Neutron Imaging Detector Suite

The most commonly used detector at the NIST imaging beamlines is a lens coupled camera detector box shown in Figure 1. The spatial resolution and field-of-view can be adjusted by switching between various photo lenses. Field-of-view decreases with increasing resolution. Example expected pixel sizes and field-of-view for the 62 Megapixel camera system are given in Table 2.

Table 2: Pixel size, best case resolution, and field-of-view for 62 MP camera with a 9576 X 6388 pixel array. Please note that the resolution shown here is a Nyquist-Shannon sampling limit and actual resolution depends on how an experiment is conducted.

The high megapixel cameras will produce vary large, reconstructed 3D datasets that can be difficult to analyze. A 3000 x 3000 x 6000 voxel volume is 216 GB, double that if including neutron and X-ray volumes, and would require a computer with 512 GB of RAM to fully open at the same time. Other CMOS cameras available include 16 MP cameras with 3.76 μm native pixel pitch, and 100 MP cameras with 3.76 μm native pixel pitch.

Macroscope

Users can also make use of a macroscope using two lenses [1]. The macroscope configuration has higher numerical aperture (better light collection) than the directly coupled configuration using either 100 mm or 200 mm macrolenses. The macroscope allows magnifying the scintillation light, with magnification given by the ratio of the two focal lengths; a maximum magnification of 4 is currently possible. Two image intensifiers are also available to amplify low light signals as wells as the ability to image individual neutron capture events in our P43 screens to yield ~1 µm spatial resolution images. The thinnest P43 screen on hand is a ~2 μm thick Gd-157 enriched screen.

Flat Panel Detectors

A Varian Paxscan 2520 amorphous silicon flat panel detector is available which has an active area of 25 cm × 20 cm, a pixel pith of 127 µm, a maximum frame rate of 30 Hz, and employs a 250 µm thick LiF:ZnS scintillator screen in direct contact with the light-sensitive amorphous silicon sensor (see Figure 2). This detector is well characterized with respect to dark noise, lag, and point spread function.

Microchannel Plate Detectors

Boron and gadolinium doped microchannel plates were first proposed in 1990 by Fraser et al [2]. Later a series of detectors based on these neutron sensitive plates were developed [3]. Currently two high resolution, high event rate, neutron sensitive microchannel-plate detectors are available. One has a 40 mm diameter field of view with 10 % deadtime at a random event of 1 MCPs (shown in Figure 3). The second has a 100 mm × 100 mm field of view with 10 % deadtime at a random event rate of 4 MCPs. Both detectors can operate in event mode and be synchronized through a clock reset function to capture repetitive processes with high time resolution (about 100 ns).

References

[1] A. Rack, S. Zabler, B.R. Müller, H. Riesemeier, G. Weidemann, A. Lange, J. Goebbels, M. Hentschel, W. Görner “High resolution synchrotron-based radiography and tomography using hard X-rays at the BAMline (BESSY II)”, Nuclear Instruments and Methods in Physics Research A 586 (2008) 327–344

[2] Fraser, et al, NIMA, 377, p119, (1990).

[3] O. Siegmund, A. Tremsin, J. Vallerga, and J. McPhate, “Microchannel plate cross-strip detectors with high spatial and temporal resolution”, NIMA., 610(1), 118–122 (2009).