Gamma rays are used to sterilise equipment, diagnose blood flow problems and treat cancer. Infrared radiation is used to treat muscle injuries and in thermograms. Ultraviolet radiation is used to treat skin diseases, such as psoriasis. (a) Radio waves are used in radio and TV communications. Microwaves are used by mobile phones. (a) Infrared radiation is used by remote controls and heaters. Microwaves are used to heat food. Gamma rays don’t diffract easily and are dangerous to humans. 1.09 ms (a) 3.08 m 2.2 ms 1.44 x 1011 m Visible light. Diffraction (p11) Diffraction is the bending of waves around an obstacle. (a) (b) (a) Radio waves diffract more easily because they have a long wavelength. Reception will likely be poor. Wavelength is higher than even TV waves so diffraction is less likely. Surface wave. It diffracts along the surface of the Earth so must have a long wavelength. Refraction (p12 – 13) Refraction is the change in speed / wavelength / direction of light as it moves from one medium to another. Diffraction does not involve waves changing medium. The largest angle of incidence at which refraction of light will occur at a glass/air interface is 41°. (a) Z Z X Y Draw around the Perspex block. Shine a ray of light through it and change the angle of incidence until the angle of refraction is 90°. Mark the incident ray on the paper. Measure the angle of incidence with the protractor. (Shorter focal length) The focal length is the distance between a lens and a screen where a sharp image of a far away object can be seen.
Activity is the number of decays that happen in a second. Radioactivity decay is when an unstable atom emits a radioactive particle and a becomes a different element. 3.5 Bq 60 000 450 s Connect the G-M tube to the counter. Move it close to the radioactive source. Measure how many counts are in 30 seconds. Calculate activity using A = N/ t. 6.5 Bq 30 Bq Half Life (p20 – 21) Activity decreases. Half life is the time taken for the activity of a radioactive source to reach half of its original value. 25 kBq 3 years 960 Bq 9pm on Thursday 9 months Calculate the activity of a source using the G-M tube, stop watch and the counter. Repeat this until the activity is halved. Check how long has passed with the clock. This is the half life. 15 minutes B Gamma can penetrate tissue. The half-life is a reasonable value to be useful and safe. Absorbed Dose (p22) Absorbed does is the amount of energy absorbed from a radiation by a kilogram of a material. (a) 2 x 10-5 Gy 1.4 x 10-4 Gy 4.4 μJ 16.9 μJ 0.3 kg 0.15 kg 17.5 μGy 0.42 kg 7.65 μJ Equivalent Dose (p23 – 25) Equivalent dose is a measure of the biological harm of exposure to a radiation. (a) 4.2 μSv 5.1 x 10-5 Sv 6.8 μGy 1.75 μGy 10 3 4.5 μSv 0.4 mSv (a) 20
Alpha. (a) 1.0 x 10-4 Gy 1 mSv (a) 0.03 μSv 20 times. See diagrams to right. Dalbeattie has a granite quarry nearby and many houses are made of this material. This is a source of Radon gas. Benefits: Smoke alarms, Medicine, Generation of energy. Risks: Overexposure can kill or cause cell mutations. Nuclear Fission and Fusion (p26) Nuclear fission is when a neutron collides with a nucleus, causing it to split. When the nucleus is split, further neutrons break off and cause further fission reactions. Heat energy is produced by the bonds of the nucleus breaking. Boron Control Rods absorb neutrons. Graphite Moderator slows down neutrons. Uranium Rods are the fuel for the reactions. Carbon Dioxide cools the reactor and passes heat energy to the boiler. The Containment Vessel stops any harmful radiation from escaping. Heat energy heats water in the boiler. Water turns in to steam. Steam turns a turbine. The turbine turns a generator. The generator makes electricity. Nuclear fusion is when two nuclei collide and combine with each other. Heat energy is produced when nuclei combine. Advantages: No air pollution, lots of energy, will last for a long time. Disadvantages: Nuclear waste, reactor failure is potentially dangerous to millions.