Now that we are familiar with the basic particles emitted by radioactive materials, let's examine some natural nuclear reactions - that is, nuclear reactions that occur spontaneously in nature, as opposed to nuclear reactions that people set up in laboratories. An element that is emitting particles is said to be undergoing radioactive decay, or nuclear decay.
Isotopes of some elements produce radiation naturally, An example is radium-226. When it is undergoing nuclear decay, radium emits alpha particles and actually becomes another element. We call this nuclear transformation, and we can represent it by the following equation:
226/88Ra 4/2He + ?
What is the unknown element? Subtraction tells us that it must be the element whose atomic number is 86 and whose mass number is 222. We look at the periodic table and find that element 86 is radon (Rn). So we can write the reaction in this manner:
226/88Ra 4/2He + 222/86Rn
In the balanced nuclear equation, the sum of the superscripts, and also the sum of the subscripts, is the same on both sides of the arrow.
The isotope thorium-234 produces radiation by emitting beta particles. We can write the nuclear reaction as:
234/90Th 0/-1e + ?
What is the other element that is being formed? Since we know the formation of a beta particle increases an element's atomic number by 1 the unknown element must be the element whose atomic number is 91. The periodic table tells us that element 91 is protactinium. So we can write the equation as:
234/90Th 0/-1e + 234/91Pa
Once again the sums of both superscripts and subscripts are the same on both sides of the arrow.