An isotope is a variant of a chemical element that has:

• The same number of protons (which defines the element)
• But a different number of neutrons in the nucleus

This means isotopes of the same element share the same atomic number but differ in mass number.

When one of these particles strikes an atom, it can dislodge one or more protons and/or neutrons from that atom, producing a different element or a different isotope of the original element.

Hydrogen has three naturally occurring isotopes. These are Protium (the most abundant one), Deuterium (found in heavy water) and Tritium (used in nuclear fusion processes).

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Despite their differences in mass and nuclear behavior, they all behave chemically like hydrogen.

Stable isotopes are used in climate studies (Oxygen isotopes in ice cores), medical diagnostics (Carbon-13 in metabolic tests) and archaeology (Carbon-14 dating).

Radioactive isotopes (or radioisotopes) can be used in cancer treatments (Cobalt-60), imaging (e.g., Technetium-99m), and power generation (Uranium-235).

In rocks and materials of a similar density, most of the cosmic ray flux is absorbed within the first metre of exposed material in reactions that produce new isotopes called cosmogenic nuclides.

On the surface, most of these nuclides are produced by neutron spallation reactions.

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