Mainz 2012 – scientific programme
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HK: Fachverband Physik der Hadronen und Kerne
HK 42: Instrumentation
HK 42.8: Talk
Thursday, March 22, 2012, 18:30–18:45, P 3
Depolarization in Polarizing Neutron Supermirrors — •Christine Klauser1,2, Thierry Bigault1, Pierre Courtois1, David Jullien1, Alexander Petoukhov1, Nataliya Rebrova3, and Torsten Soldner1 — 1Institut Laue-Langevin, F-38042 Grenoble, France — 2Atominstitut, Vienna University of Technology, Stadionallee 2, A-1020 Vienna, Austria — 3Physikalisches Institut, University of Heidelberg, D-69120 Heidelberg, Germany
Absolute measurements of correlation coefficients in neutron beta decay are presently limited to a relative accuracy in the orders of 10−3 by systematics and statistics. Next-generation instruments aim for 10−4 accuracy. This requires a 10−4 accuracy for the polarization for a large cold neutron beam. State-of-the-art polarizing super mirrors in X-SM geometry deliver about 99.7% polarization only. It appears that depolarization by the supermirrors is a limitation to the performance of this type of device.
We present a systematic study of depolarizing effects in polarizing supermirrors. Cold neutrons with a wavelength of 5.3 Å are polarised to 99.98 % by a 3He spin filter and their polarisation after one reflection on a polarizing supermirror is measured with another 3He spin filter; the set-up uses the highly sensitive opaque test bench. Varying parameters such as the magnetizing field (from 0.02 T to 0.82 T) and materials (Co-Ti, Fe-Si), we find the number of layers and the field strength to be important factors in depolarization. Other parameters such as the scattering angle and the wavelength only have little effect on the amount of depolarization.