Section 6.2.1.4.2. Image plates

The principles underlying the operation of an image plate (IP) are presented in detail in Chapter 7.2 . Briefly, the important difference between an IP for X-ray and neutron detection is the presence of a converter (either Gd₂O₃ or ⁶Li). The role of the converter is to capture an incoming neutron and create an event within the IP that mimics the detection of an X-ray photon. For example, neutron capture in Gd produces conversion electrons that exit the Gd₂O₃ grains, enter neighbouring photostimulated luminescence (PSL) material and create colour centres to form a latent image (Niimura et al., 1994; Takahashi et al., 1996). A neutron IP may have a virtually unlimited area and a shape limited only by the requirement to locate the detection event in a suitable coordinate system. With a neutron-detection efficiency of up to 80% at ~1–2 Å, a dynamic quantum efficiency of ~25–30% can be obtained. The dynamic range is intrinsically 1:10⁵. The spatial resolution is primarily limited by scattering processes of the readout laser beam, and measured line spread functions are typically 150–200 µm. The γ sensitivity is high and may restrict the application to instruments with low ambient γ background.

Neutron IPs are integrating devices well suited to data-acquisition techniques with long accumulation times, such as Laue diffraction (Niimura et al., 1997) and small-angle scattering. On-line readout is a distinct advantage (Cipriani et al., 1997).