Training for Users of Radiation Producing Devices This training course has been partially adapted...
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Transcript of Training for Users of Radiation Producing Devices This training course has been partially adapted...
Training for Users of Radiation Producing Devices
This training course has been partially adaptedfrom slides provided by Steve Backurz, RadiationSafety Officer of The University of New Hampshire
Elayna MellasRadiation Safety Officer
Environmental Health & Safety ManagerClarkson UniversityDowntown Snell 155
Tel: [email protected]
Subject Slides
Nuclear Physics 3-17
Biological Effects 18-43
Radiation Exposure and Dose 31-47
Uses of Radiation 48-51
Radiation Hazards 52-59
Radiation Detection 60-66
Lab Procedures at Clarkson 67-74
Table of Contents
Introduction• Radiation is a valuable tool used in research
at Clarkson– Electron microscopes– X-ray fluorescence spectrometry– X-ray diffraction analysis of samples for
chemistry and engineering research• Radioactive materials and X-ray machines
are very safe if used properly and simple precautions are followed
Radioactivity ("Activity")Definition: A collection of unstable atoms that undergo spontaneous transformation that result in new elements.
An atom with an unstable nucleus will “decay” until it becomes a stable atom, emitting radiation as it decays
Sometimes a substance undergoes several radioactive decays before it reaches a stable state
The “amount” of radioactivity (called activity) is given by the number of nuclear decays that occur per unit time (decays per minute).
Ion
Any atom or molecule with an imbalance in electrical charge is called an ion
In an electrically neutral atom or molecule, the number of electrons equals the number of protons
Ions are very chemically unstable, and will seek electrical neutrality by reacting with other atoms or molecules
Radiation
Definition: Energy in the form of particles or waves
Types of Radiation Ionizing: removes electrons from atoms
Particulate (alphas and betas)Waves (gamma and X-rays)
Non-ionizing (electromagnetic): can't remove electrons from atoms
infrared, visible, microwaves, radar, radio waves, lasers
The Electromagnetic Spectrum
Radiation Wavelength in Angstrom Units
Photon Energy in Million Electron Volts (MeV)
108 106 104 102 1 10-2 10-4 10-6
X-RaysRadio Infrared Visible
Ultra-VioletLight
Gamma Rays
Cosmic Rays
10-10 10-8 10-6 10-4 10-2 1 10222 4 10
Gamma Radiation
Wave type of radiation - non-particulate Photons that originate from the nucleus of unstable atoms
No mass and no chargeTravel many feet in airLead or steel used as shielding
X-Rays Wave type of radiation - non-particulate Photons originating from the electron cloud Same properties as gamma rays relative to mass,
charge, distance traveled, and shielding Characteristic X-rays are generated when electrons fall
from higher to lower energy electron shells Discrete energy depending on the shell energy level
of the atom Bremsstrahlung X-rays are created when electrons or
beta particles slow down in the vicinity of a nucleus Produced in a broad spectrum of energies Reason you shield betas with low density material
Bremsstrahlung Radiation
Energy is lost by the incoming charged particle through a radiative mechanism
Beta Particle
-Bremsstrahlung Photon
+ +
Nucleus
X-Ray Machine Components
High Voltage
Power Supply
Tungsten Filament
Target
Glass Envelope
Tube Housing
CathodeAnode
Current
X-Ray Machine Basics
kVp - how penetrating the X-rays are Mammography - 20 - 30 kVp Dental - 70 - 90 kVp Chest - 110 - 120 kVp
mA - how much radiation is producedTime - how long the machine is on Combination of the above determines exposure
Types of Radiation
Mass (amu) Charge Travel Distance in Air
Alpha
Beta Plus
Beta Minus
Gamma
X-Rays
Neutron
4.0000
0.0005
0.0005
0.0000
0.0000
1.0000
+2
+1
-1
0
0
0
few centimeters
few meters
few meters
many meters
many meters
many meters
Interaction of Radiation with Matter
Radiation deposits small amounts of energy, or "heat" in matter
alters atomschanges molecules
damage cells & DNA similar effects may occur from chemicals Much of the resulting damage is from the
