This process initially seemed mysterious, because the energy of the emitted alpha particle is much lower than the energy needed to shoot an alpha particle into the nucleus.
The particular decay channel than makes americium useful for this application is an "alpha decay," in which a very heavy nucleus decays by spitting out a helium nucleus: two protons and two neutrons tightly bound together. When heavy smoke particles enter the region between the plates, they also get ionized by the radiation, but are too heavy to be deflected into the plates, and the current flow drops, triggering the alarm. One of the two main processes used to make modern smoke detectors uses a small amount of radioactive americium to ionize air molecules, producing a steady flow of current between two plates inside the detector. This has a surprisingly direct application to an everyday technology, though, in the form of a smoke detector. This is bizarre to contemplate with everyday objects- a dog isn't going to quantum tunnel through a fence into the neighbors' yard (though a bad dog might classically tunnel through the dirt under the fence.).
#WIERD PHENOMENA FREE#
But if there's another free region on the far side of the barrier, quantum mechanics tells us it has some (tiny) probability of turning up there, as if it passed through some sort of magic tunnel from one side to the other. This ought to make it turn around, in the same way that a ball thrown into the air can't rise above the height where its potential energy due to the Earth's gravity equals the kinetic energy with which it was thrown.
#WIERD PHENOMENA PLUS#
We talk about this in terms of passing an energy barrier: a particle that's in motion with some total energy (kinetic plus potential) comes to the edge of a region where interactions with other stuff would create a potential energy greater than the total energy it has available. Quantum Tunneling: One of the most surprising predictions of quantum physics, in terms of our normal intuition for how physics should work, is the phenomenon known as "tunneling," in which quantum particles have some probability of turning up in places that, classically speaking, they just don't have enough energy to reach.
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