Quantum tunneling can occur with a variety of subatomic particles, including protons, neutrons, electrons, and others. It applies to particles that have quantum properties and can be observed in a variety of contexts. Here are some of the particles and phenomena in which tunneling can occur:
1. *Electrons: Electron tunneling is the most common example, especially in electronic devices such as **tunnel diodes* and *tunnel effect transistors. It also occurs in the phenomenon of **scanning tunneling microscopy (STM)*, which allows mapping of surfaces at the atomic scale.
2. *Protons: Protons can also undergo tunneling. A classic example is quantum tunneling in stars, where protons inside atomic nuclei can “cross” the Coulomb barrier, allowing nuclear fusion. This is fundamental to the process that powers the Sun and other stars.
3. *Neutrons*: Although neutrons are neutral particles (without charge), they can also tunnel. One example is the behavior of neutrons in certain materials, such as in nuclear reactions. They can pass through potential barriers in nuclear reactors.
4. *Photons: These are particles of light (without mass), they can undergo a type of tunneling in phenomena such as **evanescence* or the *optical tunnel effect*, where light passes through a dielectric barrier.
5. *Ions*: Ions, which are atoms or molecules that have gained or lost electrons, can also experience tunneling. This can occur in chemical reactions, especially in electron transfer phenomena.
6. *Alpha particles: In **alpha decay* processes, the nucleus of an unstable atom emits alpha particles (two protons and two neutrons). Quantum tunneling is crucial to explain how these alpha particles “escape” from the atomic nucleus, even though, according to classical physics, they do not have enough energy to overcome the nuclear barrier.
7. *Quarks*: Although quark tunneling is a more theoretical concept, quarks (the constituents of protons and neutrons) can also undergo tunneling under certain conditions within nuclear interactions, although this is a field of advanced research and less applied to directly observable phenomena.
In short, quantum tunneling can occur with any particle that follows the laws of quantum mechanics and can encounter an energy barrier. This includes particles with or without electric charge, particles with or without mass, and even composite particles such as alpha particles (made of protons and neutrons). This phenomenon is a manifestation of the probabilistic properties of the quantum world.
