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Large Area High Resolution Detector for Thermal Neutron Radiography

The US Army is very interested in neutron radiography of munitions and/or ordnance in general prior to deployment in combat zones to ensure safety and reliability. With this intention, munitions inspection at the Armaments Research Development and Engineering Center (ARDEC) Radiography Laboratory (RDAR-EIQ-EB), Picatinny Arsenal has invested in a laboratory thermal neutron source capable of providing high flux of <4x105 n/cm2/sec of thermal neutrons. To enable high throughput NDE of munitions we are developing a novel high-resolution, high efficiency digital radiography detector capable of acquiring thermal neutron images over a large 43×43 cm2 area, with high contrast and enhanced signal-to-noise ratio (SNR). The design involves use of a commercial 139 μm pixel size a-Si:H flat panel detector coupled to a neutron sensitive scintillator. The key to the success is formulation of a novel LixNa1-xI:Eu (LNI) scintillator screen that simultaneously provides bright emission, high thermal neutron absorption efficiency, and high spatial resolution. This new material is vapor grown in a columnar structure that permits scintillation light transmission without self-attenuation and preserves spatial resolution due to its structure. A few millimeter thick scintillator can provide thermal neutron efficiency in excess of 90% without substantial penalty in resolution. Here we will present performance of these scintillators under thermal and cold neutron exposure and the data will be compared to traditional powdered scintillators including Gd2O2S:Tb or 6LiF/ZnS. Sensitivity of the selected scintillators to both neutrons and X-rays makes it disruptive to the traditional film based or the computed radiography (CR) technology and will bring about transformational impact in combined X-ray/neutron radiography in general and in neutron NDT in particular.

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