Radioactivity in question

Radioactivity in question

Types of radiation and their penetration power

• Helium core: the alpha emission can be stopped by a simple sheet of paper
• Electron: the beta emission can be stopped by a few millimetres of aluminium
• Gamma: Gamma radiation can stopped by a few dozen of centimetres of concrete or several centimetres of lead

Radiation measurements and units

– Becquerel (Bq)

The activity of a radioactive source is expressed in Becquerel. It designates the number of decays of unstable nuclei per second.

– Gray (Gy)

The dose received is expressed in Gray. A Gray designates the dose of ionizing radiation absorbed by the matter.

– Sievert (Sv)

Effective dose and equivalent dose are expressed in Sievert. The Sievert designates the biological effects of ionizing radiation on living matter.

Effective dose and equivalent dose

• Absorbed dose D (Gy): The absorbed dose is the amount of energy absorbed per unit of mass. It is expressed in Gray (1 Gray=1J/kg)
• Equivalent dose H (Sv): The equivalent dose is equal to the absorbed dose multiplied by the weighting factor, which depends on the type of radiation.
• Effective dose E (Sv): The effective dose is equal to the equivalent dose multiplied by the tissue weighting factor.

Few figures

• 10,000 Bq = Natural radioactivity of a 70kg man
• 4.6 mSv/year = Average exposure of the French population
• 15 Gy = Lethal dose in the event of whole body exposure

Examples of doses received

• 0.001 mSv = Annual exposure in France related to the nuclear industry
• 0.034 mSv = Cosmic radiation doses during a Paris/Dallas flight
• 0.1 mSv = Chest X-ray
• 0.5 mSv = Additional exposure due to a 3-month stay in a granitic region
• 1 mSv = Average medical radiation exposure of the population in France
• 2 mSv = Cosmic radiation exposure of aviation aircrew
• 12 mSv = Abdominal and pelvic CT scan
• 50 mSv = Average dose received in 1986 by a person residing 30km from Chernobyl

Source: ASN / IRSN / CIPR