IAEA Natural Terrestrial Radiation Day 3 – Lecture 7 Sources of Radiation 1

IAEA OBJECTIVE To discuss about the natural terrestrial radiation, radioactive decay chains, important radionuclides, radon and its significance, NORM, TENORM and NARM 2

IAEA Content  Terrestrial decay chains  Important radionuclides  Radon and its health significance  NORM  TENORM  NARM 3

IAEA Radioactivity in Nature  Primordial – existing since the creation of the Earth  Cosmogenic – formed as a result of cosmic ray interactions  Human produced – enhanced or formed due to human actions 4

IAEA Primordial Nuclides NuclideHalf-lifeNatural Activity 235 U7.04 x 10 8 yr0.711% of all natural uranium 238 U4.47 x 10 9 yr99.275% of all natural U; 0.5 to 4.7 ppm total U in common rocks 232 Th1.41 x yr1.6 to 20 ppm in common rocks

IAEA NuclideHalf-lifeNatural Activity 226 Ra1,600 yr16 Bq/kg in limestone and 48 Bq/kg in igneous rock 222 Rn3.82 daysNoble gas; average annual air concentrations in US range from 0.6 to 28 Bq/m 3 40 K1.28 x 10 9 yr0.037 to 1.1 Bq/g in soil Primordial Nuclides

IAEA Background Radiation  There are three decay “chains” that occur in nature:  the uranium series, beginning with 238 U  the thorium series, which originates with 232 Th  the actinium series, which originates with 235 U  Once upon a time there was also a neptunium series, which originated with 241 Pu, that has a half-life of only 14 years. The only remaining member of this series is 209 Bi with a half-life of 2E18 years. 7

IAEA 238 U Decay Chain 8

IAEA Natural Radioactivity in Soil Element* Assumed Activity** Mass of Element* Activity Uranium25 Bq/kg2,200 kg31 GBq Thorium40 Bq/kg12,000 kg 52 GBq Potassium Bq/kg2,000 kg500 GBq Radium48 Bq/kg1.7 g63 GBq Radon10 kBq/m 3 11  g 7.4 GBq * Potassium-40 is a radionuclide** per kg of soil

IAEA Natural Radioactivity in Building Materials (mBq/g) MaterialUraniumThoriumPotassium Granite Sandstone67414 Concrete Wallboard Gypsum Clay Brick

IAEA Natural Radioactivity in the Oceans Nuclide* Assumed Activity PacificAtlanticAll Oceans Uranium33 mBq/L22 EBq11 EBq41 EBq 40 K11 Bq/L7400 EBq3300 EBq14000 EBq 3H3H0.6 mBq/L370 PBq190 PBq740 PBq 14 C5 mBq/L3 EBq1.5 EBq6.7 EBq 87 Rb1.1 Bq/L700 EBq330 EBq1300 EBq *Uranium is an element

IAEA Background Radiation - Radon  Radon is a noble gas (also called “inert”).  Radon is chemically like other members of this group of the periodic table, namely He, Ne, Ar, Kr, and Xe, gas. The noble gases do not readily form compounds due to their stable electron shell configuration. With the exception of helium, they all have 8 electrons in their outer shell (ns 2 np 6 for you chemists in the audience). 12

IAEA Background Radiation - Radon  The average dose from radon-222 ( 222 Rn) is approximately 2000  Sv per year. Radon is an alpha emitter. Many of the radon decay products are also alpha emitters.  Radon is produced from the radioactive decay of 238 U an isotope of uranium which is naturally present in the environment. In fact, in some areas of the western US, the concentration of natural uranium is high enough that is it mined to provide a source of uranium for reactors. 13

IAEA Production of 222 Rn by Decay of 238 U

IAEA Background Radiation - Radon  Just as helium can diffuse through a balloon, radon can diffuse through the soil and foundations of homes. The diffusion is greater when the soil has low moisture content.  Radon is a radiological hazard because the decay products are alpha emitters. Since they are formed by emission of alpha particles, the resulting decay products have an electrostatic charge and are attracted to particulates in the air. These may become deposited in the lung. These particles then decay by alpha emission, which results in a dose to the lung. 15

IAEA Radon Diffusion Through Soil

IAEA Radon Transport Into Homes

IAEA Background Radiation - Radon  The concern is really not with the radioactive decay of radon, but with the radon progeny (also called “daughter products”), that are produced when radon decays. Since radon decays by alpha emission, the radon “daughters” have a ++ charge and so are electrostatically attached to particulates in the air. These decay products are also radioactive, and many decay by alpha particle emission.  The alpha particle energy delivers a dose to the lung where the particles are deposited. The dose to the lung is attributed to the development of lung cancer for uranium miners (hence the regulatory limits for radon and radon daughter concentrations). 18

IAEA Relative Risk from Radon 19

IAEA Radionuclides Found in Your Body Nuclide* Total Mass of Nuclide Found in the Body Total Activity of Nuclide Found in the Body Daily Intake of Nuclides Uranium 90  g 30 pCi (1.1 Bq) 1.9  g Thorium 30  g 3 pCi (0.11 Bq) 3  g 40 K17 mg120 nCi (4.4 kBq)0.39 mg Radium31 pg30 pCi (1.1 Bq)2.3 pg 14 C 95  g0.4  Ci (15 kBq)1.8  g *Uranium, Thorium and Radium are elements 20

IAEA Natural Radiation Exposure Around the World 21

IAEA Effective Dose Equivalent to a Member of the Population of the United States Source Average Annual Effective Dose Equivalent  Sv mrem Inhaled (radon and decay products) Other Internally Deposited Radionuclides Terrestrial Radiation28028 Cosmic Radiation273 Cosmogenic Radioactivity101 Rounded Total from Natural Sources Rounded Total from Artificial Sources60060 Total

IAEA Per Capita Annual Dose – UNSCEAR 2008 × Others include Fallout, Nuclear Power Production, Occupational exposures etc. 23

IAEA Per Capita Annual Doses from Natural Sources – UNSCEAR

IAEA NORM and NARM  NORM Naturally Occurring Radioactive Material  TENORM Naturally Occurring Radioactive Material enhanced by processing is called TENORM  NARM Naturally Occurring and Accelerator-Produced Radioactive Material 25

IAEA Summary  Natural terrestrial radiation was discussed  Important radionuclides and their distribution was discussed  Radon in particular and its significance was discussed  NORM, TENORM and NARM were defined 26

IAEA Where to Get More 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) 27