Radioactivity
The year 2006 was observed as the 100th anniversary of the discovery of radioactivity. During these years, the untiring work and research of scientists have resulted in a wide range of uses for radioactivity, all the benefit of mankind..
Radioactivity is the spontaneous disintegration of an unstable nucleus accompanied by the emission of energetic particles or protons.
Understanding the nucleus of an atom
Nucleus
Gieger-Marsden Experiment
In 1906, Rutherford noticed that many alpha particles could pass through a very thin sheet of mica as if the mica was not there. Two of his assistants, Geiger and Marsden, investigated the scattering of alpha particles by thin gold foils as shown in figure above. They found that most of the alpha particles passed through the gold foil with little or no deflection. However, to their amazement, a very small but significant number of alpha particles bounced back from the gold foil.
Rutherford proposed in 1911, a nuclear model of the atom as shown in Figure below, the atom has a very small dense core called the nucleus. All the positively charged particles and most of the mass of the atom are contained in the nucleus. The electrons move in orbits around the nucleus.
Rutherford-Model
Nucleons
The particles in a nucleus are called nucleons. There are two types of nucleons, protons and neutrons. A proton is a positively charged particle. It carries a charge of +e, where e = 1.6 x 10 power of -19 C.
The number of protons in a nucleus is known as the proton number, Z.
The nucleon number, A gives the total number of protons and neutrons in a nucleus. It is also known as the mass number.
The number of neutrons in a nucleus is A+Z.
Nuclide notation
Nuclide is a type of nucleus with a particular proton and nucleon number.
Isotopes
The nuclide is used to specify an atom or a nucleus with a particular proton-neutron combination. The number of protons in each atom of a particular element should be the same. However in some cases, the neutron numbers maybe different. Isotopes are atoms of an element which have the same proton number but different nucleon numbers.
Radioactivity-Nuclear
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