Radiation Safety for Radiographers

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Radiation Safety for Radiographers

• Bruce Busby
• Certified Health Physicist

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Agenda

• Why Training?
• Radiation and Sources of Radiation
• Radiation Protection
• Dosimetry
• Instruments

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WAC 246-243-050 Internal inspection program and
training.

• The licensee shall provide annual refresher
  safety training for each radiographer and
  radiographer's assistant at intervals not to
  exceed twelve months.
• Each licensee shall maintain the following
  records for three years after the record is
  madeFor annual refresher safety training, the
  record shall include    (i) A list of the
  topics discussed    (ii) The dates the training
  was conducted and    (iii) Names of the
  instructors and attendees.

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Regulatory Authority

• Nuclear Regulatory Commission (16)
• Idaho, Alaska, Hawaii, Montana, Wyoming
• Agreement States (34)
• Washington, Oregon, California, Utah
• Washington State WAC 246 220-254
• Department of Health, Office of Rad Protection
• Oregon ORS 453.605-453.807
• Department of Human Services, Public Health
  Division, Rad Protection Services

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Sources of Radiation
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The Atom

• Nucleus
• Protons
• Neutrons
• Stability of the nucleus determined by the number
  of neutrons and protons
• Extra-nuclear
• Electrons

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Radiation

• Radiation Energy in transit, either as
  particles or electromagnetic waves
• Ionizing Radiation Radiation with enough energy
  to cause an electron to leave an atom
• 4 main types
• Alpha particles
• Beta Particles
• Neutrons
• Gamma and X-ray

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Types of Radiation
Lead
Paper
Plastic
Concrete
Alpha
Beta
Gamma and X-rays
Neutron
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Electromagnetic Spectra
Long wave length
Short wave length
RF microwave infrared UV x-ray
g-ray cosmic

High energy
Low energy
visible
NOTE NOT TO SCALE!!!
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Radioactive Material

• Radioactive material consists of atoms with
  unstable nuclei
• The atoms spontaneously change (decay) to more
  stable forms and emit radiation
• A person who is contaminated has radioactive
  material on their skin or inside their body

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Example of Radioactive Material
Gamma Rays (317 and 296 keV)
Parent Nucleus Ir-192
Daughter Nucleus Pt-192
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Half-Life
Ir-192 73.8 days Co-60 5.27 years
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X-Ray Production (Bremsstrahlung)
Electron
X-Ray
Target Nucleus Tungsten
Anode ()
Cathode (-)
X-Rays
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Radiation Interactions with Matter

• Radiation with enough energy causes ions to be
  formed
• The amount of ions formed is based on the energy
  deposited
• Use this principle to our advantage for shielding
• Causes all effects of radiation good and bad

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Radiation Protection
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Gamma/X-ray Interactions

• Gamma and x-rays - photons
• Photon energy converted to excitation or
  ionization of electrons
• Photoelectric Effect - electron
• Compton Scatter - electron and gamma
• Pair Production - two gamma result
• Probability of interaction based on electron
  density and energy of photon

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Units

• Roentgen
• Rad
• Rem

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Roentgen (R)

• Measure of exposure
• Charge produced in a specific
• volume by gamma or x-rays
• 1 R 2.58 x 10-4 C/kg
• SI unit is C/kg
• Meters (Ion Chambers and GM detectors) often read
  out in mR/hr

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RAD

• Radiation Absorbed Dose
• Energy deposited per unit mass
• 1 rad 100 erg/gm
• Does not account for different radiation damages
• SI unit is the gray (Gy)
• 100 rad 1 Gy

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REM

• Measure of Biological Damage
• Effective Dose Equivalent
• Dose Effective
• TEDE and CEDE
• rad x QF rem
• SI unit is sievert (Sv)
• 100 rem 1 Sv

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Good News

• For protection
• x-ray, beta and gamma radiation
• 1 R ? 1 rad ? 1 rem
• For alpha and neutron, have to take into account
  the quality factor
• rad x QF rem
• QF for alpha is 20, neutron 2-20, gamma/beta is 1

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Measures of Radioactivity

• The quantity of radioactive material present at
  a given time
• Curie (Ci) 3.7x1010 disintegration per second
  (dps)
• or
• Becquerel (Bq) 1 dps

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Radiological Controls
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ALARA

• As Low As Reasonably Achievable
• REASONABLE is a key word here
• Minimizing the External and Internal radiation
  exposure
• Can you reduce your dose to Zero?????

