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Example Question #66 : Atomic And Nuclear Physics
Suppose that an atom undergoes a series of decays. First, it undergoes two alpha decays, followed by two positron decays, and then finally by two gamma decays. How has the atomic number of this atom changed?
In this question, we're told that an atom undergoes a series of decays. We're then asked to determine how the atomic number of that atom has changed.
Let's look at the first type of decay, alpha decay. During alpha decay, the atom emits a helium nucleus, which consists of two protons and two neutrons. Thus, for each alpha decay, the atom will lose two protons. So two alpha decays would result in a net loss of four protons.
Next, let's look at positron decay. In this type of decay, a proton is converted into a positron and a neutron. The neutron stays in the atoms's nucleus, while the positron is emitted. Thus, positron decay results in a loss of one proton. Consequently, two positron decays result in a total loss of two protons.
Finally, gamma decay does not cause a change in the atom's atomic number or mass number. Gamma decay simply releases energy.
So, in total, we have four protons lost from alpha decays and two protons lost from positron decays. Thus, there is a total loss of six protons, corresponding to a decrease in the atomic number by six.