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RADON MEASUREMENT OPERATORS PROFICIENCY COURSE

RADON MEASUREMENT OPERATORS PROFICIENCY COURSE. IN CONCERT WITH UNIVERSITY OF ILLINOIS AT CHICAGO AND ILLINOIS DEPARTMENT OF NUCLEAR SAFETY. Physics of Radon and its Decay Products. Introduction to Radon and Radioactivity. Radon Characteristics. Colorless gas Odorless gas Tasteless gas

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RADON MEASUREMENT OPERATORS PROFICIENCY COURSE

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  1. RADON MEASUREMENT OPERATORS PROFICIENCY COURSE IN CONCERT WITH UNIVERSITY OF ILLINOIS AT CHICAGO AND ILLINOIS DEPARTMENT OF NUCLEAR SAFETY Illinois Department of Nuclear Safety

  2. Physics ofRadon and its DecayProducts Illinois Department of Nuclear Safety

  3. Introduction to Radon andRadioactivity Illinois Department of Nuclear Safety

  4. Radon Characteristics • Colorless gas • Odorless gas • Tasteless gas • Naturally Occurring • Radioactive • Inert, does not chemically react (Noble Gas)

  5. Simple Model of an Atom • Atom comprised of: • Nucleus • Protons (+) • Neutrons (neutral) • Electrons (-)

  6. The Nucleus • Made up of positively charged protons and neutral neutrons. • The number of protons and neutrons combined is called the “mass number” (or atomic mass). • The number of neutrons is generally more than the number of protons. • The number of protons is the atomic number (which identifies the element). • The number of electrons is normally equal to the number of protons, so that the total atom has no net charge.

  7. Isotopes • An isotope is any atom with the same number of protons as another atom, but a different number of neutrons. • Radon-220 (thoron) is an isotope of Radon-222, since it also has 86 protons, but it has 134 rather than 136 neutrons.

  8. Isotope Example 1P 1P, 1N 1P, 2N Atomic # ? Atomic Mass?

  9. = 86 = 136 = 222 = 86 A Radon - 222 Nucleus • Protons • Neutrons • Atomic Mass • Atomic Number • This isotope of radon is further identified by its mass number, hence the name radon-222

  10. Rn 86 222 Periodic Table of the Elements

  11. Radioactive Decay • Occurs spontaneously • An atom changes identity due to change in number of protons. (-2) • Radiation is released in the process. Radon-222 Alpha Radiation Gamma Radiation Polonium 218

  12. Radon Radium Uranium Radon Entry

  13. Uranium-238 (solid) 4.47 billion years Radium-226 (solid) 1,620 years Radon-222 (gas) 3.8 days Abbreviated Uranium-238Decay Series • Uranium decays to Radium and then to Radon. • Uranium and Radium as solids are trapped in soil, but radon gas can move. • The decay rate is expressed by “half life”.

  14. The Meaning of Half Life • Half Life is the time required for half of the atoms to decay. • It is not the time for all of the atoms to decay.

  15. Uranium-238 Radon-222 Bismuth-210 Thorium-234 Polonium-210 Protactinium-234 Uranium-234 Thorium-230 Lead-210 a,g a,g b,g Polonium-218 b,g a,g a,g Lead-214 Lead-206 (Stable) b,g b,g Bismuth-214 a,g b,g Polonium-214 Uranium 238 Decay Series a,g a,g Radium-226 a,g b,g

  16. Radon Decay Product Characteristics • Source of cell damage in lungs • Short-lived decay products most significant • Have static charges • Chemically reactive • Solid particles • Heavy Metals

  17. Fate of Indoor Radon • Airborne • Breathable • Measurable Radon Decay Products Radon-222 • Plated Out • Non-Breathable • Non-Measurable

  18. Alpha Radiation (a) • Alpha radiation is a particle released when the nucleus kicks out 2 neutrons and 2 protons (mass number changes by 4 and atomic number changes by 2). • Alpha particle • relatively massive • relatively slow • total charge of +2

  19. Beta Radiation (b) P+ N b- • Beta Radiation is a particle which is released when the nucleus changes a neutron into a proton and a beta particle (atomic mass number remains unchanged). • Beta particle • Relatively small mass • Relatively fast moving • Total charge of -1

  20. Rn 86 Radon & Short-Lived Decay Products b- b- +1P +1P Pb Bi Po At 82 83 84 85 -2 P -2N -2 P -2N a a

  21. Gamma Radiation (g) • Gamma radiation is pure energy. It is released from the nucleus whenever an alpha or a beta is emitted. • Gamma ray • No mass • Moves at the speed of light • No charge

  22. Relative Penetrating Power Alpha Beta Gamma Paper Concrete

  23. Plastic chip from passive radon test (alpha track). Magnified only 100 times. 3 months at EPA to Action Level of 4 pCi/L. Alpha Particles Are Strong Enough To Pit Plastic

  24. Ionization Caused by Radiationcan occur with a a, b, or g Atom in air Ion in air (net charge +1) Before Collision After Collision

  25. Ion • Normally, the number of electrons orbiting the nucleus is equal to the number of protons inside the nucleus, so that the net charge of the atom is zero. • An ion is an atom that has either lost or gained electrons. It has a net positive or negative charge.

