Radioactive Decay and Nuclear Reactions

Conservation of mass and charge are used when writing nuclear reactions. For example, let s consider what happens when uranium-238 undergoes alpha decay. Uranium-238 has 92 protons and 146 neutrons and is symbolized as After it emits an alpha particle, the nucleus now has a mass number of 234 and an atomic number of 90. 

Because the atomic number of the nucleus is 90, the element becomes thorium, Th. The overall nuclear reaction can be written as 

Notice that in this equation mass is conserved, 238 = 234 +4, and charge is conserved, 92 = 90 + 2. In a chemical reaction, reactants are transformed into products. In a nuclear reaction, the terms parent and daughter correspond to reactants and products, respectively. In our example, the U-238 was the parent that decayed into the Th-234 daughter. 

During beta decay a neutron is transformed into a proton. If Th-234 were to emit a beta particle, it would be transformed into protactinium-234 according to the equation  

both mass and charge are conserved. Gamma emission often accompanies both alpha and beta decay, but because gamma emission does not change the parent element it is often emitted when writing nuclear reactions. 

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