Credit: National Cancer Institute
License: CC BY-NC 3.0
Positron emission tomography, or PET scan, of a patient undergoing treatment.
Positron emisson tomography, or PET scan, helps diagnose patients by tracking the movement of mildly radioactive material injected into the patient. It is one of a many techniques using nuclear properties to diagnose and treat disease. Many people consider all nuclear applications dangerous, but this is often based on misunderstanding. This chapter covers structure of the nucleus, nuclear forces, radioactive half-life, fission and fusion, and the Standard Model.
- Atoms are always neutral; that is, they have the same number of protons in the nucleus as electrons about the nucleus.
- Neutrons and protons are called nucleons since they form the atomic nucleus.
- The atomic number of an atom is the number of protons in its nucleus. It is expressed symbolically as Z.
- The total number of nucleons in the nucleus is called the atomic mass number. It is expressed symbolically as A.
- The nuclei that contain the same number of protons but a different number of neutrons are called isotopes. All chemical elements have multiple isotopes.
- The nucleus is often represented symbolically as AZX.
- Experimental evidence shows that the total mass of a stable nucleus is smaller than the sum of the masses of its components. The energy equivalent of this mass difference Δm, or mass deficit, can be used to find the binding energy of the nucleus.
- The binding energy is found from the Einstein equation E=Δmc2.
- The half-life is the amount of time required for half of the radioactive parent atoms to transform into the daughter atoms.
- The amount of a sample No of radioactive material remaining after n doublings of its half-life is N, given by the equation N=(12)nNo.
- The splitting of an atom with a large atomic mass into at least two relatively equal parts, with an accompanying release of energy, is called nuclear fission.
- The process in which the nuclei of lighter elements combine and form heavier elements, with an accompanying release of energy, is called nuclear fusion.