u235 

proton 92 92.669392

neutron 143 144.238952

total = 236.908344 

actual = 235.0439299 Da

weight loss = 1.8644141

u238

proton 92  92.669392

neutron 146 147.264944

total = 239.934336

actual = 238.05078826 Da

weight loss = 1.88354774

proton mass 1.007276466621(53) Da

neutron mass 1.00866491588(49) Da

由上可知鈾238的BOnding 能量更高因而更穩定