High Data Rate Detectors for Neutron Reflectometers

Proportional Technologies, Inc. (PTI) proposes the development of a neutron detector based on inclined layers of sealed boron-coated cells, to satisfy the requirements of neutron reflectometers such as the Magnetism Reflectometer MAGREF instrument at Spallation Neutron Source (SNS), ORNL which serves as an example of use of reflectrometry for important science missions. Detectors for these instruments require very high data rates of 20 MHz, spatial resolution of 1-2 mm, efficiencies greater than 60% at 2 Å, and gamma rejection on the order of 2x10-6 or better. Current solutions cannot support the high rate capability required. PTI will develop and build a boron-coated structure that satisfies the above requirements in an array of inclined panels. Each panel consists of a substrate, made of aluminum or other rigid material, supporting a 1  30 array of channels, lined on the bottom side with enriched boron carbide (10B4C). Channel dimensions will be 5 mm  1 mm  150 mm. Resistive wires tensioned at the center of each channel will act as the anode, and all channels will be sealed inside an aluminum welded case to allow operation in vacuum. Wires will be read out individually, in order to decode the channel ID. Charge division will be used to decode the event position along the length of the wire. The panels will be oriented such that neutrons are incident at an angle of 5. The space between panels is dictated by the angle and the length of each panel, calculated as 150·sin(5)=13 mm. A total of 11 panels (330 channels) will be needed to form a sensitive area of approximately 150150 mm2. The proposed detector with improved count rate capability can take advantage of the more intense beams available in neutron science facilities. It will help achieve important scientific objectives and make much better use of expensive accelerator, beam lines and instruments.