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INTRODUCTION TO RADIATION PROTECTION
Sources of ionizing radiationAtomic structure and radioactivityRadiation interaction with matterRadiation units and doseBiological effects
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Wilhelm C. Roentgen (1845-1923)In 1895, while working
with electrically-energized, sealed-glass “Crookes”tubes, he discovered that photographic plates kept near the tubes become darkened.
2
X-Ray Photography
Roentgen assumes previously unknown “X-RAYS” are escaping the tube.
Roentgen makes photo images with x-rays and shows they easily penetrate soft tissue.
3
Henri Becquerel(1852 – 1908)In 1896, discovered
other invisible rays coming from natural Uranium would also darken photo plates.
4
Ionizing Radiations(causing alteration of photo media) are generated by high energy natural or man-made processes occurring within the atom.
Roentgen and Becquerel had discovered IONIZING RADIATION
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Ionizing Radiation
Possess enough energy to remove electrons from atoms, creating ion pairs.
These ion pairs then go on to create highly reactive chemicals that can damage DNA and other important cellular molecules.
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We live in a sea of ionizing radiationTerrestrial Cosmic Human generated• Accelerators• Reactors• Medical procedures• Industrial (radiography, airports,
interrogation)
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Radiation Use
Availability and use of radioactive materials “exploded” after World War II.
Availability and use of radioactive materials “exploded” after World War II.3/14/2018 8
ResearchMedicine
Radiation in the Workplace
Nuclear Medicine
Radiation Therapy
IrradiationsLaboratory Use
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Radiation in the WorkplaceMeasure Thickness
Measure DensityIndustrial Radiography
Measurement and Quality Control
Static Control
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Baggage X-ray
Radiation in the Workplace
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Biomedical/Industrial wastes or byproducts
Lost sources
Radiation in the Environment
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Active Production or Processing Sites
Closed/Abandoned Production or
Processing Sites
Radiation in the Environment
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Nuclear Accidents
Radiation in the Environment
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Detecting Incoming Radioactive Materials
Seaports
Airports
Borders
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Where does it come from?
• Can be naturally occurring or man-made• Produce radiation at all times, but decays away
over time.• If unsealed and loose, it can be easily spread
around (contamination).
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ISOTOPE ½ Life APPLICATIONS
Uranium billions of years
Natural uranium is comprised of several different isotopes. When enriched in the isotope of U-235, it’s used to power nuclear reactor or nuclear weapons.
Carbon-14 5730 y Found in nature from cosmic interactions, used to “carbon date” items and as radiolabel for detection of tumors.
Cesium-137 30.2 y Blood irradiators, tumor treatment through external exposure. Also used for industrial radiography.
Hydrogen-3 12.3 y Labeling biological tracers.Iridium-192 74 d Implants or "seeds" for treatment of cancer. Also
used for industrial radiography.Molybdenum-99 66 h Parent for Tc-99m generator.
Technicium-99m 6 h Brain, heart, liver (gastroenterology), lungs, bones, thyroid, and kidney imaging, regional cerebral blood flow, etc..
Machine ProducedWhere does it come from?
• X-ray Machines, cyclotrons, accelerators, etc.• Most produce x-rays but particles also possible.• Only produce radiation when energized.• High energy machines can activate materials to
create radioactive materials.
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Atomic Structure and RadioactivityNuclear notationTerminologyDecay modesX-raysHalf life
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Nuclear notation
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Li-7Not actual sizeNot to scale
TerminologyRadioactivity – processRadiation - energyActivity – “quantity”Contamination – materialHalf life - time
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RadioactivityThe process by which an energetically unstable
nucleus spontaneously transforms to a more stable energy state and in the process emits radiation.
Radiation means matter or energy moving outward from a point of origin.
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Radiation from a point source decreases as a function of the square of the distance (1/R2)
Five basic types of radiation
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From the nucleus
From the electron shells
Electromagnetic Radiation
• No Mass• No Charge• Very Penetrating
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X-ray/Gamma Same except for originPhoton Can be stopped by layers of lead or concreteHazardous to tissues and organs Common photon emitters: Tc-99m, I-125Characteristic x-rays and gamma are essentially
monoenergetic Bremsstrahlung x-rays can be a spectrum
Characteristic X-rays
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Characteristic X-rays are emitted when outer-shell electrons fill a vacancy in the inner shell of an atom, releasing X-rays in a pattern that is "characteristic" to each element.
