femtometrejä

Femtometri, often abbreviated as fm, is a unit of length in the International System of Units (SI). It is equal to one quadrillionth of a meter, or 10^−15 meters. The name "femtometer" is derived from the Danish word "femten," meaning fifteen, and "meter." It is a very small unit, far smaller than atoms themselves.

To provide some perspective, a typical atomic nucleus has a radius on the order of a few femtometers. For example, the nucleus of a helium atom measures approximately 1.7 fm, while a uranium nucleus is around 7.4 fm. The femtometer is primarily used in nuclear physics and particle physics to describe the dimensions of subatomic particles and the distances involved in nuclear reactions.

The femtometer is a sub-multiple of the meter, defined in 1964 by the Conférence Générale des Poids et Mesures (CGPM). Its precursor, the fermi, was named after the physicist Enrico Fermi. While the fermi is still sometimes used colloquially, the femtometer is the officially recognized SI unit. The symbol fm is universally accepted for this unit.