University of Illinois at Chicago Radiation Safety Section Environmental Health and Safety Office Physics 108, 244 Radiation Safety Physics Lecture

University of Illinois at ChicagoUniversity of Illinois at ChicagoRadiation Safety SectionRadiation Safety Section

Environmental Health and Safety OfficeEnvironmental Health and Safety Office

Physics 108, 244 Physics 108, 244

Radiation Safety Physics Lecture

Ionizing RadiationIonizing Radiation

Radiation that can cause ionization of the material through which it passes either directly or indirectly

Electromagnetic radiation

Particulate radiation

Electromagnetic RadiationElectromagnetic Radiation Electro-magnetic waves (uncharged packets of energy)

propagated through space or a material medium

Wavelength, m

Frequency, s-1

Energy of one photon, eV

E ~ ν ~ 1λ_

Particulate RadiationParticulate RadiationMatter that that is propagated through space

or through a material medium

Alpha ParticlesBeta Particles (Electrons, Positrons)Neutrons (uncharged)ProtonsHeavy IonsFission Fragments

Sources of Ionizing RadiationSources of Ionizing Radiation

Radioactive Materials H-3, C-14, P-32, S-35, I-125, etc.

Radiation Producing Machines X-Ray equipment Accelerators Computer Tomography, C.T. Fluoroscopy Mammography

Radioactive DecayRadioactive Decay

Atoms that have a neutron to proton ratio that is too high or too low undergo the process of radioactive decay

Radioactive decay is the spontaneous emission of matter and/or energy from the nucleus of the atom– Particles: Alpha and/or Beta Particles– Energy: Gamma Rays and X-Rays

As a result of radioactive decay the atom transforms into a different element, which can be either stable or also radioactive

Nature of Radioactive DecayNature of Radioactive DecayDecay is random, predicting when a

given atom will decay is impossible

In sufficient numbers, the probability of decay becomes well defined

Decay Constant (λ) = The probability that any one atom will decay

ActivityActivity Activity is the rate at which nuclear transformations

occur in a radioactive material (rate of decay):

A= λN Number of radioactive atoms and, as a result,

activity decreases exponentially with time:

N = N0exp(-λt)

A = A0exp(-λt)

Half-LifeTime required for a radioactive substance to lose 50% of its activity by radioactive decay

• ½ the activity • ½ the number of radioactive atoms• ½ the radiation intensity

λT1/2 =

ln2

T1/2 T1/2 T1/2

1/2

1/4

1/8

Units of ActivityUnits of ActivityModern SI Unit

– Becquerel (Bq)– 1 Bq = 1 decay per second

Traditional Unit– Curie (Ci)– The number of radioactive decays

occurring in one gram of pure Ra-226

1 Ci = 3.7 x 1010 Bq = 37 GBq

Modes of Radioactive DecayModes of Radioactive Decay

Alpha Decay– Lowers the n/p ratio– Usually occurs when atomic number is > 83

Beta Decay (- or +)– Negative Betas (Negatrons) - Lowers the n/p ratio– Positive Betas (Positrons) - Raises the n/p ratio

Electron Capture

– Raises the n/p ratio

Beta DecayBeta Decay

A neutron transforms into a proton, an electron, and an anti-neutrino

H-3He-3

Gamma EmissionGamma Emission

After decay, some nuclei (called isomers) are left in an excited state (extra energy)

Excitation energy may be emitted as a gamma ray

Gamma Decay (Cs-137)Gamma Decay (Cs-137)

Cs-137

T1/2 30 yr

Ba-137m

T1/2 2.55 min

Ba-137

STABLE

661 keV GammaBeta

Tl-204 DecayTl-204 Decay

Tl-204 (T1/2 3.779 yr)

Pb-204Hg-204

97.4%2.6%

Absorbed DoseAbsorbed DoseABSORBED DOSE - The amount of

energy imparted per unit mass at a given location within irradiated material

RAD (rad) - The traditional unit of dose, defined as the absorption of 100 ergs per gram (0.01 J / kg or 0.01 Gy)

GRAY (Gy) – The SI unit of dose, defined as the absorption of 1 joule per kilogram (100 rads)

1 Gy = 100 rad

ExposureExposure

A measurement of the amount of ionization created by X-rays or gamma rays in a volume of air

Roentgen = 2.58 × 10-4 Coulombs / kg air

Exposure to 1 R delivers a dose of 0.96 rad to tissue

Biological EffectivenessBiological Effectiveness

Equivalent Dose – A quantity that expresses the biological effect of exposure to the different types of radiation.

