Measurement of the Tensor Analysing Power Ayy Near the Value Ay= 1 in d-α Elastic Scattering

It has recently been shown that a point with Ay= 1 may existl,2) in d-α elastic scattering near 30 MeV and θcm = 155°. Such a situation would imply that the tensor analysing power Ayy is equal to 1 also 3). The recent beginning of operation of the polarized ion source at the SIN injector cyclotron made it possible to investigate this question at 30 MeV. A vector and tensor polarized deuteron beam from this atomic beam type source was accelerated in the cyclotron to 30.1 MeV and brought to a scattering chamber. The recoil α-particles were detected at an angle Blab equal to 12° corresponding to a deuteron scattering angle θcm 156.0°. Assuming an Ay= 1, a beam polarization of 72% of the theoretical value was found. Based on the well known ratio of tensor to vector polarization in the beam, the tensor analysing power could be determined in the same measurement. The result Ayy = 0.829 ± 0.030 shows clearly that at the energy and angle measured no double maximum exist. If such a point is present nearby, the Ayy maximum is fairly sharp peaked in energy as well as in angle since another measurement at θcm = 125.9° reveal values Ay =0.392 ± 0.041 and Ay = − 0.316 ± 0.042. The latter value is in agree-ment with measurements of the Berkeley group1).