Radioactive dating after 2 half lives
The unstable nuclide is called the parent nuclide; the nuclide that results from the decay is known as the daughter nuclide.
The daughter nuclide may be stable, or it may decay itself.
In most cases, the energy emitted will be in the form of an X-ray.
Like positron emission, electron capture occurs for “proton-rich” nuclei that lie below the band of stability.
Ernest Rutherford’s experiments involving the interaction of radiation with a magnetic or electric field (Figure 2) helped him determine that one type of radiation consisted of positively charged and relatively massive α particles; a second type was made up of negatively charged and much less massive β particles; and a third was uncharged electromagnetic waves, γ rays.
We now know that α particles are high-energy helium nuclei, β particles are high-energy electrons, and γ radiation compose high-energy electromagnetic radiation.
The beta particle (electron) emitted is from the atomic nucleus and is not one of the electrons surrounding the nucleus. Emission of an electron does not change the mass number of the nuclide but does increase the number of its protons and decrease the number of its neutrons.
This “tagged” compound, or radiotracer, is then put into the patient (injected via IV or breathed in as a gas), and how it is used by the tissue reveals how that organ or other area of the body functions. A PET scanner (a) uses radiation to provide an image of how part of a patient’s body functions.
Gamma emission (γ emission) is observed when a nuclide is formed in an excited state and then decays to its ground state with the emission of a γ ray, a quantum of high-energy electromagnetic radiation.
The presence of a nucleus in an excited state is often indicated by an asterisk (*).
Cobalt-60 emits γ radiation and is used in many applications including cancer treatment: Positron emission is observed for nuclides in which the n:p ratio is low. Positron decay is the conversion of a proton into a neutron with the emission of a positron.
The n:p ratio increases, and the daughter nuclide lies closer to the band of stability than did the parent nuclide.