Optimization of a Bonse–Hart Ultra-Small-Angle Neutron Scattering Facility by Elimination of the Rocking-Curve Wings

Abstract

The ORNL Ultra-Small-Angle Neutron Scattering (USANS) facility at the High Flux Isotope Reactor (HIFR) has been recently upgraded, using the BonseHart technique. Si(111) triple-bounce channel-cut single crystals have been used for both the monochromator and analyzer. The total width of the rocking curve of the analyzer is about 1.6" and the wavelength of the primary neutron beam is 2.59 ,~,. It has been demonstrated that, owing to the low neutron absorption of silicon, the wings of the rocking curve are generally contaminated by neutrons propagating and diffracting inside the walls of channel-cut crystals. This parasitic intensity has been eliminated by the cutting of a groove in the long wall and the insertion of a cadmium absorber (0.6 mm thick). This modification effectively suppresses the wings of the rocking curve by over two orders of magnitude and thus dramatically improves the sensitivity of the diffractometer. The upgraded facility has been tested with several samples, including a polystyrene latex with a radius of 2.50 × 104 ,~ as determined by optical microscopy. The average radius calculated from USANS data is 2.48 × 104/~, in excellent agreement with independently determined dimensions. The minimum accessible scattering vector of the upgraded USANS facility is Qmin "~ 2 x 10 -5 ~-1, which corresponds to a maximum resolvable real-space dimension of 27t/Qmi n ~ 3 x 105 ,~ (30 ~tm).

Fractal approach in petrology: combining ultra small angle, small angle and intermediate angle neutron scattering

“…It is a Bonse-Hart double-crystal diffractometer equipped with triple-bounce Si(111) channel-cut crystals, which have been modified by cutting an additional groove for a cadmium adsorber (Agamalian, Wignall & Triolo, 1997) and by very deep surface etching (Agamalian et al, 1998). Data obtained in three sections characterized by different theta-steps and accumulation times, have been desmeared (Lake 1967, Feigin & Svergun, 1987, normalized by the primary incident neutron beam fluctuations, intensity variations due to monochromator positioning, sample thickness and sample transmission and then conference papers spliced to the high angle portion by means of standard techniques (Agamalian, Wignall & Triolo, 1997). As the USANS camera becomes unreliable for q > 0.003, there is a small region of q not covered by both USANS and LOQ instruments.…”

“…The size limit of this technique is at least two orders of magnitude below the lower limit of the optical microscope. However, recent progress in ultra-small angle neutron (USANS) and X-ray scattering (USAXS) instrumentation enables one to access the microstructure of rocks well beyond the above limit of about 2000 Å (Agamalian, Wignall & Triolo, 1997, Radlinski et al, 1999. In this paper, by applying fractal theory to rocks, we present new USANS, SANS and intermediate angle neutron scattering (IANS) experiments performed on various rocksamples from different localities, with an accuracy previously unobtainable.…”

Coherence approach to neutron polarization propagation in instruments

“…Incoherent scattering, large angle coherent scattering, or absorption can be taken into account by a suitable imaginary part of the refraction index. 5 The approximation is valid for thermal neutrons as used in spin echo small angle neutron scattering [18][19][20][21] ͑SESANS͒ or ultrasmall angle neutron scattering [22][23][24] as the refractive index is close to unity. Note that the deviation from unity of the refractive index is proportional to the square of the wavelength so it increases rapidly for increasing wavelength.…”

Analysis of structures of rubber-filler systems with combined scattering methods

“…Bonse-Hart cameras for neutron scattering experiments are also available at neutron facilities. [23][24][25][26] Silicon single crystals are used as the monochromators and the analyzers in this technique as well as in the USAXS instruments. Bonse-Hart cameras used in neutron scattering experiments can cover 2 Â 10 À4 oqo4 Â 10 À3 nm À1 with an incident neutron wavelength of 0.2 nm.…”