Download Radiation in a Radioactive World

Radiation in a Radioactive World
Nuclear Physics and Engineering
By: Douglas Osborn
Is this what you think when I say nuclear?
Is this only thing something nuclear can do?
Do you think of these people when
I say RADIATION?
Do you think of these things as well?
• Food
• Space
• Utilities
• Consumer Products
• Medicine
RADIOLOGICAL
FUNDAMENTALS
Atomic Structure
Definitions
Types of Ionizing Radiation
Units of Measure
Atomic Structure
•
•
•
•
•
Atomic Structure Particles
Elements & Isotopes
Stable vs. Unstable
Standard Nomenclature
Ions
Atomic Structure
Particles
Protons (positive)
Neutrons (neutral)
Electrons (negative)
Proton
Nucleus
Neutron
P+ N
Nucleus
eElectron
Elements
• The number of protons in the nucleus
determines the element
• If the number of protons changes, the
element changes
P+
hydrogen
P+ N
N
P+
helium
N
P+
N
P+
N
P+
N
lithium
Isotopes
• Isotopes - atoms of the same element which
have the same number of protons, but a
different number of neutrons
• Isotopes have the same chemical properties;
however, the nuclear properties can be quite
different
P+
Hydrogen
(protium)
P+ N
Hydrogen
(deuterium)
P+ N
N
Hydrogen
(tritium)
Stable vs. Unstable Atoms
If there are too many or too few neutrons for a
given number of protons, the nucleus will not
be stable
P+
e-
P+ N
N
e-
Hydrogen
(protium)
Hydrogen
(tritium)
STABLE
“Non-Radioactive”
UNSTABLE
“Radioactive”
Standard Nomenclature
60
A
# of protons
and neutrons
Co
X
Z
27
27
# of protons
Represents
element
Ions
Ions are atoms with positive or negative charge:
eN
e-
N
N
P+ P+ P+
N
N
eNeutral
N
P+ P+ P+
e-
N
e-
N
Positive
Ions
e-
N
e-
N
P+ P+ P+
N
e-
N
e-
Negative
Definitions
•
Ionization
•
Radiation
•
Ionizing vs. Non-Ionizing
•
Radioactivity & Radioactive Decay
•
Radioactive Half-Life
•
Radioactive Material
•
Radioactive Contamination
Ionization
The process of removing electrons from
neutral atoms
AND
Free ejected
electron
Radiation
• Energy released from unstable atoms and
some devices in the form of rays or
particles
• Can be either ionizing or non-ionizing
ENERGY
RADIATION
UNSTABLE
ATOM
PARTICLE
Ionizing Radiation
• Radiation that possesses enough energy
to cause ionization in the atoms with
which it interacts
• Released from unstable atoms and some
devices in the form of rays or particles
- alpha a
- beta b
- gamma/x-ray g
- neutron 0n1
Non-Ionizing Radiation
• Radiation that doesn’t have the amount of
energy needed to ionize the atom with
which it interacts
• Examples:
- radar waves
- microwaves
- visible light
- infrared radiation
- ultraviolet radiation
Radioactivity
The process of unstable (or radioactive)
atoms becoming stable by emitting radiation.
This event over time is called radioactive
decay.
P+ N
N P+
P+ P+ N P+
N P+
P+ P+ N
N
N P+P+
P+
N
P+
N
N P+NP+ NN N
P+ P+ N P+ N P+N P+
N P+NP+ P+ P+P+
P+ N
N N
N
N P+N N N
P+ P+ P+ P+P+NNP+
P+P+
P+P+
NP+NNP+
N
P+
N
N
N
N
P+
P+
N
P+
N NNP+ N N
Large, unstable nucleus
alpha
beta
gamma
N P+
e-
neutron
N
Excess
Energy
Released
Decay Chain
After 18 decays we arrive at stable:
238
234
234
206
UTh
Pa
Pb
929091
82
b
Radioactive Half-Life
The time it takes for one half of the
radioactive atoms present to decay
Example: Co-60 = 5 years
Ni-60
Co-60
100 atoms
today
Co-60
50 atoms
after 5 yrs
Ni-60
Co-60
25 atoms
after 10 yrs
Ni-60
Co-60
12 atoms
after 15 yrs
Radioactive Decay
Develop a model for radioactive decay.