Bremstrahlung x-rays
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Alpha αMade up of 2 neutrons and 2 protons
(nucleus of the Helium atom) Travel short distances, stopped by paper and
dead layer of skin Mainly an internal hazard in the bodyCommon Alpha emitters: Uranium, Thorium,
Radon and radon daughtersCharacteristically mono energetic
Beta βEnergetic electronCan be stopped by 1 cm of plasticHazard to skin and eyes and when taken internallyCommon Beta emitters: Phosphorus, Tritium,
Carbon, SulfurSpectrum of energies are emitted (βmax)Most beta emitters are also gamma emitters
Neutron
Has no chargeRange in air is very far. Easily can go several
hundred feet. High penetrating power due to lack of charge
Can be a hazard to whole bodyCommon neutron emitter: Cf-252
After Time
Pure SampleFull Activity
Decayed SampleLower Activity
Radioactive Decay
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Half lifeThe radioactive half-life for a given radioisotope
is the time for half the radioactive nuclei in any sample to undergo radioactive decay.
Simple Half-Life Calculation
Activity decreases over time by a rate defined as the half-life
Where n is the number of half lives:
A = Ao/2n
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Thus after one half-life the nuclide will be half of its original activity, after two half-lives, one quarter, and etc.After 7 half lives less than 1% of the original activity remains
Activity
“Activity” describes how much radioactive material is present at any given time
Curie (Ci): 37 Billion transformations per secondUsually expressed as milli (10-3) or micro (10-6)
Bequerel (Bq): 1 transformation per secondUsually expressed in Mega (106) or Giga (109)
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Interaction of ionizing radiation with matter
Alpha and Beta – energy is lost by transfer of energy to electrons via electrostatic interaction
Photons – all or part of its energy is transferred to an orbital electron via collision
Neutron – energy and material dependent (Z#)• <0.5 MeV - elastic scattering with nucleus• >0.5 MeV - inelastic scattering with nucleus• Thermal – absorption in the nucleus
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Interaction of ionizing radiation with matter
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Penetration ability of some radiations
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Radiation Absorbed Dose (rad)Rad- A measure of energy deposition per unit mass
irradiated1 Rad = 100 ergs per gram of materialSI Unit is Gray 1Gy = 1 joule per kilogram (J kg –1)1 Gy = 100 rad
Dose equivalent (rem)rem: absorbed dose (D) modified by a radiation
weighting factor (wR ) or quality factor (Q) which accounts for the different biological effects of different types of radiation
rem = rad x QIn the SI system of units, it is replaced by the special
name sievert (Sv) where Sv = Gy x wR
1 Sv = 100 rem
Quality Factor (10CFR20)Type of radiation Quality
FactorX-, gamma, or beta radiation 1
Alpha particles, multiple-charged particles, fission fragments and heavy particles of unknown charge
20
Neutrons of unknown energy 10
High-energy protons 10
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Average dose equivalent = 620 mrem/yr
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Typical medical dosesChest X-ray = 2 mremMammogram = 13 mremAbdomen CT = 1000 mrem (1 rem)Heart stress test = 585 mrem
Terrestrial Radiation Levels
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Cosmic Radiation Levels
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Health physics nerd funWhat is the radiation dose equivalent for flying
across the United States?Seattle WA - Washington DC:• 37, 000 ft; 4.1hours• 0.0192 mSv (which is how many millirem?)
Reference: DOT/FAA/AM-03/16 Office of Aerospace Medicine Washington, DC 20591 “What Aircrews Should Know About Their Occupational Exposure to Ionizing Radiation”
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Could be partial or whole body.
Usuallymuch greater at entrance than exit.
May come from inhalation, ingestion, injection, absorption, or injury
Often concentrates in particular organs.
Radiation Hazards
External vs. Internal
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Biological Effects
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Acute effectsChronic effects Linear non-threshold modelBasis for regulatory limits
Biological EffectsMany groups and individuals exposed to
ionizing radiation at high levels resulted in adverse effects
Somatic effects– Prompt - skin burns and cataracts– Delayed - cancer
Genetic effectsTeratogenetic effects
Biological EffectsBiological effects are caused by chemical
changes in the cell brought about by the conversion of kinetic energy to chemical energy
Direct effects – caused by initial ionizationIndirect effects – free radicals and ions (mostly
from water) interact with cell material
Fate of Early Radiologists
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Radiologist Fingers
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1898 Photograph shows severe chest burn on a United States soldier in the Spanish-American War, caused by repeated exposure to X rays.
