Transcript Slide 1

Nuclear Science Merit Badge:
Radiation Health & Safety
Radiation
Learning Objectives
• Types of Radiation
• Consequences of
exposure to radiation
• Uses in the medical
field
• Radiation containment
What is Radiation?
• Radiation is the process in which
energetic particles or waves travel
through a medium or space.
• Generally refers to electromagnetic (EM)
radiation (charged particles)
• Examples: Sunlight, Microwaves,
Sound waves (non-EM)
Types of EM Radiation
• Non-Ionizing
– Radio waves
– Visible light
– Microwaves
• Ionizing
– X-rays
– Gamma rays
Ionizing Radiation
• Ionization is caused when an electron is
added to or removed from an atom.
• Ionizing radiation is radiation that has
sufficient energy to strip electrons from
atoms, thus making them ions.
• The remaining positively charged atom
and the free electron are called “ion
pairs.”
Ionizing Radiation
• An X-ray is a type of
ionizing radiation that has a
wavelength in the range of
0.01 to 10 nanometers.
• A Gamma ray is a type of
ionizing radiation that has
higher energy than X-rays
and has a wavelength less
than .01 nanometers.
• Concrete or lead are
needed to shield against
these radiations
Electroscope
History Behind Radiation
• X-rays were first
discovered by Wilhelm
Roentgen in 1895.
• He noticed how the rays
could pass through some
materials and not others.
• The rays could be
detected using a
photographic plate
History Behind Radiation
• Henri Becquerel discovered
that uranium caused a
photographic plate to be
fogged, just like X-rays.
• In 1898, Marie Curie gave this
property the name
radioactivity.
• Radioactivity is the tendency
of an element to give off
charged particles or rays (i.e.,
to emit energy).
Charged Particles
• Two charged
particles that are
emitted by a
radioactive
element are
Alpha (α)
particles
Beta (β)
particles
Charged Particles
• An alpha
particle has two
protons and two
neutrons
Same as He2+
Mass: 4 AMU
No electrons!
Charged Particles
• A beta particle
is an electron or
a positron.
Electron charge:
-1 e
Positron charge:
+1 e
Cloud Chamber
• A cloud chamber can
be used to track the
path of electrically
charged particles.
• When a magnetic field
is applied it is able to
identify the charge and
velocity of the particle.
• Cloud Chamber Video
Radioisotopes
• Isotopes of an atom that are radioactive are
called radioisotopes.
• These atoms are radioactive because they
have too much energy to be stable; they will
release energy until they become stable.
• This is called radioactive decay. The
modern words are “spontaneous nuclear
transformation.”
Radioactive Decay
• In the process of radioactive
decay, an atom actually
changes from one element
to another by changing its
number of protons.
• The half-life of a
radioactive substance is the
amount of time required for
it to lose one half of its
radioactivity and transform
into another element.
Activity Time!!
Let’s demonstrate half-life using a piece
of paper!
Radioactive Decay
• Radioactivity (or “activity”) is
measured in units of:
– “curie”
• Ci
• Defined as 3.7 x 1010 decays per second
• The traditional unit
– “becquerel”.
• Bq
• Defined as 1 decay per second
• The SI unit
Types of Radioactive Decay
• Alpha decay
– Nucleus emits an α
particle
– Loses 2 protons, 2
neutrons
• Beta decay
– Nucleus emits a β
particle
– Converts a neutron into
a proton and an electron
(i.e., the beta particle)
Examples
Half life = 5.2 years
•colbolt-60 that is used in cancer therapy, decays to
nickel-60 with loss of a β particle.
Half life = 4,468,000,000 years
•radioactive decay of Uranium-238 by alpha emission.
Radiation Hazards and
Safeguards
The International
Radiation Symbol
• The international radiation
symbol (also known as
trefoil) first appeared
in 1946, at the University of
California,
Berkeley Radiation
Laboratory.
• At the time, it was rendered
as magenta with
a blue background.
• The modern version is black
against a yellow
background
Why should ionizing
radiation be controlled?
• Ionizing radiation can damage living
tissue in the human body.
• It can create reactive molecules that
are poisons in the body.
