Sources de rayonnements Rayonnement naturel - Rayons Cosmiques- Now let’s discuss cosmic radiation and its significance from dose standpoint. Jour 3 – Presentation 8

Objectif Apprendre davantage sur le rayonnement cosmique provenant de l'espace, les radionucléides cosmo-géniques, la variance du rayonnement cosmique avec la latitude et de l'altitude et de l'exposition au rayonnement cosmique

Contenu Rayonnement cosmique Radionucléides Cosmo-géniques Variation du rayonnement avec la latitude et l’altitude Débit de dose du au rayonnement cosmique

Types du rayonnement cosmique Rayonnement cosmique Primaire Rayonnement cosmique Secondaire Cosmic radiation interacts with our atmosphere to produce cosmogenic radionuclides. It also is responsible for whole body doses. Cosmic radiation is really divided into two types, primary and secondary.

Rayonnement cosmique Primaire Constitué de particules d'énergie extrêmement élevées (jusqu’à 1018 eV) Composé essentiellement de protons ou de particules parfois plus lourdes Un pourcentage important vient de l’extérieur du système solaire Certains proviennent de soleil (éruptions solaires) Primary cosmic radiation is made up of extremely high energy particles (up to 1018 eV), and are mostly protons or sometimes larger particles. A large percentage of it comes from outside of our solar system and is found throughout space. Some of the primary cosmic radiation is from our sun, produced during solar flares.

Rayonnement cosmique Secondaire Produit par l'interaction du rayonnement cosmique primaire avec l'atmosphère C’est ce que nous recevons actuellement au niveau de la terre Rayonnement de faible énergie sous forme de photons , électrons, neutrons, et muons Little of the primary cosmic radiation penetrates to the Earth's surface, the vast majority of it interacts with the atmosphere. When it does interact, it produces the secondary cosmic radiation, or what we actually see here on Earth. These reactions produce other lower energy radiations in the form of photons, electrons, neutrons and muons that make it to the surface.

Bruit de fond naturel Le rayonnement provenant des galaxies est une composante du bruit de fond au niveau de la terre Most of the cosmic rays incident on the earth’s atmosphere are believed to be of galactic origin and to have been accelerated to their present energies by interstellar magnetic fields. During solar flares the sun contributes significantly to the low-energy (mostly less than 1 GeV) cosmic-ray flux arriving at the earth. Another important effect of the sun is the decrease in galactic cosmic-ray flux reaching us during periods of intense sun-spot activity; this is most likely a magnetic phenomenon.

Bruit de fond naturel Le rayonnement cosmique contribue dans le bruit de fond au niveau de la terre. L’atmosphère constitue un écran de protection contre la plupart du rayonnement cosmique . The atmosphere and the Earth's magnetic fields also act as shields against cosmic radiation, reducing the amount that reaches the Earth's surface. With that in mind, it is easy to see that the annual dose you get from cosmic radiation depends on what altitude you are at.

Bruit de fond naturel La dose due aux rayons cosmiques est réduite au niveau des basses altitudes par un écran additionnel constitué par l’atmosphère terrestre . From cosmic radiation, the average person in the U.S. will receive a dose of 0.27 mSv per year and this roughly doubles every 1,829 m increase in elevation.

Radionuclides Cosmogéniques Dem-vie Source Activité naturelle 14C 5730 a Interaction-rays cosmiques, 14N(n,p)14C 0.22 Bq/g 3H 12.3 a Interaction-rays cosmiques avec N et O 1.2 x 10-3 Bq/kg 7Be 53.3 j Interaction-rays cosmiques avec N et O 0.01 Bq/kg Cosmic radiation permeates all of space, the source being primarily outside of our solar system. The radiation is in many forms, from high speed heavy particles to high energy photons and muons. The upper atmosphere interacts with many of the cosmic radiations, and produces radioactive nuclides. They can have long half-lives, but the majority have shorter half-lives than the primordial nuclides. The above table shows some common cosmogenic nuclides. Tritium is formed directly by a process called “spallation” ( interactions of very high energy particles with heavier nuclei, resulting in formation of lighter nuclei). It is also formed indirectly by fast neutrons reacting with nitrogen, according to the reaction: 14N (n, 3H)12C. Some other cosmogenic radionuclides are 10Be, 26Al, 36Cl, 80Kr, 14C, 32Si, 39Ar, 22Na, 35S, 37Ar, 33P, 32P, 38Mg, 24Na, 38S, 31Si, 18F, 39Cl, 38Cl, 34mCl.

Doses du Rayt. Cosmique Vol Subsonique à 11 km Itinéraire Durée de vol (hrs) Dose par aller-retour (µGy) Los Angeles – Paris 11.1 48 Chicago – Paris 8.3 36 New York - Paris 7.4 31 New York - London 7.0 29 Los Angeles - New York 5.2 19 Sydney - Acapulco 17.4 44 Flying can add a few extra mSv to your annual dose, depending on how often you fly, how high the plane flies, and how long you are in the air.

Doses du Rayt. Cosmique Vol Subsonique à 19 km Itinéraire Durée de vol (hrs) Dose par aller et retour (µGy) Los Angeles – Paris 3.8 37 Chicago – Paris 2.8 26 New York – Paris 2.6 24 New York – London 2.4 22 Los Angeles - New York 1.9 13 Sydney - Acapulco 6.2 21 Doses are less as compared with the previous slide since, although the altitude is higher, the exposure time (flight duration) is less for the supersonic flights.

Débits de dose typiques du Ryt. cosmique 4 x 10-8 Sv/hr au niveau du sol dans le Nord des États-Unis 2 x 10-7 Sv/hr à 4.6 km d’altitude 3 x 10-6 Sv/hr à 16.8 km d’altitude There is only about a 10% decrease at sea level in cosmic radiation rates when going from pole to the equator, but at 55,000 feet the decrease is 75%. This is on account of the effect of the earth's and the Sun's geomagnetic fields on the primary cosmic radiations.

Exposition à la radioactivité naturelle dans le monde Exposure from cosmic rays varies somewhat around the world but is not nearly as variable as, for example, exposure from radon. For the countries shown in the figure, dose from cosmic rays is highest in Switzerland. Also, the dose from cosmic rays is small compared to that from natural terrestrial radiation such as radon.

Equivalent de dose efficace Équivalent de dose efficace à un membre de la population des États-Unis Source Equivalent de dose efficace Moyenne annuelle µSv mrem Inhalé (radon et produits de décroissance) 2000 200 Autres radionucléides déposés à l’intérieur 390 39 Rayonnement Terrestre 280 28 Rayons cosmiques 27 Radioactivité Cosmogénique 10 1 Total arrondi des Sources naturelles 3000 300 Total arrondi de sources artificielles 600 60 3600 360 The average person in the US receives about 3600 Sv from all background radiation sources, 2000 Sv of which comes from Rn-222 and its decay products. Clearly, radon is the largest single contributor to radiation dose from naturally occurring radioactivity. In general, this true for the world as a whole.

Sources d’exposition radiologique Aux USA This graph shows that average annual exposure in the US from cosmic radiation is only 8% of the total average annual exposure.

Où trouver plus d’Information Cember, H., Johnson, T. E, Introduction to Health Physics, 4th Edition, McGraw-Hill, New York (2009) UNSCEAR, Sources and Effects of Ionizing Radiation, 2008 Report to the General Assembly with Scientific Annexes, United Nations, New York, 2008 International Atomic Energy Agency, Postgraduate Educational Course in Radiation Protection and the Safety of Radiation Sources(PGEC), Training Course Series 18, IAEA, Vienna (2002)