Gamma-ray polarization sensitivity of the Gammasphere segmented germanium detectors

• Published in: Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment Accelerators, spectrometers, detectors and associated equipment, 1998-11, Vol.417 (1), p.95-110
• Main Authors: Schmid, G.J., Macchiavelli, A.O., Asztalos, S.J., Clark, R.M., Deleplanque, M.A., Diamond, R.M., Fallon, P., Kruecken, R., Lee, I.Y., MacLeod, R.W., Stephens, F.S., Vetter, K.
• Format: Article
• Language: English
• Subjects: 197Pb level scheme; Gamma-ray polarimeter
• ISSN: 0168-9002; 1872-9576
• DOI: 10.1016/S0168-9002(98)00624-X

We present a technique for operating the Gammasphere segmented Ge detectors as γ-ray polarimeters. Using γ-rays of known polarization, we have measured the polarization sensitivity, Q( E γ), of these detectors in the energy range E γ=0.4–1.4 MeV. The experimentally obtained value of Q ranges from 5% at 415 keV to 4% at 1368 keV. The magnitude and energy dependence of Q( E γ) has also been determined theoretically by means of a Monte Carlo simulation, and the agreement between experiment and theory is within 20% over the energy range measured. In order to investigate the potential for operating Gammasphere as a γ-ray polarimeter in a high background environment (one which is typical of high-spin nuclear structure studies), we also discuss data that we have analyzed from the 176 Yb ( 26 Mg, 5n) 197Pb reaction at E=135 MeV. Although the polarimeter performance of Gammasphere is seen to be relatively poor, we are still able to demonstrate, by way of γ-ray polarization measurements, that “Shears Band 1” in 197 Pb should have negative parity.