Acute (Deterministic)
Radiation Effects
• Acute radiation symptoms are caused by
high levels of radiation usually over a
short period of time
• They cannot be predicted with certainty.
• Examples: erythema (redness of the
skin) and epilation (hair loss)
Chronic (Stochastic)
Radiation Effects
• Chronic radiation symptoms are
caused by low-level radiation over a
long period of time.
• Effects are based on probabilities.
• Exposure to low levels of radiation
increase a person’s chances to get
cancer.
Radiation Exposure
Levels & Effects
0.62 rem/y – average annual radiation exposure
in the U.S.
2 rem/y – international radiation exposure limit
5 rem/y – current US NRC radiation exposure
limit
25 rem – measureable blood changes
100 rem – onset of radiation sickness
Radiation Exposure
Levels & Effects
200 rem – radiation sickness with worse
symptoms in less time
400 rem – approximately the lethal dose for
50% of the population in 30 days
1,000 rem – death probable within about 2
weeks, effects on the
gastrointestinal tract
5,000 rem – death probable within 1-2 days,
effects on the central nervous
system
Nuclear Technologies
Radiation in Medicine
• Radiology: X-ray
imaging.
• Nuclear Medicine:
Following radioactive
tracers in the body.
• Radiation Therapy:
for the treatment of
cancer
http://www.missouristate.edu/assets/HPER/rib_x-ray.jpg
Radiation Therapy
• External beam
treatments
• Radionuclide
treatments
(brachytherapy)
Radiation in Agriculture
• Radiation used to kill
pests, preserve
harvested crops.
• Helps detect level of
pollution and fertilizer
in crops.
• Delay sprouting and
spoilage
Radiation in Industry
• Process control using
radiation gauges
• Check for leaks in
underground pipes.
• Control thickness of
manufactured
materials
http://www.gcsescience.com/Thickness-Control-Radioactivity.gif
Radiation in Security
• X-ray checks of
baggage
• Whole-body scanners
of passengers
• Smoke detectors in
homes and offices
Radiation in Space
• Mars rovers
• Satellites
• International Space
Station
• Deep-space Probes
• Radioisotope
Thermoelectric
Generators (RTG)
Radiation in Science
• Radiocarbon Dating –
Carbon-14
• Neutron activation “Finding a needle in a
haystack”
• Engine testing
Differences in dose types
Thought experiment
• Alpha particles do MUCH more
biological damage with a given
amount of dosage than gamma rays.
• Why?
Answer
• Gamma rays penetrate straight through
virtually any material, including tissue,
while alpha particles are easily stopped
by thin barriers, including human skin.
• Alpha particles will thus deposit their
energy into a human much more readily
than gamma rays, resulting in more tissue
damage.
Typical Radiation Detectors
• Film packet
• Thermoluminescent Dosimeter (TLD)
• Ionization chamber
• Geiger-Müller (GM) Detector
• Scintillation Detector
Radiation Kit
Thought experiment 2
• How does distance effect the
measurement of radiation?
• How does shielding effect the
measurement of radiation?
• How does time effect the
measurement of radiation?
Answer
• With increasing distance the radiation
dose rate drops since the
concentration of particles decreases
Answer #2
• Shielding reduces the amount of
radiation that reaches you, reducing
the dose rate
Answer #3
• A shorter time period doesn’t reduce
the dose rate, however since you’re
exposed to the source for less time
you receive less dose.
Background Radiation
•
Background Radiation is radiation that
is a natural part of our environment.
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Rocks and soil
Cosmic radiation
Solar radiation
Radon gas
Food and water
From human made sources
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X-ray machines
Other medical uses
Tritium dial wristwatches
Gas lantern mantles
Smoke detectors
Radiation Regulations
• ALARA- As Low As
Reasonably Achievable
• Time, Distance, and
Shielding
• National and International
limit – 5 rem/y (5000
mrem/y)
• Public limit – 100 mrem/y
• Radiation Hazard symbol
– Displayed at places where
radioactive materials are
used and stored.
ALARA SCENARIOS
What we learned
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Types and effects of Radiation
Uses of radiation
Consequences of exposure
Containment techniques
American Nuclear Society