University of Illinois at Chicago
Radiation Safety Section
Environmental Health and Safety Office
Radiation Safety Physics Lecture
Physics 108, 244
Ionizing Radiation
 Radiation
that can cause ionization of
the material through which it passes
either directly or indirectly

Electromagnetic radiation

Particulate radiation
Electromagnetic Radiation

Electro-magnetic waves (uncharged packets of energy)
propagated through space or a material medium
Wavelength, m
Frequency, s-1
_
1
E~ν~λ
Energy of
one photon, eV
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

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
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
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
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)
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
1/2
1/4
1/8
T1/2
T1/2
T1/2
T1/2 =
ln2
λ
Units of Activity

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
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
Beta Decay

A neutron transforms into a proton, an electron,
and an anti-neutrino
He-3
H-3
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
Gamma Decay (Cs-137)
Beta
661 keV Gamma
Cs-137
Ba-137m
Ba-137
T1/2 30 yr
T1/2 2.55 min
STABLE
Tl-204 Decay
Tl-204 (T1/2 3.779 yr)
2.6%
Hg-204
97.4%
Pb-204
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
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
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
Equivalent 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 factors
Type of Radiation
wR
X-Rays
1
Gamma-Rays
1
Beta Particles
1
Alphas
20
Neutrons
2-20
Stochastic Effects
Cancer
– Radiation is a weak carcinogen
Genetic
– Magnitude thought to be very small
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
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: 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)
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
Radiation Levels (mrem/year)
5,000,000
TYPICAL
THERAPY
X-RAY TO
SINGLE
ORGAN
(series of
exposures)
50,000
500,000
LETHAL
DOSE TO
50% OF
HUMANS
400,000
FIRST
DETECTABLE
PHYSIOLOGICAL
EFFECTS
25,000
16,000
SMOKING 30
CIGARETTES
PER DAY
SMOKING 30
CIGARETTES
PER DAY:
16,000
mrem/year
Radiation Levels (mrem/year)
5,000,000
TYPICAL
THERAPY
X-RAY TO
SINGLE
ORGAN
(series of
exposures)
50,000
500,000
LETHAL
DOSE TO
50% OF
HUMANS
400,000
FIRST
5,000
MAXIMUM
ALLOWED
ANNUAL
DOSE TO
WORKER
PART OF BODY
OCCUPATIONAL
EXPOSURE
ADULTS
MINORS
TOTAL AVERAGE ANNUAL RADIATION
5,000 mrem
500 mrem
DOSE TO THE
US RESIDENT:
620 mrem
WHOLE BODY
SKIN
EXTREMITIES
50,000 mrem
50,000 mrem
5,000 mrem
5,000 mrem
LENS OF EYE
15,000 mrem
1,500 mrem
500 mrem
N/A
DETECTABLE
PHYSIOLOGICAL
EFFECTS
25,000
16,000
SMOKING 30
CIGARETTES
PER DAY
EMBRYO/FETUS
(Declared
Pregnancies)
INDIVIDUAL MEMBERS OF THE PUBLIC - 100
mrem
Radiation Levels (mrem/year)
Natural Background:
5,000,000
50,000
500,000
Occupational:
mrem
(1.1 5,000
mSv)28 mrem 500
311
mrem110
(3.11
mSv)
Medical Exposures:
Education, Research
Medical
Cosmic in Air
300
mrem
(3.0
EPA Map
of Radon
Zones
Absorbed
Gamma
Dose
Rate
70mSv)
80
11.00%
TYPICAL
THERAPY
X-RAY TO
SINGLE
ORGAN
(series
of
Industry
exposures)
80
LETHAL
DOSE TO
50% OF
HUMANS
400,000
MAXIMUM
ALLOWED
ANNUAL
DOSE TO
WORKER
Nuclear
FIRST
DETECTABLE
Radon-222
68%
PHYSIOLOGICAL
EFFECTS
AVERAGE
NATURAL
BACKGRD
Government,AVIATION 311
310
Medicine
Terrestrial
26% Military
300
Dental bitewing
60 7.00%
MEDICAL
Interventional
Chest
Radiograph
Fluoroscopy
Radon-220
223
14% 5.00% X-RAY
DIAGNOSTICS
Mammogram
Aviation
Potassium-40
RADON
Conventional
Head CT310
5.00%
200
Radiography and
Power
190
Fluoroscopy
Barium
Enema
NUCLEAR
190
Th & U Series
AVERAGE
16,000
POWER
11%
ANNUAL
4.00%
SMOKINGOther
30 <0.01%
Chest
or abdomen
CT
CT
147
RADIATION
CIGARETTES
NCRP Report 160,
2009
EXPOSURE
NCRP
Report 160, 2009
OCCU- 110
DAY
NCRPJ.S.Duval
ReportetNo.160,
2009PERradioactivity
al, 2005, Terrestrial
andCoronary
gamma-ray
exposureCT
in the angiography
TO U.S.
PATIONAL
RESIDENT
US and Canada: U.S.G.S. Open-File Report 2005-1413
Abdomen
and pelvis
620
77 CT
NUCLEAR
Thallium myocardial
MEDICINE perfusion
CT
Nuclear
49%
25,000
< 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
Radiation Levels (mrem/year)
Cosmic Radiation:
33 mrem
(0.33 mSv)
Natural
Radionuclides
Contained In The Body:
Terrestrial Radiation:
28 (0.29
mremmSv)
(0.28 mSv)
29
mrem
5,000,000
50,000
Consumer
13 mrem (0.13 mSv)500
500,000Products:
5,000
TYPICAL
THERAPY
X-RAY TO
SINGLE
ORGAN
(series of
exposures)
LETHAL
DOSE TO
50% OF
HUMANS
Po-210
26%
400,000
Commercial
Th-232
Air Travel
FIRST
DETECTABLE
27%
Building
Materials
PHYSIORa-228
LOGICAL
EFFECTS
25,000
MAXIMUM
ALLOWED
ANNUAL
DOSE TO
WORKER
Rb-87
AVERAGE
NATURAL
BACKGRD
311
AVIATION 310
and
K-40
6% Mining
Agriculture
300
MEDICAL
2% Fossil Th-230
Fuels
223
0.6% Road
Construction
X-RAY
DIAGNOSTICS
<0.03% Glass & Ceramics
200
190
NUCLEAR
POWER
U-238
J.S.Duval et al, 2005,
Terrestrial
in
Tobacco
SMOKING
30 radioactivity and gamma-ray exposure
CT
147
the US and Canada:
U.S.G.S. Open-File Report 2005-1413
CIGARETTES
PER DAY
COSMIC
33
INTERNAL R/N
29
TERRESTRIAL
3% OtherRADON
35%
Rn-222
16,000
50
OCCU- 110
Ra-224
C-14
J.S.Duval et al, 2005, Terrestrial
radioactivity and
gamma-ray
exposure
PATIONAL
NCRP
Report
160, 2009in
the US and Canada: U.S.G.S. Open-File Report 2005-1413
77
NUCLEAR
MEDICINE
21
Radiation Levels (mrem/year)
5,000,000
TYPICAL
THERAPY
X-RAY TO
SINGLE
ORGAN
(series of
exposures)
50,000
500,000
500
5,000
NATURAL GAS:
LETHAL
DOSE TO
50% OF
HUMANS
MAXIMUM
ALLOWED
ANNUAL
DOSE TO
WORKER
2
AVERAGE
AVERAGE UIC
NATURAL
(especially residential
use)
400,000
BACKGRD
311
AVIATION 310
300
FIRST
DETECTABLE
MEDICAL
PHYSIOLOGICAL
EFFECTS
OCCUPATIONAL
COSMIC
33
INTERNAL RN
29
25,000
FALLOUT FROM WEAPONS
RADON
200
TESTING: 0.75
190
SMOKING 30
CIGARETTES
PER DAY
EXPOSURE
(751 monitored)
34
223
X-RAY
DIAGNOSTICS
16,000
5
50
TERRESTRIAL
21
NATURAL GAS
(especially
residential)
2
NUCLEAR
POWER
CT
147
OCCU- 110
Average UIC occupational
PATIONAL
exposure (751 monitored)
77
NUCLEAR
34 mrem
MEDICINE
CONSUMER
PRODUCTS
13
WEAPONS
FALLOUT
0.75
SLEEPING WITH
ANOTHER HUMAN
0.1
Exposure Rate Constant
How to calculate your radiation dose if you know
the isotope, the activity & the distance.
2
R cm
Γδ
mCi h
Exposure Rate Calculation
From a 10μCi Cs-137 Point Source at 1 cm
(3.287 is the Exposure Rate Constant for Cs-137)
•
2
R cm
X = 
X
× A mCi×
mCi h
2
1000mR
1 
-2
  cm ×
R
 d
2