  26. Impact of IonizationCaused by Radiation • Measuring ionization allows one to detect the presence of radiation: • Pulsed ion chambers, Electret ion chambers, Geiger counters • Ionization also contributes to overall health effects.

  27. Radon Measurement Units • One picocurie per liter (pCi/L) is 2.22 disintegration's per minute within a liter • This comes from the fact that one Curie is 37 billion disintegration's per second (dps) and: • One picocurie is one trillionth of a Curie, or .037 decays per second • There are 60 seconds in a minute 60 x .037=2.22, or 1 pCi/L is 2.22 dpm

  28. International Radon Unit:The Becquerel • One Becquerel per cubic meter (Bq/m3) is one disintegration per second within a cubic meter Becquerel = 1 disintegration per second 1 pCi/L = 37 Bq/m3 • In other words: • pCi/L x 37 = Bq/m3, or • (Bq/M3)/37 = pCi/L • 4pCi/l = 148Bq/m3

  29. Radon Decay Product Units:The Working Level (WL) • 1 Working Level is the total amount of energy which would be eventually released by the alpha particles coming from the short- lived RDPs. 1 WL is created by 100 pCi/L of radon • 1 Working Level is the amount of short-lived radon decay products within one liter that would ultimately come from the complete disintegration of 100 pCi/L of radon (assuming all RDPs that are produced are measured).

  30. Radon Radon Radon Decay Product Units:A More Practical Definition • 1 Working Level is the amount of short-lived radon decay products that exist at any one moment within one liter if a room, or container, is constantly maintained at 100 pCi/L (assuming all RDPs that are produced are measured.) 1 WL 100 pCi/L

  31. Secular Equilibrium • The condition where the short-lived Radon Decay Products (RDPs) have each reached the same radioactivity ( in picocuries per liter) as the radon forming them. • It takes 4 hours for this to occur.

  32. A Water Flow Experiment

  33. At EquilibriumWater Flows are Equal

  34. At EquilibriumWater Flows are Equal • The waterfalls would be measured in gallons/minute. • Replace waterfalls with radioactive decay in decays/minute, or picocuries. • The volume of water in the buckets is analogous to the number of atoms of each isotope with the short lived isotopes having the least number of atoms at any one time.

  35. At Secular Equilibrium the Decay Rates of RDPs and Radon are Equal Radon 222 - 3.8 days Po 218 - 3 min. Pb 214 - 27 min. Bi 214 - 19.7 min. Po 214 - .000164 sec. Pb 210 - 19.7 years

  36. Plated out RDPs Suspended RDPs Equilibrium Ratio (ER) • The equilibrium ratio describes the fraction of RDPs that are suspended in the air, and therefore measurable, to the total RDPs created. • ER = Measured RDPs Total RDPs

  37. Equilibrium Ratio Example • Assume that you measured the RDPs suspended in the room with a working level meter and determined there were 0.5 WL in the room. • Assume that you measured the radon and determined that there was enough radon (i.e... 100 pCi/L) to create 1 WL of RDPs. • Therefore E.R. = = 0.5 0.5 WL 1.0 WL

  38. Another Equilibrium Ratio Equation • Since the total RDPs can be found by measuring the radon, the total RDPs part of the equilibrium ratio equation can be replaced by: Total RDPs = Radon (in pCi/L) 100 pCi/L per WL • This provides a more useful equation: ER = Measured RDPs (in WL) Radon (in pCi/L) 100 pCi/L per WL

  39. Equilibrium Ratio Equation • Canceling units and moving the “100” gives: RDPs (in WL) x 100 Radon ( in pCi/L) • This equation allows one to determine an equilibrium ratio, and to convert from Radon to Working Levels, or vice versa. ER =

  40. .02 x 1002 ER = = = 0.5 4 4 Equilibrium Ratio Calculation Example • Simultaneous measurements of radon and radon decay products indicate 4.0 pCi/L and .02 WL respectively. What is the equilibrium ratio? This could also be expressed as a percent by multiplying by 100, or 0.5 x 100 = 50%

  41. Factors AffectingEquilibrium Ratio • Air circulation • Increases plate-out, thereby decreasing ER • Electronic air filters • Decreases RDPs attached to dust particles, thereby decreasing ER • Suspended dust, smoke • Increases sites for RDPs so fewer plate-out • Recent ventilation • Inadequate time for RDPs to have been formed • 0.3 < ER < 0.7 in homes.

  42. The Equilibrium Ratio Assumption • EPA and IDNS often assumes that, if nothing else is known about the home, an ER of 0.5 (50%) is a reasonable assumption. • Remember that the ER can be different, not only from house to house, but also within the same house. • Equilibrium ratios in homes range from 0.3 to 0.7

  43. WL x 100 pCi/L WL x 100 ER ER x pCi/L 100 Other Versions of theEquilibrium Equation • ER = • pCi/L = • WL = WL x 100 ER pCi/L

  44. Dynamic Equilibrium • Once the radon entry rate into a building has been altered, time is needed for radon and RDP levels to stabilize. • 12 hours is normally sufficient for dynamic equilibrium to occur in a home. 12 Hours Rn WL Measurable Radioactivity Time House Open House Closed

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