Terrestrial Radiation PDF

Terrestrial Radiation Dr. Muditha Bandara, PhD Department of Nuclear Science Intended learning objectives At the end of this lecture, you should be able to, explain terrestrial radionuclides list down some of the terrestrial radionuclides compare different types of exposure...

Terrestrial Radiation Dr. Muditha Bandara, PhD Department of Nuclear Science Intended learning objectives At the end of this lecture, you should be able to, explain terrestrial radionuclides list down some of the terrestrial radionuclides compare different types of exposure discuss the importance of various radionuclides Terrestrial Radiation? Naturally occurring radionuclides of terrestrial origin Primordial radionuclides Present in various degrees in all media in the environment, including the human body itself.  Only those radionuclides with half-lives comparable to the age of the earth, and their decay products, exist in significant quantities in these terrestrial materials. The rocks and soils contain small quantities of radioactive elements. Thus, the dose rate depends on the geographic location.  Terrestrial Radiation - Sources The irradiation of human body from external sources is mainly from gamma radiation. 40K, 238U and 235U 232Th 87Rb 238U and 232Th decay series Exposure from terrestrial radionuclides  External exposure Outdoor exposure The main out door exposure comes from the gamma emitting radionuclides present in soil. Mainly 40K and the 238U and 232Th families. The average outdoor dose rate is 59 nGy/h  Areas of markedly high absorbed dose rates in air around the world are associated with thorium bearing and uranium bearing materials. Mineral sands containing monazite are examples. Ex: kerala, india Espirito santo, Brazil Authgama – Beruwala - Induruwa in SW sector and Kudiramalai in NW sector of the island. In addition, Monazite and Thorianite sands are reported to occur in lesser concentrations within Pulmuddai, Thirukkovil and Galle. Sri Lankan Terrestrial Radiation Map  Number of thorium bearing mineral occurrences have been identified. These include, Thorianite, Thorite and Allenite. Thorianite was first discovered in Sri Lanka in 1904 by Dr. Ananda Coomaraswamy. During this period, it was reported that several tons of thorianite were exported. Indoor exposure Indoor exposure depend on the outdoor soil and building material. Average activity concentrations are higher in most building materials than in soil Granite and marble has, 226 Ra – 77 Bq/kg Granite has 40K - 1200 Bq/kg 232Th - 84 Bq/kg  Greater than the outdoor exposure if the building material is derived from earth (40%). Buildings made up of wood? Worldwide average indoor absorbed dose rate is 84 nGy/h. National average indoor absorbed dose rate could vary from 20 – 200 nGy/h. Lowest values Highest values (< 40 nGy/h) (95-115 nGy/h) New Zealand Hungary Iceland Malaysia United states Australia Stone/ masonry Wood frame materials in houses buildings Internal Exposure Internal exposure arise from the intake of terrestrial radionuclides by 1. Inhalation 2. Ingestion 3. Via skin Doses due to inhalation result from dust particles containing radionuclides of the 238U and 232Th decay chains present in air.  Inhalation The dominant components of exposure due to inhalation are the short - lived decay products of radon. The inhalation of natural radionuclides other than radon and it’s decay products makes only a minor contribution to the internal exposure.  The radionuclide concentration in air depends on soil class, climate and concentration in soil. What happens when burning fuel???  Ingestion Doses by ingestion are mainly due to 40K and 238U and 232Th series radionuclides present in foods and drinking water.  The ingestion of the radionuclides depends on the consumption rates of food and water radionuclide concentration Ex: Milk consumption in Asia and leafy vegetable consumption in Africa is low Bananas Bananas contain the radionuclide 40K This is a naturally occurring isotope of the element potassium Potassium is essential in muscle function and concentrates in the muscle Who is more radioactive, males or females? Salt Substitute Some individuals cannot use regular salt (NaCl) to season their food They use KCl instead But the KCl is radioactive because of the K-40 that is present in the salt substitute Activity about 450 pCi/g  Salmon Salmon are born in fresh water but live their life in the ocean Natural radioactivity from the rocks and soil is washed into the oceans The salmon tend to concentrate this radioactive material in their flesh – typical values are 20 pCi/g Brazil Nuts These nuts concentrate Ra-226 from the soil These nuts are probably the most radioactive foodstuff we consume Yet the radioactivity is so low that it is difficult to measure it From 0.2 to 7 pCi/g  Via skin Radioactive material is spilled or aerosolizes onto the skin and absorbed or enters through cuts or scratches. Internal deposition may also result from contaminated hands, with subsequent eating or rubbing of eyes.  