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This is 2007 Exam Paper Medical Physics

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Surname Other Names For Examiner's Use
Centre Number Candidate Number
Candidate Signature
General Certificate of Education
January 2007
Advanced Level Examination
APPLIED SCIENCE SC08
Unit 8 Medical Physics
Tuesday 23 January 2007 9.00 am to 10.30 am
For this paper you must have: For Examiner's Use
! a pencil and a ruler
! a calculator. Question Mark Question Mark
Time allowed: 1 hour 30 minutes 1 5
2 6
Instructions
! Use blue or black ink or ball-point pen.
3
! Fill in the boxes at the top of this page.
! Answer all questions. 4
! Answer the questions in the spaces provided.
! Do all rough work in this book. Cross through any work you do not Total (Column 1)
want to be marked.
! Show the working of your calculations. Total (Column 2)
Information TOTAL
! The maximum mark for this paper is 80.
Examiner's Initials
! The marks for questions are shown in brackets.
! You are expected to use a calculator where appropriate.
M/Jan07/SC08 SC08

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Answer all questions in the spaces provided.
1 A medical technician is using an EEG machine to study a patient's brain activity.
To do this, she attaches electrodes to the patient's skin.
(a) How does the technician ensure that there is good electrical contact between the
electrodes and the skin?
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(1 mark)
(b) Why is it important for the patient to keep still while the EEG is taken?
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(ii) When do beta waves normally occur?
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(1 mark)
(iii) When do delta waves normally occur?
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2 Radiographers use X-rays to help diagnose many medical conditions.
(a) A diagram of an X-ray machine is shown below.
(i) Add the correct label to each part indicated in the diagram above.
(4 marks)
(ii) Explain how the anode is prevented from overheating.
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(2 marks)
(b) X-rays are very dangerous.
(i) State one precaution that the radiographer takes to protect the patient who is
receiving X-rays.
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(1 mark)
(ii) Explain how this precaution protects the patient.…read more

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(iii) State one medical problem or condition that can be caused by over exposure to
X-rays.
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(1 mark)
(iv) The terms stochastic and somatic can be used to describe the types of damage
caused by X-rays.
State what each term means.
Stochastic ..................................................................................................................
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Somatic ....................................................................................................................
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(2 marks)
(c) Although X-rays are very dangerous, they are still often the first choice of diagnostic
technique because they produce high contrast images.
(i) What is meant by high contrast?
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3 Radiologists use radioisotopes for both diagnosis and therapy.
The choice of radioisotope to be used for a particular task often depends on its half-life.
(a) (i) What does the term half-life mean?
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(1 mark)
(ii) Radioisotope A has a half-life of 6 hours.
A hospital has 2 g of active radioisotope A available at a particular time.
Assuming none was used, how much active radioisotope A would be left
24 hours later?
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Activity
(counts per
minute)
Time (months)
(ii) Use your graph to find an accurate value for the half-life of radioisotope B.
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half-life =........................months
(2 marks)
(c) (i) Give two reasons why radioisotope B has a suitable half-life for use as a tracer.
Reason 1 ....................................................................................................................
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Reason 2 ....................................................................................................................
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(ii) Both radioisotopes A and B are believed to emit gamma radiation only.
Design an experiment you could carry out to test whether a radioisotope emits
only gamma radiation.
Explain what you would do and how the results of your experiment would tell
you whether the sample emitted gamma radiation only and not alpha or beta
radiation.
Suggest a possible source of error in your experiment.
You may use diagrams to illustrate your answer.
Experiment ................................................................................................................
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(d) Radioisotopes used as tracers must emit gamma radiation and should emit little or no
alpha or beta radiation.
Explain why.
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(4 marks)
(e) Radioisotope A has a suitable half-life and emits only gamma radiation. However, a
medical physicist decides that it is not suitable to use as a tracer.
State and explain two possible reasons for this decision.
Reason 1 .............................................................................................................................
Explanation ........................................................................................................................
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Reason 2 .............................................................................................................................
Explanation .........................................................................................................................
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4 Manufacturers of optical instruments know that endoscopes must be made from glass fibres
with a high refractive index. A technician is testing a new type of glass to find out if its
refractive index would make it suitable to use in an endoscope.
He found the critical angle, c, to be 48°.
(a) Calculate the refractive index, n, for this glass sample.
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n = .............................…read more

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