P3 Exam Preparation

Gases Absolute zero = -273 ºC, 0 ºC = 273 K Increasing the temperature of a gas increases the speed of its particles The average kinetic energy of its particles is proportional to the temperature of a gas in Kelvin

Gases Gas pressure is caused by particles colliding with the container wall The faster the particles (the higher the temperature) the greater the pressure In all situations: P 1 V 1 / T 1 = P 2 V 2 / T 2

Atoms and nuclei Nuclei contain protons and neutrons Neutrons are difficult to detect because the have no charge As a result of β- or β+ decay nuclei often undergo rearrangement with a loss of energy as gamma radiation In nuclear equations: –Mass is conserved (top number) –Charge is conserved (bottom number)

Properties of Radation RadiationMassChargePenetration Ionising Ability Alpha42lowhigh Beta (β-)1 / 2000medium Positron (β+)1 / 20001medium Neutron10high not directly ionising Gamma00highlow

N - Z plot for stable isotopes N = Z β- β+ α β- n-1 p+1 β+ n+1 p-1 α n-2 p-2

Fundamental and other Particles Fundamental particles are not made up of other, smaller particles eg: –Electron –Positron (anti-electron) –Quark –Netrinos –Muons A positron has the same mass as an electron and all other properties are opposite ie charge = +1

Scientists are creating fundamental particles, such as anti-matter, in particles accelerators which smash particles into each other providing enough energy for the fundamental particles can exist on their own These project are normally international collaborative projects due to the cost The proton and neutron are not fundamental particles because they are made up of quarks

Quarks 'Flavour'ChargeMass 'UP'+ 2/3 e1/3 u 'DOWN'- 1/3 e1/3 u ParticleChargeQuarks Proton+1UUD Neutron0DUD

Beta Decay and Quarks β- decay involves a down quark changing into an up quark (one neutron becomes a proton and an electron) β+ decay involves one up quark changing into a down quark (a proton becomes a neutron and a positron)

Electrons and Electron Beams Thermionic emission is when charged particles are emitted ‘boiled off’ a filament due to thermal energy Uses of electron beams include: –TV picture tubes –computer monitors –oscilloscopes –the production of X-rays

Cathode Ray Tubes Cathode (filament) Accelerating Anode Steering plates Accelerating Voltage Heating Current Thermionic Emission Electron Accelerated Steered by magnetic or electric field Electron strikes screen Kinetic Energy converted to Light Energy Vacuum Increasing heating current Increases numbers electrons boiled Increasing accelerating voltage Increases the KE of the electrons Both increase the brightness of the screen

Cathode Ray Tubes kinetic energy = electronic charge × accelerating voltage KE = e × V a beam of electrons is equivalent to an electric current I = ( n x e ) / t You’ll be given: e = 1.6 x

Beam Deflection An electron beam, or a stream of charged particles (for example ink drops), can be deflected by the electric field between parallel charged metal plates The amount of deflection increases when: –Mass of particle is decreased –The time in the field is increased Larger plates Slow particle

Methods of ‘seeing’ inside the body

Refraction of a wave, is the change in direction (or bending) caused by the change in speed of the wave This usually due to a change in density of medium

TIR – Fibre Optics

Radiation Radiation is the spreading out of energy –Light (EM Spectrum) –Radioactive radiation (Alpha & Beta particles) –Sound

Radiation Medical applications of radiation: –Reflection X-rays – bones may reflect the x-rays Ultrasound scan (echocardiogram) –Total internal reflection Endoscopes (Keyhole surgery, colonoscopy) –Absorption Pulse oximetry X-rays – bones may absorb the x-rays Radiotherapy Remember the light is absorbed by the medium not the other way round

Pulse Oximeter

Energy and the body Work done is equal to energy transferred work done = force × distance (moved in the direction of the force) W = F × s power = work done / time taken P = W / t basal metabolic rate (BMR) is the minimum amount of energy required to stay alive

Electricity in the body frequency = 1 / time period f = 1 / T Action potentials can be measured with an Electrocardiogram (ECG) to monitor heart action

ECG Probes The probes are able to measure the potential differences between the heart and the rest of the body This potential difference is known as the action potential and makes the heart muscles contract

Normal ECG Contraction of the atria Contraction of the ventricles Relaxation of the ventricles

Heart Problems Bradycardia = low heart rate Tachycardia = high heart rate Arrhythmia = uneven heart rate

Positron Emission Tomography (PET) Radioactive tracer is injected into blood Tracer emits positron Positron annihilates an electron Emits a pair of gamma rays in opposite directions Gamma rays are detected by an array of gamma cameras 3D map of body is created showing where the tracer accumulated

Ionising radiation may cause: –Tissue damage –Mutations The larger the dose of radiation the bigger the risk Risk minimised by minimising the: –Intensity –Duration of exposure

Tumours irradiated by radiation are affected more than normal cells Palliative care is the treatment of the symptoms when the cause can not be cured Social and ethical issues of (new/newer) techniques in medical physics: –Cost of treatment –Geographical availability –Potential risks

Physics theory in medical care intensity = power of incident radiation/area I = P/A Double the distance => Quarter the Intensity I α 1 / r 2 r = distance from source Intensity depends on the nature of the medium the radiation is travelling through: Higher density => Higher absorption => Lower Intensity of radiation

Physics theory in medical care balancing nuclear equations that use thermal neutrons In nuclear equations: –Mass is conserved (top number) –Charge is conserved (bottom number) 235 U+ 1 n→ 92 Kr+ 141 Ba+ 3 1 n

Collisions Energy conservation Total Energy Before = Total Energy After ½ m 1 v ½ m 2 v 2 2 = ½ m 1 v 1’ 2 + ½ m 2 v 2’ 2 + Sound & heat Energy etc Momentum conservation Total Momentum Before = Total Momentum After m 1 v 1 + m 2 v 2 = m 1 v 1’ + m 2 v 2’

Physics theory in medical care The bombardment of certain stable elements with proton radiation can result in making them into radioactive isotopes that usually emit positrons The production of gamma rays by annihilation of electron and positron as the rest energies (E = mc 2 ) are converted from matter into (lots of) pure energy – gamma rays

Physics theory in medical care Annihilation of electron and positron to form gamma rays is an example of momentum and mass energy conservation: –Energy of gamma ray = rest energies of particles + KE of particles –Pairs of gamma rays are given out in opposite direction to maintain momentum