A concept of advanced broad-band solid-state supermirror polarizers for cold neutrons

详细信息    查看全文

• 作者：A.K. Petukhov ^{petukhov@ill.fr" class="auth_mail" title="E-mail the corresponding author} ; V.V. Nesvizhevsky ; ^{nesvizhevsky@ill.eu" class="auth_mail" title="E-mail the corresponding author} ; T. Bigault ^{bigault@ill.fr" class="auth_mail" title="E-mail the corresponding author} ; P. Courtois ^{courtois@ill.fr" class="auth_mail" title="E-mail the corresponding author} ; D. Jullien ^{djullien@ill.fr" class="auth_mail" title="E-mail the corresponding author} ; T. Soldner ^{soldner@ill.fr" class="auth_mail" title="E-mail the corresponding author}
• 关键词：Neutron ; Super-mirror ; Polarizing bender ; Solid-state polarizer
• 刊名：Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment
• 出版年：2016
• 出版时间：1 December 2016
• 年：2016
• 卷：838
• 期：Complete
• 页码：33-38
• 全文大小：1671 K

文摘

An ideal solid-state supermirror (SM) neutron polarizer assumes total reflection of neutrons from the SM coating for one spin-component and total absorption for the other, thus providing a perfectly polarized neutron beam at the exit. However, in practice, the substrate's neutron-nuclei optical potential does not match perfectly that for spin-down neutrons in the SM. For a positive step in the optical potential (as in a Fe/SiN_x$\mathit{Fe}/\mathit{Si}{N}_x$ SM on 2d0f3159d56d" title="Click to view the MathML source">Si$\mathit{Si}$ substrate), this mismatch results in spin-independent total reflection for neutrons with small momentum transfer Q$Q$, limiting the useful neutron bandwidth in the low-Q$Q$ region. To overcome this limitation, we propose to replace Si$\mathit{Si}$ single-crystal substrates by media with higher optical potential than that for spin-down neutrons in the SM ferromagnetic layers. We found single-crystal sapphire and single-crystal quartz as good candidates for solid-state Fe/SiN_x$\mathit{Fe}/\mathit{Si}{N}_x$ SM polarizers. To verify this idea, we coated a thick plate of single-crystal sapphire with a m=2.5$m=2.5$Fe/SiN_x$\mathit{Fe}/\mathit{Si}{N}_x$ SM. At the T3 instrument at the ILL, we measured the spin-up and spin-down reflectivity curves with $\lambda =7.5\AA$ neutrons incident from the substrate to the interface between the substrate and the SM coating. Results of this experimental test are in excellent agreement with our expectations: the bandwidth of high polarizing power extends significantly into the low-Q$Q$ region. This finding, together with the possibility to apply a strong magnetizing field, opens a new road to produce high-efficiency solid-state SM polarizers with an extended neutron wavelength bandwidth and near-to-perfect polarizing power.