Pulsed-Beam Measurments of Nuclear Reactions at UNC's Laboratory for Experimental Nuclear Astrophysics (2015)

Undergraduate: Eric Machado

Faculty Advisor: Christian Iliadis
Department: Physics & Astronomy

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UNC's Laboratory for Experimental Nuclear Astrophysics (LENA) is home to a sophisticated proton accelerator of the highest intensity of any currently in use in our field. The purpose of this accelerator is to utilize gamma-ray spectroscopy to study the nuclear reactions that occur in the cores of massive stars. In the type of reactions measured at LENA, a proton of a given kinetic energy is incident on a target nucleus, leaving a product nucleus in an excited state. The excited nucleus then decays down to the ground state through a series of intermediate decays. The ratio of decays of a certain decay mode to the total decays is called the branching ratio. Recently, we have worked to replace our old acceleration column with a column that will improve intensity by a factor of ten. We have also improved the proton beam-transport system by adding new beam-focusing lenses as well as new beam-stops to measure the improved beam current. Along with these improvements, we have demonstrated the ability to pulse the beam with a duty cycle of 10%. By collecting the spectra separately when the beam is on and when the beam is off, we are able to more easily analyze spectra, since we can discriminate which gamma-radiation comes from the reaction and which comes from the background.