Radiation weighting factor (wR) - estimate of the effectiveness per unit dose of the given radiation relative a to low-LET standard (X-ray or gamma)

Equivalent Dose = Absorbed Dose × wR

Equivalent DoseEquivalent Dose

REM (rem) - The traditional unit of dose of any radiation which produces the same biological effect as a 1 rad of absorbed dose of x- or gamma-rays

Sievert (Sv) – The SI unit of dose of any radiation that produces the same biological effect as a 1Gy of absorbed dose of x- or gamma-rays

1 Sv = 100 rem

Radiation weighting factorsRadiation weighting factors

Type of Radiation wR

X-Rays 1

Gamma-Rays 1

Beta Particles 1

Alphas 20

Neutrons 2-20

Stochastic EffectsStochastic Effects

Cancer – Radiation is a weak carcinogen

Genetic– Magnitude thought to be very small

Stochastic RisksStochastic RisksThe PROBABILITY that an effect occurs

is related to the magnitude of the radiation dose

No relation between magnitude and severity of the effect – all or none response for an individual

Same effect can be seen in unexposed individuals

Radiation Risk EstimatesRadiation Risk Estimates

International Commission on Radiological Protection (ICRP) Publication 103 (2007)

Nominal Risk for Stochastic Effects After Exposure to 1 Sv at Low Dose Rates:

Cancer 5.5% (0.055% per 1 rem)

Heritable Effects 0.2% (0.002% per 1 rem)

For acute exposures a factor of 2 is used for risk estimates

U.S. Cancer death rate: 21.20% (40.6% total)

With exposure to 5 rem: 21.48%

Radiation Levels (mrem/year)

5,000,000

TYPICAL RADIATION THERAPY:

5,000 cGy =

5,000,000 mrem

TO SINGLE ORGAN

(delivered in series of exposures)

5,000,000

TYPICAL THERAPY X-RAY TO SINGLE ORGAN (series of exposures)

500,000

LETHAL DOSE TO 50% OF HUMANS

400,000


5,000,000


500,000


400,000

50,000

FIRST DETECTABLE

PHYSIO-LOGICAL EFFECTS

25,000

SMOKING 30 CIGARETTES

PER DAY

16,000

SMOKING 30 CIGARETTES PER DAY:

16,000

mrem/year


50,000

FIRST DETECTABLE


25,000


PER DAY

16,000

5,000,000


500,000


400,000

5,000 PART OF BODY

OCCUPATIONAL EXPOSURE

ADULTS MINORS

WHOLE BODY

SKIN

EXTREMITIES

LENS OF EYE

5,000 mrem

50,000 mrem

50,000 mrem

15,000 mrem

500 mrem

5,000 mrem

5,000 mrem

1,500 mrem

EMBRYO/FETUS

(Declared Pregnancies)

500 mrem N/A

INDIVIDUAL MEMBERS OF THE PUBLIC - 100 mrem


TOTAL AVERAGE ANNUAL RADIATION DOSE TO THE US RESIDENT:

620 mrem

MAXIMUM ALLOWED

ANNUAL DOSE TO WORKER

5,000

MAXIMUM ALLOWED


5,000,000


500,000


400,000

50050,000

FIRST DETECTABLE


25,000


PER DAY

16,000

620

AVERAGE ANNUAL

RADIATION EXPOSURE

TO U.S. RESIDENT

AVERAGE NATURAL BACKGRD

311310AVIATION

200RADON

28 mrem


MEDICAL

300

X-RAY DIAGNOSTICS

223

NUCLEAR MEDICINE

77

CT 147

190NUCLEAR POWER

OCCU- PATIONAL

110

Cosmic 11.00%

Terrestrial 7.00%

Radon-220 5.00%

Potassium-40 5.00%

Th & U Series 4.00%

Other <0.01%

Radon-222 68%

NCRP Report No.160, 2009

Natural Background: 311 mrem (3.11 mSv)

EPA Map of Radon Zones

J.S.Duval et al, 2005, Terrestrial radioactivity and gamma-ray exposure in the

US and Canada: U.S.G.S. Open-File Report 2005-1413

Absorbed Gamma Dose Rate in Air

CT 49%

Nuclear Medicine 26%

InterventionalFluoroscopy 14%

ConventionalRadiography andFluoroscopy 11%

Medical Exposures: 300 mrem (3.0 mSv)

NCRP Report 160, 2009

Dental bitewing

Chest Radiograph

Mammogram

Head CT

Barium Enema

Chest or abdomen CT

Coronary CT angiography Abdomen and pelvis CT

Thallium myocardial perfusion

< 10 mrem

10-20 mrem

30-60 mrem

100-200 mrem

300-600 mrem

500-700 mrem

500-1200 mrem

800-1100 mrem

3500-4000 mrem

Aviation 310Nuclear

Power 190

Industry 80

Medical 80

Education, Research 70

Government, Military 60


Occupational: 110 mrem (1.1 mSv)


5,000,000


500,000


400,000

5,000

MAXIMUM ALLOWED


500 50

29

INTERNAL R/N

TERRESTRIAL

21

COSMIC

33

50,000

FIRST DETECTABLE


25,000


PER DAY

16,000


311310AVIATION

200RADON

MEDICAL

300

X-RAY DIAGNOSTICS

223

NUCLEAR MEDICINE

77

CT 147

190NUCLEAR POWER

OCCU- PATIONAL

110

K-40

C-14

Rb-87Po-210

Th-230

Rn-222 U-238

Ra-228

Ra-224

Th-232

Natural Radionuclides Contained In The Body:

29 mrem (0.29 mSv)