Uranium - 238 Half life = 4.468×109 years 238U is retained in the body primarily in the skeleton. Small concentration is found in soft tissues, from which lungs and kidneys have relatively high concentrations.  Both Ra and Pb are retained in the bone. Po is mainly distributed in soft tissues. Po is the main contributor to the annual effective dose. Even in the absence of direct intake, both Pb and Po will present in the body. The presence of 210Pb and 210Po in tobacco greatly increases the intake of these radionuclides by smokers. 210Po concentration in lungs of a smoker is about 3x that of a non-smokers  Fiesta Ware Some of these plates are glazed with uranium The uranium has the chemical form U3O8 This form is called “yellowcake” because it is bright yellow in color Firing the plate in a kiln turns the color orange Green Bathroom Tile Dates from the 1930’s Analysis showed it contains natural uranium Dose rate in the bathroom was about 10 times the normal background (0.1 mR/h)  Uranium Glass Uranium was discovered in 1792 by a German chemist named Klaproth It has been used in making glass since the early 1800’s Concentration of uranium temperature and annealing procedure can determine the colors Vaseline Glass Under UV Light A Uranium Glass Marble Under UV Light Cloisonné Jewelry Fine jewelry formed on metal frame with fine glass powder poured into frame Glass is melted at about 850 °C Uranium oxide is used to produce ivory, yellow and gold colors Typically about 7% UO2  Dentures Uranium is added to false teeth to provide a shine to the material (about 10% of the teeth) Concentration of uranium is quite low – about 300 parts per million  Phosphate Fertilizer About 150 million tons of phosphate are mined annually Ore contains uranium, thorium and radium as well as K-40 Produces 12 to 15 million tons of phosphate fertilizer Total activity of Ra-226 in the fertilizer tonnage is about 12 Ci Cat Litter Most cat litter made from clay (e.g., bentonite) Contains elevated levels of naturally occurring radionuclides Contains 4 pCi/g of uranium series, 3 pCi/g of thorium series, and 8 pCi/g of K-40  Penetrators Armor-piercing bullets and shells Are made from “depleted” uranium (DU) DU is the U-238 left when most of the U- 235 had been removed Uranium metal is very dense and it burns spontaneously upon impact  Thorium - 232 Half life = 1.405×1010 years Following intake by ingestion and inhalation, Th is deposited mainly on bone surfaces, where it is retained for long periods. Thorium Lantern Mantles Welding Rods Thorium oxide is also used in tungsten welding rods It increases the current carrying capacity of the rod Production is 1-5 million rods per year Concentration of ThO2 is usually 1-2% (15-30 Ci) Some welding rods have concentrations up to 4% Camera Lenses Th-232 is added to the lenses to increase the index of refraction Some lenses have up to 12% thorium Use began around the late 1930’s Use ceased in the late 1980’s Military lenses may still show radioactivity  Other Uses of Thorium This tape dispenser has sand mixed with epoxy resin in its base The sand is called Monazite (a black sand) Monazite sand contains up to 10% thorium  Potassium - 40 Half life = 1.248×109 years. K is distributed in various organs and tissues in the body. The concentration is under homeostatic control. Red bone marrow receive the highest annual dose. The annual effective dose from 40K is 170 µSv. Besides bananas, other foods that are rich in potassium (and therefore in 40K) are potatoes, kidney beans, sunflower seeds and nuts. Brazil nuts are rich in 40K but also radium, and may have up to 444 Bq/kg– five times the radioactivity of bananas. Rubidium - 87 Pure beta emitter. Half life = 4.9 x 1010 Biological half life = 30 days Measurements in food stuff and humans indicate that, human body retains Rb more than K. Rb is distributed in various organs and tissues in the body. Bone lining cells receive the highest annual dose. The annual effective dose from 87Rb is 6 µSv.  Radon Inert, noble gas. Most common isotope is 222Rn. Arises in the radioactive decay chain of 238U. Some fraction of radon produced in rocks & soils escapes to the air; therefore radon is present in the atmosphere. Radon is soluble in water.  Thoron (220Rn) arises in the radioactive decay chain of 232Th. The production of 222Rn & 220Rn in terrestrial materials depend on the concentration of 226Ra & 224Ra present in them. Granites are high in radium and basalts are low. Radon in your house! Risk with radon??? Radon breaks down (decays) into solid radioactive elements such as 218Po, 214Po & 214 Pb. These daughter products attach themselves to dust particle within few seconds from their origin. The main exposure arises from inhaling these dust particles. Once inside the lungs, the dust particles get deposited on the walls of airways of the bronchial tree. The cells & the DNA inside them, get distorted because of the radiation emitted by these daughter products. Exposure to radon causes tens of thousands of deaths from lung cancer each year globally.