Welcome to homepage of the development of the BT7 Dual Array Neutron Monochromator (BT7-DAM) for use at the NIST Center for Neutron Research (NCNR). The Instrument Development Group (IDG) at The Johns Hopkins University is proud to embark on the second double focusing monochromator for NIST.

I would first like to thank those responsible for the existence of this project.

 

	Dr. Paul Brand Materials Research Engineer NIST Center for Neutron Research Dr. Brand made invaluable contributions to the development of the MACS-DFM both on a technical and managerial level.   Dr. Collin Broholm Professor of Physics & Astronomy Johns Hopkins University Dr. Broholm provided the initial funding to begin the development of the MACS-DFM and conceived the revolutionary idea of bending a thin member to achieve vertical focusing.   Dr. Stephen Smee Mechanical Engineer & Manager Instrument Development Group Dr. Smee received his PhD in Mechanical Engineering from the University of Maryland. For his dissertation, he developed the MACS-DFM. The primary reason for the success of the project was his innovations in blade technology.   Mr. Joseph Orndorff Electronics Engineer Instrument Development Group Mr. Orndorff completely designed and implemented the control electronics and wrote all the software for the MACS-DFM. Mr. Orndorff's robust control software allowed the IDG to easily test, revise and finalize several mock-ups and, most importantly, the full-up design.     Mr. Dwight Barry Machinist/EDM Specialist NIST Shops Division Mr. Barry's hard work and machining experience proved to be vital during the creation of the blade. His attention to detail and EDM know-how provided the IDG with blades that conformed to the tightest tolerances and utmost precision.
The acquisition of this project is largely due to the success of the MACS-DFM (Multi Axis Spectrometer Double Focusing Monochromator). This was the first monochromator developed by The IDG. The MACS-DFM is able to achieve double focusing with a significant reduction in background. This is done by choosing a neutron friendly material and exploiting its physical properties to position the focusing crystals.   Aluminum is found to be "transparent" to neutrons. In other words, neutrons can pass through it almost unaffected. Similar to light passing through clear glass. However other materials, such as steel, interact with the neutrons and can scatter or absorb them. Therefore, aluminum is used as the primary structural material for any instrument that will be located in the neutron beam's path. Another advantage to using aluminum is its machinibility and elasticity.   BLADE TECHNOLOGY   The crystal positioning device is simply a thin member of aluminum with a varying cross section (we call it a blade) that, when subjected to an axial displacement, buckles and creates a profile that follows the arc of a circle. The radius of this circle is easily controlled by adjusting the amount of this displacement. With crystals attached to the blade's circular surface, a vertically focused array of crystals is created. We call the implementation of this design blade technology.   Horizontal focusing is achieved by the ability to rotate each blade along the buckling axis. The system becomes low background due to the minimization of materials in the beam. In a perfect world, one would just have the crystals sitting in space, positioned perfectly for an experiment, however one finds out quickly that this is not possible. So, the IDG is able to come very close to this situation by designing a system that has a small amount of hardware in the beam's path.    Along with this remarkable blade technology, a full control system was also developed by The IDG. This includes an electronics rack full of controlling hardware (indexers, limit switch control, etc...) and a control program using LabVIEW to accurately position and monitor all axes of the instrument. The reason to mention these aspects of the MACS-DFM is because the same technology will be used to create a monochromator for The BT7 Experiment at NIST. There are several requirement changes from the MACS-DFM to the BT7 Monochromator, however, the most evident is the introduction of a second array. Due to the location and "inaccessibility" of this monochromator, it is advantageous to incorporate two arrays, each consisting of different crystals. While the MACS-DFM uses pyrolitic graphite (PG) as its focusing crystals, the BT7 Monochromator will incorporate both PG crystals and Copper 220 crystals.   I am looking forward to another successful effort from the members of The IDG as we embark on the BT7 Dual Array Monochromator.   Cheers,   Gregg Scharfstein, Project Manager: BT7 Dual Array Monochromator