Decay schemes provided here come from the following sources (noted beside each figure):

• [1] James E. Martin, Physics for Radiation Protection, Wiley-VCH, 2006.
• [2] C. Michael Lederer, Jack M. Hollander, and Isadore Perlman, Table of Isotopes, 6th Edition, John Wiley & Sons, 1967.

Additional information (e.g. X-ray lines, lifetimes) can be found from the online Radioactive Table of Isotopes maintained by the International Atomic Energy Agency as an interactive table at https://www-nds.iaea.org/relnsd/vcharthtml/VChartHTML.html or as a static table at https://www-nds.iaea.org/xgamma_standards/genergies1.htm.

Annotated decay scheme for Sodium-22.  Note that decay schemes are published in black and white; the scheme above has been color-coded to highlight the different features that are present.

Horizontal lines [purple] represent energy levels and are arranged so that higher energy states are placed above lower energy states. (Note that separations are not, in general, to scale.) The value written next to a horizontal line [teal] is the energy of that state, usually in MeV, relative to the lowermost energy state in the diagram. The lowermost (ground) state is at zero energy and is the stable, final state of the decay.

Some energy levels may also have an indicated lifetime [red]. If no lifetime is given, it is usually safe to assume that the decay from that state to a lower energy is nearly instantaneous.

Diagonal lines [green] represent decay processes which take one nuclear species to another (e.g. ${}^{22}_{11}\textrm{Na}$  to ${}^{22}_{10}\textrm{Ne}$ ). Possible processes include the following:

• Electron Capture (EC): The nucleus captures an electron from one of the inner shells and the electron is used to convert one of the protons in the nucleus into a neutron. The resulting nucleus usually is left in an excited state and an electron neutrino is emitted from the proton conversion.
• Note that in addition to leaving the daughter nucleus in an excited state, EC leaves a hole in an electron shell. One of the electrons in a higher electron state will quickly fall to fill that hole, releasing a photon in the process. However, the energy of this photon will not appear on the decay scheme since it it not produced directly by the nucleus. Such photons are typically $K_\alpha$ , $K_\beta$  or $L_\alpha$  X-rays; values for these photons can be found in standard tables like this one. 
• $\boldsymbol{\beta}^\bf{-}$  emission: A neutron in the nucleus decays into a proton, an electron and an electron neutrino. The electron and neutrino are emitted (and carry away some kinetic energy), usually leaving the nucleus in an excited state.
• $\boldsymbol{\beta}^\bf{+}$ emission: A proton in the nucleus decays into a neutron, a positron and an electron antineutrino. The positron and antineutrino are emitted (and carry away some kinetic energy), usually leaving the nucleus in an excited state.
• One can think of $\beta^+$  emission as a relative of EC. If the difference in energies between the initial and final nuclear states is at least $2m_ec^2$ , the excited nucleus can spontaneously form an electron-positron pair and use the electron to convert a proton into a neutron; the extra positron is then emitted. Therefore, whenever $\beta^+$  emission is a possible decay mode, EC is also a possible decay mode. The opposite is not true.
• $\boldsymbol{\alpha}$  emission: A heavy nucleus may decay by releasing an alpha particle (a bare nucleus of 2 protons and 2 neutrons, i.e. ${}^{2}_{4}\textrm{He}^{2+}$ ), lowering its charge by 2 units and the number of nucleons by 4. This usually leaves the daughter nucleus in an excited state.

Vertical lines [orange] represent transitions from a higher nuclear energy state to a lower nuclear energy state. In most cases, a gamma ray (high energy photon) is emitted carrying away the difference in energy. These emissions are analogous to the more familiar photons emitted when electrons transition among energy levels, but the energy scales are typically much bigger.

Multiple possible transitions: In elements with multiple excited energy states, there may be multiple possible decays. In these instances, each vertical transition is labeled with a relative probability and an energy.

For example, looking at the cobalt-60 decay, the nickel nucleus can transition from the 2.158 MeV state to either the 1.3325 MeV excited state or the ground state. However, the transition to the 1.3325 MeV state is over ten times more likely (as indicated by the prefixes). Thus, we should expect to see substantially more 830 keV gammas than 2.158 MeV gammas.

Some nuclei can also undergo a process called internal conversion (IC) where the excited nucleus gives its excess energy directly to an electron, liberating that electron from its shell and sending it off with some extra kinetic energy. IC is possible only in high Z nuclei (where the electron binding energy is comparable to the excited energy of the nucleus) and only from metastable states (where the lifetime for the normal photon emission is quite long, giving enough time for the probability for an electron's wavefunction to overlap with the nucleus' wavefunction to become non-negligible).

Decay schemes also contain information about nuclear excitation states, Q values, and ln(ft) values that are not commonly used in this course.