1
$\begingroup$

I'm studying the classification of radiation in 'Radiation Physics for Medical Physicists' by Ervin B. Podgorsak.

At some point in the explanation of the two-step process of ionization for indirectly ionizing radiation it reads:

'(...) photons release either electrons or electron/positron pairs, neutrons release protons or heavier ions (...)'

Can photons really release electrons? Doesn't that violate the conservation of electric charge?

Secondly, can neutrons release heavier (charged) particles than the proton? Doesn't that violate the conservation of energy? Can it really decay into something that is heavier and, thus, has more rest energy?

I haven't found any source in here or elsewhere that'd validate or refute both these statements.

What's your take on this? My take is that this part of the book is incorrect.

$\endgroup$
6
  • 2
    $\begingroup$ I suspect you are misreading the text, and that the high-energy photons cause these actions when they hit the target atoms, and similarly shooting neutrons at a nucleus stimulate release of various particles $\endgroup$ Aug 12 at 14:45
  • 1
    $\begingroup$ Can you quote the whole paragraph instead of just pay off a sentence? $\endgroup$
    – The Photon
    Aug 12 at 14:46
  • $\begingroup$ Thank you for the clarification @CarlWitthoft. I may be misreading it! $\endgroup$ Aug 12 at 14:47
  • $\begingroup$ The whole sentence reads: "In the first step a charged particle is released in the absorber (photons release either electrons or electron/positron pairs, neutrons release protons or heavier ions)." $\endgroup$ Aug 12 at 14:48
  • 1
    $\begingroup$ You might be misreading "release": it does not mean "decay". It probably means: "impacting something (a nucleus?) they chip off e- s, e+ e- pairs, etc...". So no charge or, significantly, fermion number is violated if the remnant ion is ignored. as in place. Likewise, a neutron missile may chip off something heavier off a large nucleus, or... Anyway, protons can produce neutrons too, via nuclear spallation. $\endgroup$ Aug 12 at 14:49
3
$\begingroup$

At some point in the explanation of the two-step process of ionization for indirectly ionizing radiation it reads:

'(...) photons release either electrons or electron/positron pairs, neutrons release protons or heavier ions (...)'

The word "ionization" means the physical process of getting a neutral atom,( an atom with a number of electrons in orbitals about the positive nucleus), ionized. i.e. an electron is kicked off the atom, leaving a positive ion. So the "release" by the photon means that enough energy has been exchanged with the atom, in order to get an electron out of an energy level orbital. Electron positron pairs can be generated by photons in the field of a nucleus, see this .

It is sloppy terminology, particularly

neutrons release protons or heavier ions (...)'

It is true that a neutron hitting the nucleus of an atom may kick out a proton, and this proton will be an ion,until it catches an electron. It is also true that a neutron may start the breakup of a nucleus, which means new lighter atoms will form that, until neutralized by electrons, will be positive ions, but it is a bad way of describing the processes.

$\endgroup$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.