Call it the radioactive decay law.
How do we describe the rate of de-energization?
 Observations in Nature:
 Decay / De-energization
Occurs
 Number of Radioactive
Nuclides decreases with time
 De-energization of a single
nuclide is a statistical
process
 Let’s perform a simulation
Rules
• DON’T OPEN the packages until I give you
instructions !!
• Need one volunteer from each table group You are
the data runner.
• Carefully open the package.
• Pour the contents onto your desk – carefully. DO NOT
EAT THEM!
• Determine the total number in the bag.
– Report this number to the data runner.
• Count those with the “M” UP and return them to the
bag.
– Report this count to the data runner.
– Eliminate (eat?) those not returned to the bag.
• Calculate and record total counts
• Shake the bag and repeat the above.
Total
Counts
Counting
Period
Counts
From Table
Group 1
Counts
From Table
Group 2
Counts
From Table
Group 3
Normalized
Value
One Sigma Error
Counts
From Table
Group 4
(Semilog Plot)
 N
100 *
N
%
N
(Linear Plot)
Initial
Count
844
677
968
685
3174
56.3
1.8
1.000
Count 1
435
331
456
316
1538
39.2
2.5
0.485
Count 2
201
163
250
187
801
Count 3
96
81
111
86
374
Count 4
53
42
72
51
218
Count 5
21
28
36
21
106
Count 6
13
12
17
16
58
Count 7
5
4
12
4
25
Count 8
3
2
2
3
10
Count 9
2
0
1
0
3
Count 10
2
0
0
0
2
Count 11
1
0
0
0
1
Count 12
0
0
0
0
0
0.252
19.3
5.2
0.118
0.069
10.3
9.7
0.033
0.018
5.0
20.0
0.008
0.003
1.7
57.7
0.001
0.001
1.0
100.0
0.000
0.000
Graphical Outputs
3500
3000
2500
2000
1500
1000
500
0
1
3
5
7
9
11
13
10000
1000
100
10
1
1
3
5
7
9
11
13
Next Question:
What have we observed?
• Decay / De-energization Occurs
• Number of Radioactive Nuclides decreases with
time
• De-energization of a single nuclide is a statistical
process
– This being the case, at the beginning of the deenergization process when a lot of radioactive
nuclides are present, the statistics are much better
– Thus sample counting statistics are much better in the
beginning than after most of the nuclides have deenergized
– Why is this?
Counting Statistics: Randomness
• De-energization events are random
– Quantity per unit time depends on the total number of
radioactive nuclides present
– Thus the quantity decreases with time
• Detection events also are random within the
counting media depending on random processes
associated with the detector
– Probability of penetration into the detector
– Probability of interaction in the detector
• Variability and precision of repeated counts can
be described with reasonable rigor based solely
on the total number of detected events
Counting Statistics – Variability
• Variability refers to the distribution of a number of repeated
counts around a true value or a mean value
• Repeat counts follow a Poisson Distribution, but when a
large number of repeat counts are taken, the Normal
Distribution is a good approximation
• The shape of the Normal curve can be described by using
only the mean, m, and the standard deviation, s or s
• The mean is the arithmetic average of all counts
• In the normal distribution, about
– 68% of all counts will fall within one standard deviation
– 95% within 1.96 standard deviations
– 99% within 2.58 standard deviations
• A property of the Poisson Distribution is that the Standard
Deviation is simply the square root of the mean
Precise Example of a Normal
Distribution
• Note the symmetry
• Note how the “counts” are distributed
Counting Statistics – Precision
• Precision refers to the repeatability of a single count
– How close will a repeated count be to the previous count – or to the next
count?
– How close will one count be to the “true mean” of many repeated
counts?
– If we have only one count, we expect the true mean is probably different
from our one count
• Probability that the true mean lies within specific limits around the count is
determined from the shape of the normal error curve, the Normal Distribution
– The obtained (measured) count, N, is taken as the mean value, and the
standard deviation, s or s, is then the square root of the measured count:
s N
– Thus there is a 68% probability that the true mean lies within one
standard deviation, or the square root of the measured count
• The “error” in a given count is then generally considered to be:
% Error  
N
x100%
N
Counting Statistics: Precision Decision
• How good is good enough in practice?
