1. 1
   A school laboratory technician uses a Geiger-Muller tube connected to a counter to measure the count rate produced by a radioactive source, noting the reading before and after the source is brought close to the tube.

   (a)

   Before bringing the source near the tube, the counter already registers a small, non-zero count rate. What is this initial count rate called?

   [1 mark]

   • ABackground radiation
   • BHalf-life
   • CIonisation current
   • DCorrected count rate

   (b)

   Which of the following is a source that makes a significant contribution to background radiation?

   [1 mark]

   • AStreetlights
   • BRadon gas in the air
   • CWi-Fi routers
   • DHousehold batteries

   (c)

   The counter reads 42 counts/minute with no source present, and 187 counts/minute when the source is placed near the tube. Calculate the corrected count rate due to the source alone, and state why this correction is necessary.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A nuclear medicine department stores several sealed radioactive sources in a locked, lead-lined cupboard when they are not being used for patient scans, and staff routinely check the count rate near the cupboard using a detector.

   (a)

   Which detector is commonly used to measure ionising radiation and is connected to a counter to give a numerical reading of count rate?

   [1 mark]

   • AA voltmeter
   • BA thermometer
   • CA Geiger-Muller tube
   • DA barometer

   (b)

   Staff at the department measure the count rate near the cupboard in counts per minute. Which of these is a correct unit for expressing count rate?

   [1 mark]

   • AKelvin
   • BCoulombs
   • CWatts
   • DCounts/minute

   (c)

   Staff notice that the count rate measured just outside the cupboard is only slightly higher than the background count rate measured in a different room with no sources nearby. Explain what this observation suggests about how well the cupboard is shielding the radioactive sources.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A geography field trip group measures background radiation levels at several locations, including a granite quarry, a sandy beach and an airport departure lounge, using a Geiger-Muller tube connected to a portable counter.

   (a)

   State three different sources that contribute to the background radiation the group might detect at these locations, and explain briefly why the readings might differ between locations.

   [3 marks]

   (b)

   The group takes three one-minute readings at the granite quarry: 58, 63 and 55 counts. At the beach, they take three one-minute readings: 24, 27 and 21 counts. Explain how the group should combine these readings to obtain a reliable estimate of the background count rate at each location, calculate the mean count rate at each location, and suggest one reason why the readings vary between the three attempts at the same location.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A university physics department runs a demonstration in which a Geiger-Muller tube connected to a counter is used to investigate a sealed radioactive source kept in the laboratory for teaching purposes.

   (a)

   Describe how the department could use this equipment to obtain a reliable value for the corrected count rate due to the source, including the steps needed to account for background radiation and to reduce the effect of the random nature of radioactive decay on the result.

   [6 marks]

   (b)

   After obtaining a reliable corrected count rate for the source, the department wants to investigate how the count rate changes as the Geiger-Muller tube is moved further away from the source, and how the type of material placed between the source and the tube affects the reading. Describe an experiment the department could carry out to investigate these two factors, explaining what results they would expect to observe and why, in terms of the properties of the emitted radiation.

   [6 marks]

   Total for question 4: 12 marks

End of questions