Dr Mark Marais

May 2025

more processes leading

to forms of radiation

Pair Production,

Internal Conversion, Electron Capture

Dr Mark Marais - 2025

• understand and describe radiation interaction with matter

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• complete nuclear reactions involving pp, ic, ec

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let’s aim to

Dr Mark Marais - 2025

Dr Mark Marais - 2025

Electron Positron Pair Production

Pair production is the production of a particle-antiparticle pair from a pulse of electromagnetic energy traveling through matter, usually in the vicinity of an atomic nucleus.

Dr Mark Marais - 2025

https://makeagif.com/gif/pair-production-OWrIRb

Electron Positron Pair Production

Dr Mark Marais - 2025

The rest mass energy of an electron is 0.511 MeV, so the threshold for electron-positron pair production is 1.02 MeV. For x-ray and gamma-ray energies well above 1 MeV, this pair production becomes one of the most important kinds of interactions with matter. At even higher energies, many types of particle-antiparticle pairs are produced.

Internal Conversion

Dr Mark Marais - 2025

• unstable nucleus transfers its excited energy to an inner orbital electron - in K or L shell
• the electron is then ejected from its orbital
• higher orbital electron falls into the vacancy left by electron in the lower orbital
• the space left by the higher orbital electron itself is filled by an electron from a yet, higher orbital - and so on, thus, an electron cascade ensues
• every time an electron drops to a lower orbital, an x-ray, or Auger electron, is released

Internal Conversion

Dr Mark Marais - 2025

Electron Capture

Dr Mark Marais - 2025

• parent nucleus may capture one of its orbital electrons and emit a neutrino
•  process leaves a vacancy in the electron energy level from which the electron came
• that vacancy is either filled by the dropping down of a higher-level electron with the emission of an x-ray
• or by the ejection of an outer, Auger electron
• this is a process which competes with positron emission and has the same effect on the atomic number
• most commonly, it is a K-shell electron which is captured, and this is referred to as K-capture

This is a schematic that grossly distorts the picture relative to a scale model of the atom. The electron orbit radii are tens of thousands of times the diameter of the nucleus.

Electron Capture

Dr Mark Marais - 2025

Auger electron

-ray

Electron Capture

Dr Mark Marais - 2025

⁷₄Be + ⁰_-1e → ⁷₃Li + ν

examples…

+ ν