NSF Award
2320400
The study of neutron-rich atomic nuclei can reveal effects about how protons and neutrons interact inside nuclei. These play an important role in the formation of the elements in the universe and help scientists understand how the nuclear core of atoms form. One of the ways to investigate these nuclei at the edge of stability is to measure their breakup products, which includes the neutrons that are not needed to hold the smaller nuclei together. The detection of neutrons is challenging because they have no charge and only interact with the nuclear core of atoms. This award will support the development, building, and commissioning of a modular array based on plastic scintillator for the detection of fast (between one third and one half the speed of light) neutrons. The new detector array will significantly improve how precisely we can determine the neutrons’ position compared to current neutron detectors because it will make use of state-of-the-art photo-sensors, and as a result enable nuclear structure measurements with superior precision. The detector modules will be built and tested to a large extent at the seven participating undergraduate institutions, allowing undergraduate students to learn key technical skills and to contribute to nuclear physics research in a meaningful way. Scintillation detectors, i.e. detectors that measure the scintillation light that stems from subatomic particles interacting within the detector, are widely employed in research, industry, and medical imaging, so these skills can be applied in many crucial fields.<br/><br/>Contemporary fast neutron detectors use conventional detector configurations of long plastic scintillator bars read out by pairs of photo-multiplier tubes (PMTs). The position of the neutron interaction is deduced from the time difference of the signals measured by each PMT at opposite ends of the detector bar, and from which detector bar has been hit. A different approach to scintillation-light collection is pursued in this new detector using arrays of Silicon Photo-Multipliers (SiPMs), overcoming the limitations of current designs and resulting in improved position resolution for fast neutron detection. This also allows a tiled design that offers much more flexibility in adjusting the active area of the array to specific experiment needs. Invariant-mass spectroscopy of neutron-unbound states in elements beyond oxygen requires such an experimental setup with improved resolution. As one moves to heavier unbound systems one faces higher level densities. To resolve these in the reconstructed decay energy spectrum requires higher momentum (and thus position) resolution. A high position resolution also improves the discrimination of double-scattered events and allows the use of higher beam energies that are available at the rare-isotope beam facilities such as the Facility for Rare Isotope Beams (FRIB). The completed instrument will serve the broad FRIB user community and enable invariant mass measurements at the resolution that is required for heavier and more exotic isotopes that are available with FRIB beams.<br/><br/>This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.
