Input Energy of Radioactive Decays

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Discussion Overview

The discussion revolves around the input energy required for radioactive decays, including alpha decay, spontaneous fission, and cluster decay. Participants explore the concept of energy barriers and quantum mechanical tunneling as it relates to these processes.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • Some participants propose that radioactive decays require energy to separate nucleons within a nucleus.
  • Others argue that decays must overcome an energy barrier through quantum mechanical tunneling, contrasting this with fusion processes.
  • A participant requests further clarification on the nature of the energy barrier and the probability of decay.
  • There is mention of tunneling phenomena, such as field emission and the photoelectric effect, as examples of particles overcoming energy barriers.
  • Some participants note that the energy released during decay is related to, but not directly equivalent to, the energy barrier that must be overcome.
  • Questions arise regarding the conditions under which decay occurs, particularly in scenarios where energy may not be readily available.
  • It is asserted that decay can still occur due to quantum tunneling, even when classical energy thresholds are not met.

Areas of Agreement / Disagreement

Participants generally agree that radioactive decays involve overcoming energy barriers through quantum tunneling. However, there are differing views on the implications of energy availability and the nature of the probability associated with decay processes.

Contextual Notes

Some assumptions regarding the nature of energy barriers and the conditions for decay are not fully explored, leaving room for further discussion on these topics.

A M
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TL;DR
We know that nuclear fusion doesn't occur under normal conditions (e.g. in a helium balloon).
Because for the fusion of even the lightest elements (like hydrogen isotopes), fairly high energy is needed to 'break' the electrostatic repulsion barrier; although the released energy might be much higher.
But how about some radioactive decays? (α, SF, CD, ...)
Don't we need energy to to separate some nucleons of a radioactive nucleus?
 
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Yes, decays also need to overcome an energy barrier. This is done through quantum mechanical tunneling through the energy barrier. The difference in relation to fusion is that you only have a single radioactive particle and even a small probability per time of decaying will eventually lead to a decay. For fusion, the particles also need to meet up and when they do they have a single chance of tunneling through the energy barrier with very low proability.
 
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Orodruin said:
Yes, decays also need to overcome an energy barrier.
Would you please explain a little more?
 
For example of tunnelling where it is electrons that tunnel: we can observe both field emission and photoelectric effect. There is a definite energy barrier (as demonstrated by photoelectric effect) and yet electrons do have a small chance of getting through without any additional energy (as shown by field emission).
 
Orodruin said:
Yes, decays also need to overcome an energy barrier. This is done through quantum mechanical tunneling through the energy barrier. The difference in relation to fusion is that you only have a single radioactive particle and even a small probability per time of decaying will eventually lead to a decay.
What does this probability come from? The higher energy they need to overcome that barrier or sth more complicated?
 
Yes. We had this discussion and even a graph for alpha decays in the previous thread. The energy released is not directly the same as the energy barrier but the two are closely linked.
 
Thank you for the reply, but I haven't quite understood.
What if the nuclei were in a situation without that amount of energy available? The decay wouldn't occur?
 
A M said:
Thank you for the reply, but I haven't quite understood.
What if the nuclei were in a situation without that amount of energy available? The decay wouldn't occur?
Yes it would. It is quantum tunnelling. In quantum mechanics a particle can pass an energy barrier that it classically would not be able to.
 
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