University of Illinois at Chicago Radiation Safety Section Environmental Health and Safety Office Physics 108, 244 Radiation Safety Physics Lecture

Ionizing Radiation Radiation that can cause ionization of the material through which it passes either directly or indirectly Electromagnetic radiation Particulate radiation

Electromagnetic Radiation Electro-magnetic waves (uncharged packets of energy) propagated through space or a material medium Wavelength, m Frequency, s -1 Energy of one photon, eV E ~ ν ~ 1 λ _

Particulate Radiation Matter that that is propagated through space or through a material medium Alpha Particles Beta Particles (Electrons, Positrons) Neutrons (uncharged) Protons Heavy Ions Fission Fragments

Sources of Ionizing Radiation Radioactive Materials H-3, C-14, P-32, S-35, I-125, etc. Radiation Producing Machines X-Ray equipment Accelerators Computer Tomography, C.T. Fluoroscopy Mammography

Radioactive Decay Atoms that have a neutron to proton ratio that is too high or too low undergo the process of radioactive decay Radioactive decay is the spontaneous emission of matter and/or energy from the nucleus of the atom – Particles: Alpha and/or Beta Particles – Energy: Gamma Rays and X-Rays As a result of radioactive decay the atom transforms into a different element, which can be either stable or also radioactive

Nature of Radioactive Decay Decay is random, predicting when a given atom will decay is impossible In sufficient numbers, the probability of decay becomes well defined Decay Constant (λ) = The probability that any one atom will decay

Activity Activity is the rate at which nuclear transformations occur in a radioactive material (rate of decay): A= λ N Number of radioactive atoms and, as a result, activity decreases exponentially with time: N = N 0 exp(- λt) A = A 0 exp(- λt)

Half-Life Time required for a radioactive substance to lose 50% of its activity by radioactive decay ½ the activity ½ the number of radioactive atoms ½ the radiation intensity λ T 1/2 = ln2 T 1/2 1/2 1/4 1/8

Units of Activity Modern SI Unit – Becquerel (Bq) – 1 Bq = 1 decay per second Traditional Unit – Curie (Ci) – The number of radioactive decays occurring in one gram of pure Ra Ci = 3.7 x Bq = 37 GBq

Modes of Radioactive Decay Alpha Decay – Lowers the n/p ratio – Usually occurs when atomic number is > 83 Beta Decay (- or +) – Negative Betas (Negatrons) - Lowers the n/p ratio – Positive Betas (Positrons) - Raises the n/p ratio Electron Capture – Raises the n/p ratio

Beta Decay A neutron transforms into a proton, an electron, and an anti-neutrino H-3 He-3

Gamma Emission After decay, some nuclei (called isomers) are left in an excited state (extra energy) Excitation energy may be emitted as a gamma ray

Gamma Decay (Cs-137) Cs-137 T 1/2 30 yr Ba-137m T 1/ min Ba-137 STABLE 661 keV Gamma Beta

Tl-204 Decay Tl-204 ( T 1/ yr ) Pb-204 Hg % 2.6%

Absorbed Dose ABSORBED DOSE - The amount of energy imparted per unit mass at a given location within irradiated material RAD (rad) - The traditional unit of dose, defined as the absorption of 100 ergs per gram (0.01 J / kg or 0.01 Gy) GRAY (Gy) – The SI unit of dose, defined as the absorption of 1 joule per kilogram (100 rads) 1 Gy = 100 rad

Exposure A measurement of the amount of ionization created by X-rays or gamma rays in a volume of air Roentgen = 2.58 × Coulombs / kg air Exposure to 1 R delivers a dose of 0.96 rad to tissue

Biological Effectiveness Equivalent Dose – A quantity that expresses the biological effect of exposure to the different types of radiation. Radiation weighting factor (w R ) - estimate of the effectiveness per unit dose of the given radiation relative a to low-LET standard (X-ray or gamma) Equivalent Dose = Absorbed Dose × w R

Equivalent Dose REM (rem) - The traditional unit of dose of any radiation which produces the same biological effect as a 1 rad of absorbed dose of x- or gamma-rays Sievert (Sv) – The SI unit of dose of any radiation that produces the same biological effect as a 1Gy of absorbed dose of x- or gamma-rays 1 Sv = 100 rem

Radiation weighting factors Type of RadiationwRwR X-Rays1 Gamma-Rays1 Beta Particles1 Alphas20 Neutrons2-20

Stochastic Effects Cancer – Radiation is a weak carcinogen Genetic – Magnitude thought to be very small

Stochastic Risks The PROBABILITY that an effect occurs is related to the magnitude of the radiation dose No relation between magnitude and severity of the effect – all or none response for an individual Same effect can be seen in unexposed individuals

