RADIATION PROTECTION PRINCIPLESINTERPRETING MEASUREMENTS & EVALUATION

3/15/2018 1

Dose limitsRadiation detectionDose measurement and monitoringALARA principlesReasons for doing surveysSurvey documentationThe importance of “zero”Case studies

Radiation dose limitsWhat are the basis for limits?Who establishes limits?TerminologyRadiation dose limitsMortality risk for the limits

3/15/2018 2

Basis for federal regulatory limitsICRP, IAEA and NCRP recommendations (since 1928)U.S. National Academy of Sciences Committee on Biological

Effects of Atomic Radiation (BEAR I)/Genetics Panel in 1956: Linear Non-threshold model should be used to establish limits

The Federal Radiation Council guidelines issued in 1960EPA issued its guidance on occupational exposure limits in 1994

and promoted the ALARA principleOSHA, NRC, DOE and DOD have statutory authority for workers

3/15/2018 3

Protection & RegulationNuclear Regulatory Commission (NRC)

Environmental Protection Agency (EPA)

Department of Homeland Security (DHS)

Radioactive Materials

Radiation Machines

Environmental Protection

Nuclear Security

Food & Drug Administration (FDA)

Agreement States

Department of Transportation (DOT)Transport

StatesManufacture Use

3/15/2018 4

TerminologyEffective dose equivalentCommitted effective dose equivalentsDerived air concentration (DAC)Annual limit on intake (ALI)

3/15/2018 5

Effective dose equivalentThe sum of the products of the dose equivalent to the organ or

tissue and the weighting factors applicable to each of the body organs or tissues that are irradiated.

3/15/2018 6

Committed dose equivalent The dose equivalent to organs or tissues of reference that will be

received from an intake of radioactive material by an individual during the 50-year period following the intake.

3/15/2018 7

Committed effective dose equivalent The sum of the products of the weighting factors applicable to

each of the body organs or tissues that are irradiated and the committed dose equivalent to these organs or tissues.

3/15/2018 8

Derived air concentration (DAC)The concentration of a given radionuclide in air which, if

breathed by the reference man for a working year of 2,000 hours under conditions of light work (inhalation rate 1.2 cubic meters of air per hour), results in an intake of one ALI.

Annual limit on intake (ALI): The derived limit for the amount of radioactive material taken into the body of an adult worker by inhalation or ingestion in a year.

3/15/2018 9

Internal dose must be calculated• Can be based on air sampling results• Whole body counting detects residual radioactivity for gamma

emitters (e.g. Co-60, Cs-137)• Bioassay is used for beta and alpha emitters (e.g. H-3, P-32, Sr-

90, Pu-238)• Assignment of dose is calculated using models published by the

International Council on Radiation Protection• ALIs tables in the regulations are derived from the models

3/15/2018 10

Radiation Dose Limits (10CFR20)Annual Limit

Total effective dose equivalent (total body) 5 rem (0.05 Sv)

Skin and individual tissues (except the lens) 50 rem (0.5 Sv)

Lens of the eye 15 rem (0.15 Sv)

Embryo/fetus* (for the duration of the pregnancy) 0.500 rem (5e-3 Sv)

Minors 0.500 rem (5e-3 Sv)

General public 0.100 rem (1e-3 Sv)

3/15/2018 11

*Declared pregnancy

What is the mortality risk for the limits?ICRP No. 26 "...the mortality risk factor for radiation-induced cancers is

about 10-4 per rem, as an average for both sexes and all ages... ." The risks of average occupational exposures (about 0.5 rem/year) are

roughly comparable to risks experienced in safe industries, 10-4 annually. At the permissible limit of 5 rem/year, the risk is comparable with that

experienced by some workers in occupations having higher-than-average risk.

For members of the public, the ICRP considered that an annual risk in the range of 10-6 to 10-5 would likely be acceptable (ICR77). The ICRP recommended an annual individual dose limit of 100 mrem (1 mSv) from all radiation sources.

3/15/2018 12

What is the ALARA principle?ALARA is an acronym used in radiation safety for “As Low As

Reasonably Achievable.” The ALARA radiation safety principle is based on the minimization of radiation doses and limiting the release of radioactive materials into the environment by employing all “reasonable methods.”

ALARA is a sound radiation protection principle and it is a regulatory requirement for all radiation protection programs.

3 Principal Means to Reduce External Exposure

Time - reducing the amount of time around a radiation source directly reduces radiation exposure.

Distance - exposure reduces exponentially with increased distance from the source.

Shielding - stops alpha and beta particles and greatly reduces x-ray and gamma radiation.

14

Follows 1/r2

relationship

For example; doubling your distance cuts exposure to 1/4, and tripling distance cuts exposure to 1/9.

