![]() A more realistic value of luminous flux density might be around 100 Lux.Įxample 2: If 100 Lux of illumination is measured on a surface that is one meter away from a light source, the illumination would be one quarter as bright, or 25 Lux two meters away, and 1/9th as bright, or 11.1 Lux three meters away, and so on. This example is a very low value of illumination, but it does illustrate the concept of the inverse square law. Illumination of a surface drops with the square of the distance Illumination (lux) =\fracĮxample 1: If 1 Lux of illumination is measured on a surface that is one meter away from a light source, the illumination would be 1/4th as bright, or ¼ Lux two meters away, and 1/9th as bright, or 1/9th Lux three meters away. Apply a diagrammatic model utilising intensity to explain the behaviour of the inverse square law, and make predictions based on the model 6. Seems obvious, but it is worth noting that the level of illumination on a surface drops with the square of the distance. Accurately sketch and switch between graphical and algebraic representations of the inverse square law 45, 7). Inverse square law is used in the calculation of the geometric effectiveness of collimators used in nuclear medicine 5.Put simply, the further an object or surface is from a light source, the less light will hit that object or surface. In science, an inverse-square law is any scientific law stating that the observed 'intensity' of a specified physical quantity is inversely proportional to the square of the distance from the source of that physical quantity. Using tongs or long-handled tools when handling radiopharmaceutical products can increase the distance of the source from the handler, thus reducing radiation exposure 4. When not dealing with radiopharmaceuticals, standing 6 feet away can reduce the radiation exposure to 2.8% when compared to the radiation dose when standing at 1 foot away from the source 4. Meanwhile, the automatic brightness control (ABC) will increase the X-ray tube output to increase the brightness, thus causing increased dose to the patient 6. ![]() If the image intensifier is too far away from the patient, the brightness output will reduce. Demonstrate proportional reasoning using the inverse square law 13. Meanwhile, the image intensifier (which intensifies the X-ray photons to produce a bright image) should be as close to the patient as possible to reduce image blur and maintain the brightness for the image intensifier, thus reducing the patient's dose. Accurately sketch and switch between graphical and algebraic representations of the inverse square law 45, 7). In fluoroscopy, there should be a minimum distance between the X-ray tube and the patient of about 30 to 38 cm to reduce the skin entrance dose of the patient. Thus doubling the distance will reduce the dose by a factor of four. Therefore, the dose is proportional to the inverse of the square of the radius. Where A is the area and r is the radius of the sphere. As the radius increases, the area over which the dose is distributed increases according to A=4πr 2 The radiation will spread equally in all directions over a spherical area. The source can be considered as a "point" source if the distance is more than 7 times the dimensions of the source 4. The inverse square law describes the principle of dose reduction as the distance from the source increases.
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