Radiation Safety for Radiographers

Bruce Busby

Certified Health Physicist

Agenda

Why Training?

Radiation and Sources of Radiation

Radiation Protection

Dosimetry

Instruments

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 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 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

Sources of RadiationSources of Radiation

The Atom

Nucleus– Protons– Neutrons– Stability of the

nucleus determined by the number of neutrons and protons

Extra-nuclear– Electrons

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

Types of Radiation42

00

Alpha

Beta

Gamma and X-rays

Neutron

Paper Plastic Lead Concrete

01

n10

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 NucleusIr-192

Daughter NucleusPt-192

0~1

Half-Life

0200

400600800

10001200

New 1Half-Life

2Half-Lives

3Half-Lives

4Half-Lives

Activity

Ir-192 – 73.8 days

Co-60 – 5.27 years

X-Ray Production (Bremsstrahlung)

ElectronX-Ray

Target NucleusTungsten

Cathode(-)

Anode (+)

X-Rays

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

Radiation ProtectionRadiation Protection

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

Units

Roentgen Rad Rem

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

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

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

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

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

Radiological Controls Radiological Controls

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?????

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

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

Time

Reduce your time in radiation fields Preplan Prep Practice

Know your area, work in low radiation fields as much as possible

Distance

Inverse square law for radiation Gamma and x-ray Point source calculation

Dr1(R1)2=Dr2(R2)2

i.e., Double the distance, dose rate goes down by factor of 22 or 4

Example

Example – Distance

On contact

200 rem/h

1 in 2 in 3 in 4 in 5 in 6 in

20 rem/h5 rem/h

2 rem/h1 rem/h

0.8 rem/h0.5 rem/h

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

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

Shielding

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

Signs of Radiography

Caution RAM Posting/Labeling

On RAM Room or storage where radioactive

materials can be found

Regulation states minimum amount that requires posting

Public Dose Limits

2 mrem in one hour

100 mrem per year

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

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

Very High Radiation Area

Dose rates where a person can receive a whole body dose of

500 rads in one hour

Grave Danger

Dosimetry Dosimetry

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.

Dosimeters

TLD Film

Pocket dosimeters (0-200 mrem) Electronic Dosimeters

Others….

Pocket Ion Chamber

How to Wear

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

Dose Records

Access– Private– Upon request– Annual report

Legal Permanent Can be requested after you leave only by

yourself

Instruments Instruments

Detector Types

Gas Filled Detectors– G-M Detector– Energy Compensated– Ion Chambers

Scintillation Detectors– NaI Detector

Solid State Detectors

Meter Components

Measuring Device

Detector(Probe)

(Instrument)

Gas Filled Detectors

Air or Other Gas

Incident Ionizing Radiation

ElectricalCurrent

Measuring Device

+

-

Cathode -

Anode +

+ + +

- - -

+ -

Voltage Source

Selector switchX .1, 1, 10, 100, 1K

Faceplate0-10 mR/hr

Battery

Detector(s)

Types of Gas Filled Detectors

Geiger Mueller (GM) Energy compensated GM

– Single of multiple tube Side window, end window GM Proportional Counter Ion Chamber

Instrument Checks Battery Check

Make sure the battery is strong enough to operate the instrument.

Calibration CheckMake sure the instrument has been properly calibrated

Physical CheckCheck 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

Must be turned on Must have good battery Must be used correctly Must be with you

GM meters may peg and then read zero

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.

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

Questions?