Question

Which of the following is the correct unit for measuring nuclear radii?
A.Micron
B.Millimeter
C.Angstrom
D.Fermi

Answer 1

Hint: A unit of length is used to measure the nuclear distances which are equal to ${10}^{-15}$ meter. In $1901-1954$, the unit is named for the Italian physicist Enrico Fermi. Now, it is replaced by the SI unit femtometre.

Complete step by step answer:
Fermi is used for measuring the nuclear radii but this unit is no longer in use. Instead of Fermi, the unit used is known as Femtometre. It is represented by the symbol of fm. $1$ Fermi is equal to ${10}^{-15}$ meter and it is equal to a quadrillionth of one. The femtometre term is derived from the Danish and Norwegian word ‘femten’ which means ‘fifteen’. The distance of nuclear radii can also be called a fermi. It is a typical length – scale of nuclear physics.
Hence, option D is correct.

Additional information:
The word Fermi is coined by Robert Hofstadter. In $1956$, a paper published in reviews of modern physics entitled “Electron Scattering and Nuclear Structure”. Fermi is widely used by particle and nuclear physicists.
$$1,000,000femtometres=10angstrom=1nanometre$$
For example, charge on the radius of a proton is approx. $0.831$ femto metres whereas the radius of a gold nucleus are approx. $8.45$ femtometers.


Note:
A Fermi is the older non – SI measurement unit of length since it is a typical length – scale unit which is used in nuclear physics and now the metric unit femtometer is used and its prefix is Femto.