The Effect Of Inverse Square Law On A Beam Of X Ray Photons

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Experiment 1

The aim of this experiment is to investigate the effect of the inverse square law on a beam of x-ray photons. The inverse square law states that the intensity of an x-ray beam is inversely proportional to the square of the distance (Ball, J.L., Moore, A.D. and Turner, S., 2008). Similar triangles (Appendix A- Image 1) are a proof of the inverse square law as it shows that if the distance from the beam is doubled, the intensity falls to one-quarter of its original value. If it is trebled the intensity falls to one-ninth and at four times the distance it is one-sixteenth its value, etc (Holmes, K., Elkington, M. and Harris P., 2013). The formula used to calculate this is:

This law only applies if the radiation is from a point source, the radiation of the beam is homogenous (the photons must all have the same energy) and if there is no attenuation between the source of radiation and the detector (Holmes, K., Elkington, M. and Harris P., 2013). However, the x-ray beam cannot satisfy these three conditions of the inverse square law. This is because the x-rays produced are not emitted from a true point source as the focal spot has a finite size. They are not emitted equally in all directions as the anode heel effect causes the intensity to vary across the beam and the absorption and scattering of the x-ray beam occur as it passes through the air (Graham, D., Cloke, P. and Vosper, M., 2012). Despite this, the inverse square law can still be applied
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