Radiation Safety
Radiation Safety
Radiation Interaction with Matter:
What happens when radiation hits us (or a detector)?
General:
Matter = Atoms (small positively charged nucleus orbited by
negatively charged electrons, electron orbits about factor 105 larger
than nuclear radius)
In radiation interaction with matter:
- Energy is transferred from the radiation to the absorbing medium
(which can be us)
- Results usually in ionization and excitation of atoms or molecules in
the absorber. (This can cause dissociation of the molecule.)
- Transferred energy is eventually dissipated as heat.
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Radiation Safety
Types of radiations (I)
Alpha particles α = 42He2++
Interactions between the electric field of an alpha and orbital electrons cause
ionization and excitation. Alpha particles lose their energy over a relatively short
range.
One α-particle will cause tens of thousands of ionizations per centimeter in air.
Path is relatively straight as α-particle much heavier than the collision partners
(electrons).
Range in air: for 5-8 MeV alphas ~ 8-10 cm (less in denser materials, shielding
by a piece of paper)
α-sources are usually open (handled only by instructor)
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Radiation Safety
Types of radiations (II)
Beta particles: β+, βEnergy transfer through collisions with atomic electrons leading to ionization and
excitation. Due to its much lower mass a β-particle has a much higher velocity
than α-particles of comparable energy.
As the collision partners (atomic electrons) have the same rest mass, large
deflection can occur resulting in many path changes.
Additionally:
- Bremsstrahlung (X-rays) is produced when β-particle passes near the
atomic nucleus
- Positrons are antimatter and annihilate with atomic electrons to produce
gamma radiation (511 keV)
For shielding use low Z-material to avoid X-ray production
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Radiation Safety
Types of radiations (III)
Gamma (γ) X-Ray 10-100 KeV, Gamma-Ray higher energies Both are photons
photons, electromagnetic radiation energy range keV – tens of MeV
Zero rest mass photons traveling at the speed of light. They are basically distortions
in the electromagnetic field of space and interact thus electrically with atoms even
though they have no net electrical charge.
While alphas and betas have a finite maximum range and can therefore be
completely stopped with a sufficiently thick absorber, photons interact in a
probabilistic manner. This means that an individual photon has no definite maximum
range. However, the total fraction of photons passing through an absorber decreases
exponentially with the thickness of the absorber.
Energy transfer mechanisms:
- Photoelectric effect
- Compton effect (elastic scattering)
- Pair production (Matter – Antimatter production)
Shielding with high electron density materials = Lead (Pb)
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BIOLOGICAL EFFECTS OF
RADIATION
• At the molecular level, the
energy carried by the incident
radiation is transferred to the
DNA, leading damages in the
DNA structure.
DNA double helix
• The energy transfer has
direct and indirect pathways,
in the latter the energy is
transferred to water first to
produce free radicals. The
highly reactive free radicals
then diffuses to DNA and
causes damages.
Radiation Safety
Activity & Exposure
Activity:
is the rate of decay (disintegrations/time) of a given amount of
radioactive material.
1 Bequerel (Bq) = 1 disintegration/second
Old unit: 1 Curie (Ci) = 3.7 1010 Bq
Exposure:
is a measure of the ionizations produced in air by x-rays or gamma
radiation.
1 Roentgen (R) = quantity of radiation that causes
ionization = 2.58 10-4 C/kg
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Radiation Safety
Dose
Dose:
is
1- A measure of energy deposited by radiation in a material (absorbed
dose)
2- A measure of the relative biological damage produced by that amount of
energy given the nature of the radiation (dose equivalent)
Absorbed dose: 1 Gray (Gy) = 1 Joule/kg
Old unit: 1 rad = 1/100 Gy (1 R exposure ~ 0.87 rad dose)
Dose equivalent:
includes the biological effectiveness (for cell damage)
 multiplication with quality factor Q:
Gammas, X-rays = 1
Beta particles = 1
Alpha particles = 20 (because of ionization power)
1 Sievert (Sv) = Q * absorbed dose (Gy)
Old unit: 1 rem = Q * absorbed dose (rad) (1 Sv = 100 rem)
 Still most important in the US.
