BSM-PM: WoU-MMA: A Single Atom Microscope for Measuring the Ne-22 + He-4 Reaction

Michigan State University, East Lansing MI

Investigators

Abstract

Most of the chemical elements across the periodic table are formed inside of stars as the stars age and subsequently die. Roughly half the chemical elements that are heavier than iron, such as copper and silver, are formed by the slow capture of neutrons as certain types of stars age. The sources of these neutrons are nuclear reactions involving the capture of a helium nucleus by a neon nucleus. This particular nuclear reaction produces both a neutron and a magnesium nucleus and has a very low probability of taking place. The goal of this project is to develop and test a laser-based detector that is capable of efficiently capturing all the product magnesium atoms and selectively identifying and counting them with single atom sensitivity. In the first phase of this project, the atom capture and laser detection process will be studied and optimized. In the second phase, a proof-of-principle measurement using this new laser-based detector will be carried out. Eventually this laser-based detector and technique will be used to determine the cosmological origin of elements such as copper and silver. This project is the Ph.D. dissertation research for one graduate student and will also provide research experience to undergraduate students majoring in physics and astronomy. As a public outreach component of this project, the PI will produce a stand-alone planetarium show which tells the story of chemical element formation inside of stars. The program can be delivered at planetariums around the country without the need for a live in-person narrator. This is an extension of the PI’s previous NSF-funded public outreach activities and will provide scientific training and experience to additional undergraduate students majoring in the creative arts. The primary goal of this project is to demonstrate the feasibility of using optical single atom detection in cryogenic noble gas solids for detecting the atomic products of low yield nuclear reactions and rare nuclear decays. In the so-called Single Atom Microscope (SAM) technique, the recoiling product nucleus in the form of a neutral atom is implanted in and captured by a cryogenic noble gas solid host. The host solid can be grown sufficiently free of impurities, which minimizes optical backgrounds, and is adequately transparent at the relevant optical wavelengths, which allows for laser probing of the product atoms. Laser induced fluorescence (LIF) emitted by the product atoms is then imaged onto a CCD camera, which spatially resolves each individual product atom. Single atom detection of Ba in solid xenon has been demonstrated, while promising results for Rb in solid neon have also been reported. The motivation for developing the SAM technique includes measuring key nuclear reaction cross sections relevant for nuclear astrophysics and the search for neutrinoless double beta decay. Within the scope of this proposal over the next three years, the PI aims to first perform a proof-of-principle nuclear reaction cross section measurement of the Ne-22+alpha to neutron+Mg-25 nuclear reaction at a well-known resonance to ``shake down'' the technique. This will first require measurements of the fluorescence yield of neutral Mg in solid Ne as well as attempts to demonstrate the optical single atom detection of Mg in solid Ne. The long-term goal is to perform the definitive nuclear cross section measurements of the Ne-22+alpha reactions. Roughly half of the elements heavier than iron are produced by the slow neutron capture process (s-process) inside of stars. One of the key sources of neutrons that feeds the s-process is the Ne-22+alpha to neutron+Mg-25 reaction. Using the SAM technique, coupled with a modest recoil separator for isotope selectivity, to measure these reactions by detecting the product Mg atoms would provide a crucial independent cross check of complementary completed and planned experiments. This proposal is a step towards developing the SAM technique for this application. Along the way, this project will add to the knowledge of the laser induced fluorescence behavior of atoms inside noble gas solids which has applications in detection for nuclear astrophysics, quantum sensing, and tagging for neutrinoless double beta decay searches. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.