Radiation Risk Estimates International Commission on Radiological Protection (ICRP) Publication 103 (2007) Nominal Risk for Stochastic Effects After Exposure to 1 Sv at Low Dose Rates: Cancer5.5% (0.055% per 1 rem) Heritable Effects0.2% (0.002% per 1 rem) For acute exposures a factor of 2 is used for risk estimates U.S. Cancer death rate: 21.20% (40.6% total) With exposure to 5 rem: 21.48%

Radiation Levels (mrem/year) 5,000,000 TYPICAL RADIATION THERAPY: 5,000 cGy = 5,000,000 mrem TO SINGLE ORGAN (delivered in series of exposures)

5,000,000 TYPICAL THERAPY X-RAY TO SINGLE ORGAN (series of exposures) 500,000 LETHAL DOSE TO 50% OF HUMANS 400,000 Radiation Levels (mrem/year)

5,000,000 TYPICAL THERAPY X-RAY TO SINGLE ORGAN (series of exposures) 500,000 LETHAL DOSE TO 50% OF HUMANS 400,000 50,000 FIRST DETECTABLE PHYSIO- LOGICAL EFFECTS 25,000 SMOKING 30 CIGARETTES PER DAY 16,000 SMOKING 30 CIGARETTES PER DAY: 16,000 mrem/year Radiation Levels (mrem/year)

50,000 FIRST DETECTABLE PHYSIO- LOGICAL EFFECTS 25,000 SMOKING 30 CIGARETTES PER DAY 16,000 5,000,000 TYPICAL THERAPY X-RAY TO SINGLE ORGAN (series of exposures) 500,000 LETHAL DOSE TO 50% OF HUMANS 400,000 5,000 PART OF BODY OCCUPATIONAL EXPOSURE ADULTSMINORS WHOLE BODY SKIN EXTREMITIES LENS OF EYE 5,000 mrem 50,000 mrem 15,000 mrem 500 mrem 5,000 mrem 1,500 mrem EMBRYO/FETUS (Declared Pregnancies) 500 mremN/A INDIVIDUAL MEMBERS OF THE PUBLIC mrem Radiation Levels (mrem/year) TOTAL AVERAGE ANNUAL RADIATION DOSE TO THE US RESIDENT: 620 mrem MAXIMUM ALLOWED ANNUAL DOSE TO WORKER

5,000 MAXIMUM ALLOWED ANNUAL DOSE TO WORKER 5,000,000 TYPICAL THERAPY X-RAY TO SINGLE ORGAN (series of exposures) 500,000 LETHAL DOSE TO 50% OF HUMANS 400, ,000 FIRST DETECTABLE PHYSIO- LOGICAL EFFECTS 25,000 SMOKING 30 CIGARETTES PER DAY 16, AVERAGE ANNUAL RADIATION EXPOSURE TO U.S. RESIDENT AVERAGE NATURAL BACKGRD AVIATION 200 RADON 28 mrem Radiation Levels (mrem/year) MEDICAL 300 X-RAY DIAGNOSTICS 223 NUCLEAR MEDICINE 77 CT NUCLEAR POWER OCCU- PATIONAL 110 Cosmic 11.00% Terrestrial 7.00% Radon % Potassium % Th & U Series 4.00% Other <0.01% Radon % NCRP Report No.160, 2009 Natural Background: 311 mrem (3.11 mSv) EPA Map of Radon Zones J.S.Duval et al, 2005, Terrestrial radioactivity and gamma-ray exposure in the US and Canada: U.S.G.S. Open-File Report Absorbed Gamma Dose Rate in Air CT 49% Nuclear Medicine 26% Interventional Fluoroscopy 14% Conventional Radiography and Fluoroscopy 11% Medical Exposures: 300 mrem (3.0 mSv) NCRP Report 160, 2009 Dental bitewing Chest Radiograph Mammogram Head CT Barium Enema Chest or abdomen CT Coronary CT angiography Abdomen and pelvis CT Thallium myocardial perfusion < 10 mrem mrem mrem mrem mrem mrem mrem mrem mrem Aviation 310 Nuclear Power 190 Industry 80 Medical 80 Education, Research 70 Government, Military 60 NCRP Report 160, 2009 Occupational: 110 mrem (1.1 mSv)