0.6% Road Construction

35%Tobacco

27%Building Materials

26%CommercialAir Travel 6% Mining and

Agriculture

2% Fossil Fuels

<0.03% Glass & Ceramics

3% Other


Consumer Products: 13 mrem (0.13 mSv)

Cosmic Radiation: 33 mrem (0.33 mSv)

J.S.Duval et al, 2005, Terrestrial radioactivity and gamma-ray exposure in the US and Canada: U.S.G.S. Open-File Report 2005-1413

J.S.Duval et al, 2005, Terrestrial radioactivity and gamma-ray exposure in the US and Canada: U.S.G.S. Open-File Report 2005-1413

Terrestrial Radiation: 28 mrem (0.28 mSv)Terrestrial Radiation: 28 mrem (0.28 mSv)Terrestrial Radiation: 28 mrem (0.28 mSv)Terrestrial Radiation: 28 mrem (0.28 mSv)

CONSUMER PRODUCTS

13

TERRESTRIAL

21

29

INTERNAL RN

COSMIC

33

CT 147

500


311310AVIATION

200RADON

MEDICAL

300

X-RAY DIAGNOSTICS

223

NUCLEAR MEDICINE

77

190NUCLEAR POWER

OCCU- PATIONAL

110

5,000,000


500,000


400,000

50,000

FIRST DETECTABLE


25,000


PER DAY

16,000

5,000

MAXIMUM ALLOWED


50 5NATURAL GAS: 2

(especially residential use)

34

AVERAGE UIC OCCUPATIONAL

EXPOSURE (751 monitored)

2

NATURAL GAS (especially residential)

SLEEPING WITH ANOTHER HUMAN

0.1

0.75

WEAPONS FALLOUT


FALLOUT FROM WEAPONS TESTING: 0.75

Average UIC occupational exposure (751 monitored)

34 mrem

Exposure Rate ConstantExposure Rate Constant How to calculate your radiation dose if you know How to calculate your radiation dose if you know

the isotope, the activity & the distance.the isotope, the activity & the distance.

δΓ2R cm

mCi h

Exposure Rate CalculationExposure Rate CalculationFrom a 10From a 10μμCi Cs-137 Point Source at 1 cmCi Cs-137 Point Source at 1 cm

(3.287 is the Exposure Rate Constant for Cs-137)(3.287 is the Exposure Rate Constant for Cs-137)

=

2

-22 1

dcm

R cm 1000mRX × mCi× ×m

ACi h R

=

2

3.287Rh

0.011000mRX × × ×1

1 R

= 32.87mRXh

X•

X•

•X

Exposure Rate at Various Exposure Rate at Various Distances From 10Distances From 10μci of Cs-137μci of Cs-137

0.1 cm 3287 mR/h1.0 cm 32.87 mR/h10 cm 0.3287 mR/h100 cm 0.003287 mR/h

CONSUMER PRODUCTS

13

TERRESTRIAL

21

29

INTERNAL RN

COSMIC

33

CT 147

500


311310AVIATION

200RADON

MEDICAL

300

X-RAY DIAGNOSTICS

223

NUCLEAR MEDICINE

77

190NUCLEAR POWER

OCCU- PATIONAL

110

5,000,000


500,000


400,000

50,000

FIRST DETECTABLE


25,000


PER DAY

16,000

5,000

MAXIMUM ALLOWED


50 5

34

AVERAGE UIC OCCUPATIONAL

EXPOSURE (751 monitored)

2

NATURAL GAS (especially residential)

SLEEPING WITH ANOTHER HUMAN

0.1

0.75

WEAPONS FALLOUT


CONSUMER PRODUCTS: 0.03

(without building materials and tobacco)

10 hours of Physics Lab using

10 µCi Cs-137 source: 0.03

ALARA PolicyALARA PolicyAsLowAsReasonablyAchievable

Standard Warning SignStandard Warning SignFor Radioactive Material Use AreasFor Radioactive Material Use Areas

Used to indicate an area is authorized for radioactive material use – BUT only by projects that have it listed in their authorization!

Lab Entrance LabelingLab Entrance Labeling

LOW

MEDIUM

HIGH

Basic Principles of Basic Principles of Radiation ProtectionRadiation Protection

Time

Distance

Shielding

Contamination Control

TimeTime

Radiation dose is directly proportional to the time of exposure

DistanceDistance Inverse Square

Law

Radiation intensity is inversely proportional to the distance squared d1 d2

I1 I2

I1

I2d2

2

d12

=

ShieldingShielding

Rules for Handling SourcesRules for Handling SourcesDO NOT place your

finger or any other part of your body directly over the face of the source

Handle the sources only by their edges

Minimize the time sources are handled

Increase distance to minimize exposureSign sources in and out with the T.A.

Lab CoatsLab Coats

You will be working with Sealed Sources only.

Lab coats and gloves are to be worn in the lab when handling UNSEALED radioactive material.

When working with SEALED radioactive sources, lab coats and gloves are NOT required.

Documents

University of Illinois at Chicago Radiation Safety Section Environmental Health and Safety Office Physics 108, 244 Radiation Safety Physics Lecture