– Analyzing the %Error formula clearly says that the more counts you
are able to obtain, the more precise your measurement will be.
– The %Error formula states there is a 68% probability that the true
value lies within + one standard deviation of the single measured
count
– This can also be stated as being within the 68% Confidence Interval
– This is a good estimate for general applications
• For more precise work, it’s preferred to be within the 95% Confidence
Interval
1.96 N
% Error 
x100%
N
• And for critical work, you may need to be within the 99% Confidence
Interval
% Error 
2.58 N
x100%
N
Counting Statistics – Examples
Sample Confidence Interval Error Estimates
68% C.I.
Measured
Counts, N
N
N
N
95% C.I.
1 . 96
N
99% C.I.
N
2 . 58
N
20
4.5
0.224
0.438
0.577
50
7.1
0.141
0.277
0.365
100
10.0
0.100
0.196
0.258
200
14.1
0.071
0.139
0.182
1,000
31.6
0.032
0.062
0.082
5,000
70.7
0.014
0.028
0.036
10,000
100.0
0.010
0.020
0.026
40,000
200.0
0.005
0.010
0.013
70,000
264.6
0.004
0.007
0.010
N
Derivation of the Radioactive
Decay
Law
• Define
Activity  Rate of Decay  A
•
Mathematically
dN(t)
A
 N(t)
dt
Where N(t) is the
number of radioactive
nuclei present at time t
• Need a constant of proportionality
  Radioactiv e Decay Constant
dN(t)
A
 N(t)  -N(t)
dt
• Why do we have a minus sign in the formula?
Activity (Continued)
dN(t)
A
 N(t)  -N(t)
dt
dN(t)
A
 -N(t)
dt
Rearrange the terms
dN(t)
dN
 dt 
 dt 
N(t)
N
N(t)

No
t
dN
   dt
N
0
N(t)
N(t)
 t
 t


ln
 t 
 e  N t  No e
No
No
Units of Activity
• Curie
–
–
–
•
The traditional unit of activity
1 Ci = 3.7x1010 disintegrations/second
Based on the disintegration rate of 1 gm of Ra-226
Becquerel
– SI Unit
– 1 Bq = 1 dis/sec
Half-life
• Half Life Definition
 The average amount of time required for the sample
size or activity t o decrease to 1/2 of its initial amount.
• Derivation => initial conditions:
No
N(t) 
: t  t 12
2
No
1
 t1/2
 N oe
  e t1/2   ln( 2)  t1/2
2
2
ln( 2) 0.693
0.693
t1/ 2 



t1/2
t1/2
Mean Lifetime
• Half life is the average amount of time for
half of a large sample of nuclides to deenergize
• Mean lifetime is the average (statistical
mean) amount of time a single nucleus
exists before de-energizing
– It can be shown that this is

1

Radioactive Decay on a
Linear Scale
Normalizing has been done
for illustration only. It is
NOT necessary!!
Radioactive Decay on a
Semi-Log Scale
Normalizing has been done
for illustration only. It is
NOT necessary!!
