1. The NSCL is funded in part by the National Science Foundation and Michigan State University. The MoNA Detector of NSCL She Has Secrets To Tell! Gary Kunzi Jenison Public High School Gary Kunzi Jenison Public High School J.T. Miller Thornapple Kellogg High School J.T. Miller Thornapple Kellogg High School Rich Lund St. Johns High School Rich Lund St. Johns High School MoNA, (the Modular Neutron Array), is a large-area high efficiency neutron detector housed at the National Superconducting Cyclotron Laboratory, NSCL. The detector was designed and built by a collaboration of 10 colleges and universities in conjunction with the NSCL with support from the National Science Foundation. MoNA is also quite capable of detecting muons, which are a form of high energy lepton. All of Earth’s naturally occurring muons are formed by cosmic rays (mostly high energy protons) interacting with the atmosphere. When cosmic rays collide with the nuclei of air molecules, they form pions which quickly decay into muons, just in time for MoNA to detect them. During the PAN program at NSCL, Science Instructors are given the opportunity to study neutron emitting radioactive sources along with cosmic ray muons using MoNA’s finely tuned talents. In order to fully grasp what MoNA’s 144 scintillating detection bars are up to on a daily basis, it was necessary for the teams of PAN to study an individual bar using an oscilloscope and a neutron emitting radioactive source (in this case, Californium-252). When a neutron collides with a hydrogen nucleus, vibrations cause the release of many photons which travel down both sides of the bar. The signal is then amplified using 12 stages of dynodes which converts the photons to an electric pulse. In the images to the left, Gary Kunzi and J. T. Miller are observing the oscilloscope which graphs the electric pulse strengths from both the right and left end of the bar. Graphs can be compared to deduce any time difference in the signals at both ends which indicates which path (left or right) took light longer to travel through. By analyzing the strengths of the pulse along with time differences, the position of a radioactive source can be determined. Source at far LeftSource at far RightSource at CenterSource at Unknown Location Using the program “SpecTcl”, thousands of data points can be analyzed rather than manually recording one at a time. By interpreting the graphs below of a radioactive source at three known positions along one of MoNA’s bars, an equation could be deciphered which would allow the team to calculate the uknown location of a source of radiation. The calibration graphs above were used to create three separate graphs whose best fit lines would indicate any possible position of a radiation source detected by MoNA. The graphs shown are position vs. time difference, position vs. Q difference (which indicates intensity), and position vs. COG (center of gravity). Peak Value = 5.4ns The distance muons selected for travel on average the height of MoNA, 1.5m. Cosmic rays are primarily high energy protons which come from all directions of space and strike the earth’s atmosphere. When the proton collides with the nucleus of an air molecule atom, a nuclear process occurs producing multiple pions, kaons, and mesons which decay into muons. A muon has an extremely short half life of 2.2μs. (That’s faster than you can blink!) However, when it is produced it is traveling at near the speed of light, and because of relativistic effects, some of them remain long enough to be detected by MoNA. The muons which come from directly above MoNA travel through its thickness, 1.5m. These are the muons that are most often detected, as they have taken the least amount of time to reach MoNA after being produced. The graph to the right was analyzed by team Up And Atom from the I layer of MoNA and showed a peak value of 5.4ns. If on average it takes 5.4ns to pass through the 1.5m thickness of MoNA, the velocity of the muons can be calculated as: V = d / t = 1.5m / 5.4 x 10-9s = 2.8 x 10 8 m/s The atmosphere protects you from cosmic rays. Radioactive Man protects you from all the rest! Using each graph’s best fit line for the data, the position of the source was found to be 1.26m, 1.22m, and 1.22m respectively, which gave team Up And Atom an average position of 1.23m. (Actual position was 1.264m) Louis de Broglie the Pug Team Consultant