Gamma decay consists of the emission of pure electromagnetic energy; no particles are emitted during this process, and it is symbolized by equation;00g. After beta, positron, or alpha decay, the nucleus is left in a high-energy state, and at this point it will often emit gamma rays, which allows it to relax to its lower-energy ground state. Since gamma rays do not affect charge or mass, they are often not included in nuclear equations.
Positron emission occurs when an atom becomes more stable by emitting a positron 01e, which is the same size and mass as an electron but has a positive charge. This process converts a proton into a neutron; the positron is emitted and the neutron remains behind in the nucleus, decreasing the atomic number by 1.
Often the emission of an alpha or a beta particle creates another radioactive species, which undergoes further radiation/emission in a cascade called a radioactive series. Notice that in the course of all of these types of radioactive decay, neither protons nor neutrons are either created or destroyed: this is due to what’s known as the law of conservation of matter, which states that mass is neither created nor destroyed. So when you see radioactivity equations on the SAT II Chemistry test, one of the most important things to remember is that the sum of the mass numbers and the sum of the atomic numbers must both be equal on both sides of the equation.
Example
Write the equation for the alpha decay of radium-221.Write the equation for the beta decay of sulfur-35.
Explanation
The radium-221 atom has atomic number (A) = 88 and mass number (Z) = 221. When an alpha particle is emitted, the atomic number is reduced by 2 and the mass number is reduced by 4. The atomic number of the resulting atom is 86, so the element created as a result of this radioactive decay is radon-217.
The sulfur-35 atom has an atomic number of 16 and a mass number of 35. When it undergoes beta decay, the atomic number is increased by 1 and the mass number remains the same. The atomic number of the atom created is 17, so the atom is chlorine-35.
Fission and Fusion
There are two main types of nuclear reactions: fusion and fission. In fusion reactions, two light nuclei are combined to form a heavier, more stable nucleus. In fission reactions, a heavy nucleus is split into two nuclei with smaller mass numbers. Both processes involve the exchange of huge amounts of energy: about a million times more energy than that associated with ordinary chemical reactions. In either case, if the new particles contain more stable nuclei, vast quantities of energy are released.
Nuclear power plants rely on fission to create vast quantities of energy. For example, U-235 nuclides can be bombarded with neutrons, and the result is lots of energy, three neutrons, and two stable nuclei (Kr-92 and Ba-141). The three neutrons formed can collide with other U-235 atoms, setting off a chain reaction and releasing tons of energy.
