Nuclear Science Merit Badge:
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Transcript of Nuclear Science Merit Badge:
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Radiation Health & Safety
Nuclear Science Merit Badge:
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Radiation
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• Types of Radiation
• Consequences of exposure to radiation
• Uses in the medical field
• Radiation containment
Learning Objectives
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• 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)
What is Radiation?
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Types of EM Radiation
• Non-Ionizing – Radio waves– Visible light– Microwaves
• Ionizing– X-rays– Gamma rays
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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.”
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• 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
Ionizing Radiation
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Electroscope
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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
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• 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).
History Behind Radiation
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• Two charged particles that are emitted by a radioactive element are Alpha (α)
particles Beta (β)
particles
Charged Particles
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• An alpha particle has two protons and two neutrons Same as He2+
Mass: 4 AMU No electrons!
Charged Particles
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• A beta particle is an electron or a positron. Electron charge:
-1 e Positron charge:
+1 e
Charged Particles
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• 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
Cloud Chamber
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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.”
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• 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.
Radioactive Decay
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Activity Time!!
Let’s demonstrate half-life using a piece of paper!
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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
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• 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)
Types of Radioactive Decay
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Examples
Half life = 5.2 years
Half life = 4,468,000,000 years
• colbolt-60 that is used in cancer therapy, decays to nickel-60 with loss of a β particle.
•radioactive decay of Uranium-238 by alpha emission.
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Radiation Hazards and Safeguards
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• 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
The International Radiation Symbol
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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.
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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)
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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.
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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
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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
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Nuclear Technologies
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• Radiology: X-ray imaging.
• Nuclear Medicine: Following radioactive tracers in the body.
• Radiation Therapy: for the treatment of cancer
Radiation in Medicine
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• External beam
treatments
• Radionuclide
treatments
(brachytherapy)
Radiation Therapy
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• Radiation used to kill pests, preserve harvested crops.
• Helps detect level of pollution and fertilizer in crops.
• Delay sprouting and spoilage
Radiation in Agriculture
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• Process control using radiation gauges
• Check for leaks in underground pipes.
• Control thickness of manufactured materials
Radiation in Industry
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• X-ray checks of baggage
• Whole-body scanners
of passengers
• Smoke detectors in homes and offices
Radiation in Security
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• Mars rovers• Satellites• International Space
Station• Deep-space Probes• Radioisotope
Thermoelectric
Generators (RTG)
Radiation in Space
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• Radiocarbon Dating – Carbon-14
• Neutron activation - “Finding a needle in a haystack”
• Engine testing
Radiation in Science
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Differences in dose types
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Thought experiment
• Alpha particles do MUCH more biological damage with a given amount of dosage than gamma rays.
• Why?
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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.
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Typical Radiation Detectors
• Film packet
• Thermoluminescent Dosimeter (TLD)
• Ionization chamber
• Geiger-Müller (GM) Detector
• Scintillation Detector
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Radiation Kit
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• How does distance effect the measurement of radiation?
• How does shielding effect the measurement of radiation?
• How does time effect the measurement of radiation?
Thought experiment 2
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Answer
• With increasing distance the radiation dose rate drops since the concentration of particles decreases
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Answer #2
• Shielding reduces the amount of radiation that reaches you, reducing the dose rate
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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.
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• Background Radiation is radiation that is a
natural part of our environment.
– Rocks and soil
– Cosmic radiation
– Solar radiation
– Radon gas
– Food and water• From human made sources
– X-ray machines
– Other medical uses
– Tritium dial wristwatches
– Gas lantern mantles
– Smoke detectors
Background Radiation
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• 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.
Radiation Regulations
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ALARA SCENARIOS
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• Types and effects of Radiation• Uses of radiation• Consequences of exposure• Containment techniques
What we learned
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American Nuclear Society