College Park, Maryland      June 6 - 10 , 2004

TP38: A semiconductor based transmission monitor for the SAND instrument at IPNS

P. Thiyagarajan (Intense Pulsed Neutron Source, Argonne National Lab), Patrick M. De Lurgio (CIS-EL, Argonne National Laboratory, 9700 South Cass Avenue, Argonne, IL 60439), Raymond T. Klann, Charles Fink (NE, Argonne National Laboratory, 9700 South Cass Avenue, Argonne, IL 60439), Douglas S. McGregor (Kansas State University, 151 Rathbone Hall, Manhattan, KS 66506), Istvan Naday (CIS-EL, Argonne National Laboratory, 9700 South Cass Avenue, Argonne, IL 60439), Denis Wozniak, Ed Lang (Intense Pulsed Neutron Source, Argonne National Lab)

A semiconductor based neutron detector was developed for the time-of-flight Small Angle Neutron Diffractometer (SAND) instrument at the Intense Pulsed Neutron Source, Argonne National Laboratory for the simultaneous measurement of transmitted neutron beam intensity and the scattering data. SAND uses neutrons from a pulsed spallation source moderated by a coupled solid methane moderator that produces useful neutrons in the wavelength range of 0.5 to 14 angstroms that are sorted by time-of-flight into 68 constant dT/T=0.05 channels. In addition to allowing effective use of valuable beam time this detector offers higher precision data in the experiments involving complicated sample environment and samples. The detector is constructed using a 0.5 micron thick coating of boron-10 on a gallium-arsenide semiconductor wafer and is mounted directly within a cylindrical (2.2 cm dia. and 4.4 cm long) enriched boron10-carbide beam stop in the SAND instrument. Since this detector is buried inside the beam stop it does not cause any additional parasitic background. The boron-10 coating on the GaAs detector enables the detection of the cold neutron spectrum with reasonable efficiency. This detector can be readily adapted for the SANS instruments at the steady-state sources as well. This paper describes the details of the detector fabrication, the beam stop monitor design, gamma rejection, radiation resistance and overall performance based on the experience during several run cycles at the IPNS.

This work benefited from IPNS, ANL funded by U.S. DOE-BES under contract W-31-109-ENG-38 to U of Chicago and SNS, ORNL funded by DOE-BES under contract DE-AC05-00OR22725 to UT-Battelle, LLC.

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