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Refresher Training for Users of Radiation Producing Devices
Elayna MellasRadiation Safety Officer
Environmental Health & Safety ManagerClarkson UniversityDowntown Snell 155
Tel: 315-268-6640emellas@clarkson.edu
This training course has been partially adaptedfrom slides provided by Steve Backurz, RadiationSafety Officer of The University of New Hampshire
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
The Basics: Definitions• Radioactivity: The spontaneous disintegration or decay of an
unstable atom, resulting in the release of energy (radiation).
• Radiation: Energy in the form of particles or waves
• Radioactive material: Any material that is composed of (or contains) radioactive atoms.
• Ion: Any atom or molecule with an imbalance in electrical charge. Ions are very unstable and will seek electrical neutrality by reacting with other atoms or molecules
• Activity: The number of disintegrations (decays) occurring per unit of time.
• Half Life: The time it takes for an amount of radioactive material to lose half (50%) of its activity because of decay.
The Particles• ALPHA PARTICLE (): A high energy particle emitted
from the nucleus during the decay of an atom.
– Travel a few centimeters in air
– Stopped by a sheet of paper or layer of skin
– Not an external hazard; ingestion or inhalation concern
• BETA PARTICLE (): A high energy particle emitted from the nucleus during the decay of an atom
– Travel 10 to 20 feet in air
– Stopped by a book
– Shielding high energy betas with lead can generate more radiation due to Bremsstrahlung x-rays
• GAMMA RADIATION (): Electromagnetic radiation emitted from the nucleus during decay
– No mass, no charge
– Travel many feet in air
The Electromagnetic SpectrumRadiation 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
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
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
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 Erythema Fatigue
Vomiting Hemorrhage Epilation Diarrhea
Mortality
Effects of Acute Whole Body Exposure on Man
Absorbed Dose (rads)
Effect
10,000 Death in a few hours
1,200 Death within days
600 Death within weeks
450 LD 50/30
100 Probable Recovery
50 No observable effect
25 Blood changes definite
5 1st blood changes observed
Biological Effects• 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 lifetime– Long Term Effects
• Increased Risk of Cancer• 0.07% per rem lifetime exposure• Normal Risk: 30% (cancer incidence)
Background Exposure Your exposure to radiation can never be zero because
background radiation is always present Natural Sources (Radon), Cosmic, Terrestrial, Medical
Diagnostic, Consumer Products, etc
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
Annual Dose from Background Radiation
• Occupational Limits (Researchers) 5 rem per year (total effective dose equivalent: TEDE) 50 rem per year (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) Declaration is voluntary and must be submitted to RSO in
writing (see form on website)
Standards for Rad Protection
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)
The goal of radiation protection is to keep radiation doses As Low As Reasonably Achievable and eliminate any unnecessary dose to yourself, coworkers, and the public
Clarkson is committed to keeping radiation exposures to all personnel ALARA
What is reasonable? Includes:
State and cost of technologyCost vs. benefitSocietal & socioeconomic
considerations
A sL owA sR easonablyA chievable
Reducing Exposure
Practicing ALARA
Time: 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: place a barrier between you and the radioactive source Source Reduction: order and use the smallest amount of radioactive
materials as necessary Protective clothing: protects against contamination only - keeps
radioactive material off skin and clothes
Protect Yourself & Your Colleagues!
OPTIMIZE USE OF ALL PROTECTIVE MECHANISMS TO MINIMIZE DOSE.
Shielding Recommendations:• Betas (ex: 32P):
– Use material with low atomic number, such as:
• Plastic, lucite, acrylic• Wood, paper, cardboard
• Gammas (ex: 125I or 51Cr):– Use material with high
atomic number, such as:• Lead, concrete, bricks,
stainless steel, cast iron
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
Survey Meters are portable instruments that can be used to detect most spots of contamination - except for 3H.
Wipe Testing must always be done for 3H and lower activities (100 µCi or less) of 35S and 14C.
Detecting Contamination
Detecting Common Isotopes
Sodium Iodide (NaI)
Probe
Survey Meter
Geiger- Mueller
(GM) Probe
3H Liquid Scintillation Counter
14C
GM Probe with
Survey Meter32P
33P
35S
51Cr GM or NaI Probe w/ Survey Meter
125I NaI Probe w/ Survey Meter
Liquid Scintillation Counter
• Check calibration date (not older than 12
months)• Batteries must be fresh / good• Background count rate• Detector/instrument must be responsive• Miscellaneous conditions…?
•Check Physical Condition•Cables, Connections, Damage•Select Proper Scale•Response Time (Fast or Slow?)•Audio (On or Off)
Survey Meter Operability
Each USER must verify that the survey instrument is in good working order before each use.
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
Each detector will have its own background level.
1st check the background level - use it as a baseline. Observed:
Background:
Zero:
Any reading higher than the background level means the item is radioactive.
Remember that background is radiation coming from the environment, and it cannot be prevented or eliminated.
Survey Meter “Background” Levels
• 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
• 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 Mellas268-6640emellas@clarkson.edu
Acknowledgements
This training course has been adapted from slides provided by Steve Backurz, Radiation Safety Officer of The University of New Hampshire and Eric Andersen, Radiation Safety Officer at the Dana-Farber Cancer Institute.
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