Edexcel IGCSE Physics 复习笔记 7.2.4 Contamination & Irradiation

Contamination

• Contamination is defined as:

The unwanted presence of materials containing radioactive atoms on other materials

• A substance is only radioactive if it contains radioactive atoms that emit radiation
• Contamination occurs when a radioactive isotope gets onto a material where it should not be
  • This is often due to a radiation leak

   

• As a result of this, the small amounts of the isotope in the contaminated areas will emit radiation and the material becomes radioactive

The Assassination of Alexander Litvinenko

• Contamination is almost always a mistake or an accident
  • However, in 2006 a former Russian spy was poisoned by a radioactive isotope

   

• His name was Alexander Litvinenko and he was contaminated with the isotope polonium-210
  • He died because of the poisoning

   

It is believed that the polonium-210 that poisoned Alexander Litvinenko was secretly put into a cup of tea he was drinking

Irradiation

• Irradiation is defined as:

The process of exposing a material to alpha, beta or gamma radiation

• Irradiating a material does not make that material radioactive
  • However, it can kill living cells

   

This sign is the international symbol indicating the presence of a radioactive material

• Irradiation can be used as a method of sterilisation:
  • Surgical equipment is irradiated before being used in order to kill any micro-organisms on it before surgery
  • Food can be irradiated to kill any micro-organisms within it
  • This makes the food last longer without going mouldy

   

Hazards of Irradiation and Contamination

• Although irradiation can cause harm, contamination has the potential to cause far more harm, due to the continuous exposure to radiation that it will produce
• Contamination is particularly dangerous if a radioactive source gets into the human body
  • The internal organs will be irradiated as the source emits radiation as it moves through the body

   

Comparison of Irradiation and Contamination Table

Protecting against Irradiation and Contamination

• It is important to reduce the risk of exposure to radiation
• Radiation can mutate DNA in cells and cause cancer
• Shielding is used to absorb radiation
  • Lead lined suits are used to reduce irradiation for people working with radioactive materials
  • The lead absorbs most of the radiation that would otherwise hit the person

   

• To prevent contamination an airtight suit is used by people working in an area where there may have been a radiation leak
  • This prevents radioactive atoms from getting inside the person

   

Lead shielding is used when a person is getting an x-ray, as well as for people who work with radiation. Contamination carries much greater risks than irradiation

(a) Sources with short half-lives present a greater risk of irradiation

• • A short half-life means a source has a high activity
  • This means there is a high rate of radioactive emissions, compared to a source with a long half-life

   

(b) Sources with long half-lives present a greater risk of contamination

• • Sources with long half-lives will remain radioactive for longer
  • They need to be controlled for longer, to prevent them spreading
  • Shielding and storage may be required