only other thing that springs to mind is that, if the concentration is the same for say both solid and liquid, does the structure of the matter have an effect? eg, in certain substances a solid will have a set lattice with a particular. perhaps crystalline, orientation and in it's liquidus state, it will have a seemingly random structure with no common orientation.
     
  5. Apr 23, 2010 #4
    The size of crystal lattices are of the same order as the wavelengths of Xrays so this form of electromagentic radiation intracts strongly with solid materials.
    I think Xray diffraction is still on the A level syllabus?
     
  6. Apr 23, 2010 #5
    Yea defiantly, I discussed this with my physics teacher between posts as I had a lesson in between posts, I forgot to mention that I wasn't restricting my question to just x-rays as my last post was more general, due to the fact that I began discussing a scenario of a lead rod which was heated at one end. Meaning that one end for example would have a martensitic structure whilst the other end had a structure say formed of Austenite. Resulting in the discussion of what kinda of structures in say solely solids would have what effects on the coefficient. And obviously, the effect of the orientation of a structure. Since going back to the original question, liquids lack such defined structures.
     
  7. Apr 23, 2010 #6
    Density of the material used to shield X-rays plays an important role in shielding.
     
  8. Apr 23, 2010 #7
    In this scenario providing the mass stays constant, the density is the same. That was the point of eliminating that factor to ask the question I wanted.
     
  9. Apr 23, 2010 #8
    Martensite and Austenite are alloys of iron and carbon eg in steel.

    I'm very glad to hear you are discussing things with your teacher.

    Way to go.

    PS Try to frame a clear question as your subsequent posts have got me muddled.
     
  10. Apr 23, 2010 #9
    Yea, sorry. That's the problem when I discussed the same problem with two different sets of people. And yes, you're right about iron and carbon. Unfortunately I have a bad habit of saying half of what I mean or think, which on an online MB, that leaves everyone guessing and scratching there heads at what I mean. In future, I will bare in mind my messiness.
     
  11. Apr 28, 2010 #10
    I don't know if orientation affects x-ray absorption because it is electronic- maybe you are even wondering into quantum mechanics here with uncertainties in where the electrons are (very complex and generally unsolvable for large molecules). For a solid in a lattice this might be true, but I agree with you in a liquid and gas these will not lead to any macroscopic dependency on orientation.

    All I can say is it sounds very complicated, and if you adjust thermodynamic parameters to somehow ensure absorber concentration is uniform across all three states, you are still left with a very hard problem I think!
     
  12. Apr 28, 2010 #11
    Most certainly agree with you there. Think I may keep this somewhere and revisit it when I get to university and then see if I can have another go when my knowledge and mathematical/physics skills are that bit higher.
     
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