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

2. Ionizing Radiation
Radiation that can cause ionization of the material through which it passes either directly or indirectly
Electromagnetic radiation
Particulate radiation

3. Electromagnetic Radiation
Electro-magnetic waves (uncharged packets of energy) propagated through space or a material medium
Wavelength, m
Frequency, s-1
E ~ ν ~ 1 λ _
Energy of one photon, eV

4. Particulate Radiation
Matter that that is propagated through space or through a material medium
Alpha Particles
Beta Particles (Electrons, Positrons)
Neutrons (uncharged)
Protons
Heavy Ions
Fission Fragments

5. Sources 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

6. Radioactive 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

7. Nature of Radioactive Decay
Decay 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

8. A= λN N = N0exp(-λt) A = A0exp(-λt) Activity
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)

9. Half-Life
Time 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 λ
T1/2 =
ln2
1/2
1/4
1/8
T1/2
T1/2
T1/2

10. Units of Activity 1 Ci = 3.7 x 1010 Bq = 37 GBq Modern 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

11. Modes 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

12. Beta Decay
A neutron transforms into a proton, an electron, and an anti-neutrino
H-3
He-3

13. Gamma Emission
After decay, some nuclei (called isomers) are left in an excited state (extra energy)
Excitation energy may be emitted as a gamma ray

14. Gamma Decay (Cs-137) Cs-137 Ba-137m Ba-137 T1/2 30 yr T1/2 2.55 min
Beta
661 keV Gamma
Cs-137
T1/2 30 yr
Ba-137m
T1/ min
Ba-137
STABLE

15. Tl-204 Decay
Tl-204 (T1/ yr)
97.4%
2.6%
Hg-204
Pb-204

18. Absorbed Dose
ABSORBED 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

19. Exposure
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

20. Biological 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

21. Equivalent Dose 1 Sv = 100 rem
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

22. Radiation weighting factors
Type of Radiation wR
X-Rays 1
Gamma-Rays
Beta Particles
Alphas 20
Neutrons
2-20

23. Stochastic Effects Cancer Genetic Radiation is a weak carcinogen
Magnitude thought to be very small

24. Stochastic Risks
The 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

25. Radiation 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: % (40.6% total)
With exposure to 5 rem: %

26. 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)

27. Radiation Levels (mrem/year)
5,000,000
TYPICAL THERAPY X-RAY TO SINGLE ORGAN (series of exposures)
500,000
LETHAL DOSE TO 50% OF HUMANS
400,000

28. Radiation Levels (mrem/year)
5,000,000
TYPICAL THERAPY X-RAY TO SINGLE ORGAN (series of exposures)
500,000
LETHAL DOSE TO 50% OF HUMANS
400,000
50,000
SMOKING 30 CIGARETTES PER DAY:
16,000
mrem/year
FIRST DETECTABLE PHYSIO-LOGICAL EFFECTS
25,000
SMOKING 30 CIGARETTES PER DAY
16,000

29. Radiation Levels (mrem/year) OCCUPATIONAL EXPOSURE
PART OF BODY
OCCUPATIONAL EXPOSURE
ADULTS
MINORS
WHOLE BODY
SKIN
EXTREMITIES
LENS OF EYE
5,000 mrem
50,000 mrem
15,000 mrem
500 mrem
1,500 mrem
EMBRYO/FETUS
(Declared Pregnancies)
N/A
INDIVIDUAL MEMBERS OF THE PUBLIC mrem
5,000,000
TYPICAL THERAPY X-RAY TO SINGLE ORGAN (series of exposures)
500,000
LETHAL DOSE TO 50% OF HUMANS
400,000
50,000
FIRST DETECTABLE PHYSIO-LOGICAL EFFECTS
25,000
SMOKING 30 CIGARETTES PER DAY
16,000
5,000
MAXIMUM ALLOWED ANNUAL DOSE TO WORKER
TOTAL AVERAGE ANNUAL RADIATION DOSE TO THE US RESIDENT: mrem

30. Radiation Levels (mrem/year)
Cosmic
11.00%
Terrestrial
7.00%
Radon-220
5.00%
Potassium-40
Th & U Series
4.00%
Other <0.01%
Radon-222
68%
NCRP Report No.160, 2009
Natural Background:
311 mrem (3.11 mSv)
5,000,000
TYPICAL THERAPY X-RAY TO SINGLE ORGAN (series of exposures)
Aviation
310
Nuclear
Power
190
Industry 80
Medical
Education, Research 70
Government,
Military 60
NCRP Report 160, 2009
Occupational: 110 mrem (1.1 mSv)
500,000
LETHAL DOSE TO 50% OF HUMANS
400,000
50,000
FIRST DETECTABLE PHYSIO-LOGICAL EFFECTS
25,000
SMOKING 30 CIGARETTES PER DAY
16,000
5,000
MAXIMUM ALLOWED ANNUAL DOSE TO WORKER
28 mrem
500 CT
49%
Nuclear Medicine
26%
Interventional
Fluoroscopy
14%
Conventional
Radiography and
11%
Medical Exposures: mrem (3.0 mSv)
NCRP Report 160, 2009
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
Absorbed Gamma Dose Rate in Air
AVERAGE NATURAL BACKGRD
311
310
AVIATION
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
mrem
mrem
mrem
mrem
mrem
mrem
MEDICAL
300
X-RAY DIAGNOSTICS
223
200
RADON
190
NUCLEAR POWER
620
AVERAGE ANNUAL RADIATION EXPOSURE TO U.S. RESIDENT CT
147
OCCU- PATIONAL
110
NUCLEAR MEDICINE 77

