Radiation Safety for Radiographers Bruce Busby Certified Health Physicist

Agenda u Why Training? u Radiation and Sources of Radiation u Radiation Protection u Dosimetry u Instruments

WAC Internal inspection program and training. u The licensee shall provide annual refresher safety training for each radiographer and radiographer's assistant at intervals not to exceed twelve months. u Each licensee shall maintain the following records for three years after the record is made: For 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.

Regulatory Authority u Nuclear Regulatory Commission (16) –Idaho, Alaska, Hawaii, Montana, Wyoming u Agreement States (34) –Washington, Oregon, California, Utah u Washington State WAC –Department of Health, Office of Rad Protection u Oregon ORS –Department of Human Services, Public Health Division, Rad Protection Services

Sources of Radiation

The Atom u Nucleus –Protons –Neutrons –Stability of the nucleus determined by the number of neutrons and protons u Extra-nuclear –Electrons

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

Types of Radiation Alpha Beta Gamma and X-rays Neutron PaperPlastic Lead Concrete

Electromagnetic Spectra RF microwave infrared UV x-ray  -ray cosmic Low energy High energy Long wave length Short wave length NOTE: NOT TO SCALE!!! visible

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

Example of Radioactive Material Gamma Rays (317 and 296 keV) Parent Nucleus Ir-192 Daughter Nucleus Pt-192

Half-Life Ir-192 – 73.8 days Co-60 – 5.27 years

X-Ray Production (Bremsstrahlung) Electron X-Ray Target Nucleus Tungsten Cathode (-) Anode (+) X-Rays

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

Radiation Protection

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

Units u Roentgen u Rad u Rem

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

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

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

Good News u For protection –x-ray, beta and gamma radiation 1 R  1 rad  1 rem u For alpha and neutron, have to take into account the quality factor rad x QF = rem u QF for alpha is 20, neutron 2-20, gamma/beta is 1

Measures of Radioactivity The quantity of radioactive material present at a given time: Curie (Ci) : 3.7x10 10 disintegration per second (dps) or Becquerel (Bq): 1 dps

Radiological Controls

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

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

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

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

Distance u Inverse square law for radiation u Gamma and x-ray Point source calculation Dr 1 (R 1 ) 2 =Dr 2 (R 2 ) 2 i.e., Double the distance, dose rate goes down by factor of 2 2 or 4 u Example

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

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

Shielding - Regulation u 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 (5) Equipment performance requirements

Shielding

Signs and Labels u Caution RAM –Caution Radioactive Materials u Radiation Area u High Radiation All areas in which industrial radiography is being performed shall be conspicuously posted as required

Signs of Radiography

Caution RAM Posting/Labeling u On RAM u Room or storage where radioactive materials can be found u Regulation states minimum amount that requires posting

Public Dose Limits u 2 mrem in one hour u 100 mrem per year

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

High Radiation Area u Dose rates where a person can receive a whole body dose of  100 mrem in one hour u Requires extra precautions u Caution or Danger

Very High Radiation Area u Dose rates where a person can receive a whole body dose of  500 rads in one hour  Grave Danger

Dosimetry

WAC Says… u 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.

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

Pocket Ion Chamber

How to Wear u Whole Body –Must be worn on the front of the body –between waist and neck –facing out

Dose Records u Access –Private –Upon request –Annual report u Legal u Permanent u Can be requested after you leave only by yourself

Instruments

Detector Types u Gas Filled Detectors –G-M Detector –Energy Compensated –Ion Chambers u Scintillation Detectors –NaI Detector u Solid State Detectors

Meter Components Measuring Device Detector (Probe) (Instrument)

Gas Filled Detectors Air or Other Gas Incident Ionizing Radiation Electrical Current Measuring Device + - Cathode - Anode Voltage Source

Selector switch X.1, 1, 10, 100, 1K Faceplate 0-10 mR/hr Battery Detector(s)

Types of Gas Filled Detectors u Geiger Mueller (GM) u Energy compensated GM –Single of multiple tube u Side window, end window GM u Proportional Counter u Ion Chamber

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.

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

Surveys are Required … u 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. u 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. u the boundary of the restricted area during radiographic operations not employing shielded room radiography.

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

Questions?