What is a medical tracer?

It is a radioactive substance given to a patient so that the radiation leaving the body can be detected to show how an organ is working.

Why would an alpha emitter be a very poor choice of tracer?

Its radiation would be absorbed within the body so nothing could be detected outside, and it would heavily ionise the surrounding tissue.

Give an example of an organ investigated using a tracer, and say what the tracer shows.

A tracer containing iodine collects in the thyroid gland, and how much it takes up shows whether the gland is working properly.

What is radiotherapy?

It is the treatment of cancer by using high-energy radiation to kill the cells of a tumour.

OCR GCSE Physics A J249

Electricity

Topic overview Charge, and producing static electricity Transfer of electrons, and electric fields Current as a rate of flow of charge Charge, current and time Series and parallel circuits, and circuit symbols Current, potential difference and resistance Resistors whose resistance changes, and investigating them Linear and non-linear circuit elements from graphs Net resistance in series and parallel Circuits for measurement, and electrical power

Energy

Topic overview Conservation of energy, and energy stores Energy changes on heating, and calculating them Energy of a moving body, a spring and a raised object Dissipation, and energy transfer in domestic devices Power ratings, efficiency, and increasing it Reducing unwanted energy transfer, and the rate of cooling

Forces

Topic overview Measuring distance and time, and calculating speed Converting units, and rates Vectors and scalars in motion Distance-time and velocity-time graphs Average speed, and the equations of uniform motion How objects interact, and forces as vectors Newton's first law Resolving forces, and free body diagrams Resultant forces, and balanced forces Newton's second law, and inertia Momentum, and force as a change in momentum Work done, and stored energy Power, and Newton's third law Circular motion and changing velocity Stretching, bending and compressing; elastic and plastic Force and extension, linear and non-linear The spring constant, and work done in stretching Gravitational fields, weight and free fall Calculations with weight and gravitational field strength Turning forces and the moment of a force Levers and gears Pressure in fluids, and the force on a surface

Global Challenges

Topic overview Typical speeds and everyday accelerations Reaction time, stopping distance and the dangers of large decelerations Estimating stopping distances and the forces in a collision Energy resources, and trends in their use The national grid, and step-up and step-down transformers Why the national grid is efficient, and the transformer equation Mains electricity: a.c., d.c. and the domestic supply Live, neutral and earth wires, and electrical danger Red-shift and the Big Bang The formation of the Sun, and radiation from bodies The solar system Circular orbits and stable orbits Radiation and the temperature of a body, and seismic waves and sonar

Magnetism and Magnetic Fields

Topic overview Permanent and induced magnets, and magnetic poles Magnetic fields, and the dipping compass The magnetic effect of a current, and solenoids The motor effect and Fleming's left-hand rule The force on a conductor, and how a motor turns Induced potential, alternators and dynamos Transformers and the turns ratio The microphone

Matter

Topic overview How the atomic model changed, and the structure of the atom The size of atoms, and defining density Density of the states of matter, and density calculations Conservation of mass in changes of state Heating a system, and specific heat capacity Calculations with specific heat capacity and latent heat Gas molecules, temperature and pressure Compressing a gas, and changing its volume Doing work on a gas Atmospheric pressure and why it varies with height Floating, sinking and pressure in a liquid

Radioactivity

Topic overview Protons, neutrons and isotopes Unstable nuclei and the emissions they give out Balancing nuclear equations Electron energy levels, and radiation from atoms Half-life and the randomness of decay Penetration of alpha, beta and gamma Contamination and irradiation, and half-life as a hazard Uses of nuclear radiation Nuclear fission and fusion

Waves in Matter

Topic overview Amplitude, wavelength, frequency and period The wave equation Transverse and longitudinal waves Sound crossing a boundary; reflection, transmission and absorption Converting sound to vibrations, and the range of hearing Modelling waves with ripples and sound Electromagnetic waves as transverse, and energy transfer Frequency and wavelength across the spectrum What our eyes detect, and light as an electromagnetic wave Uses of electromagnetic waves Hazards of ultraviolet, X-rays and gamma rays Exploring structures with waves, and producing radio waves Absorption, transmission, refraction and reflection Ray diagrams for reflection and refraction How colour arises

Radioactivity

Uses of nuclear radiation

3 things to know
Paper 4

Overview

Medical tracers, why gamma emitters suit them and alpha emitters do not, how a tracer is detected and used to check the thyroid, radiotherapy with external beams from several directions and with implanted sources, and why the dose must be controlled carefully.

What you need to know

Answer each one before you reveal it.

Your recallNot started

Key term

In radiotherapy, why is the beam aimed from several directions, how is a source used inside the body, and why must the dose be controlled?

Key term

Why is a gamma emitter chosen as a tracer for looking at an organ?

Key term

How is the radiation from a tracer detected once it has been given to a patient?

Questions from this subtopic

Each one with the model answer underneath.

1
What is a medical tracer?
Model answer
It is a radioactive substance given to a patient so that the radiation leaving the body can be detected to show how an organ is working.
2
Why is a gamma emitter chosen as a tracer for looking at an organ?
Model answer
Gamma radiation is penetrating enough to pass out of the body to a detector, and it is not strongly ionising inside the patient.
3
Why would an alpha emitter be a very poor choice of tracer?
Model answer
Its radiation would be absorbed within the body so nothing could be detected outside, and it would heavily ionise the surrounding tissue.
4
How is the radiation from a tracer detected once it has been given to a patient?
Model answer
A detector or camera outside the body picks up the gamma radiation and builds a picture of where the tracer has collected.
5
Give an example of an organ investigated using a tracer, and say what the tracer shows.
Model answer
A tracer containing iodine collects in the thyroid gland, and how much it takes up shows whether the gland is working properly.
6
What is radiotherapy?
Model answer
It is the treatment of cancer by using high-energy radiation to kill the cells of a tumour.

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AGamma radiation is the most penetrating.

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