Convergent-beam neutron crystallography

Two monolithic polycapillary optics of different focal length and beam convergence are employed to investigate the use of focusing lenses for the neutron convergent-beam method for time-of-flight crystallography with a broad neutron wavelength bandwidth. The optic of short output focal length (15.5 mm) with a beam convergence of 16.8 (10)° has a focal spot diameter of ∼100 µm for 3.2 Å neutrons. For an MnF₂ single-crystal sample of this diameter on a pulsed neutron source, this lens gives an expected integrated intensity gain of ∼100 for a 020 Bragg peak. Further measurements on a powder diffractometer show that the expected diffracted beam intensities for Ni have gains in excess of 500 for powder samples of this diameter. The degradation of resolution is minimized in the backscattering geometry.