A technique for establishing the total neutron rate of a highly-collimated monochromatic cold neutron beam was demonstrated using an alpha-gamma counter. The method involves only the counting of measured rates and is independent of neutron cross sections, decay chain branching ratios, and neutron beam energy. For the measurement, a target of 10B-enriched boron carbide totally absorbed the neutrons in a monochromatic beam, and the rate of absorbed neutrons was determined by counting 478 keV gamma rays from neutron capture on 10B with calibrated high-purity germanium detectors. A second measurement based on Bragg diffraction from a perfect silicon crystal was performed to determine the mean de Broglie wavelength of the beam to a precision of 0.024%. With these measurements, the detection efficiency of a neutron monitor based on neutron absorption on 6Li was determined to an overall uncertainty of 0.058%. We discuss the principle of the alpha-gamma method and present details of how the measurement was performed including the systematic effects. We also describe how this method may be used for applications in neutron dosimetry and metrology, fundamental neutron physics, and neutron cross section measurements.

中文翻译：

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精确测定绝对中子通量

使用α-伽玛计数器演示了一种确定高度准直单色冷中子束总中子率的技术。该方法仅涉及测量速率的计数，并且与中子截面、衰变链分支比和中子束能量无关。在测量中，富含 10B 的碳化硼靶材完全吸收了单色束中的中子，并通过使用校准的高纯锗探测器对 10B 上的中子捕获中的 478 keV 伽马射线进行计数来确定吸收中子的速率。进行了基于完美硅晶体布拉格衍射的第二次测量，以确定光束的平均德布罗意波长，精度为 0.024%。通过这些测量，基于 6Li 中子吸收的中子监测仪的检测效率确定为 0.058% 的总体不确定度。我们讨论了 alpha-gamma 方法的原理，并介绍了如何进行测量的详细信息，包括系统效应。我们还描述了如何将该方法用于中子剂量测定和计量、基础中子物理和中子截面测量中的应用。