Transcript Radiation and Radioactivity

Science of Nuclear Energy and Radiation
Science Teacher Workshop
University of Richmond
Richmond, VA
July 18, 2007
Biological Effects of Ionizing Radiation
Carl A. Tarantino, CHP
Corporate Health Physicist
Dominion Generation
Solar Radiation
Radiation in Life
Nuclear
Medicine
Cosmic Rays
X-Rays
Radon
Consumer
Products
Each
Other
Radioactive
Waste
Terrestrial
Radiation
Food &
Drink


Nuclear
Power

Ionizing Radiation Units
Old Units
SI Units
1 C kg-1 = 3876 R
rad
Gray
1 Gy = 100 rad
rem
Sievert
1 Sv = 100 rem
What It Is
Measuring Radiation Effects
How much radiation is produced

–
Activity: decays per time (Curie (Ci), Becquerel (Bq))
How much energy absorbed by tissue

–
Dose
How much biological damage does the radiation
do per energy absorbed

–
Dose equivalent
Ionizing Radiation Effects
Absorption of Radiation
Ionization
Chemical Change
Repair or Damage
High Dose Effects
Cell killing
Tissue or organ effects
Whole body effects
Low Dose Effects
Mutations
Cancer
Effects to unborn
Cellular Organization
Potential Radiation Damage to DNA
Most critical molecule within humans: DNA

Direct effect on
molecule by
ionization or
excitation of the
molecule and
subsequent
dissociation of
the molecule
Other Damage to DNA
 Many
other entities cause breaks in DNA
– Temperature, chemicals, etc.
 Human
DNA suffer millions of DNA breaks
daily
– Most repaired
Radiation Induced Decomposition
of Water Within a Cell
Most abundant molecule within humans: Water
H2O
H2O+
H2
Incoming
Radiation
e-
+
H
WATER
OH
Ho
HO2
H2O2
OHo
Production of free radicals within the cell can result in indirect effects
Potential Outcomes of Radiation
Damage to Parent Cells
Radiation Dose
Cell Repair after
Chronic Dose Damage
Reparable
Accumulated Irreparable
Time
Cellular Radiosensitivity:
Law of Bergonie and Tribondeau
The basic law of Bergonie and Tribondeau
is that young and rapidly dividing cells are
more sensitive than cells with adult
development. Cells tend to be
radiosensitive if they have three
properties:
» Cells that have high division rate
(the time between divisions)
» Cells that have long dividing future
(immature cells in early cellular life)
» Cells that are unspecialized
(cells which have a widely diverse future)
Relative Sensitivity of
Cell and Tissue Types
 Lymphocytes
 Spermatogonia
 Hematopoietic (Blood Forming)
 Intestinal Epithelium
 Skin
 Nerve Cells
 Muscle Tissue
 Bone
 Collagen
Hematological Response
1 Sv (100 rems)

Hematological Response
3 Sv (300 rems)

Possible Radiation Dose
Response Curves

1- Linear (Non-Threshold)
2 - Linear-Quadratic
3 - Threshold
4 - Supralinear

Effects



Dose (rem)
Most conservative model:
An increase in dose
results in a proportional
increase in risk
At low doses there is only
a slight increase in risk
that becomes proportional
to dose at higher doses
There is a threshold for
dose response at which
lower doses do not result
in increased risk
At low doses there is a
higher risk that becomes
proportional to dose at
higher doses
Hormesis model (not
shown): Low doses of
radiation have a positive
effect and decrease risk
Hormesis


Some data indicate that low doses of radiation are
beneficial
Not widely accepted
– Conservative is better
But not impossible
Risk
Benificial Detriment

Dose
Risk Terms

Acute
A large dose of radiation in a short period of time

Chronic
Small doses of radiation protracted over a long period of
time

Stochastic
Health effects that occur randomly and for which the
probability of the effect occurring, rather than its severity,
is assumed to be a linear function of dose without
threshold

Non-stochastic
Health effects which do not appear until a threshold value
is exceeded and for which the severity of the effect
increases with dose beyond the threshold

Somatic
Effects which occur in the exposed individual

Genetic
Effects which occur in the progeny of the exposed
individual due to chromosome aberrations in the parent

Teratogenic
Effects to the unborn fetus irradiated in-utero
Risk Examples







Hereditary effects
Cancer (leukemia, tumors)
Erythema (skin reddening)
Cataracts
Sterility
Epilation (hair loss)
Hematological effects
Genetic; stochastic
Somatic; stochastic
Somatic; non-stochastic
Somatic; non-stochastic
Somatic; non-stochastic
Somatic; non-stochastic
Somatic; non-stochastic
Biological Effects from
Low Doses of Radiation
Biological effects from low doses potentially occur
due to chronic exposures. A chronic exposure
occurs when a relatively small amount of radiation is
absorbed by tissue over a long period of time.
 Under 5 rad of exposure - No detectable health
effects in exposed individual
 Chronic exposures result in an increased risk
in latent adverse health effects
 Health effects could be genetic effects or
somatic effects
Latency Period
Latency period is the time
from time of exposure until
the effect is exhibited

Radiation exposure does
not produce cancer in
every exposed person

Effects can be immediate
or years later for acute,
high-level exposures
Time radiation dose received
Latent period
Period at risk
Risk curve
Risk