Increase Distance

3/15/2018 15

16

Shielding components on TMI-2 Reactor Building El. 305’

Methods to reduce radiation exposure• Use engineering controls if possible (e.g.

shielding, ventilation)• Maintain knowledge and awareness of

hazards• Maintain area control: signage, records, and

security• Design appropriate facilities and equipment

for use and control of radioactive materials

3/15/2018 17

Methods to reduce internal intake• Containment and/or exhaust (e.g., fume

hoods in labs)• Contamination surveys• Good hygiene - washing hands,

contaminated skin, and contaminated articles

• Good personal habits – no hand to face/mouth contact, no eating/drinking, no application of cosmetics

• Use of protective clothing and personal protective equipment

3/15/2018 18

Additional methods to reduce radiation exposure• Use good work planning and control• Maintain training and qualifications• Walk down the job using the procedure• Create mockups for high dose work• Ask questions and listen to the answers (i.e. consider all points

of view)

3/15/2018 19

Radiological Controls• Provide hazard communication to workers and public• Establish posting notification to restrict access and control

dose• Contain and maintain control of radioactive material• Control release of radioactive effluents to the environment• Provide real time monitoring of radiological conditions

3/15/2018 20

Posting requirements• Radiation area: > 0.005 rem (0.05 mSv) in 1 hour• High radiation area: >0.1 rem (1 mSv) in 1 hour• Airborne contamination area: > 1 DAC • Contamination area: control of loose surface contamination• Radioactive material storage area: storage and control of

radioactive material

3/15/2018 21

Radiation detectionPrinciples of radiation detectionTypes and uses of radiation detectors

3/15/2018 22

Dose measurement and monitoring

3/15/2018 23

Main methods of radiation detection instrumentsIonization of a gas and

collection of charged particles

3/15/2018 24

25

Geiger Mueller detector

G/M probe is good for detecting gamma at levels needed to establish radiation area posting

“Pancake” probe is good for detecting beta/gamma contamination

3/15/2018 26

Photoluminescent detectors

3/15/2018 27

Luminescence of a solid or a liquid and amplification of the signal through a photomultiplier tube

ZnS scintillator detector

3/15/2018 28

High efficiency for detecting alpha

Very thin mylar window keeps light out but allows alpha to pass through

Luminescent personal dosimeters

3/15/2018 29

Personal dosimeter

3/15/2018 30

• Provides real time monitoring of individual radiation dose

• Digital dosimeters can set alarms for dose rate and total dose

31

Instrument Types Detection Principle ApplicationsIon chamber (IC) Ionization of air

(or other gases)Direct measurement of exposure or exposure rates, with minimal energy dependence.

Geiger-Mueller (GM)Proportional counter (PC)

Ionization of gas withmultiplication ofelectrons in detector

Detection of individual events, i.e. alpha or beta particles & secondary electrons, for measuring activity (in samples or on surfaces) & detecting low intensities of ambient x or gamma radiation; precautions required due to energy dependence.

Solid state diodes Ionization ofsemiconductor

Detection & energy measurement of photons or particles; primarilyfor laboratory use.

Solid state diodes Ionization & excitationfollowed by light emission

Detection of individual events

Solids NaI (Tl) - photons; energy spectrometryZnS (Ag) - alpha particles; detection only

Liquid Detection of low-energy beta emitters mixed with the scintillation fluid.

Luminescent dosimeter

Excitation of crystal;light release by heating or light

Personal and environmental exposure monitoring.

Why we measure anything

3/15/2018 32

Processes,Conditions,Behaviors

Reasons for doing surveys/monitoring

• Compliance with requirements (posting, controls, levels)

• Verifying what should be there• Looking for something that shouldn’t be there• Looking for changes

3/15/2018 33

How to interpret measurements

Do the survey/monitoring results:• Reflect anticipated conditions?• Reveal unexpected/expected changes in

conditions?• Seem unusually high/low?

3/15/2018 34

Places you might see contamination Broken or leaking containersWhen opening, pouring, or dispensing Spills or airborne releases Inadequate clean up

Regulatory requirements for surveysWAC 246-221-110 “Surveys” – says you have to do them

WAC 246-221-230 “Records important to radiation safety” – tells you how to document them

3/15/2018 36

Survey documentationEstablishes legal proof of complianceEnables verification of radiological conditionsEnables trending to provide early detection of adverse conditionsProvides effective hazard communication to workers

3/15/2018 37

Why a measured “zero” is so important

A documented “zero” provides incontrovertible, legal proof of a verified physical measurement

Some companies try to save money on dosimetry if they can demonstrate individuals are below 100 mrem/yr by surveys and area monitoring.

If individuals are working inside a “restricted area” they should have personal dosimetry

3/15/2018 38

Case studies1. Contaminated shoes in nuclear repair facility2. Internal dose mystery at Three Mile Island3. Elevated radiation levels near Brookhaven National Lab4. Fukushima scare in Half Moon Bay, CA5. Radioactive waste from a screw factory

3/15/2018 39

More Health Physics fun• Cascade Chapter of the Health Physics Society

May 4, 2018 (follow us on Facebook!)• Joint ANS/HPS topical symposium Tri-Cities

Sept 30 – Oct 3, 2018http://www.lowdoserad.org

3/15/2018 40