Isodiaphers
The two nuclides having the same neutron difference are known as isodiaphers . The neutron difference is otherwise known as isotopic number or isotopic excess. The neutron difference is the difference between the number of neutrons and number of protons. eg: A 1 X Z 1 and A 2 Y Z 2 are two nuclides X contains Z 1 protons and (A 1 - Z 1 ) neutrons so its Neutron difference= (A 1 - Z 1 ) - Z 1 = (A 1 - 2Z 1 ) Y contains Z 2 protons and( A 2 - Z 2 ) neutrons so its Neutron difference= (A 2 - Z 2 ) - Z 2 = (A 2 - 2Z 2 ) If (A 1 - 2Z 1 ) = (A 2 - 2Z 2 ) X and Y are isodiaphers . 234 U 90 and 238 U 92 are isodiaphers in both cases neutron number is the same (234-2×90) =54= (238-2×92) The isodiaphers usually result by an α ( 4 He 2 ) particle emission, the nuclide formed after emission and mother nuclide will be isodiaphers. 238 U 92 ------ à 234 U 90 + 4 He 2 In some cases nuclear number can be zero also.