For a finite-type integer algebra, a nonnilpotent element gives a nonzero localization of a ring . A maximal ideal there has finite residue field by the finite-field theorem for finitely generated integer algebras. The image of in that field is a finite integral domain, hence a field. Its kernel is therefore maximal in and avoids . Nilpotents lie in every maximal ideal, proving the radical equality. Applying the same argument to every prime quotient shows that these algebras are Jacobson rings. Merely contracting a localized maximal ideal without the finite-image argument would not prove maximality.
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