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Radiation and Doses
Radiation Safety
• A number of units are used to describe radiation and its
effects on biological material
Common Unit
SI Unit
Description
Application
1 Curie (C)
3.7x1010 decays
1Becquerel (Bq)
1 decay
Activity
Describe amount of
material
ie 1 μC of 137Cs
Rad
0.01 Joule/Kg
Gray (G)
1Joule/Kg
Absorbed Dose
How much Energy
is absorbed
Equivalent Dose
Absorbed x Relative
Biological
Effectiveness (RBE)
Biological Damage
RBE
10-20
Alpha
1-2
Beta
1
Gamma
REM
Rad x RBE
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Radiation Safety
Calculations of Activities
Radioactive decay law:
ln 2
Activity: A(t) = A(0)*exp(-λt) = A(0)*exp(- 0.693 t/T1/2)
with: T1/2 Half-life of specific nucleus (tabulated)
(time required for one half of a collection
of atoms of that nuclide to decay)
Example:
32P:
T1/2 = 14.3 days
Original activity (January 10): 10µCi
I use the same source on February 6: ∆T = 27 days
A (Feb 6) = A(Jan10)*exp(-0.693*27/14.3) = 2.7 µCi
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Calculation of exposure rates
(rules of thumb – Rad) for γ’s and X-rays
6 . Ci . n . E  Rad/hour at 30 cm (1 foot)
Source strength
(in Curie)
Fraction of decays
resulting in photons
with energy E
Energy of the emitted photon in MeV
Radiation Protection, A guide for Scientists, Regulators, and Physicians,
Jacob Shapiro, La Editorial, UPR, 2002 ISBN 0674007409, 9780674007406
Calculation of exposure rates
(rules of thumb – Rad) for γ’s and X-rays
6 . Ci . n . E  Rad/hour at 30 cm (1 foot)
Source strength
(in Curie)
Fraction of decays
resulting in photons
with energy E
Energy of the emitted photon in MeV
Example from this lab: 1µCi 137Cs, n=1, E=0.663 MeV
6 . 1.10-6 . 1 . 0.663 R/hr at 30cm  3.10-6 Rad/hr at 30 cm
with quality factor Q=1  3.10-6 rem/hour at 30 cm
Radiation Safety
Exposure Rate (II)
For 1µCi 137Cs source  3.10-6 rem/hr @ 30 cm Dose Equivalent
6 hour lab course  2.10-5 rem = 0.02 mrem (millirem) per lab session
To be compared to:
Chest X-ray ~ 10 mrem
Cosmic Rays + Other Natural Activity ~ 100 – 200 mrem/year
Cosmic rays @ sea level ~ 26 mrem/year
Denver ~ 50 mrem/year
smoking ~ 50-200 mrem/year !
We also have a 5 mCi source  Shielded with lead (Pb)…
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Radiation Safety
6 . Ci . n . E  Roentgen/hour at 30 cm (1 foot)
Sources in your pocket = BAD !!!
1/r2 law applies
in pocket: d = 1 cm
 factor (30)2 = 900
 >18 mrem / lab session !
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Radiation Safety
Factors which influence
biological effects
• Type of Radiation
• Energy
• Time of exposure
• External / Internal
• Selective uptake
• Organ sensitivity
• Chemical characteristics
• Biological half-life (how long it takes for the body to get rid of half of it)
• Physical characteristics
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BACKGROUND RADIATION
DOSE
BACKGROUND RADIATION DOSE
•
We all live in an environment of
radiation.
•
The sources of background
radiation include cosmic rays,
natural radioactive elements in
earth, medical treatments, and
consumer products.
•
On average, each member of
general public receives 620
mrem of radiation dose per
year from the background
(NCRP Report 160, 2006).
MEDICAL X-RAY DOSE
Type of Exam
Patient Dose Per
Exam
Background Equivalent
Pelvic CT
400 - 1200 mrem
1- 2 years
Spine
130-270 mrem
2-6 months
Mammogram
45 mrem
4 weeks
Dental
10 mrem
1 week
Chest
5 - 8 mrem
4 days
DEXA hip or spine
1 - 6 mrem
< 4 days
DEXA wrist, heel
<1 mrem
< 1 day
OCCUPATIONAL DOSE LIMITS
•
•
The governmental agency regulating
occupational use of radiation is the
Nuclear Regulatory Commission (NRC).
NRC Dose limits:
– Adult workers: 5,000 mrem/yr whole
body; 50,000 mrem/yr to any organs
– Pregnant workers: 500 mrem during the
gestation period
– Minors: 10% of adult’s limit
– General public: 100 mrem/yr and not to
exceed 2 merm in any single hour.
Radiation Safety
Protection Against External Exposure
• Time
• Distance
• Shielding
Principle for exposure planning
ALARA: As
Low
As
Reasonably
Achievable
Internal exposure is usually a more serious threat to health… (time = depends
of the physical and/or biological half-life, Distance = 0, Shielding = 0)
ex: Plutonium (Pu), α-emitter, T1/2 = 24400 y,
when inhaled, the body cannot get rid of it.
