Abstract: Neutron Depth Profiling (NDP) is a nondestructive analytical technique used to characterize the concentration of certain light isotopes in a material as a function of depth. The technique is based on the principle of measuring the residual energy of charged particles in neutron induced reactions. Historically, NDP has been performed using a single detector, resulting in low intrinsic detection efficiency, and limiting the technique largely to high flux research reactors. This work describes a new NDP instrument design with higher detection efficiency, achieved by summing the spectrum obtained from multiple detectors. A digital data acquisition system was chosen over the typical analog system for this instrument, as it allowed for an economical implementation of multiple detectors and a streamlined process for spectrum summing. This design is capable of acquiring a statistically significant charged particle spectrum at facilities limited in neutron flux and operation time. The spectrum obtained from a sample of Borophosphosilicate (BPSG) with this multidetector instrument was compared to the analysis performed on the same sample at the National Institute of Standards and Technology (NIST), using a benchmarked, single detector NDP instrument. Results of the analysis indicate the resolution of the multidetector instrument suffers slightly due to gamma contamination in the beam, but is capable of achieving nearly half the count rate of the NIST instrument. A model of the instrument investigating BPSG was constructed using the GEANT4 toolkit, and used to compare against the experimental results. A section of 6Li enriched scintillation screen was also analyzed using the multidetector instrument. This analysis gave insight into the concentration profile of this particular neutron converter, something that had previously been unknown.

The depth profiles of intentional or intrinsic constituents of a sample provide valuable information for the characterization of materials. For example, the subtle differences in spatial distribution and composition of many chemical species in the near surface region and across interfacial boundaries can significantly alter the electronic and optical properties of materials. A number of analytical techniques for depth profiling have been developed during the last two decades. neutron Depth Profiling (NDP) is one of the leading analytical techniques. The NDP is a nondestructive near surface technique that utilizes thermal/cold neutron beam to measure the concentration of specific light elements versus their depth in materials. The depth is obtained from the energy loss of protons, alphas or recoil atoms in substrate materials. Since the charged particle energy determination using surface barrier detector is used for NDP, the depth resolution is highly dependent on the detectors an d detection instruments. The depth resolutions of a few tens of nm are achieved with available NDP facilities in the world. However, the performance of NDP needs to be improved in order to obtain a few A depth resolutions.

The classic case for why government must support science—with a new essay by physicist and former congressman Rush Holt on what democracy needs from science today Science, the Endless Frontier is recognized as the landmark argument for the essential role of science in society and government’s responsibility to support scientific endeavors. First issued when Vannevar Bush was the director of the US Office of Scientific Research and Development during the Second World War, this classic remains vital in making the case that scientific progress is necessary to a nation’s health, security, and prosperity. Bush’s vision set the course for US science policy for more than half a century, building the world’s most productive scientific enterprise. Today, amid a changing funding landscape and challenges to science’s very credibility, Science, the Endless Frontier resonates as a powerful reminder that scientific progress and public well-being alike depend on the successful symbiosis between science and government. This timely new edition presents this iconic text alongside a new companion essay from scientist and former congressman Rush Holt, who offers a brief introduction and consideration of what society needs most from science now. Reflecting on the report’s legacy and relevance along with its limitations, Holt contends that the public’s ability to cope with today’s issues—such as public health, the changing climate and environment, and challenging technologies in modern society—requires a more capacious understanding of what science can contribute. Holt considers how scientists should think of their obligation to society and what the public should demand from science, and he calls for a renewed understanding of science’s value for democracy and society at large. A touchstone for concerned citizens, scientists, and policymakers, Science, the Endless Frontier endures as a passionate articulation of the power and potential of science.