Summary of Concepts
Activity
A  N
Radioactive Decay Law (Two identical expressions)
Nt   No e
 t
At   Ao e t
Half Life and the Radioactive Decay Constant
ln( 2) 0.693


t1/2
t1/2
t1/ 2 
0.693

Radioactive Material
Radioactive material is any material
containing unstable atoms that emit
radiation
Radioactive Contamination
• Radiation is energy
• Radioactive material is the
physical material emitting
the radiation
• Radioactive contamination
is radioactive material
that is uncontained and in
an unwanted place
• Exposure to radiation
does not result in
contamination
Types of Ionizing Radiation
• Alpha (a - particle
• Beta (b - particle
• Gamma (g - ray
• Neutron (h - particle
Alpha Radiation (a)
Particle, Large Mass,
Characteristics
+2 Charge
Range
Very Short
1 - 2” in air
Shielding
Paper
Outer layer of skin
Hazards
Internal
Sources
Plutonium, Uranium,
Americium
Beta Radiation (b)
Characteristics
Particle, Small Mass,
-1 Charge
Range
12ft / MeV in air
Shielding
Plastic, glass,
aluminum, wood
Hazards
Internal and the
skin and eyes
Sources
Tritium, Sr-90,
Fission products
Gamma Rays (g) and X-Rays
No mass, no charge
Characteristics electromagnetic
Range
Hundreds of feet
in air
Shielding
Lead, Steel
Concrete
Hazards
External Source
Whole Body
Penetrating
Sources
Co-60, Kr-88, Cs-137
Neutron Radiation (h)
Characteristics
Particle with
no charge
Range
Hundreds of feet
in air
Shielding
Hazards
Sources
Hydrogenous
material water, polyethylene
External Source
Whole Body
Penetrating
Uranium, Plutonium,
Californium
Units of Measure
• Radiation
Energy
Roentgen, RAD, REM
• Radioactivity
Rate
dpm, Curie
• Contamination
Radioactivity
Area or volume
Spread
Roentgen (R)
• Unit for measuring exposure
• Defined only for ionization in air
• Applies only to gamma and x-rays
• Not related to biological effects
Wilhelm Roentgen
1845 -1923
Discovered X-rays
RAD (Radiation Absorbed Dose)
• Unit for measuring absorbed dose in any
material
• Applies to all types of radiation
• Does not take into account the potential
effect that different types of radiation have
on the body
REM (Roentgen Equivalent Man)
• Unit for measuring dose equivalence
• Most commonly used unit
• Pertains to the human body
• Takes into account the energy absorbed
(dose) and the biological effect on the body
due to the different types of radiation
Quality Factor (QF)
The QF is used as a multiplier to reflect the
relative amount of biological damage caused
by the same amount of energy deposited in
cells by the different types of ionizing
radiation.
Alpha
20
rad x QF = rem
Neutrons
2 - 11
Betas
1
Gamma &
X-rays 1
Conversion of rem to
millirem
1 rem = 1000 millirem (mrem)
500 mrem =
0.8 rem =
0.25 rem =
0.5
rem
800
mrem
250
mrem
Dose
Rate Rate
DoseDose
vs.
Dose
• Dose rate is themrem/hr
rate at which you receive
the dose
• Dose rate = dose divided by time (rad/hr,
mrad/hr)
• Dose is the amount of radiation you
receive
mrem
0 0
0
1 0
2 5
Measuring Radioactivity
A measure of the number of disintegrations
radioactive material undergoes in a certain
period of time
We measure the rate of decay which will lead
us to the quantity of radioactive material
present
Radioactivity Units
Basic unit
 disintegration per minute (dpm)
 derived from the number of counts
measured by instrument and the
efficiency of the instrument
Traditional unit
 Curie (Ci)
 1 Ci = 3.7 x 1010 dpm
Marie Curie
1867 - 1934
Discovered
radium & polonium
Contamination Units
How spread out is the radioactive material?
Radioactivity
Area or Volume
10 cm
Radioactivity
L X W X H
10 cm
dpm
microcurie
100 cm2
milliliter
BIOLOGICAL EFFECTS
• Background Sources
• Radiation Effects
• Prenatal Exposure
• Risks in Perspective
Background Sources
• Natural
• Manmade
• U.S. Average
Background Radiation
Background = natural + manmade
We are constantly exposed
to background radiation,
from both natural and
manmade sources
Background Radiation Sources
CONSUMER
CONSUMERPRODUCTS
PRODUCTS
INDUSTRIAL
INDUSTRIAL
ATMOSPHERIC
ATMOSPHERIC TESTING
TESTING
MEDICAL
INTERNAL
INTERNAL
RADON
RADON
TERRESTRIAL
TERRESTRIAL
COSMIC
NATURAL
MANMADE
Natural Background Sources
SOURCE
AVG DOSE
COSMIC - outer space
28 mrem/yr
TERRESTRIAL - Earth
28 mrem/yr
INTERNAL - our body
40 mrem/yr
RADON - Earth
200 mrem/yr
Manmade Background Sources
SOURCE
AVG DOSE
MEDICAL
54 mrem/yr
CONSUMER PRODUCTS
10 mrem/yr
INDUSTRIAL USES
<3 mrem/yr
ATMOSPHERIC Testing
<1 mrem/yr
Medical Procedures
PROCEDURE
AVG DOSE
THERAPY
600 rem to tumor
CAT SCAN
5.8 rem to head
MAMMOGRAM
0.4 rem to breast
CHEST X-RAY
10 mrem
Consumer Products
Radium Dial Factory
PRODUCT
AVG DOSE
TOBACCO PRODUCTS
1.3 rem/yr
DENTURES
60 rem/yr - gums
TINTED GLASSES
4 rem/yr - eyes
BUILDING MATERIALS
7 mrem/yr
U.S. Average
The average annual dose
to the general population
from natural background and
manmade sources is about:
360 mrem.
mrem.
