Edexcel P3 Radiation in Medicine, Ionising radiation and Kinetic Theory Physics Pre exam presentation By Mr Nesbo

Units! You need to know the units for each value (or ANY equation): some tricky ones! Temperature – K (kelvin) or ͦC (degrees Celsius) Momentum – Kg m/s (kilogram meters per second) Charge – C (coulomb) Energy of an electron/photon (small particle) – eV (electron volt) Refractive index, n, does not have units Sin r and Cos r (or i) does not have units Power of a lense – D (dioptre) Intensity – W/m 2 (Watts per meter square)

Radiation for Diagnosis Radiation detected How it forms an imageWhere it is used Visible light Light reflects off features to form an image Endoscopes X-rays X-rays are absorbed by some materials inside the body but not others. X-ray photography and CAT scanners Gamma rays Positron annihilates with electrons in the body producing 2 gamma rays PET scanners UltrasoundHigh-frequency sound waves reflect off features inside the body. Ultrasound scanners

Higher Intensity = power of incident radiation / area I = P / A Power measured in watts (W), area measured in meters squared (m 2 ) so intensity is measured in watts per square meter (W/m 2 ).

How the eye works

Iris controls the amount of light entering the eye.

Lenses Key language: Magnified means larger. Diminished means smaller. A real image (on the other side of the lens to the object). A virtual image (on the same side of the lens as the object).

Power of a Lens 1 / f = 1 / u + 1 / v u is the object distance, v is the image distance. If the image is virtual then v is a negative number.

Reflection and refraction

Snell’s law sin I / sin r = n r / n i (a constant number) focus on equation ‘i/r’ then ‘r/I’

X-ray machines uses an evacuated tube (so travelling electrons don’t collide with air particles) with a negative electrode (cathode). When heated thermionic emission fires electrons towards a rotation positive electrode (anode). The electrons collide with the anode passing energy to the metal particles which in turn emit x-rays.

Equations for flowing particles Higher Flow of electrons equation: I = N x q where I = current in amperes (A), N = number of electrons flowing each second and q = charge of each electron Kinetic energy equation: E k = ½ m * v 2 (m is mass in kg, v is velocity of the electron in m/s). Energy can be measured in eV (electron volts, electron charge * 1 volt).

CAT scans: 2D image is formed from several directions and can be used to form a 3D image. Fluoroscope: 2D image is taken to in one direction. A camera can be used to form a real time video clip.

Electron and positron radiation Neutron changes into a proton => emits an electron (beta minus decay). Atomic number increases. Higher Down quark changes to up quark. Proton changes into a neutron => emits a positron (beta plus decay). Atomic number decreases. Up quark changes to down quark 6 protons 8 neutrons 7 protons 7 neutrons 6 protons 4 neutrons 5 protons 5 neutrons

Temperature – ͦK (degrees kelvin) or ͦC (degrees Celsius) Momentum – Kg m/s (kilogram meters per second) Charge – C (coulomb) Energy of an electron/photon (small particle) – eV (electron volt) Refractive index, n, does not have units Sin r and Cos r (or i) does not have units Power of a lense – D (dioptre) Intensity – W/m 2 (Watts per meter square) Quarks: Proton = u + d + u = p (total = +1e) Neutron = d + u + d = n (total = 0) Don’t forget about units!

Radiation in hospitals Palliative care help issues but does not cure them. Beta emitters are used for internal radiotherapy. Gamma sources and high-frequency X-rays are used for external radiotherapy. Tracers vary so that they will be absorbed by specific parts of the body. A tracer can be a radioactive isotope of the normal substance which the body part absorbs. The tracer must have a short half-life so that the body is not exposed more than needs be. Due to this the isotopes are made close by.

PET scans (positron emission tomography) PET scan uses a positron emitting tracer. The positrons annihilate with electrons in the body producing two gamma rays in opposite directions.

Circular Motion The LHC (Large Hadron Collider) is a particle accelerator. It accelerates two beams of protons or ions to high speed in opposite directions eventually causing them to collide. Circular motion uses the concept of ‘resultant force’. The momentum/velocity of an object wants to travel in a straight line. The centripetal force acts at a right angle towards the centre of a circular path. The result is a motion between the two. As this continues the direction of motion continues to turn towards the centre.

Cyclotrons Cyclotrons are used to make the isotopes for PET scans.

Collisions Momentum is always conserved (involves direction). Inelastic collision kinetic energy is not conserved. Elastic collision kinetic energy is conserved. Momentum equation: Momentum of an object = mass * velocity Total momentum before an interaction (collision or explosion) = sum of momentum of all objects (taking into account direction, choose one direction to be +ve and the other –ve)

Kinetic Theory Temperature is a measurement of the average kinetic energy of the particles [in a gas]. Pressure is the force particles exert on a surface/wall of a container when collide. Measured in pascals (Pa) where 1 Pa = 1 N / m 2. Absolute zero is the lowest temperature (or average kinetic energy) and occurs at -273 ͦC, also known as 0 ͦK (zero degrees kelvin).

Changes in temperatures, volumes and pressures Under medium temp. and pressure the balloon has a normal volume (A). If the temp. inside increases and/or the pressure outside decreases the balloon, the volume of the balloon increase (B). The opposite applies if conditions are reversed.

alpha radiation – Positively charged particles made up of two protons and two neutrons. background radiation – Constant low-level radiation from food and environmental sources. beta radiation – High-energy electrons emitted by some radioactive materials. gamma radiation – Short-wavelength electromagnetic radiation emitted during radioactive decay. Geiger-Müller tube – A device used to detect and measure radiation from radioactive materials. ionizing radiation – High-energy radiation capable of ionizing substances through which it passes. radioactivity – The spontaneous emission of radiation from the nucleus of an unstable atom. Nuclear glossary

ParticlesSymbolStructure Relative charge PenetratingStopped by Alpha α Helium nucleus 2x neutron 2x proton +2 The least Paper 10cm – 1m of air Beta β Electron (high speed) A lot Aluminium 10m of air Gamma ɣ Light ray (EM radiation) 0The most Lead Not stopped by air 30cm of concrete Nuclear characteristics

Nuclear reactors Safety: Radioactive materials produce dangerous radiation Students frequently refer to protective gear needing to be worn when asked about safety HOWEVER this is only one area of importance. THERE ARE DANGERS AND SAFETY POINTS YOU CAN DISCUSS!

different types of ionising radiation produce different dangers energy from the ionising radiation can be absorbed by the human body (prolonged) exposure to radiation can cause {tissue / cell} damage and {mutation/ damage to DNA} increased risk due to long term exposure to raised background levels of radiation Risks Safety precautions protective clothing and handling systems should be used minimise exposure to the ionising radiation intensity of radiation decreases with distance from the source personal radiation dose should be monitored monitoring of background levels of radiation