Focusing and polarized neutron small‐angle scattering spectrometer (SANS‐J‐II). The challenge of observation over length scales from an ångström to a micrometre

SANS‐J (a pinhole small‐angle neutron scattering spectrometer at research reactor JRR3, Tokai, Japan) was reconstructed as a focusing and polarized neutron small‐angle scattering spectrometer (SANS‐J‐II). By employing focusing lenses of a biconcave MgF 2 crystal or of a sextupole permanent magnet and a high‐resolution photomultiplier, the minimum accessible magnitude of the scattering vector q min was improved from 3 × 10 −3 Å −1 to an ultra‐small‐angle scattering (USAS) of 3 × 10 −4  Å −1 . Compared with a Bonse–Hart double‐crystal method, the advantages of focusing USAS are the efficient detection of anisotropic USAS with an area detector, an improvement in q resolution Δ q / q at conventional magnitudes of the scattering vector q ~ 10 −3  Å −1 and a gain in neutron flux in the conventional q region of q ~ 10 −3  Å −1 .