Sources de rayonnements Rayonnement naturel terrestre

Présentation au sujet: "Sources de rayonnements Rayonnement naturel terrestre"— Transcription de la présentation:

1 Sources de rayonnements Rayonnement naturel terrestre
Now let’s discuss natural sources of terrestrial radiation (i.e. radiation coming from the earth). Jour 3 – Leçon 7

2 OBJECTIF Discuter le sujet de la radioactivité naturelle terrestre, chaînes de décroissance radioactive, les radionucléides importants, le Radon et sa signification, NORM, TENORM & NARM We will discuss natural radioactive decay chains occurring in the earth and some important, specific radionuclides which contribute to our exposure.

3 Contenu Chaînes de désintégration terrestres Radionucléides Importants
Radon et son importance pour la santé NORM TENORM NARM We will focus on radon because of its health significance. We will define NORM and NARM.

4 Radioactivité dans la Nature
Primordial – existant depuis la création de la Terre Cosmogonique – formé à la suite de l'interaction des rayons cosmiques Activités Humaines - amélioration ou formé en raison des actions humaines There are three primary sources of radiation exposures to humans around the world.

5 Nucléides Primordiaux
Demi-vie Activité Naturelle 235U 7.04 x 108 a 0.711% de l’uranium naturel 238U 4.47 x 109 a 99.275% de tout l’U nat. ; 0.5 à 4.7 ppm de l’U total dans les roches 232Th 1.41 x 1010 a 1.6 to 20 ppm dans les roches Three very important naturally occurring terrestrial radionuclides include U-238, U-235, and Th They are actually parents of three long radioactive decay chains, which end in stable lead. Some nuclides, like Th-232 have several members in their decay chains. You can roughly follow the chain starting with Th-232 Th > Ra-228--> Ac >Th > Ra > Rn-220--> Po > Pb-212--> Bi > Po > Pb-208 (stable) Some other primordial radionuclides are: V-50, Rb-87, Cd-113, In-115, Te-123, La-138, Ce-142, Nd-144, Sm-147, Gd-152, Hf-174, Lu-176, Re-187, Pt-190, Pt-192, and Bi-209.

6 Nucléides Primordiaux
Demi-vie Activité Naturelle 226Ra 1,600 a 16 Bq / kg dans le calcaire et 48 Bq / kg dans la roche ignée 222Rn 3.82 j Gaz Noble: concentrations moyennes dans l’air en US gamme de 0.6 à 28 Bq/m3 40K 1.28 x 109 a 0.037 to 1.1 Bq/g dans le sol Additional important primordial radionuclides include Ra-226, Rn-222, and K-40. Ra-226 decays to Rn K-40 is found in not only the soil but in foods such as bananas. Rn-222, which is formed by decay of Ra-226, is much more important from a dose standpoint than is Rn-220, which is formed from the Th-232 decay chain. This is because the half-life of Rn-220 is very short (55 s) compared with the 3.8 day half-life of Rn-222.

7 Bruit de fond naturel Il y a trois chaînes de désintégration qui se produisent dans la nature: la série de l'uranium, en commençant par 238U la série de thorium, qui est originaire de 232Th la série de l'actinium, qui provient de 235U Il était une fois, il y avait aussi une chaîne de Neptunium, qui a pris naissance avec 241Pu, qui a une demi-vie de 14 ans seulement. Le seul membre restant de cette série est 209Bi avec une demi-vie de 2E18 ans. There are three naturally occurring radioactive decay chains.

8 Chaîne de décroissance de 238U
The U-238 decay chain is one of the most important from a dose consequence. It forms Rn-222 and ends in stable lead. Half-lives of its member radionuclides vary greatly. Although this figure shows only alpha and beta radiation being emitted, gamma rays and x-rays are also emitted from this decay chain.

