I am a general reader.I found in a book:"Three quarks with I=(1/2) can combine to form I_tot=(1/2) [did not understand] or (3/2) [OK].I_tot = (1/2) gives the nucleons while I_tot = (3/2) forms the baryons. Now,using u and d isospin doublet,I expressed the baryons:uuu,uud,udd,ddd.And found that I_tot= (3/2).It is OK. But I cannot see how I_tot=(1/2) [I have not considered I_3 component,however] for nucleons.Forming the doublet of p and n I saw that they conforms to uud and udd (which I got in baryons,too).So,what makes these different from them?
