Linear polarization measurement of gamma rays in Gd-155 by using a segmented Compton polarimeter

A linear polarization measurement for gamma rays has been performed to directly determine the parities for the levels in Gd-155. High-spin states in Gd-155 were populated in the Sm-154(alpha,3ngamma)Gd-155 reaction by using 35-MeV alphas. Linearly polarized gamma rays emitted from oriented states were measured by using a Compton polarimeter which is made of a planar-type germanium crystal and is segmented into 25 cathodes. The linear polarization of the gamma rays was measured by selecting Compton-scattered events fired in coincidence between two adjacent cathodes. The sign of the measured linear polarization enabled us to distinguish between electric and magnetic types of gamma-ray transitions. Accordingly. the parities of the high-spin states in Gd-155 were directly determined. Our parity assignment is in excellent agreement with a previous one.