A Large-Area Detector for Fundamental Neutron Science

The Science

How long do neutrons live? The answer could change how we think everything from the cosmos to coffee cups works, or in scientific terms, moving beyond the Standard Model. Yet, scientists do not agree on the neutrons longevity. The disagreement is fanned by the limitations of today’s instruments. Now, a highly efficient multilayer surface detector is helping to resolve this puzzle using a unique magneto-gravitational trap located at the Los Alamos Neutron Science Center.

The Impact

The multilayer solid state detector is more efficient and reduces systematic errors in neutron measurements. Both are important considerations to achieving a neutron lifetime measurement accuracy within 1 second, a threshold critical to getting accurate answers. This type of detector can also be used in ultracold neutron (UCN) counting, UCN spectroscopy, and other fundamental UCN science and applications.

Summary

A multilayer surface detector for ultracold neutrons (UCNs) has been demonstrated recently by a multi-institutional team led scientists at Los Alamos National Laboratory. This detector has applications to nuclear physics experiments. The top boron-10 layer is exposed to the vacuum chamber and directly captures UCNs. The ZnS:Ag layer beneath the boron-10 layer is a few microns thick, which is sufficient to detect the charges from the ¹⁰B(n, α)⁷Li neutron-capture reaction, while thin enough so that light generated by neutron capture is easily detected by photomultiplier tubes and other light-sensors including silicon photomultipliers. A 100-nm-thick boron-10 layer gives high UCN detection efficiency, as determined by the mean UCN kinetic energy and others. Low background, including negligible sensitivity to ambient neutrons, has also been verified through pulse-shape analysis and comparisons with other existing helium-3 and boron-10 detectors.

Funding

This work was funded by the Los Alamos National Laboratory Laboratory Director’s Research and Development program.

Publications

Z. Wang, M. A. Hoffbauer, C. L. Morris, N. B. Callahan, E. R. Adamek, J. D. Bacon, M. Blatnik, A. E. Brandt, L. J. Broussard, S. M. Clayton, C. Cude-Woods, S. Currie, E. B. Dees, X. Ding, J. Gao, F. E. Gray, K. P. Hickerson, A. T. Holley, T. M. Ito, C. Y. Liu, M. Makela, J. C. Ramsey, R. W. Pattie, Jr., D. J. Salvat, A. Saunders, D. W. Schmidt, R. K. Schulze, S. J. Seestrom, E. I. Sharapov, A. Sprow, Z. Tang, W. Wei, J. W. Wexler, T. L. Womack, A. R. Young, and B. A. Zeck, “A Multilayer Surface Detector for Ultracold Neutrons.” Nuclear Instruments and Methods in Physics Research Section A 798, 30-35 (2015). [DOI: 10.1016/j.nima.2015.07.010]