Radioactivity measurements of the Farmville meteorite using gamma-gamma coincidence spectrometry (2015)

Undergraduate: Brenden Longfellow

Faculty Advisor: Christian Iliadis
Department: Physics & Astronomy

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Meteoroids are exposed to cosmic radiation from the Sun and from outside the solar system. Cosmic radiation consists mainly of high energy protons and ¿¿-particles and initiates nuclear reactions in meteoroids that lead to the production of radioactive cosmogenic nuclides, or radionuclides. Once a meteorite has fallen to Earth, the atmosphere shields against further cosmogenic production of radionuclides and the radionuclide abundance begins decaying exponentially over time. Measurement of this decay provides information on the irradiation conditions of the meteorite fragment, the intensity of cosmic rays in the inner solar system, and variations of the solar magnetic field strength over the past few hundred years. This project reports on the measurement of the activity of the radionuclide 26Al in a sample of the Farmville meteorite, which fell in Farmville, North Carolina on December 4, 1934. The decay of 26Al through positron emission simultaneously produces three ¿¿-rays, a characteristic photon of 1808.7 keV energy and two 511 keV photons that are emitted back-to-back. Measurements were made using a cost-effective ¿¿¿¿-coincidence spectrometer system consisting of two NaI scintillation detectors. In ¿¿¿¿-coincidence spectrometry, only events that are recorded by both detectors within a given time window and within a given energy range are kept, significantly reducing the background.