Background Radiation | Physics for Grade 10 PDF Download

Introduction

• It is important to remember that radiation is a natural phenomenon
• Radioactive elements have always existed on Earth and in outer space
• However, human activity has added to the amount of radiation that humans are exposed to on Earth
• Background radiation is defined as:
  • The radiation that exists around us all the time
• There are two types of background radiation:
  • Natural sources
  • Man-made sources
    
    Background radiation is the radiation that is present all around in the environment. Radon gas is given off from some types of rock
• Every second of the day there is some radiation emanating from natural sources such as:
  • Rocks
  • Cosmic rays from space
  • Foods
• Man-made sources of radiation increase the background radiation levels, examples include:
  • Fallout from nuclear weapons testing and nuclear accidents
  • Exposure from medical testing

Example: A student is using a Geiger-counter to measure the counts per minute at different distances from a source of radiation. Their results and a graph of the results are shown here.
Determine the background radiation count.

Step 1: Determine the point at which the source radiation stops being detected

• The background radiation is the amount of radiation received all the time
• When the source is moved back far enough it is all absorbed by the air before reaching the Geiger-counter
• Results after 1 metre do not change
• Therefore, the amount after 1 metre is only due to background radiation

Step 2: State the background radiation count 

• The background radiation count is 15 counts per minute

Measuring Radiation Dose

• It is important to regulate the exposure of humans to radiation
• The amount of radiation received by a person is called the dose and is measured in sieverts (Sv)
• One sievert is a very big dose of radiation
  • It would cause acute radiation poisoning
• People would normally receive about 3 mSv (0.003 Sv) in one year
• To protect against over-exposure, the dose received by different activities is measured
• A dosemeter measures the amount of radiation in particular areas
  
  A dosemeter, or radiation badge, can be worn by a person working with radiation in order to keep track of the amount of radiation they are receiving

Differences in Exposure

• The level of background radiation and radiation dose may be affected by a person’s occupation or location
• Some areas around the world have higher background radiation because they are closer to sources of radiation
• People that work with nuclear radiation receive more radiation
  • The UK limit for nuclear industry employees is 20 mSv in one year
• The diagram below compares the dose received by some different activities
  
  All living things emit a small amount of radiation: the amount of radiation within a banana is tiny, and not at all dangerous!

Tips

You have been introduced to three different units to do with radiation:

• Becquerels measure the amount of radiation emitted by a source every second
• Counts per second measures the rate at which radiation hits a particular location
• Sieverts measure the received dose of radiation

They are not the same thing!