Atomic nuclei with an overabundance of relative to the number of protons are known to The Drip Line is the jagged line on the chart of nuclides that marks the boundary between neutron bound exhibit different structural properties than their more stable counterparts. For example, the and neutron unbound isotopes. Unbound isotopes have a binding energy of 0 for at least one of their constituent 13Be is neutron unbound and lies just beyond the Neutron Drip “shells” in which the neutrons arrange themselves are known to change far from stability, resulting neutrons, meaning the outermost valence neutrons spontaneously fall off the nucleus until the nucleus becomes Line. In fact, it is surrounded on three sides by neutron-bound from a relative shifting of the discrete energy states that are available to the valence particles. The neutron bound. Unbound nuclei decay by neutron emission mediated by the strong nuclear force. Theoretically isotopes yet decays 18 orders of magnitude faster than any of exotic neutron-rich nucleus 13Be provides an excellent opportunity to explore the effects of neutron there are numerous nuclei near the Neutron Drip Line (and the Proton Drip Line) that have not been studied. them. Furthermore, it is just one neutron away from a closed

excess on shell behavior since it has one more neutron than an established closed shell at neutron Because the area of known nuclei is so small compared with the entire nuclear landscape, the rules formed to shell (12Be has N=8). Thus, 13Be affords an excellent opportunity L i f e number N = 8. The ultimate goal of this research is to understand the decay process by which 13Be describe the behavior to study nuclear shells far from stability. -

12 13 disintegrates into a neutron and a Be nucleus, to identify and measure the energy states of Be of nuclei in the H a l f and infer the energy levels occupied by its valence neutrons, and to compare the measured results known region do not to contemporary shell model calculations. In November, 2010, an experiment was conducted at the necessarily hold up National Superconducting Cyclotron Lab at Michigan State University that produced 13Be and for nuclei in general.

recorded events associated with its disintegration. The work accomplished this summer has The purpose of this Data Source: nndc.bnl.gov 12 focused on calibrations of the various detector systems used to record and track the Be nuclei research is to study Shown at left are two shell-model calculations that use different 13 that result from the decay of Be. These included position and energy-sensitive calibrations that and understand the effective particle interactions ("SFO" and "PSDMK") to predict 12 are necessary to track the trajectories and measure the energies of the Be nuclei. Such territory beyond the the energy levels of 13Be, in comparison with the energy levels 12 calibrations are essential to the proper identification of Be, which eventually will lead to Neutron Drip Line. measured experimentally from previous research. 13 inferences about the structure of Be just prior to its dissociation. Conspicuously, there is disagreement amongst all three. This

Source: Y. Kondo et al., Phys. Lett. B 690, 245 (2010) research seeks to confirm the pictured experimental result.

MoNA (Modular Neutron Array): 14 Work this summer has focused on calibrations of the detector systems. Below are a few examples of those calibration procedures. Be enters the Neutron detector. experiment vault. Scintillator Design (Left) Schematic of the scintillator design 13 14Be Be n n (thin scint. pictured, thick scint. similar). Units consist of a transparent scintillating 12 Be material surrounded by 4 photomultiplier tubes (PMTs) that detect the flashes of passing particles. CRDC (Cathode Readout Drift (Right) The gains of the 4 PMTs must be Pot Scint. Timing Chamber) gas filed position matched so each provides the same output detector. detectors. A1900 Timing Detector. response given the same input light signal. This corresponds to aligning the centroids of Reaction Target: Converts 12 the Gaussian peaks shown in the output 14Be to 13Be. Be Ion Chamber: Not used in this experiment. charge histograms. Sweeper Magnet: Sweeps (Bottom) Light intensity varies with distance charged 12Be daughter squared. However the thin and thick TCRDC gas filled Counts nucleus toward the CRDC position detectors. Thin Scintillator: Measures the Thick Scintillator: Measures the scintillators are not position detectors and detectors. The neutron change in energy of the passing total energy and stops the must be calibrated to correctly measure proceeds straight ahead, particle as well as the time at particle. particle energies regardless of their unaffected by the which it passes. trajectories through the scintillators. magnetic field.

This work is being undertaken by the members of the MoNA Collaboration*, an undergraduate Charge (Arbitrary Units) research initiative funded in part by grants from the National Science Foundation and consisting of BEFORE AFTER 10 primarily undergraduate institutions partnering with Michigan State University. Currently under study by the members of the MoNA Collaboration are 13Be, 23O, and 24O. These experiments are

conducted at the National Superconducting Cyclotron Laboratory at Michigan State University. Counts

I would like to acknowledge and thank the Research Experience for Undergraduates (REU) program

of the National Science Foundation for providing funding for my research this summer and Ohio Units) (Arbitrary Charge Wesleyan University for hosting me. *Members: Augustana College, Central Michigan University, Concordia College, , , Indiana University-South Bend, Michigan State University, , Rhodes College, Wabash College, Westmont College X-Position (mm) Charge (Arbitrary Units)