Quantum tunnelling/alpha decay

In summary, the Phd student asked about how an alpha particle overcomes the strong nuclear force in alpha decay and was told about the concept of quantum tunneling. However, the probability of quantum tunneling is highly dependent on the relevant energies, making only certain isotopes of an element radioactive. This is because the elements we consider stable have a very low probability of decaying. Additionally, the explanation of tunneling based on the uncertainty principle is not entirely accurate and the wave nature of matter provides a better explanation for the phenomenon.
  • #1
tmv3v
17
0
Im a uni student and a Phd student asked me in an alpha decay,
the helium nuclei is bounded by the strong nuclear force, how do the alpha particle overcome such a strong force and shoot out? And he told me it is because of quantum tunnelling.
To my understanding quantum tunnelling is an effect that due to Heisenberg's Uncertainty principle, a particle can have a distribution of energy, which there is a very low but finite probability that a particle can have enough energy to go over the energy barrier.
But I then don't understand why only certain isotopes of an element is radioactive since for those stable elements, quantum tunnelling will still take place. Someone could explain to me:D? Thanks!
 
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  • #2
The probability for quantum tunneling to occur is extremely sensitive to the relevant energies (the binding energy of the nucleus, the energy levels occupied by its components, etc.) Technically all elements besides hydrogen are indeed radioactive in that they have a non-zero probability of spontaneously breaking apart. However, the elements we classify as 'stable' have a such a low probability of decaying that their half lives are very long (often many orders of magnitude longer than the age of the universe).
 
  • #3
Ah ok so everything is radioactive and having one more or less neutron will change the probability of quantum tunneling dramatically!
Thank you!
 
  • #4
You're welcome. I would also add that the uncertainty principle explanation of tunneling isn't really correct. For one thing, uncertainty in momentum doesn't necessary imply uncertainty in energy. Also, you can have tunneling even when the energy of a system is precisely defined. The wave nature of matter is a better explanation: the wavefunction associated with a particle is a continuous, twice differentiable function (since it has to satisfy the Schrodinger equation) which means it can't abruptly stop if the external potential is well-defined everywhere. So, the particle's wavefunction can't just stop at the barrier, and since it continues through it (though falling off exponentially with distance) there is a non-zero probability of the particle being on the other side.
 

1. What is quantum tunnelling?

Quantum tunnelling is a phenomenon in which a particle can pass through a barrier even though it does not have enough energy to overcome it. This is possible because at the quantum level, particles behave as both waves and particles, and can exist in multiple places at once.

2. How does quantum tunnelling work?

Quantum tunnelling occurs when a particle approaches a barrier and has a small probability of passing through it. This happens because of the uncertainty principle, which states that the position and momentum of a particle cannot be known simultaneously. The wave-like nature of particles allows them to pass through the barrier, even though they do not have enough energy to do so in classical physics.

3. What is alpha decay?

Alpha decay is a type of radioactive decay in which an alpha particle (two protons and two neutrons) is emitted from the nucleus of an atom. This process occurs in unstable atoms, as a way to become more stable by releasing excess energy.

4. What causes alpha decay?

Alpha decay occurs in atoms that have an excess of protons and neutrons in their nucleus. This excess makes the atom unstable, and the nucleus tries to reach a more stable state by emitting an alpha particle. This process is governed by the strong nuclear force, which holds the nucleus together.

5. How is alpha decay related to quantum tunnelling?

In alpha decay, the alpha particle is confined within the nucleus due to the strong nuclear force. However, according to quantum mechanics, there is a small probability that the alpha particle can tunnel through the potential barrier and escape the nucleus. This is similar to the concept of quantum tunnelling, where particles can pass through barriers that they do not have enough energy to overcome.

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