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Q1. Graphite is used in nuclear reactors as a moderator to reduce the speed of fast neutrons and ensure a sustained nuclear chain reaction. It degrades over time and a good indicator of its condition is the linear thermal expansion coefficient, which is defined as the fractional change in length per degree of temperature change: 1 AL a= L, AT where Lo is the original length and AL is the change in length due to a change in temperature AT. Nuclear engineers require a non-contact way of measuring a inside the reactor and have asked you to develop a prototype system based on speckle interferometry. They provide you with graphite samples cut as a prism of dimensions 100 mm x 20 mm x 20 mm. The following components are available for you to assemble your setup: He-Ne laser (wavelength: 2=632.8nm); CCD camera with 1280 x 1280 square pixels with dimensions 6um x 6um with no dead areas between pixels; Imaging lens with magnification M=1/10; Various beam splitters, mirrors, collimating lenses and microscope objectives; a non-contact digital thermometer with an uncertainty of 0.1°C; a thermal chamber with temperature control; a phase shifting device (mirror on PZT transducer with controller). a) Decide on an appropriate interferometer that will allow you to determine a. Justify your decision. [5 marks]