P3 Physics Medical applications Section X – rays N-T 208: Longmans: 176 a) X-rays are part of the e …………………… s………..... They have a very _________ wavelength and very _____________ frequency and cause ionisation which means that they have enough __________ to cause atoms or molecules to lose (or gain) _________s. X – rays can also be thought to consist of a beam of high energy ‘light particles’ called p_ _ _ _ _ s.

3.1.1 X - rays b) X-rays are potentially harmful to living things because their energy can be deposited in their cells. It can cause mutation and abnormal growth (cancer) or cell death and subsequent organ failure. c) X –rays are produced by very hot objects like stars and by X – ray machines. Inside an X -ray machine, atoms of a target metal are made to release the X – rays from high energy changes to their inner electrons. The result is a high energy ray with a very short wavelength.

3.1.1 X - rays Stars and the remnants of exploded stars can be studied by using the information from the X – rays they release. These can pass through gases and dust which will block out visible light. This is a supernova remnant in the constellation of Cassiopeia. The colours represent X –rays of different energies

3.1.1 X - rays The very short wavelength (about the diameter of an atom) means that X –rays can be used to image small details of the structure of solids.

3.1.1 X - rays Dr Rosalind Franklin who used X –ray diffraction to help to confirm the structure of DNA, the discovery attributed to Watson and Crick. The image has been made on photographic film

3.1.1 X - rays The technique shows that X – rays do what visible light rays can do. They can darken photographic film. X –rays are ABSORBED by metal and bone but pass through healthy flesh

3.1.1 X - rays This picture is formed on a photographic film or ‘plate’. The black areas have been exposed to the X –rays. The different shades are where the X-rays have been stopped to various degrees by structures from dense thick bone to thinner bones and less dense material (this is a collar bone break)

3.1.1 X - rays The medical uses of X –rays include: a) diagnosing bone breaks, dental problems and some diseases b) treating some cancers by using X –rays to kill the cancer cells Detailed images are produced by C-T scanning. This involves taking images from many directions and making a 3D image.

The 3D image has fine detail but the dose of radiation can be 100 times greater than that for a standard X –ray. COMPUTED TOMOGRAPHY involves rotating the beam and making images in slices. A computer combines them.

3.1.1 X - rays The medical problems associated with the use of X - rays mean that the doses must be kept to a minimum. Risk must be balanced against the benefit As well as the patients, the medical staff are also at risk.

3.1.1 X - rays 1. The use of electronic image formation by using the CCD device in digital cameras means doses can be lower than when using film. The image can then be stored electronically. 2. Shielding by using metals such as lead prevents unnecessary exposure to X – rays. 3. The radiographer will stand behind a protective screen or may not be in the same room as the patient. 4. Usually, a pregnant woman would not have an X – ray as that might affect her unborn child

3.1.1 X - rays 1.Ideas: many X –ray images and CT scans on the internet 2.Department resource of X –ray and CT photographs from hospitals 3.Questions: N-T p.224 qu. 1 Long. P.199 qu.7