Published online by Cambridge University Press: 20 November 2018
Let $m={{p}^{e}}$ be a power of a prime number $p$. We say that a number field $F$ satisfies the property $\left( {{H}^{'}}_{m} \right)$ when for any $a\in {{F}^{\times }}$, the cyclic extension $F\left( {{\zeta }_{m}},{{a}^{1/m}} \right)/F\left( {{\zeta }_{m}} \right)$ has a normal $p$-integral basis. We prove that $F$ satisfies $\left( {{H}^{'}}_{m} \right)$ if and only if the natural homomorphism $C{{l}^{'}}_{F}\to C{{l}^{'}}_{K}$ is trivial. Here $K=F\left( {{\zeta }_{m}} \right)$, and $C{{l}^{'}}_{F}$ denotes the ideal class group of $F$ with respect to the $p$-integer ring of $F$.