Dominik Wermus (Virginia Military Institute, Lexington, VA 24450), Doug Higinbotham (Thomas Jefferson National Accelerator Facility, Newport News, VA, 23606)  24 bars, no PMTs – had to be taken from old bars whose scintillating plastic had turned yellow from use  PMTs cleaned, then tested in a blackbox  PMTs attached to scintillator bars with Elastosil adhesive  Bars inspected for light leaks  Optimum operating voltages of all PMTs were determined  Began running tests with cosmic rays by stacking up detector bars in different arrangements  24 bars have been assembled, PMTs’ operating voltages determined  Results compared to known constants (frequency, angular distribution)  Bars were determined ready for use in upcoming experiments  “Veto” front layer still needs to be assembled  Array needs to be racked ABSTRACT Detecting neutrons is of high interest to scientists at Thomas Jefferson National Accelerator Facility. Neutron detectors for use in Jefferson Lab's experiments are made of rectangular bars of scintillating plastic with PMTs (photomultiplier tubes) attached to each end. When charged particles pass through, scintillator plastic releases photons, which activate the light- sensitive PMTs. Neutrons have a small but known probability of colliding with nuclei in the plastic and releasing protons, which themselves are detected. A two-inch wall of lead in front blocks out nearly all charged particles, making the array of scintillator bars a neutron detector. For several upcoming experiments in Hall A, scientists wished to add another detector, made of twenty-four one-meter-long bars stacked together. There were three stages to the project: physically assembling the bars, setting up the data acquisition system, and testing the detector with cosmic rays (high-energy particles from deep space). PMTs were taken from old bars, then were cleaned, tested and glued onto new scintillator bars. A data acquisition system composed of an ADC (analog-to-digital converter) and TDC (time-to-digital converter) was assembled, allowing for calibration and testing with cosmic rays. The known constant 2 MeV deposited per cm of scintillator was used to set the PMT high voltages. Once set, the angular distribution and cosmic ray rate of 100 rays/m 2 ·s were verified. The detector will be used for experiments such as E (Short Range Correlations for the Triple Coincidence (e, e’pn) Reaction) for detecting neutrons released in particular collisions. References: [1] R. Subedi et al., Science 320, 1476 (2008); published online 29 May 2008 ( /science ). [2] Photos by Kandice Carter and Or Chen I want to thank my mentor, Doug, Lisa Surles-Law, and everyone I’ve met and worked with this summer. This experience of meeting real scientists from around the world has been rare and worthwhile. Also thanks to Jefferson Lab, and of course the Department of Energy for providing this opportunity.  Neutrons are released in many nuclear experiment, including the upcoming Triple Coincidence (e, e’np) Reaction in Hall A [1]  Hall A Neutron Detector (HAND) is made up of stacks of scintillating plastic bars with photomultiplier tubes (PMTs) attached to each end  Scintillating plastic allows detection of charged particles – neutrons occasionally knock out protons  New detector built from 24 detector bars  Neutron detectors in Jefferson Lab’s Hall A are made up of several layers of scintillating plastic bars  Scintillators glow when charged particles (protons, electrons, etc.) pass through them  Neutrons are detected when they knock protons out of nuclei in the plastic  A two-inch wall of lead in front blocks out unwanted charged particles, forming a neutron detector  When bars completed, five at a time were arranged in detector fashion (side-by-side, one “trigger” flat on top)  Hooked up to data acquisition device consisting of ADC (analog-to- digital) and TDC (time-to-digital) components  ROOT physics software used to test bars with cosmic rays; collected and recorded energies of particles passing through  “Trigger” bar used to determine paths and timing of cosmic rays  High-energy particles originating from deep space  Flow through the Earth’s surface at about 100 times/m 2 ∙s at sea level [2]  Usually relativistic protons which crash in atmosphere, causing “particle shower”  Scintillators are usually detecting muons (heavy negatively charged particles)  Good for testing particle detectors