A prototype quasiparasitic thermal neutron beam monitor based on isotropic neutron scattering from a thin natural vanadium foil and standard ${}^3\mathrm{He}$ proportional counters is conceptualized, designed, simulated, calibrated, and commissioned. The European Spallation Source designed to deliver the highest integrated neutron flux originating from a pulsed source is currently under construction in Lund, Sweden. The effort to investigate a vanadium-based neutron beam monitor was triggered by a list of requirements for beam monitors permanently placed in the ESS neutron beams in order to provide reliable monitoring at complex beam lines: low attenuation, linear response over a wide range of neutron fluxes, near to constant efficiency for neutron wavelengths in a range of 0.6–10 Å, calibration stability and the possibility to place the system in vacuum are all desirable characteristics. The scattering-based prototype, employing a natural vanadium foil and standard ${}^3\mathrm{He}$ proportional counters, was investigated at the V17 and V20 neutron beam lines of the Helmholtz-Zentrum in Berlin, Germany, in several different geometrical configurations of the ${}^3\mathrm{He}$ proportional counters around the foil. Response linearity is successfully demonstrated for foil thicknesses ranging from 0.04 mm to 3.15 mm. Attenuation lower than 1% for thermal neutrons is demonstrated for the 0.04 mm and 0.125 mm foils. The geometries used for the experiment were simulated allowing for absolute flux calibration and establishing the possible range of efficiencies for various designs of the prototype. The operational flux limits for the beam monitor prototype were established as a dependency of the background radiation and prototype geometry. The herein demonstrated prototype monitors can be employed for neutron intensities ranging from ${10}^3–{10}^{10}\mathrm{n}/\mathrm{s}$.

中文翻译：

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钒基中子束监测仪

准寄生中子束监测器的原型，它基于天然钒箔和标准品的各向同性中子散射 ${}^3他$比例计数器被概念化，设计，模拟，校准和调试。欧洲散裂源旨在提供来自脉冲源的最高集成中子通量，目前正在瑞典隆德进行建设。永久放置在ESS中子束中的束监视仪的一系列要求触发了研究基于钒的中子束监视仪的工作，以便在复杂的束线处提供可靠的监视：低衰减，在广泛的中子范围内的线性响应通量，在0.6-10Å范围内的中子波长具有接近恒定的效率，校准稳定性以及将系统置于真空中的可能性都是理想的特性。基于散射的原型，采用天然钒箔和标准${}^3他$ 在德国柏林的Helmholtz-Zentrum的V17和V20中子束线处，以几种不同的几何构型对比例计数器进行了研究。 ${}^3他$金属箔周围的比例计数器。箔厚度范围从0.04 mm到3.15 mm，成功地证明了响应线性。对于0.04 mm和0.125 mm的箔片，热中子的衰减低于1％。模拟了用于实验的几何形状，从而可以进行绝对通量校准，并为原型的各种设计确定了可能的效率范围。建立了光束监控器原型的工作通量极限，这取决于背景辐射和原型几何形状。本文展示的原型监测器可用于中子强度范围为${10}^3–{10}^{10}\mathrm{ñ}/\mathrm{s}$。