How valuable is your x-ray or neutron beam time ?
What does it cost when you spend the night collecting data... and in the morning you find that your sample was not completely in the beam?
Is your incident beam fully aligned and uniform? Does all of the monochromator contribute equally? Have you even seen a map of the output from your neutron guide, or of the monochromator reflectivity as you rotate it through the the Bragg position? (This is especially important with composite monochromators, which depend on the relative alignment of many crystals).
Beam interlocks and safety concerns mean that remote monitoring of the beam becomes essential. The old-fashioned Polaroid camera is no longer an acceptable solution. Such cameras are no longer made, having been replaced by digital cameras using CCD chips.
Progress with CCD cameras now means that you can install an inexpensive camera in front of the beam stop and remotely visualise your sample in the beam in real time from outside the experimental zone. Or you can replace the sample by a pinhole, and visualise the reflecting surface of the monochromator, creating a video as you align it.
These cameras are much more sensitive than ordinary video cameras, since the image is integrated continuously by the camera electronics with exposures ranging from 0.5 msec to several minutes. The camera sensitivity can be controlled remotely, and is such that a few seconds exposure is sufficient in thermal neutron beams of 103 to 109 n.cm-2.sec-1.
The advantage of an integrating CCD camera is that even though exposure can readily be adjusted according to neutron flux, the integrated image can be visualised on an ordinary TV monitor or captured to a computer using the supplied USB frame grabber. The camera can be set up and used within a few minutes without any extra equipment.
NeutronOptics is a small Grenoble company specialising in CCD scintillator cameras for both neutrons and X-rays. It is managed by Dr Alan Hewat, with many years experience in neutron scattering, including 13 years as head of the Diffraction Group at the European high flux reactor of the Institut Laue-Langevin (ILL).
In all, NeutronOptics has supplied cameras to more than 30 laboratories, including many in Europe, the USA, Japan, China, India, Australia, South Africa and Asia.