The magnetic moment and the hyperfine coupling constant are related by the following formula: (μB_J)/(ℏ²IJ)=a. Assuming B_J can be determined experimentally, the value of J can be calculated for the first isotope. For another isotope, B_J and J remain the same, because the electron cloud is unaffected by adding a neutron to the nucleus. Hence, the new value of the magnetic moment can be found from the expression above.