The fractional energy loss of charged particle per radiation length

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SUMMARY

The discussion focuses on the fractional energy loss of charged particles, specifically electrons and positrons, per radiation length in lead. It highlights the unexpected behavior of energy loss at low energies, particularly around 5MeV, where the fractional energy loss exceeds 1, indicating that ionization losses are disproportionately high compared to other processes. The conversation also questions the contribution of Bremsstrahlung at 1MeV, which remains significant despite the low energy of the electron. The source of this data is from CERN's documentation on particle interactions.

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  • Understanding of particle physics concepts, particularly ionization and radiation length.
  • Familiarity with the principles of energy loss mechanisms in materials.
  • Knowledge of Bremsstrahlung radiation and its implications in particle interactions.
  • Ability to interpret scientific diagrams and data plots related to energy loss.
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  • Research the mechanisms of ionization energy loss in materials, focusing on lead.
  • Study the principles of Bremsstrahlung radiation and its effects at various energy levels.
  • Examine the concept of radiation length and its significance in particle physics.
  • Explore the implications of fractional energy loss exceeding 1 in particle interactions.
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Physicists, researchers in particle physics, and students studying radiation interactions, particularly those interested in the behavior of charged particles in materials.

CzTee96
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The figure usually has a caption that goes like this: "Fractional energy loss per radiation length as a function of electron or positron energy in lead," but I do not fathom is at (1/E)dE/dx =1, it seems like the particle is losing all of its energy at ~7MeV by ionisation. Therefore, I would not expect the other contributions will happen. However, the diagram seems to suggest that even at very low energy we still have losses through other processes and most bizarrely the "fractional loss" through ionisation even went greater than 1 at very low energy. For example, it seems like at 5MeV we have the "fractional energy loss per radiation length" is 1.2E! What does this even mean? Is it trying to say that the ionisation is "relatively higher" than the other processes, and the fraction of all the processes is not normalised to 1?
Also, I would expect at such a low energy the electron will lose all its energy via ionisation, but why there is still a contribution from the Bremsstrahlung at 1MeV, which is around 0.6?Source: https://cds.cern.ch/record/2315747/
 
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Look at the units. It's per radiation length - if one loses 6% of the energy in 0.05X0, where is that on your plot?
 
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