Download Nucleus, Radioactivity, & Nuclear Medicine

Nucleus,
Radioactivity, &
Nuclear Medicine
Dr. Michael P. Gillespie
Radioactive
Natural Radioactivity
• Radioactivity is the process by which some
atoms emit energy and particles.
• The energy and particles are termed radiation.
• Radioactivity is a nuclear event: matter and
energy released during this process come from
the nucleus.
Radioactive Atim
Types of Radiation
• Three types of radiation are emitted by
unstable nuclei:
• Alpha particles
• Beta particles
• Gamma rays
Alpha Particles α
• Alpha particles consists of 2 protons and 2
neutrons.
• They have no electrons and therefore have a +2
charge.
• They have a relatively large mass and are slow
moving. Traveling at approximately 5-10% the
speed of light.
• They can be stopped by barriers as thin as a few
pages of paper.
Alpha Particle Decay
Beta Particles β
• A beta particle is a fast moving electron.
Traveling at approximately 90% the speed of
light.
• It is formed in the nucleus by the conversion of
a neutron into a proton.
• They are more penetrating and are stopped
only by more dense materials such as wood,
metal, or several layers of clothing.
Beta Particle Decay
Gamma Rays γ
• Gamma rays are the most energetic part of the
electromagnetic spectrum and result from nuclear
processes.
• Electromagnetic radiation has no protons, neutrons, or
electrons. Unlike alpha and beta particles, gamma rays
have no matter.
• Gamma radiation is highly energetic and the most
penetrating form of nuclear radiation.
• Barriers of lead, concrete, or a combination of the two are
required to stop gamma rays.
• Travels at the speed of light.
Gamma Particle Decay
Penetration
Radioactive Decay
Properties of Alpha, Beta,
and Gamma Radiation
Name and
Symbol
Identity
Charge
Mass (amu)
Velocity
Penetration
Alpha α
Helium
nucleus
+2
4.0026
5-10% speed
of light
Low
Beta β
Electron
-1
0.000549
90% speed
of light
Medium
Gamma γ
Radiant
Energy
0
0
Speed of
light
High
Nuclear Structure and
Stability
• A measure of nuclear stability is the binding
energy of the nucleus. The binding energy is
the amount of energy required to break a
nucleus up into its component protons and
neutrons.
• The binding energy must be very large to
overcome the extreme repulsive forces of the
positive protons for one another.
Half-Life
• The half-life is the time required for one-half of
a given quantity of a substance to undergo
change.
• Each isotope has its own characteristic halflife.
• The half-life can be as short as a few millionths
of a second or as long as billions of years.
Nuclear Energy
Production
Nucular
• George W. Bush would
mispronounce the
word nuclear as
‘Nucular’
Nuclear Energy Production
• Einstein predicted that when the nucleus
breaks apart, the small amount of nuclear
mass produces a tremendous amount of
energy.
• The heat energy released converts water into
steam.
• The steam turns a turbine, which drives an
electrical generator, producing electricity.
Nuclear Fission
• Fission (splitting) occurs when a heavy nuclear
particle is split into smaller nuclei by a smaller
nuclear particle (such as a neutron).
• The splitting of the nuclear particle releases a
tremendous amount of energy.
• The fission reaction, once initiated, is selfperpetuating.
• The fission process continues and intensifies. The
process of intensification is referred to as a chain
reaction.
Energy Transformation in a
Fission Reaction
• Nucear energy  heat energy  mechanical
energy  electrical energy
Fission Chain Reaction
Nuclear Fission
Nuclear Fission
Nuclear Fusion
• Fusion (joining together) results from the
combination of two small nuclei to forma
larger nucleus with the concurrent release of
large amounts of energy.
• The Sun is a great example of a fusion reactor.
• In fusion, two isotopes of hydrogen
(deuterium and tritium) combine to produce
helium, a neutron, and energy.
