Beta radiation involves the transformation of a neutron into a proton through the emission of an electron, or the reverse process, the transformation of a proton into a neutron through the emission of a positron similar to an electron, but with a positive charge. Gamma radiation is simply a loss of energy by the nucleus, a desexcitation ; much like an emission of light or X-rays by energetic atoms. Alpha and beta decays almost always leave the nucleus in an excited state.
Gamma emission brings the nucleus down to a more stable energetic state. Alpha and beta decays are often difficult to occur. They can be very slow processes. The lifetimes of some radioactive nuclei are long for the clocks of the infinitely small.
They can also be for us. The lifetimes of natural radioactive alpha emitters such as uranium or thorium can extend to several billions of years. These emissions change the composition of the nucleus, therefore the nature of the atom. Alpha and beta radioactivities do not transform lead into gold, but transmute matter like other nuclear reactions do. Access to page in french. EN FR.
Alpha Beta Gamma rays Radioactive nuclei emit three types of radiations Physicists have called the three types of radiations emitted by nuclei, alpha , beta and gamma , the three first letters of the greek alphabet. Map of decay modes This map of the various nuclei is coloured with regards to the types of decay they undergo.
Rutherford began his graduate work by studying the effect of x-rays on various materials. Shortly after the discovery of radioactivity, he turned to the study of the -particles emitted by uranium metal and its compounds.
Before he could study the effect of -particles on matter, Rutherford had to develop a way of counting individual -particles. He found that a screen coated with zinc sulfide emitted a flash of light each time it was hit by an -particle.
Rutherford and his assistant, Hans Geiger , would sit in the dark until his eyes became sensitive enough. They would then try to count the flashes of light given off by the ZnS screen. It is not surprising that Geiger was motivated to develop the electronic radioactivity counter that carries his name. Rutherford found that a narrow beam of -particles was broadened when it passed through a thin film of mica or metal.
He therefore had Geiger measure the angle through which these -particles were scattered by a thin piece of metal foil. Because it is unusually ductile, gold can be made into a foil that is only 0. When this foil was bombarded with -particles, Geiger found that the scattering was small, on the order of one degree. These results were consistent with Rutherford's expectations. He knew that the -particle had a considerable mass and moved quite rapidly. He therefore anticipated that virtually all of the -particles would be able to penetrate the metal foil, although they would be scattered slightly by collisions with the atoms through which they passed.
In other words, Rutherford expected the -particles to pass through the metal foil the way a rifle bullet would penetrate a bag of sand. One day, Geiger suggested that a research project should be given to Ernest Marsden , who was working in Rutherford's laboratory.
Rutherford responded, "Why not let him see whether any -particles can be scattered through a large angle? Many years later, reflecting on his reaction to these results, Rutherford said: "It was quite the most incredible event that has ever happened to me in my life. It was almost as incredible as if you fired a inch shell at a piece of tissue paper and it came back and hit you.
Rutherford concluded that there was only one way to explain these results. He assumed that the positive charge and the mass of an atom are concentrated in a small fraction of the total volume and then derived mathematical equations for the scattering that would occur.
These equations predicted that the number of -particles scattered through a given angle should be proportional to the thickness of the foil and the square of the charge on the nucleus, and inversely proportional to the velocity with which the -particles moved raised to the fourth power.
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