In this activity we reviewed some facts about istopes and radioactive decay modes. Isotopes are different versions of atoms of the same element. The isotopes of an element have the same number of protons but different numbers of neutrons. Some isotopes are stable and do not decay. Some isotopes are unstable and their nuclei undergo nuclear decay to become a different isotope of a different element. To talk about isotopes it’s useful to use a symbol. In this symbol (AZX) the X stands for the atomic symbol, the A stands for the mass number (which is the sum of protons and neutrons in the nucleus) and Z stands for the atomic number (which is just the number of protons). Mass number can be calculated using a simple mathematical formula: A = Z + n0, where n0 stands for the number of neutrons. Isotopes each have their own, individual names. Since isotopes have different numbers of neutrons they have different mass numbers. The name of an isotope is the name of the element followed by the mass number, like this: calcium-40 or calcium-42. Calcium-40 has 20 protons (as all calcium atoms do) and 20 neutrons. This is because A – Z = n0. Similarly, calcium-42 has 20 protons and 22 neutrons.
Alpha decay is when an unstable atomic nucleus ejects an alpha particle. An alpha particle is an extremely high-speed helium-4 nucleus with 2 protons, 2 neutrons, and no electrons. When an atom decays by alpha decay its atomic number decreases by 2. The mass number decreases by 4. The atomic symbol for a alpha-particle is 4 2He.
Beta decay is when an unstable atomic nucleus ejects a beta particle. A beta particle is an extremely high-speed electron. Inside the nucleus a neutron, which is the origin of the electron, becomes a proton. As a result a nucleus that decays by beta decay keeps the same mass number but the atomic number increases by 1. The atomic symbol for a beta-particle is 0-1β–.
Positron decay is when an unstable atomic nucleus ejects a positron. A positron is an extremely high-speed anti-electron. Inside the nucleus a proton, which is the origin of the positron, becomes a neutron. As a result a nucleus that decays by positron decay keeps the same mass number but the atomic number decreases by 1. The atomic symbol for a positron is 0+1β+.
Electron capture decay is when an unstable atomic nucleus absorbs an electron. The orbitting electron that is absorbed joins up with a proton and together they become a neutron. As a result a nucleus that decays by electron capture keeps the same mass number but the atomic number decreases by 1. The atomic symbol for the electron that is absorbed is 0-1e–.
Nuclear equations are a way to represent a nuclear process using symbols. They follow two rules. First, the sum of the mass numbers for all particles on the left side of the arrow must equal the sum of the mass numbers on the other side. Second, the sum of the atomic numbers for all particles on the left side of the arrow must equal the sum of the atomic numbers on the other side. At right are some example radioactive decay equations.
Nuclear equations can also be used to describe other things besides nuclear decay. First, they can be used to describe nuclear fission. Fission is when an atomic nucleus splits into two smaller atomic nuclei. Second, nuclear fusion, which is when two small atomic nuclei combine to make a single, larger nucleus. And third, artificial transmutation is when atomic nuclei are smashed together at high speeds, resulting in a nucleus becoming a different element. In this activity we learned how to write balanced nuclear equations for all of these things.
Here is an example equation for nuclear fusion: 21H +
→ 42He +
10n0. Here is an example equation for transmutation: 42He +
→ 178O +
And here is an example equation for nuclear fission: 23592U + 10n0 → 14156Ba + 9236Kr + 310n0.