9 Radioactivité Naturelle dans le sol
Element* Activity** estimée Masse de l’élément* Activité Uranium 25 Bq/kg 2,200 kg 31 GBq Thorium 40 Bq/kg 12,000 kg 52 GBq Potassium-40 400 Bq/kg 2,000 kg 500 GBq Radium 48 Bq/kg 1.7 g 63 GBq Radon 10 kBq/m3 11 g 7.4 GBq How much natural radioactivity is found in an area 1 square mile, by 1 foot deep? The above table is calculated for this volume (total volume is x 105 m3) and the listed activities. Activity levels vary greatly depending on soil type, mineral make-up and density (~1.58 g/cm3). This table represents calculations using typical numbers. As can be seen from the table, the most abundant radionuclide (from an absolute total amount standpoint) is K-40. Around the world though, there are some areas with sizable populations that have high background radiation levels. The highest are found primarily in Brazil, India and China. The higher radiation levels are due to high concentrations of radioactive minerals in soil. One such mineral, Monazite, is a highly insoluble rare earth mineral that occurs in beach sand together with the mineral ilmenite, which gives the sands a characteristic black color. The principal radionuclides in monazite are from the Th-232 series, but there is also some uranium and its progeny, Ra In Brazil, the monazite sand deposits are found along certain beaches. The external radiation levels on these black sands range up to 5 mrad/hr (50 µGy/hr), which is almost 400 times normal background in the US. Some of the major streets of the surrounding cites have radiation levels as high as 0.13 mrad/hr (1.3 µGy/hr), which is more than 10 times the normal background. Another high background area in Brazil is the result of large rare earth ore deposits that form a hill that rises about 250 meters above the surrounding area. An ore body near the top of the hill is very near the surface, and contains an estimated 30,000 tons of thorium and 100,000 tons of rare earth elements. The radiation levels near the top of the hill are 1 to 2 mrad/hr (0.01 to 0.02 mGy/hr) over an area of about 30,000 m2. The plants found there have absorbed so much 228Ra that they will produce a self "x-ray" if placed on a sheet of photographic paper (an autoradiograph). On the Southwest coast of India, the monazite deposits are larger than those in Brazil. The dose from external radiation is, on average, similar to the doses reported in Brazil, mrad/yr (5 - 6 mGy/yr), but individual doses up to 3260 mrad/yr (32.6 mGy/yr) have been reported. An area in China has does rates that is about mrad/yr (3-4 mGy/yr). This is also from monazite that contains thorium, uranium and radium. From BEIR V, National Research Council report on Health Effects of Low Levels of Ionizing Radiation: In areas of high natural background radiation, an increased frequency of chromosome aberrations has been noted repeatedly. The increases are consistent with those seen in radiation workers and in persons exposed at high dose levels, although the magnitudes of the increases are somewhat higher than predicted. No increase in the frequency of cancer has documented in populations residing in areas of high natural background radiation. * Potassium-40 is a radionuclide ** per kg of soil

10 Radioactivité Naturelle dans les matériaux de construction (mBq/g)
Uranium Thorium Potassium Granite 63 8 1184 Grés 6 7 414 Béton 31 8.5 89 Plâtre 14 12 Gypse 186 66 5.9 Brique d'argile 111 44 666 Naturally occurring radioactivity in building materials contributes to external gamma ray exposure. Also of note is that Ra-226 in the building material can be a source of Rn-222 emanating out into the inside air. People inhale the air and are exposed. A well-known exposure problem historically in the western US has been the incorporation of uranium mill tailings into concrete block. This has caused concern both from an external exposure pathway (gamma exposure) and, more importantly, internal exposure from inhalation of Rn produced from Ra-226 decay.

11 Radioactivité naturelle dans les Océans
Nucléide* Activité estimée Pacifique Atlantique Tous les Océans Uranium 33 mBq/L 22 EBq 11 EBq 41 EBq 40K 11 Bq/L 7400 EBq 3300 EBq 14000 EBq 3H 0.6 mBq/L 370 PBq 190 PBq 740 PBq 14C 5 mBq/L 3 EBq 1.5 EBq 6.7 EBq 87Rb 1.1 Bq/L 700 EBq 330 EBq 1300 EBq How much natural radioactivity is found in the world's oceans? All water on the Earth, including seawater, contains radionuclides in it. In the table above, the oceans' volumes were calculated from the 1990 World Almanac: Pacific = x 1017 m3 Atlantic = x 1017 m3 Total = 1.3 x 1018 m3 The activities used in the table above are from 1971 Radioactivity in the Marine Environment, National Academy of Sciences. *Uranium is an element

12 Bruit de fond naturel- Radon
Radon gaz noble (appelé aussi inerte). Le Radon est un gaz comme les autres membres de ce groupe de la table périodique, à savoir He, Ne, Ar, Kr, Xe et gaz. Les gaz nobles ne forment pas facilement de composés en raison de la configuration de leur couche électronique stable. À l'exception de l'hélium, ils ont tous 8 électrons dans leur couche externe (ns2np6 pour vous les chimistes dans l’audience). Since radon is an inert, noble gas, it does not interact chemically (very few chemical removal processes occur) and tends to travel significant distances in air or soil, especially if the soil is porous.

13 Bruit de fond naturel - Radon
La dose moyenne due au radon-222 (222Rn) est environ 2000 Sv par an. Radon est un émetteur alpha. Beaucoup de produits de désintégration du radon sont également des émetteurs alpha. Le Radon est née par la désintégration de 238U, un isotope de l’uranium qui existe naturellement dans l’environnement. En fait, dans certaines régions de l’Amérique de l'Ouest, la concentration de l'uranium naturel est suffisamment élevée pour être exploitée et fournir de l'uranium aux réacteurs. Of all of the natural background radiation (including cosmogenic), Rn-222 is by far the most significant in terms of radiation dose and health consequences to people. The decay products of Rn-222, once inhaled, dose the lung and have been linked to lung cancer at high exposures.

14 Par désintégration de 238U
Production du 222Rn Par désintégration de 238U Rn-222 is produced from U-238 via Ra-226 decay. Since the half-life of Ra-226 is relatively long (1600 yr), it essentially acts as a constant source of Rn-222 over a human life time. Rn-222, although itself a noble gas, decays to radioactive particulate daughter products. It is these alpha-emitting decay products that produce at least 90% of the dose to the human lung.