production of ion pairs
Ionization
Ionization by a Beta particle:
-
-
-
-
The neutral absorber atom acquires a positive charge
Beta Particle
-
CollidingCoulombic Fields
ejected electron
Gamma Interactions
Gamma interactions differ from charged particle Interactions
Interactions called "cataclysmic" - infrequent but when they occur lot of energy transferred
Three possibilities: May pass through - no interaction May interact, lose energy & change
direction (Compton effect) May transfer all its energy & disappear
(photoelectric effect)
Compton Effect An incident photon interacts with an orbital electron
to produce a recoil electron and a scattered photon of energy less than the incident photon
Before interaction After interaction
-
--
Incoming photonCollides with electron
--
--
Electron is ejected from atom
-
Scattered Photon
Biological Effects of Radiation
Acute Exposure
Large Doses Received in a Short Time Period
Accidents Nuclear War Cancer Therapy
Short Term Effects (Acute Radiation Syndrome 150 to 350 rad Whole Body)
Anorexia Nausea ErythemaFatigue Vomiting Hemorrhage
Epilation Diarrhea Mortality
Effects of Acute Whole Body Exposure on Man
AbsorbedDose (Rads) Effect
10,0001,200
600450100
5025
5
Death in a few hoursDeath within daysDeath within weeksLD 50/30Probable RecoveryNo observable effectBlood changes definite1st Blood change obs
Chronic Exposure
Doses Received over Long Periods Background Radiation Exposure Occupational Radiation Exposure
50 rem acute vs 50 rem chronic acute: no time for cell repair chronic: time for cell repair
Average US will receive 20 - 30 rem lifetimeLong Term Effects
Increased Risk of Cancer 0.07% per rem lifetime exposure Normal Risk: 30% (cancer incidence)
• Ionization within body tissues: similar to water• Ionization causes many derivatives to be formed:
PeroxidesFree RadicalsOxides
• These compounds are unstable and are damaging to the chemical balance of the cell. Various effects on cell enzymes and and structures occur.
• Radiation is not the only insult responsiblePollutantsVitamin imbalance (poor diet)Sickness and Disease
Cellular Effects
Cellular Effects (con't)
Cells often recover from damageRepeated Insults may cause damage to be
permanent Cell Death Cell Dysfunction - tumors, cancer, cataracts,
blood disorders Mitosis (Cell Division) Delayed or Stopped Chromosomal breaks Organ Dysfunction at High Acute Doses
Variations in Sensitivity
Wide variation in the radiosensitivity of various species
Plants/microrganisms vs. mammalsWide variation among cell types
Cells which divide are more sensitive Non-differentiated cells are more
sensitive Highly differentiated cells (like nerve
cells) are less sensitive
Effects on the Fetus
The fetus consists of rapidly dividing cellsDividing cells are more sensitive to radiation effects than nondividing cells
Effects of low level radiation are difficult to measure
A lower dose limit is used for the fetus
Genetic EffectsIt is possible to damage the hereditary material in a
cell nucleus by external influences like Ionizing radiation, chemicals, etc.
Effects that occur as a result of exposure to a hazard while in-utero are called teratogenic effects
Teratogenic effects are thought to be more severe during weeks 8-17 of pregnancy - the period of formation of the body’s organs
A higher incidence of mental retardation was found among children irradiated in-utero during the bombings of Hiroshima and Nagasaki
Maternal Factors & Pregnancy
Statistically, a radiation exposure of 1 rem poses much lower risks for a woman than smoking tobacco or drinking alcohol during pregnancy
SmokingGeneral Babies weigh 5-9 oz. Less than average
< 1 pack/day Infant Death 1 in 5> 1 pack/day Infant Death 1 in 3
Alcohol2 drinks/day Babies weigh 2-6 oz. Less than average 1 in 10
2-4 drinks/day Fetal alcohol syndrome 1 in 3> 4 drinks/day Fetal alcohol syndrome 1 in 3 to 1 in 2
Radiation1 rem Childhood leukemia deaths before 12 years 1 in 33331 rem Other childhood cancer deaths 1 in 3571
Dose Response Curves
Dose Dose
Effects occur after a threshold
Effects occur at any level = stochastic
Acute effects Chronic effects?
