Design of Air Scattering Chamber for the Powder Diffractometer SPICA

An idea of the air scattering chamber was adopted for the multipurpose bank in the powder diffractometer SPICA at J-PARC/MLF. To design the air scattering chamber, the loss of neutrons in the chamber and the contamination of scattered neutrons by air were studied by numerical calculation and simulation. The loss is 6 to 11% although it is almost double compared to that of a conventional vacuum scattering chamber. The contamination of the scattered neutrons by air is less than 1% by placing blades made of B 4 C resin in the chamber as many as possible. The contamination is seen on the TOF spectrum as continuous backgrounds between diffraction peaks. We regard the air scattering chamber with the blades is acceptable for the multipurpose bank of SPICA.