Standard Candles A standard candle is defined as: An astronomical object which has a known luminosity due to a characteristic quality possessed by that class of object Examples of standard candles ...
Defining Luminosity Luminosity L is defined as: The total power output of radiation emitted by a star It is measured in units of Watts (W) Radiant flux intensity F is defined as: The observed amoun...
Detecting Gamma-Rays from PET Scanning The patient lays stationary in a tube surrounded by a ring of detectors Images of slices of the body can be taken to show the position of the radioactive trac...
The Process of Annihilation When a positron is emitted from a tracer in the body, it travels less than a millimetre before it collides with an electron The positron and the electron will annihilate...
Radioactive Tracers A radioactive tracer is defined as: A radioactive substance that can be absorbed by tissue in order to study the structure and function of organs in the body Radioactive isotope...
Computed Tomography Scanning A simple X-ray image can provide useful, but limited, information about internal structures in a 2D image When a more comprehensive image is needed, a computerised axia...
Attenuation of X-rays in Matter Bones absorb X-ray radiation This is why they appear white on the X-ray photograph When the collimated beam of X-rays passes through the patient’s body, they are abs...
Production of X-rays X-rays are short wavelength, high-frequency part of the electromagnetic spectrum They have wavelengths in the range 10−8 to 10−13 m X-rays are produced when fast-moving electro...
Attenuation of Ultrasound in Matter Attenuation of ultrasound is defined as: The reduction of energy due to the absorption of ultrasound as it travels through a material The attenuation coefficient...