 1   R 1000mR
X
X = 3.287 × 0.01 ×  1   h×
R
  

•
•
mR
XX = 32.87
h
Exposure Rate at Various
Distances From 10μci of Cs-137
 0.1
cm
 1.0 cm
 10 cm
 100 cm
3287 mR/h
32.87 mR/h
0.3287 mR/h
0.003287 mR/h
Radiation Levels (mrem/year)
5,000,000
TYPICAL
THERAPY
X-RAY TO
SINGLE
ORGAN
(series of
exposures)
50,000
500,000
LETHAL
DOSE TO
50% OF
HUMANS
400,000
MAXIMUM
ALLOWED
ANNUAL
DOSE TO
WORKER
500
5,000
AVERAGE
NATURAL
BACKGRD
311
AVIATION 310
DETECTABLE
PHYSIOLOGICAL
EFFECTS
AVERAGE UIC
OCCUPATIONAL
COSMIC
MEDICAL
33
INTERNAL RN
29
223
X-RAY
DIAGNOSTICS
25,000
TERRESTRIAL
RADON
10 hours of Physics Lab using
SMOKING 30
CIGARETTES
PER DAY
21
200
190
NUCLEAR
POWER
10 µCi Cs-137 source:
16,000
EXPOSURE
(751 monitored)
34
300
FIRST
5
50
NATURAL GAS
(especially
residential)
2
0.03
147
CONSUMER
PRODUCTS
OCCU- 110
PATIONAL
13
CT
CONSUMER PRODUCTS: 770.03
NUCLEAR
MEDICINE
(without building materials and tobacco)
WEAPONS
FALLOUT
0.75
SLEEPING WITH
ANOTHER HUMAN
0.1
ALARA Policy
As
Low
As
Reasonably
Achievable
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!
Lab Entrance Labeling
LOW
MEDIUM
HIGH
Basic Principles of
Radiation Protection
 Time
 Distance
 Shielding
 Contamination
Control
Time

Radiation dose is
directly proportional to
the time of exposure
Distance

Inverse Square
Law
Radiation intensity
is inversely
proportional to the
distance squared
I2
I1
=
d12
d22
I1
I2
d1
d2
Shielding
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.
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.