Nuclear Fusion
Nuclear Fusion
Nuclear Fusion
Nuclear Fusion
Nuclear Fusion
Nuclear Fusion
• No commercially successful fusion plant exists
because of the containment issues.
• The fusion reaction results in temperatures in
the millions of degrees and extremely high
pressures. These conditions are necessary to
sustain the fusion reaction.
Breeder Reactors
• A breeder reactor is a variation of a fission
reactor that literally manufactures its own fuel
from abundant starting materials.
• Breeder reactors cost a tremendous amount,
have considerable potential to damage the
environment, and create a lot of plutonium
which can be used for nuclear bombs.
Breeder Reactors
Nuclear Waste Disposal
• Solid waste is difficult enough to dispose of,
but nuclear waste poses even more of a
challenge.
• We cannot alter the rate at which nuclear
waste decays. This is determined by the halflife. Plutonium has a half-life greater than
24,000 years and it takes ten half-lives for
radiation to reach background levels.
Nuclear Waste Disposal
• Where can we store
hazardous, radioactive
material for a quarter
of a million years?
• Burial in a stable bedrock formation seems
like the best option
right now, but an
earthquake could
release this.
Nuclear Waste Disposal
Nuclear Waste Disposal
Radiocarbon Dating
• Natural radioactivity can be utilized to
establish the approximate age of
archaeological, anthropological, or historical
objects.
• Radiocarbon dating measures isotopic ratios
of carbon to estimate the age of objects.
• Carbon-14 is formed in the upper atmosphere.
Carbon-14 Enters The Food
Chain
Radiocarbon Dating
• Carbon-14 (radioactive) and carbon-12 (more
abundant) are converted into living plant
material through photosynthesis.
• The carbon-14 works its way into the food
chain.
Radiocarbon Dating
• When a plant or animal dies, the carbon-14
slowly decreases because it is radioactive and
decays to produce nitrogen.
• When an artifact is found, the relative amounts
of carbon-14 to carbon-12 are used to
approximate its age.
• Carbon-14 dating technique is limited to
objects that are less than 50,000 years old.
Carbon Dating
Isotopes Useful In
Radioactive Dating
Isotope
Half-Life (years)
Upper Limit
(years)
Dating
Applications
Carbon-14
5730
5X104
Charcoal, organic
material, artwork
Tritium
12.3
1X102
Aged wines,
artwork
Potassium-40
1.3X109
Age of earth
(4x109)
Rocks, planetary
materials
Rhenium-187
4.3x1010
Age of earth
(4x109)
Meteorites
Uranium-238
4.5x109
Age of earth
(4x109)
Rocks, earth’s
crust
Cancer Therapy Using
Radiation
• When high energy radiation, such as gamma
radiation, passes through a cell, it may collide
with one of the molecules in the cell and cause
it to lose one or more electrons. This leads to
the production of ion pairs. Consequently, this
form of radiation is referred to as ionizing
radiation.
Cancer Therapy Using
Radiation
• This ions are highly energetic, can damage
biological molecules, produce free radicals,
and damage DNA.
• This alters cell function and can even lead to
cell death.
Cancer Therapy Using
Radiation
• An organ that is cancerous has both healthy
cells and malignant cells.
• The tumor cells are undergoing cell division
more rapidly and are therefore more
susceptible to gamma radiation.
Cancer Therapy Using
Radiation
• Carefully targeted high doses of gamma
radiation will kill more abnormal cells than
normal cells.
• This can destroy the tumor and allow the
organ to survive.
• The gamma radiation can also cause cancer in
the healthy cells.
Nuclear Medicine
• Medical tracers are small amounts of
radioactive substances used as probes to
study internal organs.
• Medical techniques that utilize tracers are
referred to as nuclear imaging procedures.
Nuclear Medicine
• Certain radioactive isotopes are attracted to
particular organs.
• The radioactivity emitted allows us to track the
path of the tracer and obtain a picture of the
organ of interest.
