The high-intensity option of the SANS diffractometer KWS-2 at JCNS - characterization and performance of the new multi-megahertz detection system.

A new detection system based on an array of 3He tubes and innovative fast detection electronics has been installed on the high-intensity small-angle neutron scattering (SANS) diffractometer KWS-2 operated by the Jülich Centre for Neutron Science (JCNS) at the Heinz Meier-Leibnitz Zentrum in Garching, Germany. The new detection system is composed of 18 eight-pack modules of 3He tubes that work independently of one another (each unit has its own processor and electronics). To improve the read-out characteristics and reduce the noise, the detection electronics are mounted in a closed case on the rear of the 3He tubes' frame. The tubes' efficiency is about 85% (for λ = 5 Å) and the resolution slightly better than 8 mm. The new detection system is characterized by a dead-time constant of 3.3 µs per tube and an overall count rate as high as 6 MHz at 10% dead-time loss. Compared with the old detector this is an improvement by a factor of 60. The much higher count rate will shorten the measurement times and thus increase the number of experiments possible in a given time period by the optimal use of the high flux of up to 2 × 108 n cm-2 s-1 at the sample position. Combined with the event-mode operation capability, this will enable new scientific opportunities in the field of structural investigations of small soft-matter and biological systems. The implementation of the detector in the high-intensity concept on KWS-2, its characterization and its performance based on test experiments are reported in this paper.