5.2.1

Detection of radioactivity

10 flashcards to master Detection of radioactivity

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Definition Flip

State what is meant by background radiation.

Answer Flip

Background radiation is the low-level radiation that is present in the environment at all times. It originates from natural sources, such as radioactive materials in the Earth and cosmic radiation from space, as well as artificial sources like nuclear weapons testing and medical procedures.

Key Concept Flip

A radiation detector records a count rate of 24 counts per minute in a laboratory. Suggest two possible sources of this background radiation.

Answer Flip

Possible sources include:

1. Radioactive materials in the surrounding rocks/soil (

Example: granite, uranium).<br>2. Cosmic rays from space interacting with the atmosphere.
Key Concept Flip

State four significant sources of background radiation.

Answer Flip

1. Radon gas (in the air)
2. Rocks and buildings
3. Food and drink
4. Cosmic rays

(Each correct source is worth 0.5 marks)

Key Concept Flip

A student measures background radiation using a Geiger-Muller tube. The initial reading is 10.0 counts per minute. She then places a lead sheet in front of the tube. Suggest why the measured count rate might be slightly lower, but not zero.

Answer Flip

The lead sheet absorbs some, but not all, of the background radiation. Background radiation originates from multiple sources (radon gas, rocks, cosmic rays, food/drink) and some of these sources are not blocked by the lead sheet.

Key Concept Flip

A detector connected to a counter records 20 counts per minute due to background radiation. A radioactive source is then placed near the detector, and the counter now reads 110 counts per minute. Calculate the count rate due to the radioactive source alone.

Answer Flip

Count rate from source = Total count rate - Background count rate
Count rate from source = 110 counts/minute - 20 counts/minute
Count rate from source = 90 counts/minute

Explanation: The background radiation must be subtracted from the total count rate to determine the radiation emitted by the source only.

Key Concept Flip

A student measures the background radiation in a laboratory. Suggest two sources that contribute to this background radiation.

Answer Flip

1. Cosmic rays from space: High-energy particles from space constantly bombard the Earth.
2. Radioactive materials in the ground or buildings: Small amounts of radioactive isotopes are naturally present in rocks, soil and building materials.

Key Concept Flip

A Geiger-Muller (GM) tube detects 3960 counts in 3 minutes. Calculate the count rate in counts/second.

Answer Flip

Count rate = Total counts / Time
Count rate = 3960 counts / (3 minutes * 60 seconds/minute)
Count rate = 3960 counts / 180 seconds
Count rate = 22 counts/s

The count rate is calculated by dividing the total number of counts by the time interval in seconds.

Key Concept Flip

A radioactive source is measured to have a count rate of 10 counts/s using a Geiger-Muller tube. State what a 'count rate' is.

Answer Flip

Count rate is the number of radioactive decays detected per unit of time, typically measured in counts per second (counts/s) or counts per minute (counts/minute). It indicates the activity of the radioactive source.

Key Concept Flip

A Geiger-Muller (GM) tube detects 32 counts per minute in a laboratory. A radioactive source is then placed near the GM tube, and the count rate increases to 198 counts per minute. Determine the corrected count rate of the radioactive source.

Answer Flip

Answer:
Corrected count rate = Total count rate - Background count rate
Corrected count rate = 198 counts/min - 32 counts/min
Corrected count rate = 166 counts/min

Explanation: The background radiation must be subtracted from the total count rate to find the count rate due only to the radioactive source.

Key Concept Flip

A student measures a background radiation count of 10 counts per minute. They then place a radioactive sample near the detector and measure a total count rate of 24 counts per minute. Explain why it is important to measure the background radiation when determining the activity of a radioactive source.

Answer Flip

Answer:
Background radiation is present from sources other than the radioactive sample (

Example: cosmic rays, radon gas in the air, or radiation from building materials). If background radiation isn't accounted for, the measured count rate will overestimate the activity of the sample. Subtracting the background count provides a more accurate measurement of the radiation emitted by the source alone.

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5.1.2 The nucleus 5.2.2 The three types of nuclear emission

Key Questions: Detection of radioactivity

State what is meant by background radiation.

Background radiation is the low-level radiation that is present in the environment at all times. It originates from natural sources, such as radioactive materials in the Earth and cosmic radiation from space, as well as artificial sources like nuclear weapons testing and medical procedures.

About Detection of radioactivity (5.2.1)

These 10 flashcards cover everything you need to know about Detection of radioactivity for your Cambridge IGCSE Physics (0625) exam. Each card is designed based on the official syllabus requirements.

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