Depolarization studies on low-depolarizing Cu/Ti and Ni(Mo)/Ti neutron supermirrors
arXiv:2503.22561 · doi:10.1016/j.nima.2025.170795
Abstract
Neutron supermirrors (SMs) are a crucial part of many scattering and particle physics experiments. So far, Ni(Mo)/Ti SMs have been used in experiments that require to transport a polarized neutron beam due to their lower saturation magnetization compared to Ni/Ti SMs. However, next generation decay experiments require SMs that depolarize below per reflection to reach their targeted precision. The depolarization of a polarized neutron beam due to reflection from Ni(Mo)/Ti SMs has not yet been measured to that precision. Recently developed Cu/Ti SMs with a very low saturation magnetization compared to Ni(Mo)/Ti may serve as an alternative. In this paper, we test the performance of both mirrors. At a first stage, we present four-states polarized neutron reflectivity (PNR) curves of Ni(Mo) and Cu monolayers measured at the neutron reflectometer SuperADAM and perform a full polarization analysis, showing a difference between the magnetic scattering length density (mSLD) of both materials, with Cu having a lower mSLD than Ni(Mo). These results are corroborated with the full polarization analysis of four-states PNR curves of Ni(Mo)/Ti and Cu/Ti SMs. In a second stage, we measured the depolarization () that a polarized neutron beam suffers after reflection from the same Ni(Mo)/Ti and Cu/Ti SMs by using the Opaque Test Bench setup. We find upper limits for the depolarization of , , and at the confidence level, where (4N5) corresponds to a Ti purity of and (2N6) to . The uncertainties are statistical. These results show that all three SMs are suitable for being used in next generation decay experiments. We found no noticeable dependence of on the value or the magnetizing field, in which the samples were placed.