Radiation Levels (mrem/year) 5,000,000 TYPICAL THERAPY X-RAY TO SINGLE ORGAN (series of exposures) 500,000 LETHAL DOSE TO 50% OF HUMANS 400,000 5,000 MAXIMUM ALLOWED ANNUAL DOSE TO WORKER INTERNAL R/N TERRESTRIAL 21 COSMIC 33 50,000 FIRST DETECTABLE PHYSIO- LOGICAL EFFECTS 25,000 SMOKING 30 CIGARETTES PER DAY 16,000 AVERAGE NATURAL BACKGRD AVIATION 200 RADON MEDICAL 300 X-RAY DIAGNOSTICS 223 NUCLEAR MEDICINE 77 CT NUCLEAR POWER OCCU- PATIONAL 110 K-40 C-14 Rb-87 Po-210 Th-230 Rn-222 U-238 Ra-228 Ra-224 Th-232 Natural Radionuclides Contained In The Body: 29 mrem (0.29 mSv) 0.6% Road Construction 35% Tobacco 27% Building Materials 26% Commercial Air Travel 6% Mining and Agriculture 2% Fossil Fuels <0.03% Glass & Ceramics 3% Other NCRP Report 160, 2009 Consumer Products: 13 mrem (0.13 mSv) Cosmic Radiation: 33 mrem (0.33 mSv) J.S.Duval et al, 2005, Terrestrial radioactivity and gamma-ray exposure in the US and Canada: U.S.G.S. Open-File Report Terrestrial Radiation: 28 mrem (0.28 mSv)

CONSUMER PRODUCTS 13 TERRESTRIAL INTERNAL RN COSMIC 33 CT AVERAGE NATURAL BACKGRD AVIATION 200 RADON MEDICAL 300 X-RAY DIAGNOSTICS 223 NUCLEAR MEDICINE NUCLEAR POWER OCCU- PATIONAL 110 5,000,000 TYPICAL THERAPY X-RAY TO SINGLE ORGAN (series of exposures) 500,000 LETHAL DOSE TO 50% OF HUMANS 400,000 50,000 FIRST DETECTABLE PHYSIO- LOGICAL EFFECTS 25,000 SMOKING 30 CIGARETTES PER DAY 16,000 5,000 MAXIMUM ALLOWED ANNUAL DOSE TO WORKER 50 5 NATURAL GAS: 2 (especially residential use) 34 AVERAGE UIC OCCUPATIONAL EXPOSURE (751 monitored) 2 NATURAL GAS (especially residential) SLEEPING WITH ANOTHER HUMAN WEAPONS FALLOUT Radiation Levels (mrem/year) FALLOUT FROM WEAPONS TESTING: 0.75 Average UIC occupational exposure (751 monitored) 34 mrem

Exposure Rate Constant How to calculate your radiation dose if you know the isotope, the activity & the distance.

Exposure Rate Calculation From a 10μCi Cs-137 Point Source at 1 cm (3.287 is the Exposure Rate Constant for Cs-137) X X X

Exposure Rate at Various Distances From 10μci of Cs cm 3287 mR/h 1.0 cm mR/h 10 cm mR/h 100 cm mR/h

CONSUMER PRODUCTS 13 TERRESTRIAL INTERNAL RN COSMIC 33 CT AVERAGE NATURAL BACKGRD AVIATION 200 RADON MEDICAL 300 X-RAY DIAGNOSTICS 223 NUCLEAR MEDICINE NUCLEAR POWER OCCU- PATIONAL 110 5,000,000 TYPICAL THERAPY X-RAY TO SINGLE ORGAN (series of exposures) 500,000 LETHAL DOSE TO 50% OF HUMANS 400,000 50,000 FIRST DETECTABLE PHYSIO- LOGICAL EFFECTS 25,000 SMOKING 30 CIGARETTES PER DAY 16,000 5,000 MAXIMUM ALLOWED ANNUAL DOSE TO WORKER AVERAGE UIC OCCUPATIONAL EXPOSURE (751 monitored) 2 NATURAL GAS (especially residential) SLEEPING WITH ANOTHER HUMAN WEAPONS FALLOUT Radiation Levels (mrem/year) CONSUMER PRODUCTS: 0.03 (without building materials and tobacco) 10 hours of Physics Lab using 10 µCi Cs-137 source: 0.03

ALARA Policy As Low As Reasonably Achievable

Standard Warning Sign For Radioactive Material Use Areas Used to indicate an area is authorized for radioactive material use – BUT only by projects that have it listed in their authorization!

Lab Entrance Labeling LOW MEDIUM HIGH

Basic Principles of Radiation Protection Time Distance Shielding Contamination Control

Time Radiation dose is directly proportional to the time of exposure

Distance Inverse Square Law Radiation intensity is inversely proportional to the distance squared d1d1 d2d2 I1I1 I2I2 I1I1 I2I2 d22d22 d12d12 =

Shielding

Rules for Handling Sources DO NOT place your finger or any other part of your body directly over the face of the source Handle the sources only by their edges Minimize the time sources are handled Increase distance to minimize exposure Sign sources in and out with the T.A.

Lab Coats You will be working with Sealed Sources only. Lab coats and gloves are to be worn in the lab when handling UNSEALED radioactive material. When working with SEALED radioactive sources, lab coats and gloves are NOT required.