Progress Towards a Single Atom Microscope for Nuclear Astrophysics*

The Single Atom Microscope (SAM) project aims to measure rare, low-yield nuclear reactions relevant to nuclear astrophysics. This novel detector technique involves capturing the product atoms in a cryogenically frozen and optically transparent noble gas solid and then counting the embedded atoms via laser-induced fluorescence and optical imaging. Due to the unique absorption and emission wavelengths of the product atoms—enabled by the lattice of noble gas atoms—optical filters can distinguish between them to select the wavelength range of interest, making single-atom sensitivity feasible. Rubidium atoms embedded in solid Krypton are being used for pilot measurements because they are laser-friendly and the system is astrophysically relevant—⁸⁴Kr(p, γ)⁸⁵Rb is a key branching point for determining the reaction flow in the p-process. Results from a preliminary experiment indicate that high energy Rb ions fully neutralize in Kr, which means single atom detection of neutral Rb is an appropriate, efficient path for measuring this specific nuclear reaction. Calibrating the brightness of Rb atoms in Kr is the next step towards achieving single atom sensitivity, which will complete the trinity of high efficiency, selectivity, and sensitivity required to measure nuclear reactions in a way that is complementary to other methods.