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Radiation Safety
INCREASING DOSE
Scale of Effects
Over 5000 rem
Death within 1-2 days
1000 – 5000 rem
Death within 1-2 weeks
1000 rem
80-90% death rate
500 rem
50% death rate
100 rem
Detectable damage to bone marrow
5 rem
Annual Occupational Dose Limit
.01 rem
Chest X-ray
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1945 Japan
Radiation Safety
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Two Categories of Health Effect
Response 
PROBABILISTIC:
• Dose – Response in a large population
• Cancer, Genetic Defects
Dose 
• Dose – Response in a single individual
Threshold
Response 
DETERMINISTIC:
• Reddening of Skin, Cataracts, Hair Loss
Dose 
Theory of Dose Limits:
• Limit the chances of probabilistic effects
• Prevent the occurrence of deterministic effects
Radiation Safety
The Radium Girls
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Radiation Safety
What makes the numbers Glow? And How?
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Radiation Safety
How does Radium (or other
radioactive isotopes) make the
dials glow all the time?
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Radiation Safety
How does Radium (or other
radioactive isotopes) make the
dials glow all the time?
The electrons emitted (via beta decay) excite atoms in
fluorescent material in the paint. Electrons in these
atoms transition to higher energy states. When they
drop back to lower energy states, visible light is emitted.
Sustain fluorescence emission
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Radiation Safety
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The Radium Girls
In the early 1920s, about 70 women were hired at the radium factory in New Jersey where they worked as dial
painters and used luminescent paint. They assumed they were not using anything poisonous. Even though
some women thought it was strange that when a few of them blew their nose the handkerchief glowed in the
dark, they thought the stuff was harmless. Some women even painted their nails and their teeth to surprise their
boyfriends when the lights went out. At work, the women were painting glow-in-the-dark radium compounds on
the dials of watches and clocks. The women sat at long tables row after row. Dials waiting to be painted sat
nearby. Each day they would mix up glue, water and radium powder (a mixture of radium salts and zinc sulfide,
ZnS) into a glowing greenish-white paint. With care they would then apply it with camel hair brush to dial
numbers. As the brush lost its shape, the paint couldn't be applied accurately, so the women would put the brush
in their mouth and use the lips to make a point. The paint has no taste, and the women didn't know it was
harmful. In those days most people thought radium was a scientific miracle for curing cancer and other medical
problems. Unfortunately, for many of these women it did just the opposite. After several years of working as a
dial painter, some women's teeth started falling out and their jaws developed a painful abscess.
(…)
The glow effect that was seen with the dial painters was the result of ionization of atmospheric gases, producing
a blue glow. The blue glow can be enhanced in luminescent paints by the addition of zinc sulfide (ZnS). As the
alpha particles strike the ZnS, visible light is emitted in response to the ionizing radiation.
By the end of the 1920s, many of the dial painters died from symptoms associated with radium poisoning.
From: www.unco.edu/chemist/Bulletin/Chem101/radium.htm
Question:
Why is ingesting Radium (Ra) so harmful?
Why is ingesting Radium (Ra)
so harmful?
Why is ingesting Radium (Ra)
so harmful?
Why is ingesting Radium (Ra)
so harmful?
Radium is especially
dangerous because the
configuration of its outer
electrons are similar to that of
Calcium. So it can form
chemical bonds in the same
way that Calcium does.
Calcium is one of the elements
in bone.
Ingested Radium can replace
Calcium in bone to become a
long lasting internal radiation
source. Leukemia and other
cancers can result.
222Ra
t1/2 = 1601 years
From E-Bay Nov. 29th 2010
“FITRITE RADIUM OUTFIT NOTE!!!!!NOTE!!!!!
This is a radium outfit used to put luminous material on watch hands and/or dials.
The box says it is easily applied and dries quickly. The directions are on the box,
which is original. There are 2 cans of material, one light and one dark and they
have been used. There is a metal tool for application.” (Description posted)
Radiation Safety
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The 1987 Goiania (Brazil) event (I)
(from APS News, March 2004)
An example of massive exposure (2nd largest nuclear incident
after Chernobyl):
-
-
Two scrap metal scavengers find an abandoned (!) radiotherapy source of
137Cs Chloride 1,375 Ci (!) in soluble form removed from its protective
housing. The 2 men start vomiting because, they assumed, of bad food !
5 days later: hole made in the source, the radioactive powder leaks
Sold to a junkyard the same day, who notices the glowing blue color
Brings the capsule home to show it off !!!!
People sprinkle and rub the powder on their body like carnival glitter
Few days later, people start to develop acute radiation sickness
During the same time, two operators disassemble the whole assembly !
Both of them die.