Bio
log
ical
eff
ects
The stochastic model is more conservative, and is used to establish dose limits for occupational exposure
Rate of Absorption
Most important factor in determining when effects will occur
Recovery is less likely with higher dose rates than lower dose rates for an equivalent amount of dose = more permanent damage
More recovery occurs between intermittent exposures = less permanent damage
Area Exposed
The larger the portion - the more damage (if all other factors are the same)
Blood forming organs are more sensitive
A whole body dose causes more damage than a localized dose (such as in medical therapy).
Dose limits take this into consideration
Radiation Exposure & Dose
Background Exposure Your exposure to radiation can never be zero because
background radiation is always present Natural Sources - Radon Cosmic Terrestrial Technologically Enhanced Sources (Man-Made) Healing Arts: Diagnostic X-rays, Radiopharmaceuticals Nuclear Weapons Tests fallout Industrial Activities Research Consumer Products Miscellaneous: Air Travel, Transportation of Radioactive
Material
Annual Dose from Background Radiation
Total US average dose equivalent = 360 mrem/year
Total exposure Man-made sources
Radon
Internal 11%
Cosmic 8% Terrestrial 6%
Man-Made 18%
55.0%
Medical X-Rays
NuclearMedicine 4%
ConsumerProducts 3%
Other 1%
11
Cosmic Radiation
2 x 10 particles (mostly protons) per second are incident on the atmosphere
Energy greater than one BILLION ELECTRON VOLTS
Interact with atoms in the atmosphere and produce secondary particles
muons, electrons, photons, and neutrons responsible for cosmic dose
18
Terrestrial
Major sources Potassium - a few grams per 100 grams of
ground material Thorium and Uranium - a few grams per
1,000,000 grams of ground materialDose due mainly to photons originating near
the surface of the ground
Radon
Naturally occurring radioactive gas Second leading cause of lung cancer Estimated 14,000 deaths per year Easy to test for
short and long term tests available EPA guideline is 4 pCi/L Fixable Radon in water from drilled wells can also
be an entry method
Exposure, X
A measure of the ionization produced by X or Gamma Radiation in airUnit of exposure is the Roentgen
X = Q (charge)
M (mass of air)
Absorbed Dose, D
Absorbed Dose (or Radiation Dose) is equivalent to the energy absorbed from any type of radiation per unit mass of the absorber
Unit of Absorbed Dose is the rad1 rad = 100 ergs/g = 0.01 joules/Kg
In SI notation, 1 gray = 100 rads
Dose Equivalent, HOne unit of dose equivalent is that amount of any type of radiation which, when absorbed in a biological system, results in the same biological effect as one unit of low LET radiation
The product of the absorbed dose, D, and the Quality Factor, Q
H = D Q
Units of Dose EquivalentHuman dose measured in rem or millirem1000 mrem = 1 rem1 rem poses equal risk for any ionizing radiation
internal or external alpha, beta, gamma, x-ray, or neutron
In SI units 1 sievert (Sv) = 100 remExternal radiation exposure measured by
dosimetry Internal radiation exposure measured using
bioassay sample analysis
Quality Factors for Different Radiations
Quality FactorX and Gamma RaysElectrons and MuonsNeutrons < 10 kev >10kev to 100 Kev > 100 kev to 2 Mev >2 MevProtons > 30 MevAlpha Particles
115
1020101020
External Dose2 Standard reference points
Shallow Dose: Live skin tissue at an average depth of .007 cm.
Deep Dose: Internal organs close to the body surface, 1 cm.
Shallow Dose Equivalent, SDE Alpha radiation not a hazard consider beta and gamma radiation.
Deep Dose Equivalent, DDE Alpha and Beta radiation not a hazard. For gamma, SDE = DDE (typically)
Internal DoseAll radiation types present a hazard2 Dose quantities:
Committed Dose Equivalent, CDE (specific to a particular organ)
Committed Effective Dose Equivalent, CEDE (sum of all organs x weighting factor for importance or each specific organ)
Total Effective DoseEquivalent, (TEDE)
Used to combine internal and external doses
Puts all dose on the same risk base comparison, whether from external or internal sources.
