Alpha and beta particles in gas ionization

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Discussion Overview

The discussion centers around the comparative ionization abilities of alpha and beta particles in gases, exploring the underlying reasons for the differences in their effectiveness. It touches on concepts related to particle velocity, scattering cross-sections, and the nature of electric forces between charged particles.

Discussion Character

  • Technical explanation, Conceptual clarification, Debate/contested

Main Points Raised

  • Some participants propose that alpha particles are better at ionizing gases than beta particles due to their higher energy loss per unit distance (dE/dx).
  • One participant suggests that this is related to the scattering cross-section, which varies with the velocity of the particles, indicating that alpha particles, having lower velocities than beta particles, result in a higher cross-section for electron scattering.
  • Another participant questions the notion of "better" by asking for clarification on what is meant by the term.
  • It is noted that the force between two negative charges is equivalent in magnitude to the force between a negative and a positive charge, though the direction differs, which may influence ionization dynamics.
  • Participants reference additional factors, such as the charge of the particles, as contributing to the differences in ionization capabilities.

Areas of Agreement / Disagreement

The discussion contains multiple viewpoints regarding the effectiveness of alpha versus beta particles in ionization, with no consensus reached on the specific reasons or implications of their comparative abilities.

Contextual Notes

Participants have not fully defined the parameters of "better" in the context of ionization, and there are unresolved aspects regarding the influence of particle velocity and charge on ionization efficiency.

scientifico
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Hello, why alpha particles are better at ionizing gases than beta particles ?
shouldn't the negative particles repel more electrons ?

thanks
 
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scientifico said:
Hello, why alpha particles are better at ionizing gases than beta particles ?
shouldn't the negative particles repel more electrons ?

thanks

Try to be more specific. What do you mean by "better"?
 
I assume "better" refers to the fact that dE/dx is much higher.

This is basically because Rutherford-like scattering has a cross-section that varies as v^{-2} (because high-velocity particles aren't deflected very much). MeV alphas have much lower velocities than MeV betas, and therefore the cross-section for an electron to scatter off of them is much higher.

There are lots of other factors involved (e.g., the square of the charge), but this is the dominant one in this comparison. For more detail: http://en.wikipedia.org/wiki/Bethe_formula
 
scientifico said:
shouldn't the negative particles repel more electrons ?
The magnitude of the force between two negative charges is the same as the force between one negative and one positive charge - the direction is different, but that does not matter here.
For the comparison alpha<->beta, see bcrowell's explanation.
 

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