Sections
Section Summary
Section Summary
14.1 Radiation Detection and Detectors
- Radiation detectors are based directly or indirectly upon the ionization created by radiation, as are the effects of radiation on living and inert materials.
14.2 Substructure of the Nucleus
- Two particles, both called nucleons, are found inside nuclei. The two types of nucleons are protons and neutrons; they are very similar, except that the proton is positively charged while the neutron is neutral. Some of their characteristics are given in Table 14.1 and compared with those of the electron. A mass unit convenient to atomic and nuclear processes is the unified atomic mass unit (u), defined to be
- A nuclide is a specific combination of protons and neutrons, denoted by is the number of protons or atomic number, X is the symbol for the element, is the number of neutrons, and is the mass number or the total number of protons and neutrons
- Nuclides having the same but different are isotopes of the same element.
- The radius of a nucleus, is approximately where Nuclear volumes are proportional to There are two nuclear forces, the weak and the strong. Systematics in nuclear stability seen on the chart of the nuclides indicate that there are shell closures in nuclei for values of and equal to the magic numbers, which correspond to highly stable nuclei.
14.3 Nuclear Decay and Conservation Laws
- When a parent nucleus decays, it produces a daughter nucleus following rules and conservation laws. There are three major types of nuclear decay, called alpha beta and gamma The decay equation is
- Nuclear decay releases an amount of energy related to the mass destroyed by
- There are three forms of beta decay. The decay equation is
- The decay equation is
- The electron capture equation is
- is an electron, is an antielectron or positron, represents an electron’s neutrino, and is an electron’s antineutrino. In addition to all previously known conservation laws, two new ones arise—conservation of electron family number and conservation of the total number of nucleons. The decay equation is
14.4 Half-Life and Activity
- Half-life is the time in which there is a 50 percent chance that a nucleus will decay. The number of nuclei as a function of time is where is the number present at and is the decay constant, related to the half-life by
- One of the applications of radioactive decay is radioactive dating, in which the age of a material is determined by the amount of radioactive decay that occurs. The rate of decay is called the activity
- The SI unit for is the becquerel (Bq), defined by
- is also expressed in terms of curies (Ci), where
- The activity of a source is related to and by
- Since has an exponential behavior as in the equation the activity also has an exponential behavior, given by where is the activity at
14.5 Binding Energy
- The binding energy (BE) of a nucleus is the energy needed to separate it into individual protons and neutrons. In terms of atomic masses where is the mass of a hydrogen atom, is the atomic mass of the nuclide, and is the mass of a neutron. Patterns in the binding energy per nucleon, reveal details of the nuclear force. The larger the the more stable the nucleus.
14.6 Tunneling
- Tunneling is a quantum mechanical process of potential energy barrier penetration. The concept was first applied to explain decay, but tunneling is found to occur in other quantum mechanical systems.