The laser energy used to move the muon up to that unstable state can be used to calculate the radius of the helium nucleus, which is 1.67824 femtometers—one femtometer being one quadrillionth of a meter.

用于将 μ 子移动到不稳定态的激光能量可用于计算氦原子核的半径， 1.67824 ——一个是十亿分之一。