Some important words in this activity need to be defined. First, emit, which means to give off or send out. Absorb means to take in and become one thing. The parent nucleus is the unstable atomic nucleus before it decays. The daughter nucleus is the same atomic nucleus after it has decayed. Usually the daughter nucleus is a different element from the parent nucleus.
Some kinds of ionizing radiation are electro-magnetic waves. Specifically, ultraviolet light, x-rays and gamma rays. Another kind of ionizing radiation has a mass and a charge. This kind of radiation is made of particles and they are emitted from an unstable atomic nucleus.
One type of nuclear decay releases something called an alpha-particle. An alpha-particle (or α-particle) is the nucleus of a helium-4 atom. It has a mass number of 4 and an atomic number of 2. Its atomic sybmol is either 42α or 42He. When it is first emitted it has a +2 electric charge. When a nucleus decays by alpha decay it releases an alpha-particle and its mass decreases by 4 and its atomic number decreases by 2. The number of protons in the original nucleus is reduced by 2 and the number of neutrons is also reduced by 2.
Another type of nuclear decay releases something called a beta-particle. A beta-particle (or β-particle) is an electron and its mass is 5.49 × 10–4 amu and it has an electric charge of –1. The atomic symbol for a beta-particle is either 0–1β or 0–1e–. It has a mass number of zero because it has a mass much smaller than 1 amu. The mass number counts up protons and neutrons and an electron is neither of these. It has an atomic number of –1 because it has a charge of –1. Atomic number is really the number of positive charges in an atomic nucleus and although an electron is not a nucleus it does have a charge. During beta decay a nucleus does not change its mass number. The atomic number increases by 1. The number of neutrons is decreased by 1 and the number of protons is increased by 1. According to the picture in the activity a neutron is changed into a proton.
A third type of nuclear decay releases a gamma ray. A gamma ray (or γ-ray) is a photon with a very small wavelength and a very large energy. When a nucleus emits a gamma ray photon the number of protons and neutrons remains the same. The photon is simply an amount of energy that matches the difference between two energy levels within an atomic nucleus.
A fourth type of nuclear decay releases a positron from an unstable atomic nucleus. A positron is a particle of anti-matter and it is the anti-matter partner of an electron. It has the same mass as an electron but a +1 electric charge. The atomic symbol for a positron is either 0+1β+ or 0+1e+. It is also called a beta-plus-particle. Its mass number is zero because, like an electron, its mass is very small compared to even a single proton or neutron. Its atomic number is +1 because it has a positive charge, just like a proton. During positron decay a nucleus does not change its mass number. The atomic number decreases by 1. The number of protons is decreased by 1 and the number of neutrons is increased by 1. According to the picture in the activity a proton is changed into a neutron.
The fifth and final type of radioactive decay in the activity is called electron capture. In electron capture a proton in an unstable atomic nucleus absorbs an electron and becomes a neutron. When using symbols to describe electron capture the symbol 0–1e– is used for the electron.During electron capture decay the mass number of the nucleus does not change. The atomic number decreases by 1. The number of protons decreases by 1 and the number of neutrons increases by 1. Electron capture is similar to positron decay in its effects but happens by another path. Electron capture is different from the other decay modes because it involves the nucleus absorbing something instead of emitting something. For the actual event in which a nucleus captures an electron nothing observable happens so without chemical analysis to identify the elements in a sample it would not be detected.
Based on this activity it is possible to conclude that sometimes protons in unstable nuclei can become neutrons. Also, sometimes neutrons can become protons. In beta decay a neutron becomes a proton. In both positron decay and electron capture decay a proton becomes a neutron.