[1]There are exceptions. For a few elements there are no stable nuclei. In some cases, there are other differences that make certain atoms radioactive.
[2]These gamma rays (called prompt gamma rays because they are instantaneously produced when the neutron is captured) can also be used for analysis and sometimes are, but we will not be discussing this type of analysis in this booklet.
[3]Sensitivity in this case means how small an amount of an unknown element can be detected.
[4]Nuclide is a general term applicable to all atomic forms of elements. Whereas isotopes are the various forms of a single element (hence are a family of nuclides) and all have the same atomic number and number of protons, nuclides comprise all the isotopic forms of all the elements.
[5]The half-life of a radioactive nuclide is the time it takes for half the nuclei in a large sample to undergo decay. Note that after half of them are gone, a second half-life period will reduce the remainder by one half, leaving one quarter of the original number.
[6]The disintegration constant is related to the half-life, T½, by the expression: ? = natural logarithm of 2/half-life, or
[7]The detector efficiency is the ratio of the number of gamma rays detected to the number emitted by the sample.
[8]A deuteron is the nucleus of a heavy hydrogen (deuterium) atom and consists of one neutron and one proton.
[9]Not all nuclear reactors are appropriate for this work. For example, reactors designed for electric power production do not have the means built into them for inserting and removing small samples for a “short” period of irradiation.
[10]A scintillation detector is a crystalline device, usually sodium iodide containing a small amount of thallium, which has the property of emitting light when energy is absorbed from nuclear radiation.
[11]After a 10-minute irradiation and a 3-minute delay before counting, corrected for decay to a common time.
[12]One mole is the atomic weight of an atom or molecule expressed in grams, or the weight of 6.02 × 10²³ atoms or molecules per mole.
[13]ln 2 is the natural logarithm of 2.