Magnetic Resonance
Imaging (MRI)
• MRI is a noninvasive technique used to study
the body.
• It uses no radioactive substances. It is quick,
safe, and painless.
Magnetic Resonance
Imaging (MRI)
• The patient is placed in a cavity surrounded by
a magnetic field.
• An image (based on the extent of radio
frequency energy absorption) is generated,
stored, and sorted on a computer.
Magnetic Resonance
Imaging (MRI)
Biological Effects of
Radiation
• Radiation affects biological tissues.
• We must use suitable precautions when
working with radiation.
• “Tolerable levels” have been established for
radiation exposure.
Radiation Exposure and
Safety
• Factors to consider when working with
radioactive materials:
•
•
•
•
•
•
The magnitude of the Half-life
Shielding
Distance from the radioactive source
Time of exposure
Types of radiation emitted
Waste disposal
Magnitude of the Half-life
• Short half-life radioisotopes produce a larger
amount of radioactivity per unit of time than
larger half-life substances.
• Shorter half-life materials can be safer to work
with, especially if an accident occurs.
Magnitude of the Half-life
• Radioactive isotopes will eventually decay into
background radiation. This will happen faster
with a shorter half-life.
• Higher levels of exposure in a short time
produce a clearer image.
Shielding
• Alpha and beta particles are low in penetrating
power and therefore require low levels of
shielding. A lab coat and gloves are usually
sufficient.
• Gamma rays have significant penetrating
power. Lead, concrete, or both are required
for shielding from gamma rays.
• X-rays are also very high energy and require
lead and concrete shielding.
Distance from the
Radioactive Source
• Radiation intensity varies inversely with the
square of the distance from the source.
• Doubling the distance from the source
decreases the intensity by a factor of four.
• Robot manipulators can allow us to get a
greater distance between the operator and
the radioactive source.
Distance from the
Radioactive Source
Time of Exposure
• The effects of radiation are cumulative.
• Potential damage is directly proportional to
time of exposure.
Types of Radiation Emitted
• Alpha and beta emitters are generally less
hazardous than gamma rays due to differences
in energy and penetrating power that require
less shielding.
• Ingestion or inhalation of an alpha or beta
emitter can cause serious damage over time.
Waste Disposal
• Radioactive waste is created from nuclear
medicine applications, nuclear power, etc.
• Safe handling and disposal of this waste is a
serious problem.
• Temporary solutions are being used, but it is
necessary to find more suitable long-term
storage solutions.
Waste Disposal
Waste Disposal
Measurement of Radiation
• Radiation is detected using either
photographic film to create an image of the
location of the radioactive substance or using
a counter that measures the intensity of the
radiation emitted from a source.
Nuclear Imaging
• Used in nuclear medicine.
• A radioactive isotope is administered to a
patient and it concentrates on the organ of
interest.
Nuclear Imaging
• Nuclear images are taken at various intervals
using a film that is sensitive to the radiation
being emitted.
• This creates an image on the film showing the
organs uptake of the isotope over time.
Computer Imaging
• Specialized television cameras that are
sensitive to the radiation emitted from a
radioactive substance are used.
• A CT scanner records the interaction of x-rays
with biological tissue.
Geiger Counter
• A Geiger counter is an instrument that detects
ionizing radiation.
• The ionizing radiation produces a current flow
in a tube filled with ionizable gas.
• The current flow is proportionate to the level
of ionizing radiation.
Geiger Counter
Film Badges
Units of Radiation
• Intensity of the emitted radiation:
• Curie – measures the amount of radioactivity.
Independent of the nature of radiation and its
effect upon biological tissue.
• Roentgen – measures very high energy ionizing
radiation (x-ray and gamma).
Units of Radiation
• Biological effects of the emitted radiation:
• Rad – Radiation absorbed dosage – measures
the transfer of energy to matter due to
radiation.
• Rem – Roentgen equivalent for man – describes
the biological damage caused by the absorption
of different kinds of radiation.
Radioactive Waste