TEDE = CEDE + DDEAll units are in rems or Sieverts (Sv)All regulatory dose limits are based on controlling the TEDE
• Radiation Protection Program Required• Occupational Limits
5 rem per year TEDE 50 rem per year CDE (any single organ) 15 rem per year lens of the eye 50 rem per year skin dose
• Members of Public 100 mrem per year No more than 2 mrem in any one hour in
unrestricted areas from external sources• Declared Pregnant Females (Occupational)
500 mrem/term (evenly distributed)
Standards for Rad Protection
Declared Pregnant Woman
Voluntarily informs her employer in writing of pregnancy
Estimated date of conceptionDose limit is 10% of occupational limit (500 mrem)
Avoid substantial variation in doseForm for declaring pregnancy is on web site
Clarkson AnticipatedWorker Radiation Exposure
Anticipated Exposures: Less than the minimum detectable dose for film badges (10 mrem/month) - essentially zero
Average annual background exposure for U.S. population = 360 mrem/year
State and Federal Exposure Limits = 5000 mrem/year
Uses of Radiation
Consumer Products
Building materials Tobacco (Po-210) Smoke detectors (Am-241) Welding rods (Th-222) Television (low levels of X-rays) watches & other luminescent products
(tritium or radium) Gas lantern mantles Fiesta ware (Ur-235) Jewelry
Research at ClarksonUsing Radiation Sources
Radioactive Materials (both open and sealed sources)
Gas Chromatographs (sealed sources) Liquid Scintillation Counters (sealed
sources for internal standards) X-ray Diffraction equipment Electron microscopes X-ray fluorescence spectrometer
MedicalDiagnostic
X-rays Nuclear Medicine (Tc-99m, Tl-201, I-123) Positron Emission Tomography (PET)
Therapeutic X-rays (Linear Accelerators) Radioisotopes
Brachytherapy (Cs-137, Ir-192, Ra-226)Teletherapy (Co-60)Radiopharmaceuticals (I-131, Sr-89, Sm-153)
Radiological Hazards
Radiation Protection BasicsTime: minimize the time that you are in contact
with radioactive material to reduce exposure
Distance: keep your distance. If you double the distance the exposure rate drops by factor of 4
Shielding: Lead, water, or concrete for gamma & X-ray Thick plastic (lucite) for betas
External Radiation Inverse Square Law
Radiation levels decrease as the inverse square of the distance (i.e. move back by a factor of two, radiation levels drop to one fourth)
Applies to point sources (distance greater than 5 times the maximum source dimension)
where I = Intensity (exposure rate) at position 1 and 2 andR = distance from source for position 1 and 2
Position 1Position 2
(mrem/hr) (mrem/hr)
Source
222
211 RIRI
R1
R2 I2
I1
Gamma Ray Constant
Gamma Ray Constant to determine exposure rate
(mSv/hr)/MBq at 1 meterHint: multiply (mSv/hr)/MBq by 3.7 to get (mrem/hr)/uCi
Exposure Rate Calculation, X (mrem/hr) at one meter:
X =Where, A = Activity (Ci)
Gamma Ray Constant(mSv/hr)/Mbq 3.7 is the conversion factor
Sample Calculation
• 5 Curie Cs-137 Source• Calculate Exposure Rate at 1 meter
= 1.032 E-4 mSv/hr/MBq @ 1 meter
X = 1.032 E-4 * 3.7 * 5 Ci * 1000 mCi/Ci * 1000 uCi/mCi
X = 1909 mrem/hour
X = 1.91 rem/hour
Gamma Ray Shielding
Effectiveness increases with thickness, d (cm)
Variation with material, (1/cm)attenuation coefficients µHigh Z material more effective
Water - Iron - Leadgood - better - best
Shielding Beta EmittersLow energy betas (H-3, C-14, S-35) need no
shielding for typical quantities at ClarksonHigher energy beta emitters (P-32) should be
shieldedBeta shielding must be low Z material (Lucite,
Plexiglas, etc.)High Z materials, like lead, can actually generate
radiation in the form of Bremsstrahlung X-raysBremsstrahlung from 1 Ci of P-32 solution in
glass bottle is ~1 mR/hr at 1 meter
External vs Internal Dose
TEDE: Total Effective Dose Equivalent
TEDE = DDE + CEDE Total Dose = External Dose + Internal Dose
1 rem internal (CEDE) same as 1 rem external (DDE)
Internal dose is protracted over several years but calculated over 50 years and assigned in the year of intake
Radiation Detection
• Solid State Detectors Germanium Lithium
