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| Radioactive Decay or Disintegration |
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| A radioactive nucleus or element emits an alpha or a beta particle and gets converted into a new nucleus or element. |
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| The process of destruction of the original nucleus during the formation of new nucleus due to radioactivity is called Radioactive decay or disintegration. |
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When a  - particle is emitted by a nucleus, the mass of the nucleus decreased by 4 units and the charge by 2 units. |
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| In general if a radioactive element X of mass number A and atomic number Z emits an alpha particle, a new element Y (called the daughter product) is formed with mass number (A - 4) and atomic number (Z - 2). Hence the element changes into a new element with properties similar to those of an element 2 places earlier in the periodic table. The change can be represented by the following equation. |
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| For example: |
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Radium - 226 decays with the emitting an
a - particle and forms an inert gas radon  The transformation is given by |
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| Both the mass (226 - 4 = 222) and the charge (88 - 2 = 86) must be conserved. |
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Radon is unstable and also decays with the emission of an  - particle: |
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Radium emits  - rays as well as  - particle but the emission of  - rays has no effect on the charge or on the mass of the nucleus. During the emission of  - particle or  - particles the nucleus is rearranged with a decrease in energy; the surplus energy is given off in the form of  - rays. Polonium - 218 is also an  - particle emitter. |
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So far only  - particle emission has been considered. |
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| When a b- particle is emitted there is effectively no change in the mass of the nucleus because the mass of the
b - particle is very small. However, the charge increased by one unit. |
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If an element  emits  -particle and the new element Q has mass number A and atomic number Z+1. |
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| Thus the element changes into a new element with properties similar to those of an element one place later in the periodic table. |
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| For example: |
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Lead-214 decays with the emission of a  - particle. |
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The equation for charge is 82 - (-1) = 82 + 1 = 93. But the nucleus is supposed to be made up of protons and neutrons only, so how can a  - particle be emitted? A neutron in the nucleus has changed into a proton by emitting an electron. This leaves one more proton and one less neutron in the nucleus. Thus the nucleon number does not change, but the proton number increased by one. |
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(When a  - particle is emitted the number of protons increases by one hence the atom is +vely charged. It acquires the deficit electron from the atmosphere and becomes neutral) |
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| The products of the disintegration of radium atoms. |
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| Half-life |
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| Radioactive decay is a random process and different radioactive substances decay at different rates. The time taken for the number of particles emitted per unit time to drop to half of its original value is known as the half-life of the substance. In this time half of the atoms of the original material will have given off radioactive particles and changed into another substance. This new substance may or may not be unstable. |
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