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 MgF2 crystal or of a sextupole permanent magnet and a high‐resolution photomultiplier, the minimum accessible magnitude of the scattering vector qmin was improved from 3 × 10−3Å−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 Δq/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.