Toward energy and angle insensitive fast neutron detection: conceptual design of a heavy-water-moderated "³He+CF₄" scintillation neutron detector

摘要: Polyethylene-moderated ³He neutron detectors are widely used in neutron flux, fission neutron multiplicity, beta-delayed neutron emission probability, (α, n), (γ, n) and (n, xn) reaction cross-section measurements. However, this kind of detector faces the problem that its detection efficiency strongly depends on neutron emission angle, and neutron energy when neutron energy rises above 1 MeV. Therefore, a novel conceptual design of the neutron detector, composed of a large spherical heavy water tank, a layer of gas "³He + CF₄" and surrounding photomultiplier tubes, was proposed to address these problems. We used the MCNPX code to calculate detection efficiency dependency with the neutron energy and emission angle under different configurations, and obtained an optimal configuration (7.0 cm ¹¹B + 0.9 cm Be + 50.0 cm D₂O) that can achieve an unprecedentedly low flat efficiency response (1.03) across neutron energy and emission angle, while also offering a prospect of high detection efficiency. The newly designed neutron detector holds the promise of replacing polyethylene-moderated ³He neutron detector and brings the fast neutron measurements in an era of unprecedented precision.