Tailoring a target for transient field measurements of magnetic moments of short-lived excited states with radioactive beams

An understanding of target magnetization and kinematics is essential to determine $g$ factors using the Transient Field (TF) technique with Coulomb excitation of radioactive beams (RIB). With stable beams, layered targets of C/(Gd or Fe)/Cu are used. The Coulomb scattered C ions are detected in Si counters, located above and below the beam axis, in coincidence with $\gamma$-rays recorded in 4 Ge Clover detectors. With RIBs, the background from beam scattering is critical. For example, the $^ {132}$Te beam at ORNL contains $\sim10\%$ of isobaric $^{132} $Sb that decays via the $^{132}$Te, $4^+_1 \rightarrow 2^+_1 \rightarrow 0^+_1$, $\gamma$ cascade. Removing the Cu from the target greatly reduces the scattering of RIBs. Furthermore, with thinner ferromagnets, the $^{132}$Te ions decay in flight and the de-excitation $\gamma$-rays are Doppler shifted and easily distinguishable from the Sb unshifted background. While such a target without Cu backing does not provide sufficient cooling for a beam of 10$^9$ p/sec, it is adequate for a RIB of 10$^7$ p/sec. Results will be shown for both gadolinium and iron targets. Work supported by the US NSF and DOE.