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Radioactive Decay

Atoms with unstable nuclei can undergo radioactive decay to become atoms which are more stable than their parent atoms. In the process, different types of particles are emitted. We will discuss some of the important ones that you have to know from the MCAT point of view.
Alpha emission:
Alpha emission (a) is a low-penetrating emission. It is actually helium nucleus and is often represented as

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An example of radioactive decay of radium-226 is given below:

image\15733 ch 13.png


As you can see, the resulting atom has both mass number and atomic number changed. The atomic number decreases by 2, and the mass number decreases by 4.
Beta emission:
Beta particles (β) are emissions having medium level penetration. They are fast traveling electrons. As a result of beta emission, the resulting atom will have an increase in the atomic number by 1. There is no change in the mass number. In the process, there is also a proton formation from the neutron inside the nucleus, along with the electron formation. In the following example, thorium-234 decays to protactinium-234 by emitting a beta particle.

image\25332 ch 13.png

Positron emission:
Positron emission (β+ ) is the positive counterpart of an electron emission. A positron has the exact mass of an electron, but has a positive charge. During this event, a proton is converted to a neutron and a positron. The product of a positron decay will have an atomic number less than that of the decayed atom by one unit. There is no change in mass number.
Electron capture:
As a result of electron capture, a proton is converted into a neutron. The electron is usually captured from the innermost shell of the atom. The atomic number of the product will be one less than that of the original atom. There is no change in mass number.
Gamma emission:
Gamma (γ) emissions or gamma rays, as they are commonly referred to, are highly penetrating and dangerous emissions. They are high frequency electromagnetic rays. Gamma rays travel at the speed of light. The resulting product atom has the same atomic and mass numbers as those of the parent atom from which the gamma rays are emitted. Gamma rays have no charge.

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