360
Radiation Effects
• Cell Damage
• Cell Sensitivity
• Possible Effects on Cells
• Radiation Damage Factors
• Acute vs. Chronic
• Somatic vs. Heritable
Cell Damage
The human body is made up
of many organ systems.
Each system is made up of
tissues. Specialized cells
make up tissues. Ionizing
radiation can potentially
affect the normal function of
cells.
Cell Damage (cont.)
The method by which
radiation causes damage to
human cells is by ionization
of atoms in the cells. Any
potential radiation damage
begins with damage to
atoms.
Cell Damage (cont.)
Ionizing radiation can directly
rupture membranes that
surround the cells
Ionizations result in the
formation of free radicals
which can recombine to form
harmful chemicals such as
hydrogen peroxide
Cell Sensitivity
Some cells are more sensitive than others to
environmental factors such as:
– Viruses
– Toxins
– Ionizing radiation
Highest Sensitivity
• Actively dividing cells
• Non-specialized cells
• Blood forming cells
• Hair follicles
• Cells that form sperm
Lowest Sensitivity
• Less actively dividing cells
• More specialized cells
• Brain cells
• Muscle cells
Possible Effects of
Radiation on Cells
• There is no damage
• Cells repair the damage and operate normally
• Cells are damaged and operate abnormally
• Cells die
Radiation Damage Factors
•
Total Dose
•
Dose Rate
•
Type of Radiation
•
Area of Body Exposed
•
Individual Sensitivity
Total Dose
In general, the greater the dose, the greater the
potential for biological effects.
Effects
Dose
Dose Rate
The faster the dose is delivered, the less time
the body has to repair itself.
Type of Radiation
Cell damage varies with the type of radiation. For
example, internally deposited alpha emitters are
more damaging than beta or gamma emitters for
the same energy deposited.
1 MeV Beta particle creates 60 ion pairs
per 1 cm of travel
1 MeV Alpha particle creates 7000 ion pairs
per 0.1 cm of travel
Area of Body Exposed
• In general, the larger the area of the body
that receives a dose, the greater the
biological effect.
• Extremities are less sensitive than blood
forming and other critical organs.
vs.
Individual Sensitivity
• Age
The human body becomes less sensitive to
ionizing radiation with increasing age;
however, elderly people are more sensitive
than middle-aged adults.
• Genetic make-up
Some individuals are more sensitive to
environmental factors.
Acute vs. Chronic Dose
Potential biological effects depend on how
much and how fast a radiation dose is
received.
Radiation doses are grouped into:
 Acute - high
highdose
dose of radiation received in a
short period
short
periodof time (seconds to days)
small dose
dose of radiation received
 Chronic - a small
long period
periodof time (months to years)
over a long
Acute Dose
The body’s cell repair mechanisms are not as
effective for repairing damage caused by an
acute dose.
– Damaged cells will be replaced by new cells and
the body will repair itself, although this may take a
number of months.
– In extreme cases the dose may be high enough
that recovery would be unlikely.
Acute Exposure Effects
AVG DOSE
DAMAGE
> 5000 rem
Death Within 2 -3 Days
> 500 rem
Gastrointestinal Damage
450 - 600 rem
LD 50-60
200 - 500 rem
Blood System Damaged
100 - 200 rem
Radiation Sickness
25 - 50 rem
Slight Blood Changes
5 rem
Annual Limit
Effects of High-Level Acute
Doses (Skin/Extremities)
• Burns
• Necrosis
• Loss of
fingers
Chronic Dose
A small dose of radiation received over a long
period of time.
