MRI-R2: Development of a High-Flux Deuteron-Deuteron Fusion Neutron Source for 40Ar/39Ar Geochronology

Berkeley Geochronology Center, Berkeley CA

Investigators

Abstract

This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5). This project will develop a facility to use nuclear fusion of deuterium atoms and ions to create a large concentration of neutrons with uniform energy of 2.45 million electron volts. The fusion reaction has been successfully induced in previous experiments, but this project will use a novel radially inward-focussing deuterium ion beam geometry to pursue a neutron concentration 1000 or more times higher than previously achieved. This neutron generator will be used to irradiate geological samples for the argon-40/argon-39 dating method, in which potassium-39 must be converted to argon-39 through neutron capture. The source of neutrons for this widely used dating method has previously been conventional nuclear reactors powered by fission of uranium, producing a broad range of neutron energies with several suboptimal effects. In contrast, the device to be developed by this project will reduce atomic recoil and unwanted nuclear reactions, thus producing more accurate age information with less radiological risk to analysts, and without generating hazardous radioactive waste. These improvements will enhance the ability to accurately date fine-grained minerals such as clays, whose ages are often useful as a guide for petroleum and ore deposit exploration. Other likely applications include the chronology of human evolution and of the early solar system. The device will be useful for applications beyond dating, specifically including trace element geochemistry, nuclear medicine, materials science, and condensed matter physics. The ability to provide rapid neutron activation data will be applicable to the design of a next generation of fission reactors for nuclear power. The project will provide training to students and postdoctoral researchers and thus contribute to replenishing the depleted pipeline of early career scientists with expertise in nuclear sciences, thereby addressing growing concerns arising from national security and energy needs. The project will also enhance cross-disciplinary collaboration between nuclear scientists and earth scientists.