Early Radiation Injury
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Internal DoseCaused by radioactive material inside the bodyRoutes of entry:
– Inhalation– Ingestion– Absorbtion– Injection
Organs can concentrate based on chemical affinity (e.g. thyroid, bone, kidneys)
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Radiation Health EffectsHigh-level radiation effects are acute effects
which are manifested shortly after (hours, days, weeks) a large exposure (1 Sv or 100 rem+).
Low-level radiation effects are described as• latent effects, appearing many years after a
“non-lethal” acute dose, or• chronic effects after many years of small
doses (like radiation workers).
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High Level Radiation Effects
• Acute Radiation Syndrome• Bone Marrow Injury (over 1 Sv or 100 rem)– may
cause death if injury is severe.• GI Tract Injury (over 6 Sv or 600 rem) – causes
death in days or weeks. • Central Nervous System Injury (over 50 Sv or 5000
rem) – causes death in hours or days.• Radiation Burns (over 2 Sv or 200 rem) – local or whole
body • Cataracts (over 1.5 Sv or 150 rem)
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Dose (Rads*) Effects
25-50First sign of physical effects(drop in white blood cell count)
100 Threshold for vomiting (within a few hours of exposure)
320 - 360~ 50% die within 60 days (with minimal supportive care)
480 - 540~50 % die within 60 days(with supportive medical care)
1,000 ~ 100% die within 30 days
X-Ray Burns
5,000+ rad
500+ rad
CancerRadiation can damage cells through two
methods;– Production of free radicals and– Direct damage to the DNA
Risk factor for radiation dose:– 4% increase in risk of dying of cancer for
every 100 rem of dose.– Normal cancer risk is 20%.
Low Level Radiation Health Effects
Cancer – 0.1 Sv (10 rem) given to 100 people in U.S. population would be expected to cause about 1 extra cancer over a lifetime. About 42 of these people would be expected to get cancer from natural causes.
BIER VII Report
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0 10 20 30 40 50 60 70Committed Lifetime Dose (rem)
0.00
0.01
0.02
0.03
Risk
ofde
ath
f rom
can c
e r
Dose Response Relationship
Predictable EffectsRisk Is not
Predictablebelow 20 rem
Effect is Detrimentalrisk level is uncertain
Low Level Radiation Health Effects
Genetic mutations – has not been observed in humans, but has been observed in experimental animal populations
Teratogenesis - abnormalities induced in an exposed fetus – depends on dose and period of pregnancy.The risk of abnormality is considered negligible at
5 rad or less when compared to the other risks of pregnancy. (NCRP Report 54)
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Relative hazard summary1 rem received in a short period or over a long period is
safe—we don’t expect observable health effects.10 rem received in a short period or over a long period is
safe—we don’t expect immediate observable health effects, although your chances of getting cancer might be very slightly increased.
100 rem received in a short time can cause observable health effects from which your body will likely recover, and 100 rem received in a short time or over many years will increase your chances of getting cancer.
1,000 rem in a short or long period of time will cause immediately observable health effects and is likely to cause death
Health physics nerd funHow much energy is absorbed in the body for
an LD 100/30 day whole body acute dose of gamma radiation?
• LD 100/30 day dose is 1000 rads; person = 87kg (160lb)• 1000 rads x (100 ergs/gm/rad) x (87kg) = 8.7e+6 ergs• 8.3 BTU to raise 1 gallon (3.76 kg) of water 1°F = 8.8e+10erg • (1 BTU = 1.06e+10 erg)• (87kg/3.76kg) x 8.8e+10 erg = 2e+12erg to raise the body 1°F• 8.7e+6erg/2e+12 erg per 1°F= 4.3e-6 °F
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Health physics nerd fun
Compute your radiation dose exercise– https://www.epa.gov/radiation/calculate-
your-radiation-dose– http://www.ans.org/pi/resources/dosechart/
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Information sources• Health Physics Society – www.hps.org• National Council on Radiation Protection -
http://ncrponline.org/• Nuclear Regulatory Commission –
www.nrc.gov• American Nuclear Society – www.ans.org• Radiation Answers -
http://www.radiationanswers.org/
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