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.
Following the somewhat serendipitous discovery of radioactivity by Becquerel, many prominent scientists began to investigate this new, intriguing phenomenon.
Among them were Marie Curie (the first woman to win a Nobel Prize, and the only person to win two Nobel Prizes in different sciences—chemistry and physics), who was the first to coin the term “radioactivity,” and Ernest Rutherford (of gold foil experiment fame), who investigated and named three of the most common types of radiation.
During the beginning of the twentieth century, many radioactive substances were discovered, the properties of radiation were investigated and quantified, and a solid understanding of radiation and nuclear decay was developed.
The spontaneous change of an unstable nuclide into another is radioactive decay.
Electron capture has the same effect on the nucleus as does positron emission: The atomic number is decreased by one and the mass number does not change.
This increases the n:p ratio, and the daughter nuclide lies closer to the band of stability than did the parent nuclide.
The scans it produces can be used to image a healthy brain (b) or can be used for diagnosing medical conditions such as Alzheimer’s disease (c).
(credit a: modification of work by Jens Maus) O () and incorporated into a glucose analog called fludeoxyglucose (FDG).
The radiation produced during radioactive decay is such that the daughter nuclide lies closer to the band of stability than the parent nuclide, so the location of a nuclide relative to the band of stability can serve as a guide to the kind of decay it will undergo (Figure 1). A nucleus of uranium-238 (the parent nuclide) undergoes α decay to form thorium-234 (the daughter nuclide).
The alpha particle removes two protons (green) and two neutrons (gray) from the uranium-238 nucleus.
Beta (β) decay is the emission of an electron from a nucleus.