Tunnevaikutus

Tunnevaikutus, or tunneling effect in English, is a quantum mechanical phenomenon where a particle can pass through a potential energy barrier, even if its kinetic energy is less than the potential energy of the barrier. Classically, this would be impossible, as a particle would need enough energy to overcome the barrier.

In quantum mechanics, particles are described by wave functions, which represent the probability of finding the particle at a certain location. Even when a particle encounters a potential barrier, its wave function does not abruptly drop to zero at the barrier. Instead, it decays exponentially within the barrier. If the barrier is not infinitely wide or high, there is a non-zero probability that the wave function will extend beyond the barrier, meaning the particle has a chance of appearing on the other side.

The probability of tunneling depends on several factors, including the height and width of the barrier, as well as the mass of the particle. Thicker and higher barriers, and more massive particles, result in a lower probability of tunneling.

The tunnevaikutus is not just a theoretical curiosity; it has significant practical implications. It plays a crucial role in various phenomena and technologies, such as alpha decay in radioactive nuclei, the operation of scanning tunneling microscopes (STMs), and semiconductor devices like tunnel diodes. The STM, for instance, relies on the tunneling of electrons between a sharp conductive tip and a sample surface to image atomic-scale features.