Radiation Safety Series 3

Radiation Safety Series Lesson 3 Units of Measure and Dose

Units of Measurement R

Symbol for Roentgen, a unit of measure for X-ray and Gamma ray rad Symbol for Radiation Absorbed Dose Q Quality factor or relative effectiveness rem Roentgen Equivalent Man rem = rad x Q

R - Roentgen • Is a unit of measure of gamma or x-ray radiation in air. • The amount of radiation that will produce one electrostatic unit of charge in one cubic meter of air at standard temperature (32o F) and standard atmospheric pressure

rad - Radiation Absorb Dose • Roentgen is based on ionization in air and therefore it can not be used to measure radiation dose in animal tissue • Radiant energies interact differently in animal tissues • rad applies to various types of radiation including alpha, beta, gamma, x-ray and neutron

Q – Quality Factor • For each type of radiation there is a different biological effect for the same (rad) • The Quality factor formerly known a the relative biological effect has been established by the National Committee on Radiation Protection for each radiation type

SI Units of Measure • Standard International unit equivalents • Gray (Gy) is the unit of absorbed dose 1 grey = 1 joule/kilogram = 100 rad 1 rad = 100 ergs/gram = 0.01 joules/kilogram = 0.01 or 10-2 gray 1R = 2.85 x 10-2 Coulombs/kilograms air

Basic Radiation Units • milli (m) = prefix for 1/1,000 (0.001) • 1 roentgen (R) = 1,000 milliroentgen (mR) • 1 rem = 1,000 millirem (mrem)

Quality Factor / Biological Effect • Alpha exposures have a much grater biological effect • Much more damaging • X-Ray and Gamma Ray are not as damaging as alpha

Quality Factor Values Radiation Type X-Ray Gamma Ray Beta Particles Thermal Neutrons Fast Neutrons Alpha Particles

Q 1 1 1 5 10 20

Rem Calculations Radiation Type X-Ray Gamma Ray Beta Particles Thermal Neutrons Fast Neutrons Alpha Particles

rad x Q = rem 1 1 = 1 1 1 = 1 1 1 = 1 1 5 = 5 1 10 = 10 1 20 = 20

ALARA Radiation Exposure Shall Be

As Low As is Reasonably Achievable Considering the benefits derived from its use and the consequences incurred from any exposure

ALARA • Time Distance and Shielding • If the job takes two do not send ten • Use Common Sense

Determination of Occupational Dose • DDE is the dose received from x-rays and gamma rays • CEDE is a factor only if the radiographer had some form of internal dose from radioactive material (airborne) TEDE = DDE + CEDE Total Effective Dose Equivalent

Deep Dose Equivalent (External)

Committed Effective Dose Equivalent (Internal)

TEDE Radiation Dose Limits Area of exposure

Annual Dose Limits Occupational* PSE*

PSE*

5

5

25

Lens of the Eye

15

15

75

Extremities – Hands,

50

50

250

Whole body – Head And trunk (including male gonads) arms above the elbow and The knees

elbows, feet, or legs below the knee

* Dose in rems

Minor & Embryo/Fetus Exposure Minors: Age < 18 years Dose < 10% of Dose Limits Examples: Whole body < 0.5 rem/year Declared Pregnant Woman: Dose < 0.5 during entire gestation period Embryo/Fetus: Dose < 0.5 rem

Planned Special Exposure Conditions 1. 2. 3. 4. 5. 6. 7. 8. 9.

Must be exceptional situation (source retrieval) Requires prior written authority (approved procedure) Individual informed and instructed Dose from previous PSE’s and doses in excess of annual dose limits determined Must not exceed annual dose limits and lifetime PSE’s Records maintained of conduct of PSE’s Written report to NRC or regulator PSE dose recorded Individual informed of dose within 30 days

http://www.nrc.gov/reading-rm/doc-collections/fact-sheets/bio-effects-radiation.pdf

http://www.nrc.gov/reading-rm/doc-collections/fact-sheets/bio-effects-radiation.pdf

http://www.nrc.gov/reading-rm/doc-collections/fact-sheets/bio-effects-radiation.pdf

Works Sited Radiation Safety Training Series Part 1: Radiation, Rudarmel Enterprises, inc. Lake Oswego, Oregon http://www.nrc.gov/reading-rm/doc-collections/factsheets/bio-effects-radiation.pdf