Radioactivity - Section B - Six-mark questions

Six-mark questions are extended open response questions. These require longer answers than the structured questions with fewer marks. It is wise to plan your answer rather than rushing straight into it, otherwise you may stray away from the key points.

Six-mark questions are marked using a levels-based mark scheme because they are open ended. To gain full marks, you need to:

  • support explanations using scientific knowledge and understanding
  • use appropriate scientific words and terms
  • write clearly, linking ideas in a logical way
  • maintain a sustained line of reasoning, rather than getting lost or bogged down

You are likely to see command words such as:

  • 'describe' - you need to give an account but no reason
  • 'explain' - you must give reasons or explanations
  • 'devise' - you must plan or invent a procedure using your scientific knowledge and understanding
  • 'evaluate' - you must review information, including identifying strengths and weaknesses, and make a supported conclusion

Six-mark questions may be synoptic questions. These questions bring together ideas from two or more topics. For example, a question about atoms could include ideas about atomic structure, isotopes, radiation and nuclear reactions.

Remember that the topics covered in the first paper are assumed knowledge for the second paper, so questions in the second paper may need knowledge and understanding of those topics too.

The answers shown here give marking points as bullet points. You do not usually need to include all of them to gain six marks, but you do need to write in full sentences, linking them logically and clearly.

Sample question 1 - Foundation

Question

Beta radiation can be used to check the thickness of paper in factories.

A radioactive source emits beta radiation.

There is a detector for beta radiation directly underneath the paper.

Look at the diagram of the machine that is used.

A radioactive source emits beta radiation. Two rollers hold a sheet of paper which the radiation passes through and intro the radiation detector.

The owners of the factory make sure that the workers are protected from too much exposure to the beta radiation.

Explain why beta radiation is used to check the thickness of paper, and how the workers can be protected from too much exposure to this radiation. [6 marks]

OCR Gateway Science, GCE Physics, Paper B751, June 2014.

The thicker the paper, the less beta radiation penetrates the paper. If the paper is too thin, more beta radiation would penetrate and the thickness would need adjusting (rollers need to move apart). Alpha radiation cannot be used to measure thickness because it cannont pass through paper. Gamma cannot be used either because it passes easily through any thickness of paper. Workers can be protected from radiation exposure by wearing protective clothing such as gloves, masks and goggles. They could work at a distance and protect themselves using a barrier. The radiation source should be labelled and the exposure time should be made as short as possible.

Answering tip: Briefly plan the key points you want to include in your answer. For example:

  • thickness of paper and amount of radiation that goes through
  • reasons for using beta (rather than alpha or gamma)
  • give some safety precautions - must be to do with radiation

Sample question 2 - Higher

Question

A radioactive tracer is put into an underground water pipe.

A detector above the ground measures the radioactivity.

The graph shows the amount of radioactivity detected along the length of the pipe.

A radioactive tracer is put into an underground water pipe where a detector above ground measures the radioactivity. A graph displays its results.

Describe the patterns in the graph, and explain how this information can be useful. [6 marks]

OCR Gateway Science, GCE Physics, Paper B752, June 2013 - Higher.

The graph shows the level of radioactivity changing as the detector moves along the pipe. The radioactivity level is relatively low at the start but as the detector moves along the pipe, the level rises rapidly and reaches a peak. The level then falls rapidly after the peak and is lower after the peak than it was at the start.

This information can be interpreted to find where there is a problem with the pipe. The peak shows that the tracer is leaking and indicates a crack or break. There is a blockage in the pipe because the level after the blockage is lower than before the peak. The blockage lets some of the tracer through because the radioactivity is not zero. The radiation used must be gamma because it passes easily through the pipe.

Workers can use this information to dig in the right place, not waste time, energy and resources digging up the whole pipe. The peak shows where the problem is.

Answering tip: Briefly plan the key points you want to include in your answer. For example:

  • describe the graph (changes in radioactivity along the pipe)
  • say how the information can be used, eg detecting a leak
  • say how this is useful, eg where the leak is

Sample question 3 - Higher

Question

Dr Williams shows her class an experiment with radioactivity.

She uses three different radioactive sources:

  • an alpha emitter
  • a beta emitter
  • a gamma emitter

She uses different thicknesses of sheets of paper between the source and the sensor.

Dr Williams measures the nuclear radiation from each source using the sensor.

Each radioactive source emits only one type of radiation. This can be alpha, beta or gamma.

Look at her results for each source.

Thickness of sheets of paper (mm)Source X (counts per second)Source Y (counts per second)Source Z (counts per second)
0306865
0.2323660
0.4312157
0.633552
0.834148
1.029045
1.231141
1.430039
1.631038
1.830235
2.031133

Use the data to identify and explain which radiation comes from sources X, Y and Z. Comment on how useful each source is for detecting the thickness of sheets of paper up to 2 mm. [6 marks]

OCR Gateway, GCE Physics, Paper B751, June 2015 - Higher.

X is gamma, Y is alpha and Z is beta. Gamma - no difference, alpha stopped too easily and beta shows difference with paper (thickness).

Answering tip: Briefly plan the key points you want to include in your answer. For example:

  • does the paper stop, reduce or have no effect on the radiation?
  • identify the type of radiation (X, Y, Z)
  • give reasons why