α (Alpha) Particles

In 1898 Ernest Rutherford, a young research student in Cambridge University, England, discovered that radioactive substances emitted two different kinds of rays which he named α rays and β rays after the first two letters of the Greek alphabet. The negatively charged β rays turned out to be beams of electrons, and the positive α rays were found to be beams of Helium 4 nuclei. Helium 4 nuclei, consisting of 2 protons and 2 neutrons, are thus also called α particles. (Later Rutherford observed a third kind of radiation he called γ rays, which turned out to be high energy photons.) We have seen that β rays or electrons are emitted when a neutron sheds mass by decaying into a proton in a β decay reaction. But where do the α particles come from?
A nucleus with an excess of electric potential energy can lose energy by converting one of its protons into a neutron in an inverse β decay reaction. This, however, is a relatively rare event. More commonly, the number of protons is reduced by ejecting an α particle. Why the nucleus emits an entire α particle or Helium 4 nucleus, instead of simply kicking out a single proton, is a consequence of an anomaly in the nuclear force. It turns out that a Helium 4 nucleus, with 2 neutrons and 2 protons, is an exceptionally stable, tightly bound object. If protons are to be ejected, they come out in pairs in this stable configuration rather than individually.

مواضيع ذات صلة

خواص الذرات

البنية الإلكترونية للذرات

الذرات

Linear systems

Confined waves, with natural frequencies

The reflection of waves

Einstein’s laws of radiation

The Boltzmann law

Energy levels

The size of an atom

Bremsstrahlung

Synchrotron radiation