Typical examples are:
 The dose we receive from natural
background
background
 The dose we receive from occupational
occupational
exposure
Body is better equipped to tolerate chronic
doses
Effects of Chronic Doses
• Increased risk of cataract formation
• Increased risk of developing cancer
Somatic vs. Heritable
• Somatic effects appear in the exposed
exposed
individual.
individual. Some examples:
– Cells may become cancerous
– Increased risk of cataract formation
– Possible life shortening
• Heritable (genetic) effects appear in future
generations
future
generations
– Not yet observed in human populations
Prenatal Exposure
• Prenatal Sensitivity
• Potential Prenatal Effects
Prenatal Sensitivity
Embryo/fetus cells
are rapidly dividing,
which makes them
sensitive to many
environmental
factors including
ionizing radiation.
Potential Prenatal Effects
for Entire Pregnancy
Although no effects
were seen in Japanese
children conceived
after the atomic
bomb, there were
effects seen in some
children who were in
the womb when
exposed to radiation.
1. Slightly Smaller Head
Size
2. Lower Average Birth
Weight
3. Increased Incidence of
Mental Retardation
4. Increased Risk of
Childhood Cancer
Risks in Perspective
• Cancer Risk Info
• Comparison of Health Risks
• Occupational Risk Comparison
Cancer Risk Information
• Health effects have been observed in humans
at acute doses in excess of 10 rem.
• No increase in cancer has been observed in
individuals who receive a dose of ionizing
radiation at occupational levels.
• The possibility of cancer induction cannot be
dismissed even though an increase has not
been observed.
Cancer Risk (cont.)
• Current rate of cancer death among
Americans is about 20%.
• An individual who receives 25,000 millirem
over a working life increases his/her risk of
cancer by 1% to about 21%.
• The average annual dose to DOE workers is
less than 100 millirem.
Comparison of Health Risks
Health Risk
Days Lost
Unmarried Male
3500
Tobacco User
2250
Unmarried Female
1600
Overweight Individual
777
Alcohol Consumer
365
Motor Vehicle Driver
207
100 mrem/yr for 70 yrs
10
Comparison of Occupational Risk
Industry
Days Lost
Coal Miner
328
Farmer
277
Transportation Worker
164
U.S. Average
74
Manufacturer
43
Radiological Worker
40
Trades Employee
30
EO9
HOW RADIATION EFFECTS YOUR BRAIN
Nuclear Applications
•
•
•
•
•
Food
Industry
Medicine
Space
Electricity
Food
Industry
• C-14 dating
• Smoke Detectors – Am-241
• Soft drink bottles - radioisotopes are used to measure and
control how much soda there is in soft drink bottles
• Shrink wrap film/plastic insulation on wires - the plastic is
shrunk by radiation instead of using heat, which damages
the insulation
• Investigators, police, and other security groups use neutron
activation to detect explosives, such as mines, and to detect
drugs and weapons
• Companies who process materials such as coal or concrete
use neutron activation to analyze the material for quality
Medicine
• Nuclear Medicine – about 1/3 of all medical procedures
involve radiation or radioactive materials
• An estimated 10 to 12 million nuclear medicine diagnostic
and therapeutic procedures are performed each year in the
U.S. alone
• Examples:
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X-rays
NMRI
PET Scans
Radioactive Tracers
Gamma Knife
Cancer Therapy
Space
• Nuclear Jet Engine
• Radioisotope Thermoelectric Generator
• Gas Core Reactor Propulsion
Electricity
• Energy is generated from coal, gas, oil, water, wind, solar,
and nuclear. Part of that energy is used to produce
electricity. Electrical generation plants use the heat or
motion of those primary sources to generate electricity. One
way of doing this is by using nuclear power.
Alvin W. Vogtle NPP
Pressurized Water Reactor
Boiler Water Reactor
CANDU Reactor
Liquid Metal Reactor
Gas Cooled Reactor
Three Mile Island
• Middletown, PA
• March 28, 1979
• First meltdown of a full scale
nuclear power plant
• Mechanical Failure followed by
human error
Chernobyl
• Ukraine
• April 26, 1986
• First commercial reactor to have
radiation related deaths
• Human error and lack of safety
culture
• 56 deaths directly related to
accident (47 emergency workers)
F4 Sled Test
F4 Sled Test Slow Motion
Spent fuel Cask Testing (Train)
Train vs. Truck Cask Results
Spent Fuel Cask Testing (Truck)
Truck Crash Result