4.1× $10^{- 8}$ Second Metastable State in ${Pa}^{231}$

A metastable state of

{Pa}^{231}

with a half-life of (4.1±0.4)×

10^{- 8}

second has been observed. This half-life is exhibited by both 26- and 85-kev

E 1

gamma transitions. A comparison is made with the metastable state in

{Pa}^{233}

. Upper limits on lifetimes are given for the

E 1

gamma transitions in

{Np}^{239}

and

{Ac}^{225}

. The erratic variation in the lifetimes for

E 1

transitions is discussed.

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4.1×10−8Second Metastable State inPa231