A The fractional energy loss of charged particle per radiation length

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The discussion revolves around the fractional energy loss of charged particles, specifically electrons and positrons, in lead as a function of their energy. Participants express confusion over the graphical representation, particularly the notion that fractional energy loss can exceed 1 at low energies, suggesting ionization losses are disproportionately high compared to other processes. There is also a query regarding the presence of Bremsstrahlung contributions at low energies, which seems counterintuitive given the expectation that ionization would dominate. The importance of understanding these contributions and their normalization in the context of radiation lengths is emphasized. Overall, the conversation highlights the complexities of energy loss mechanisms in charged particles and the need for clarity in their graphical representations.
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?
 
Theoretical physicist C.N. Yang died at the age of 103 years on October 18, 2025. He is the Yang in Yang-Mills theory, which he and his collaborators devised in 1953, which is a generic quantum field theory that is used by scientists to study amplitudes (i.e. vector probabilities) that are foundational in all Standard Model processes and most quantum gravity theories. He also won a Nobel prize in 1957 for his work on CP violation. (I didn't see the post in General Discussions at PF on his...

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