Science Made Simple: What Are Isotopes?

Deuterium Atom. Rendering

Artist rendering of the basic structures of Deuterium atom.

What Are Isotopes?

A family of people often consists of related but not identical individuals. Elements have families as well, known as isotopes. Isotopes are members of a family of an element that all have the same number of protons but different numbers of neutrons.

The number of protons in a nucleus determines the element’s atomic number on the Periodic Table. For example, carbon has six protons and is atomic number 6. Carbon occurs naturally in three isotopes: carbon 12, which has 6 neutrons (plus 6 protons equals 12), carbon 13, which has 7 neutrons, and carbon 14, which has 8 neutrons. Every element has its own number of isotopes.

Hydrogen Natural Isotopes

Hydrogen and its two naturally occurring isotopes, deuterium and tritium. All three have the same number of protons (labeled p+) but different numbers of neutrons (labeled n). Credit: Image courtesy of Wikimedia commons

The addition of even one neutron can dramatically change an isotope’s properties. Carbon-12 is stable, meaning it never undergoes radioactive decay. Carbon-14 is unstable and undergoes radioactive decay with a half-life of about 5,730 years (meaning that half of the material will be gone after 5,730 years). This decay means the amount of carbon-14 in an object serves as a clock, showing the object’s age in a process called “carbon dating.”

Isotopes have unique properties, and these properties make them useful in diagnostics and treatment applications. They are important in nuclear medicine, oil and gas exploration, basic research, and national security.

Isotope Facts

  • All elements have isotopes.
  • There are two main types of isotopes: stable and unstable (radioactive).
  • There are 254 known stable isotopes.
  • All artificial (lab-made) isotopes are unstable and therefore radioactive; scientists call them radioisotopes.
  • Some elements can only exist in an unstable form (for example, uranium).
  • Hydrogen is the only element whose isotopes have unique names: deuterium for hydrogen with one neutron and tritium for hydrogen with two neutrons.

DOE Office of Science & Isotopes

Isotopes are needed for research, commerce, medical diagnostics and treatment, and national security. However, isotopes are not always available in sufficient quantities or at reasonable prices. The DOE Isotope Program addresses this need. The program produces and distributes radioactive and stable isotopes that are in short supply, including byproducts, surplus materials, and related isotope services. The program also maintains the infrastructure required to produce and supply priority isotope products and related services. Finally, it conducts research and development on new and improved isotope production and processing techniques.

1 Comment on "Science Made Simple: What Are Isotopes?"

  1. So many interesting things about isotopes and the fundamentals of neutrons and protons.

    In heavier radioactive isotopes a neutron can be added that changes the character of the element in several ways, it will change the half life, it can change the element from fertile to fissionable. Neutrons can decay into a slightly lighter proton and electron plus an anti neutrino, the later 2 being ejected in a -ve beta decay.

    In stars in both the slow PP and super fast CNO cyles, protons can be added to a nuclei and then decay upwards into a heavier neutron absorbing an electron but ejecting a neutrino along the way (a +ve beta decay). This happens in a roundabout way though through antimatter & gamma radiation. In this way half of all the hydrogen mass protons must be turned into neutrons in order to build all the lower elements. In the CNO cycle C12 flips between N13 and back to C13 when a proton is added then decaying to a neutron. Another proton converts C13 into N14. The same 2 steps happens again when N14 changes to O15 and back to N15, and finally the 4th added proton changes N15 to O16 and that splits right back to C12 and H4.

    Outside of the nuclius in free space, all neutrons decay back to energetic protons and electrons, ie cosmic radiation in about 15 mins.

    Almost all the even no elements on the periodic table occur an order of magnitude more frequently because when you build elements out of helium you get only even no elements. Elements much heavier than iron are made by super nova and neutron star collisions where vast amounts of neutrons become available to do fusion of free space dust with energy loss per fusion. This happens in a matter of minutes because the neutrons only have a short life.

    One of the more fascinating reads is from 1957 when the synthesis of elements was first almost completely understood in the seminal paper by Fred Hoyle and others. He also gave us the phrase the big bang because he didn’t believe in that crazy idea at the time.

    Along with this comes the special periodic table of elements by nucleosythesis, which describes which of just 6 processes made each element, color coded.

    And when looking at a periodic table, one should seek out the wide low table, not the school book folded one with the 2 rows underneath. When you look at the wide table and count the no of elements in each row, you see a beautiful pattern of double squares which relates to the electron orbital counts. 1*1*1, 2*2*2, 2*3*3, 2*4*4 which draw a parabola. The wide low table looks like a soup bowl following the square law. There are also many other periodic table representations showing a particular aspect of elements in a different way.

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