0
4
30
Time (years)
Leukemia latency and time at risk periods
Biological Effects from
High Doses of Radiation
Biological effects from high doses occur due to acute
exposures. An acute exposure occurs when a relatively large
amount of radiation is absorbed by tissue over a short period of
time; effects can occur in the short term and long term.
 Hematopoietic Syndrome: (100-200 rad or 1-2 Gray) Early
symptoms are anorexia, nausea, and vomiting followed by a phase
of bone marrow depression and subsequent susceptibility to
infection. After several weeks, death may occur.
 Gastrointestinal Syndrome: (700-1000 rad or 7-10 Gray) Early
symptoms are anorexia, nausea, and vomiting followed by fever,
diarrhea, and electrolyte imbalance due to ulceration of the
intestinal wall. Once GI system ceases to function, death will occur.
 Central Nervous System Syndrome: (2000-5000 rad or 20-50 Gray)
Symptoms occur very quickly and the brain and muscles can no
longer control bodily functions, including breathing and blood
circulation. Death within hours or within several days.
Effects From Acute, High-level Radiation Doses
Dose (rad)
0 - 100
100 - 200
200 - 600
600 - 1000
1000 - 5000
Over 5000
Incidence of
Vomiting
None
100 rad: 5%
200 rad: 50%
300 rad:
100%
100%
100%
100%
Time of Onset
------
3 hr.
2 hr.
1 hr.
30 min.
30 min.
Principal
Affected Organs
None
Diarrhea; fever;
disturbance of
electrolyte
balance
Central
nervous
system
Convulsion;
tremor;
ataxia;
lethargy
45 to 14 days
1 to 48 hrs.
Gastrointestinal
tract
Hematopoietic tissue
Characteristic
Signs
None
Moderate
leukopenia
Severe leukopenia; purpura;
hemorrhage; infection;
epilation above 300 rad
Critical Period
Post Exposure
------
------
4 to 6 weeks
Excellent
Excellent
Good
Guarded
Hopeless
Hopeless
Convalescent
Period
None
Several
Weeks
1 to 2 months
Long
------
------
Incidence of
Death
None
None
0 to 80%
(variable)
80 to 100%
(variable)
90 to 100%
90 to 100%
Death Occurs
Within
------
------
2 months
2 weeks
2 days
Cause of Death
------
------
Hemorrhage; infection
Circulatory
collapse
Respiratory
failure; brain
edema
Prognosis
Median Lethal Dose Curve
Dose (rad)
LD50 - Median Lethal Dose
LD50/30 - Lethal dose to 50% of exposed population within
30 days of irradiation, without medical attention
Defined at approximately 450 rad
What is Safe?

Driving a car is “safe”
– 1:6,000

Living at home is “safe”
– Falls -- 1:20,000
– Fires -- 1:50,000
– Poisoning -- 1:40,000
– Total -- 1:10,000

Radiation (1 mSv) is safe
– 1:20,000
Relative Risk:
Years of Life Lost
10.96
Alcoholic
10.00
Poverty
6.16
Smoking-Male
No Friends
4.50
Heart Disease
4.40
3.42
Cancer
3.15
High Risk Job
2.85
20% Overweight
2.33
H.S. Drop-Out
2.20
Orphan
0.57
Car Accidents
0
2
4
6
Years
8
10
12
Relative Risk:
Days of Life Lost
207
Car Accidents
130
Alcohol
115
Suicide
93
Murder
77
Air Pollution
55
50
50
AIDS
Energy Conservation
Spouse Smoking
30
24
23
22
20
Radon
Drowning
Radiation Worker
Drinking Water
Fire, Burns
9.3
7
Natural Radiation
Natural Hazards
0
50
100
150
Days
200
250
Relative Risk:
Hours of Life Lost
168
Natural Hazards
148.8
144
Medical Radiation
Bicycles
108
Electrocution
60
Hazardous Waste
Anti-nuclear activists
48
Nuclear Power
24
21.6
Peanut Butter
Milk
8
Live Near Nuc Plant
3
1.2
Broiled Steaks
Nuclear Power
0
Government
20
40
60
80
100
Hours
120
140
160
180
Summary of Ionizing Radiation Effects


All radiation may not be harmful
– However, data does not contradict the linear,
non-threshold theory for some effects (cancer,
genetic effects)
Effects from high doses are known fairly well
– Depending upon dose, radiation may affect
various cells, tissues, and organs
– Without medical treatment, about 50% of people
exposed to approximately 450 rad of radiation
are expected to die within 1-2 months
– Acute (short-term) effects below 100 rad are
relatively minor
Summary of Ionizing Radiation Effects

Effects from low doses occur less frequently and
take longer to develop than high dose effects
– Studies of populations chronically exposed to low
levels of radiation have not shown conclusive
evidence of increased cancer risk
– The magnitude of the risk is inferred from data at
higher doses
– The lower the dose of radiation, the longer it takes
for the cancer to develop
– Some changes in blood have been detected down
to several rad
Summary of Ionizing Radiation Effects


Genetic effects have not been detected in people
– Genetic effects may occur, but at rates so low
that they have not been detected over the rate
that occurs in the absence of radiation
The unborn child and young children appear to be
more sensitive to the effects of radiation than
adults are
– The rate that effects occur is very low
The End