Radiation Safety
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The 1987 Goiania (Brazil) event (II)
An example of massive exposure:
- a 6-year old girl plays with the colorful source powder, painted it on her
body, and ate a sandwich while her hands were contaminated
- When problem discovered: the brazilian authorities monitored over
112,000 people in the city’s stadium for radiation exposure and sickness
 249 people contaminated !
- 151 people both externally and internally
Internally exposed = Radioactive !
- 49 people admitted to the hospital, 20 received doses
from 100 to 800 rads.
- At the end: 5 dead, including the little girl
The little girl: consumed (with her sandwich) about (only) 27 mCi
 dead within a month;
Dose: 600 Rad ; LD50 ~ 300 Rad
Reading: http://www.aps.org/apsnews/0304/030415.cfm
Radiation Safety
Nov. 2006: The Litvinenko Case
Polonium 210 poisoning
Alpha emitter, half-life 138 days
First known case of fatal polonium poisoning
http://nuclearweaponarchive.org/News/Litvinenko.html
http://www.msnbc.msn.com/id/17332541/
David Hahn “The Radioactive Boyscout” 1976-
Known for attempting to make a fastbreeder reactor in his backyard at age 17
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X-RAYS
Man-made X-rays
Cathode(-)
Voltage
potential
Anode (+)
• electrons are accelerated by high
voltage, then stopped by high-density
target at the anode
• energy of electrons is converted to Xrays
X-ray
• energy of X-rays has a continuous
spectrum
Characteristic X-ray
• electrons jump from higher energy orbitals
to lower energy orbitals
• extra energy is release as X-rays
• this type of X-rays has discrete energy
spectrum
X-ray
e-
e−
HISTORY
“When the X-Ray came up, I made the first fluoroscope, using
tungstate of calcium…… I started in to make a number of these
lamps, but I soon found that the x-ray had affected poisonously my
assistant, Mr. Dally, so that his hair came out and his flesh
commenced to ulcerate. I then concluded it would not do, and that it
would not be a very popular kind of light; so I dropped it.” – Thomas
Edison
•
RADIATION PROTECTION
PRINCIPLES
There are three basic
principles in radiation
protection: time, distance
and shielding.
• Use theses principles in
addition to proper
contamination controls to
make dose ALARA
Question:
Rank particle types in order of amount of
material required to stop them
(less to more)
1: beta,gamma,alpha
2: beta,alpha,gamma
3: gama,beta,alpha
4: alpha,beta,gamma
Question:
Rank particle types in order of amount of
material required to stop them
(less to more)
1: beta,gamma,alpha
2: beta,alpha,gamma
3: gama,beta,alpha
4: alpha,beta,gamma
Question –
Which factors will all reduce exposure to external Radiation?
1. More Shielding, Less Time, Less Distance
2. Less Shielding, Less Time, More Distance
3. More Shielding, More Time, Less Distance
4. More Shielding, Less Time, More Distance
Question –
Which factors will all reduce exposure to external Radiation?
1. More Shielding, Less Time, Less Distance
2. Less Shielding, Less Time, More Distance
3. More Shielding, More Time, Less Distance
4. More Shielding, Less Time, More Distance
Radiation Safety
For Discussion.
In this course we work with radiation from 6 types of sources.
gamma (137 Cs, 60 CO) – 1-5 uC
gamma (137 Cs) 5 mC
gamma (X-Ray source)
Alpha polonium 0.001 uC
Alpha Curium
~5 uC
Cosmic Rays
discuss and rank in terms radiation safety risk (lowest
to highest)
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Radiation Safety
For Discussion.
In this course we work with radiation from 6 types of sources.
Cosmic Rays
Alpha polonium 0.001 uC
gamma (137 Cs, 60 CO) – 1-5 uC
gamma (X-Ray source)
gamma (137 Cs) 5 mC
Alpha Curium
~5 uC
rank in terms radiation safety risk (lowest to highest)
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Radiation Safety
Important points
•
Only the TA’s and Instructors handle the sources.
• Make sure the instructor/TA puts them away.
•
We need to use the sources for the next lab too.
• Do not eat them. Do not put them in your pockets
•
Be especially careful when bolting and unbolting the vacuum
system in lab 4. Do not let the alpha source assembly fall on
the floor. Yes, this happened once.
•
When working with the 137Cs source (Compton Scattering
Lab), Block the access port with a lead brick temporarily
before moving the detector arm. Stand behind the source
when you do this.
•
Do not power on the X-Ray apparatus until the instructor has
checked everything and reviewed safety procedure with you
•
Think about ALARA when setting up your apparatus
•
If you have questions or something doesn’t look right – ASK!
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