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ALARA

• Philosophy of keeping doses low as Reasonable
• Used to reduce the risks
• No dose without benefit
• Additional controls
• Administrative procedures, regulations
• Engineered - design
• Still comes down to
• Time, Distance and Shielding

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External Methods

• Time, Distance and Shielding
• Reduce time exposed
• Increase distance from source
• Use shielding between you and the source
• Reduce your waste storage
• Properly store material
• Set up lab for work stations away from sources

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Time

• Reduce your time in radiation fields
• Preplan
• Prep
• Practice
• Know your area, work in low radiation fields as
  much as possible

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Distance

• Inverse square law for radiation
• Gamma and x-ray Point source calculation
• Dr1(R1)2Dr2(R2)2
• i.e., Double the distance, dose rate goes down
  by factor of 22 or 4
• Example

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Example Distance
20 rem/h
200 rem/h
5 rem/h
2 rem/h
1 rem/h
0.8 rem/h
0.5 rem/h
On contact
3 in
1 in
4 in
6 in
2 in
5 in
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Shielding

• Shielding - use of material to reduce transmitted
  radiation
• A wall or partition may not be a safe shield for
  persons on the other side.
• More dense, the better shield

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Shielding - Regulation

• The maximum exposure rate limits for storage
  containers and source changers with the sealed
  source in the shielded position are
• (a) 2 millisieverts (200 millirem) per hour at
  any exterior surface and
• (b) 0.1 millisieverts (10 millirem) per hour at
  one meter from any exterior surface.

WAC 246-243-040 (5) Equipment performance
requirements
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Shielding
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Signs and Labels

• Caution RAM
• Caution Radioactive Materials
• Radiation Area
• High Radiation

 All areas in which industrial radiography is
being performed shall be conspicuously posted as
required
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Signs of Radiography
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Caution RAM Posting/Labeling

• On RAM
• Room or storage where radioactive materials can
  be found
• Regulation states minimum amount that requires
  posting

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Public Dose Limits

• 2 mrem in one hour
• 100 mrem per year

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Radiation Area

• Dose rates where a person can receive a whole
  body dose of
• 5 to 100 mrem in one hour
• 30 centimeters from the source
• Do not loiter

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High Radiation Area

• Dose rates where a person can receive a whole
  body dose of
• 100 mrem in one hour
• Requires extra precautions
• Caution or Danger

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Very High Radiation Area

• Dose rates where a person can receive a whole
  body dose of
• 500 rads in one hour
• Grave Danger

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Dosimetry
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WAC 246-243-150 Says

• A licensee may not permit any individual to act
  as a radiographer or as a radiographer's
  assistant unless, at all times during
  radiographic operations, the individual wears
• a direct reading pocket dosimeter,
• an alarming rate meter, and
• a NAVLAP personnel dosimeter on the trunk of the
  body.
• Note - In permanent facilities where other
  appropriate alarming or warning devices are in
  routine use, the wearing of an alarming rate
  meter is not required.

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Dosimeters

• TLD
• Film
• Pocket dosimeters (0-200 mrem)
• Electronic Dosimeters
• Others.

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Pocket Ion Chamber
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How to Wear

• Whole Body
• Must be worn on the front of the body
• between waist and neck
• facing out

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Dose Records

• Access
• Private
• Upon request
• Annual report
• Legal
• Permanent
• Can be requested after you leave only by yourself

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Instruments
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Detector Types

• Gas Filled Detectors
• G-M Detector
• Energy Compensated
• Ion Chambers
• Scintillation Detectors
• NaI Detector
• Solid State Detectors

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Meter Components
Detector
(Probe)
Measuring Device
(Instrument)
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Gas Filled Detectors
Voltage Source

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Incident Ionizing Radiation




Electrical Current Measuring Device
-
-
-
-
Anode
Cathode -
Air or Other Gas
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Faceplate 0-10 mR/hr
Detector(s)
Selector switch X .1, 1, 10, 100, 1K
Battery
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Types of Gas Filled Detectors

• Geiger Mueller (GM)
• Energy compensated GM
• Single of multiple tube
• Side window, end window GM
• Proportional Counter
• Ion Chamber

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Instrument Checks

• Battery Check
• Make sure the battery is strong enough to operate
  the instrument.
• Calibration Check
• Make sure the instrument has been properly
  calibrated
• Physical Check
• Check the physical condition of the cord, probe,
  meter face, etc.
• Source Check
• Check the instrument with a known source of
  radiation to make sure the meter responds.

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Problems with Meters

• Must be turned on
• Must have good battery
• Must be used correctly
• Must be with you
• GM meters may peg and then read zero

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Surveys are Required

• of the radiographic exposure device and the guide
  tube after each exposure when approaching the
  device or the guide tube. The survey shall
  determine that the sealed source has returned to
  its shielded position before exchanging films,
  repositioning the exposure head, or dismantling
  equipment.
• any time the source is exchanged and whenever a
  radiographic exposure device is placed in a
  storage area to ensure that the sealed source is
  in its shielded position.
• the boundary of the restricted area during
  radiographic operations not employing shielded
  room radiography.

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Summary

• Radiation is energy
• Gamma and Photons cause ionizations
• Dose is reduced with time, distance and shielding
• Wear your dosimeters
• Instruments will keep you out of trouble

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Questions?