Detecting Neutrons… with a Little Help from Magnetic Shield

You’ve heard the phrase “Big Oaks from Little Acorns Grow”? A simple request for literature right before Christmas last year led to Magnetic Shield’s involvement in a project that called for the design and production of 288 custom CO-NETIC® AA photo-multiplier shields with stainless steel flanges. The PMT shields we developed are being used to protect 288 independent photo-multipliers from stray magnetic fields. While the purchase of the shields was coordinated by a single college professor, nine individual schools of higher learning were the eventual buyers. The product in which our shields are employed is called MoNA, which stands for Modular Neutron Array, a large-area neutron detector capable of measuring the speed and direction of neutrons after an isotope beam strikes a target placed next to it. MoNA was funded by the National Science Foundation through nine individual Major Research Instrumentation (MRI) grants to the nine participating institutions.

But let’s get back to the beginning. Following up on the request for literature, Brad Friestedt, our Eastern Regional Sales Manager, contacted Bryan Luther, Visiting Associate Professor of the National Superconducting Cyclotron Laboratory at Michigan State University (East Lansing, MI) in January. The NSCL was in the process of creating the MoNA, which is to be used to study the interior of neutron isotopes with relatively short life cycles. Neutrons are the neutral particles in the core of atoms. In February we produced a prototype shield based on NSCL specifications. Then, in May, nine separate colleges and universities placed orders for 290 total shields.

The National Superconducting Cyclotron Laboratory leads the United States in rare isotope research, which has led to improvements in radiation treatments for cancer patients. With primary funding from the National Science Foundation and Michigan State, the NSCL also operates two superconducting cyclotrons.

The MoNA consists of 144 plastic scintillator bars equipped with photomultipliers that incorporate our shields on each end. Plastic scintillators are necessary to convert neutrons into charged particles to generate a measurable signal. The photomultipliers detect and measure the arrival of scintillation light and also time the light to calculate the velocity of the neutrons. In addition, MoNA detects the number of isotope fragments caused by the breakup of the isotope beam as it strikes the target.

The MoNA project also created a wide range of educational opportunities for undergraduate physics students to participate in its manufacture and use. The construction of the 144 plastic scintillator bars was spread out over the nine universities and colleges so that a diversified selection of students were able to take part in the project. The students – and Magnetic Shield as well – were fortunate enough to be able to work together to add to the world’s knowledge concerning neutrons in particular and nuclear physics in general.

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