31. Radiation Levels (mrem/year)
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
K-40
C-14
Rb-87
Po-210
Th-230
Rn-222
U-238
Ra-228
Ra-224
Th-232
Natural Radionuclides Contained In The Body: mrem (0.29 mSv)
0.6% Road Construction
35%
Tobacco
27%
Building
Materials
26%
Commercial
Air Travel
6% Mining and
Agriculture
2% Fossil Fuels
<0.03% Glass & Ceramics
3% Other
NCRP Report 160, 2009
Consumer Products: 13 mrem (0.13 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
Terrestrial Radiation: 28 mrem (0.28 mSv)
5,000,000
TYPICAL THERAPY X-RAY TO SINGLE ORGAN (series of exposures)
500,000
LETHAL DOSE TO 50% OF HUMANS
400,000
50,000
FIRST DETECTABLE PHYSIO-LOGICAL EFFECTS
25,000
SMOKING 30 CIGARETTES PER DAY
16,000
5,000
MAXIMUM ALLOWED ANNUAL DOSE TO WORKER
500 50
AVERAGE NATURAL BACKGRD
311
310
AVIATION
COSMIC 33
MEDICAL
300 29
INTERNAL R/N
X-RAY DIAGNOSTICS
223
200
RADON
TERRESTRIAL 21
190
NUCLEAR POWER CT
147
OCCU- PATIONAL
110
NUCLEAR MEDICINE 77

32. Radiation Levels (mrem/year)
5,000,000
TYPICAL THERAPY X-RAY TO SINGLE ORGAN (series of exposures)
Average UIC occupational exposure (751 monitored)
34 mrem
50,000
FIRST DETECTABLE PHYSIO-LOGICAL EFFECTS
25,000
SMOKING 30 CIGARETTES PER DAY
16,000
NATURAL GAS: 2
(especially residential use)
500,000
LETHAL DOSE TO 50% OF HUMANS
400,000
FALLOUT FROM WEAPONS TESTING: 0.75
5,000
MAXIMUM ALLOWED ANNUAL DOSE TO WORKER
500 50 5
AVERAGE NATURAL BACKGRD
311 34
AVERAGE UIC OCCUPATIONAL EXPOSURE (751 monitored)
310
AVIATION
COSMIC 33
MEDICAL
300 29
INTERNAL RN
X-RAY DIAGNOSTICS
223 2
NATURAL GAS (especially residential)
200
RADON
TERRESTRIAL 21
190
NUCLEAR POWER CT
147
CONSUMER PRODUCTS 13
OCCU- PATIONAL
110
0.75
WEAPONS FALLOUT
SLEEPING WITH ANOTHER HUMAN
0.1
NUCLEAR MEDICINE 77

33. Exposure Rate Constant How to calculate your radiation dose if you know the isotope, the activity & the distance.

34. Exposure Rate Calculation From a 10μCi Cs-137 Point Source at 1 cm (3
Exposure Rate Calculation From a 10μCi Cs-137 Point Source at 1 cm (3.287 is the Exposure Rate Constant for Cs-137) X • X • • X

35. Exposure Rate at Various Distances From 10μci of Cs-137
0.1 cm mR/h
1.0 cm mR/h
10 cm mR/h
100 cm mR/h

36. Radiation Levels (mrem/year)
5,000,000
TYPICAL THERAPY X-RAY TO SINGLE ORGAN (series of exposures)
500,000
LETHAL DOSE TO 50% OF HUMANS
400,000
50,000
FIRST DETECTABLE PHYSIO-LOGICAL EFFECTS
25,000
SMOKING 30 CIGARETTES PER DAY
16,000
5,000
MAXIMUM ALLOWED ANNUAL DOSE TO WORKER
500 50 5
AVERAGE NATURAL BACKGRD
311 34
AVERAGE UIC OCCUPATIONAL EXPOSURE (751 monitored)
310
AVIATION
COSMIC 33
MEDICAL
300 29
INTERNAL RN
X-RAY DIAGNOSTICS
223 2
NATURAL GAS (especially residential)
CONSUMER PRODUCTS:
(without building materials and tobacco)
10 hours of Physics Lab using
10 µCi Cs-137 source:
200
RADON
TERRESTRIAL 21
190
NUCLEAR POWER CT
147
CONSUMER PRODUCTS 13
OCCU- PATIONAL
110
0.75
WEAPONS FALLOUT
SLEEPING WITH ANOTHER HUMAN
0.1
NUCLEAR MEDICINE 77

37. ALARA Policy As
Low
Reasonably
Achievable

38. Standard Warning Sign For 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!

39. Lab Entrance Labeling
LOW
MEDIUM
HIGH

40. Basic Principles of Radiation Protection
Time
Distance
Shielding
Contamination Control

41. Time
Radiation dose is directly proportional to the time of exposure

42. Distance I1 I2 d22 d12 = d1 d2 I1 I2 Inverse Square Law
Radiation intensity is inversely proportional to the distance squared I1 I2 d1 d2 I1 I2
d22
d12 =

43. Shielding

44. Rules for Handling Sources
DO 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 exposure
Sign sources in and out with the T.A.

45. Lab 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.