High Purity Silicone Lithium Silicone Diode Cadmium Telluride
Radiation Detector TypesGas Filled Detectors
Geiger Mueller (GM) Gas Flow Proportional
Counters Ionization
Scintillation Detectors Sodium Iodide (NaI) Zinc Sulfide (ZnS) Anthracene Plastic Scintillators
Gas Filled Detectors Ionization detectors
High CostSurvey metersReference class calibration chambers
Proportional countersHigh costGross laboratory measurementsContamination monitors
Geiger Mueller (GM) detectorsLow costSurvey metersContamination monitors
Scintillation DetectorsOne of the Oldest Detection Methods, Still Widely Used Today
Transducer Converts Radiation Energy to Visible Light
Visible Light Signals Amplified With Photomultiplier Tube
Output PM Tube Signal ProcessedHigh Efficiency For Photon Detection Compared To Gas-Filled Detectors
Use of Survey Instruments
Check Physical ConditionCables, Connections, DamageCheck for Current Calibration (License Requirement)
Battery CheckZero CheckResponse check prior to useSelect Proper ScaleResponse Time (Fast or Slow?)Audio (On or Off)
CPM & DPM
A radiation detector will not detect every disintegration from a source (i.e., they are not 100% efficient)
Counts per minute (cpm) is the number of disintegrations that a detector “sees”
The efficiency of a detector is determined by the following:
Efficiency = net cpm / dpm= gross cpm – background cpm /
dpm
• U. S. Nuclear Regulatory Commission Regulates the nuclear industry pursuant to the
Atomic Energy Act Regulatory guides published to describe
methods for complying with regulations• Agreement States
Some states have entered into an agreement with the NRC to regulate by-product material (and small quantities of source and special nuclear material)
Currently, 30 states are agreement states including New York
Regulatory Agencies
Radiation at ClarksonActivities are licensed by the State of New YorkRadiation Safety Committee has responsibility
to review, approve, and oversee activitiesRadiation Safety Officer (RSO) runs programClarkson is required to:
Train individuals that use sources of radiation
Train non-radiation workers that work in the vicinity of radiation sources
Monitor and control radiation exposures Maintain signs, labels, postings
Posting & Labeling Notices Posting
New York Notice to employees form Caution Radiation Producing Devices or X-
Rays
Employee Rightsand Responsibilities
Right to report any radiation protection problem to state without repercussions
Responsibility to comply with the Radiation Protection Program and the RSO's instructions pertaining to radiation protection
Right to request inspectionin writinggrounds for noticesigned
Responsibility to cooperate with NY State inspectors during inspections and RSO during internal lab audits
ALARA
The goal of radiation protection is to keep radiation doses As Low As Reasonably Achievable
Clarkson is committed to keeping radiation exposures to all personnel ALARA
What is reasonable?Includes: -State and cost of technology
-Cost vs. benefit-Societal & socioeconomic
considerations
• Inspections NY shall be afforded opportunity to inspect at
all reasonable times Records shall be made available Inspector may consult with workers privately Worker may bring matters to inspector
privately Workers can request inspection
• Must be in writing • Name is not revealed
Inspections
• Internal audits by Clarkson RSO are performed in all labs on campus
• Looking for same things as state inspector Security of radiation producing devices Proper procedures in use Postings, dosimetry, survey meters,
calibrations, records of surveys, etc.
Internal Audits
Your Rolein Radiation Protection
Report anything that looks out of the ordinary or if you are uncertain about what to do, where to go, requirements, exposures:
Call the people on the emergency list
Ask the Radiation Safety Officer (RSO)Elayna [email protected]
Acknowledgements
This training course has been adapted from slides provided by Steve Backurz, Radiation Safety Officer of The University of New Hampshire