Measurement of the linear polarization of continuum gamma rays from ( 32S, xn) reactions to prolate and oblate rare-earth nuclei

Abstract

We describe the techniques and report the results of a measurement of the linear polarization, P γ of continuum γ-rays from Er and Dy nuclei produced in ( 32S, xn) reactions on 130Te and 124Sn targets. For the prolate 156–158Er isotopes we find P γ ≈ 0.35 in the γ-ray energy range if0.3 MeV ≦ E γ ≦ 1.5 MeV, thus confirming the E2 nature of the unresolved yrast cascades in rotational nuclei. In contrast, the rather small polarization P γ ≈ 0.05 for E γ ≦ 1.0 MeV measured for the oblate 151,152Dy isotopes, and the shape of the spectrum of continuum γ-rays suggest a rather direct feeding of the yrast states by statistical cascades. For 1.0 MeV ≦ E γ ≦ 1.5 MeV we find P γ ≈ 0.3 indicating collective rotations of the Dy nuclei at spin I ≧ 40 h z.shtsls; . Measurements of γ-ray angular distributions with a collimated NaI detector support these results. From the reduction of the P γ , and A 2 values of the γ-ray continuum in 156–158Er, compared to those measured for discrete E2 yrast transitions, we obtain estimates for the intensities of the M1 and statistical components in the continuum of these nuclei.