15 Bruit de fond naturel - Radon
Tout comme l'hélium peut diffuser à travers un ballon, le radon peut diffuser à travers le sol et les fondations des maisons. La diffusion est plus importante lorsque le sol a une faible teneur en humidité. Le radon présente un risque radiologique parce que ses produits de désintégration sont des émetteurs alpha. Comme ces produits sont aussi des émetteurs alpha et ont une charge électrostatique ils sont attirés par les particules dans l'air. Ceux-ci vont se désintégrer dans les poumons. Ces désintégrations vont se traduire par une dose aux poumons Being an inert, noble gas, radon can diffuse readily through soil (especially when the soil moisture content is low) and enter the air.

16 Diffusion du Radon par le sol
This slides shows the relative permeability to radon of various soil and rock types. Clay has low permeability relative to sand and gravel.

17 Transport radon dans les maisons
Depending on the type of soil and rock underlying a structure, radon can diffuse through the soil and find its way into the structure. Areas around the world where radon is such a problem include the Reading Prong area of Pennsylvania, New York, and New Jersey in the US, Sweden and Finland.

18 Bruit de fond naturel - Radon
Le problème n'est vraiment pas à la désintégration radioactive du radon, mais avec la filiation du radon (également appelés «produits de filiation»), qui sont produits lorsque le radon se désintègre. Le radon se désintègre par émission alpha, ces "fils" ont une charge ++ et sont donc attachés à électro-statiquement à des particules dans l'air. Ces produits de désintégration radioactives sont également radioactifs, et se désintègrent par émission de particules alpha.. L'énergie des particules alpha délivre une dose au poumon, où les particules se déposent. La dose au poumon est attribuée au développement du cancer du poumon chez les mineurs d'uranium (d'où les limites réglementaires pour les concentrations du radon et de ses descendants). As mentioned previously, the concern from a dose and health effects (cancer) standpoint is not Rn-222 itself but rather its radioactive particulate decay products. Rn-222 merely serves as the source (parent) of these short-lived decay products.

19 Risque relatif du Radon
The relative risk from radon (lung cancer) is second only to mortality from drunk driving.

20 Radionucléides dans Le corps humain Nucléide*
Masse du Nucléide dans le corps humain Activité Totale dans le corps humain L'apport quotidien de nucléides Uranium 90 g 30 pCi (1.1 Bq) 1.9 g Thorium 30 g 3 pCi (0.11 Bq) 3 g 40K 17 mg 120 nCi (4.4 kBq) 0.39 mg Radium 31 pg 2.3 pg 14C 95 g 0.4 Ci (15 kBq) 1.8 g You are made up of chemicals, and it should be of no surprise that some of them are radionuclides, many of which you ingest daily in your water and food. As mentioned previously, K-40 is found in bananas (bananas are a good source of potassium) and when you eat them, you ingest K-40. In this table the estimated concentrations of radionuclides are calculated for a 70,000 gram adult based on ICRP 30 data. *Uranium, Thorium and Radium are elements

21 Exposition à la radioactivité naturelle
Dans le monde This graph clearly shows that radon is the principal source of exposure from terrestrial radiation. Doses vary greatly but are highest in Finland and in Sweden.

22 Equivalent de dose efficace moyenne annuelle
Équivalent de dose efficace à un membre de la population des États-Unis Source Equivalent de dose efficace moyenne annuelle Sv mrem Inhalée (radon et produits de désintégration) 2000 200 Autres radionucléides déposés à l’intérieur 390 39 Rayonnement Terrestre 280 28 Rayons cosmiques 27 3 Radioactivité Cosmogénique 10 1 Total arrondi des Sources naturelles 3000 300 Total arrondi de sources artificielles 600 60 Total 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.

23 Dose annuelle par habitant– UNSCEAR 2008
D'autres incluent Retombées, production d'énergie nucléaire, expositions professionnelles, etc

24 Doses annuelles par habitant de Sources naturelles– UNSCEAR 2008

25 NORM & NARM NORM Naturally Occurring Radioactive Material (Matières radioactives d’origine naturelle) TENORM Naturally Occurring Radioactive Material enhanced by processing is called TENORM (Matières radioactives naturelles renforcée par le traitement est appelé TENORM) NARM Naturally Occurring and Accelerator-Produced Radioactive Material (d’origine naturelle et accélérateurs- matière radioactive produite) Two acronyms that are often used are NORM and NARM. NARM includes accelerator-produced radioactive materials. Some examples of NORM include building materials containing uranium mill tailings or phosphate slag (phosphate deposits in Florida in the US are somewhat elevated in U and Ra). Both terms refer to the occurrence of and/or enhancement of radioactivity in consumer products due to human activity.

26 Résumé Le rayonnement naturel terrestre a été discuté
Les radionucléides importants et leur répartition ont été discutés Le radon en particulier et son importance a été discuté NORM, TENORM et NARM ont été définis NORM, radioactivité naturelle renforcée et NARM ont été définis

27 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)