Quantum tunneling of the quantum mechanics
|Automatic translation||Updated December 16, 2012|
To understand the quantum tunneling, it must return to the wave-particle duality of quantum mechanics.
This uncertainty and indeterminacy that are intrinsic to the theory and thus to subatomic particles, constituents of matter. In addition to the uncertainty about the locality, quantum mechanics tolerate the existence of entangled states, i.e. at the quantum level several spatially separated objects can form a single quantum object, which react together, it is important to foresee the tunnel effect. In summary, in the quantum world, the subatomic particles, objects can be both here and there, in a state or another. We can not determine the status of a 'quantum system' except by observing it, which has the effect of destroying the state in question.
Image: Image taken with a scanning tunneling microscope. This image is about 5 nanometers shows a copper surface where the copper atoms are contained within an enclosure quantum of 48 iron atoms. The circular barrier iron has a radius of 71.3 Angstroms (71.3 x10-10) meter. We see the electrons behave like waves.
Scanning tunneling microscope (STM)
The STM is widely regarded as the instrument that opened the way for nanotechnology, the science of semiconductor, molecular biology and many other scientific disciplines.
The scanning tunneling microscope has preceded all other scanning probe microscopes, more modern, such as atomic force microscope (AFM) and near-field optical microscope.
Image: The scanning tunneling microscopy requires the use of a sample of material, conductor of electricity, but if the sample is an insulator, then used the atomic force microscopy. Omicron VT-AFM XA (AFM Atomic Force Microscope - STM Scanning Tunneling Microscope)
We now come to the tunnel effect. At any wave is associated a particle, is called the wave-particle duality. In classical physics, the particle can not escape its nucleus, if its kinetic energy is greater than the potential energy of its link with the nucleus. For an electron to pass the limit is the potential energy of the link, that is the electromagnetic force which keeps it in its enclosure. For the proton, the cross is limited to the potential energy of its link, i.e. the strong nuclear force that keeps sticking to other nucleons. In quantum physics, it happens otherwise, the particle is represented by its wave and this wave is not completely captive inside the enclosure around the nucleus, it can go to the other side of the barrier of the potential even if its kinetic energy is less than the potential energy. Of course the probability of escape from the nucleus is extremely small, but it exists. Moreover, this property of quantum mechanics explains the disintegration of matter. Everything happens as if the wave digging a 'tunnel' through the barrier of potential to move across on the other side of the slope, and released from the electromagnetic or nuclear glue, electrostatic repulsion takes over, this is known as the tunnel effect of quantum mechanics. Thus the electron can pass through the vacuum of the atom, leaving the metal that contains it and reach another conductive metal. But the image of the quantum transition is more subtle, it is comparable to the image of a ghost passing through a wall. A part of proton or electron cloud pass the barrier of the potential while the other remains in the atom 'halved' the cloud will recover on one side or the other, as if there was a nano tunnel. Proton and the electron cloud will therefore pass or not according to its kinetic energy. In summary, more the barrier of the potential is high more the thickness to cross is large and more the nucleus 'long-lived'.
Indeed, this explains the half-life times of isotopes (see note below). The half-life times are very long for some isotopes of chemical elements, such as uranium-238 (4.5 billion years), uranium-234 (240 000 years) or radium 226 (1600 years). For cons, the intense radioactivity of radon shortens its half-life, it is 3.8 days for radon-222 used in radiotherapy. If we represent by a diagram, the potential energy of a particle, like the electron or the proton bound to a nucleus, one can imagine a hill much lower than it away the center of attraction. We deduce that more the radioactivity is strong, less the tunnel to dig will be long (picture opposite). But the wave did not stop at a particular point, it spreads into the barrier, although its amplitude decreases rapidly if the potential barrier is very thin, the wave passes through like a ghost and spreads to the next point of attraction. This is a direct consequence of the probabilistic nature of the wave associated with the evolution of a quantum particle, because even if the wave function of the particle through the barrier weakened, there is a nonzero probability to pass there through.
Image: Wave representing a particle in the nucleus. The wave associated with the particle is not fully shown in the center of the nucleus but slightly overlaps the other side of the barrier of the potential with extremely small probability. More the barrier of the potential is high, more the thickness to across is great. Wikipedia.