Transcript some of it`s subatomic particles …called radioactive decay!

Radioactivity
Ch 10
Radioactivity
• is the process in which an
unstable atomic nucleus
emits charged particles &
energy
• Any atom containing
an unstable nucleus is
called a radioactive
isotope or
radioisotope
How is the Atom Unstable?
• The nuclear “glue” that holds
the nucleus together sometimes
isn’t strong enough.
• Over time the atom “drops”
some of it’s subatomic particles
…called radioactive decay!
•
39
19
New Way of Writing
Nuclides & Isotopes
K ; 4019 K
• Superscript is the mass
number
• Subscript is the atomic
number
14
12
• 6C ; 6 C
Isotopes
• have the same number of p+,
different number of no
• Another way to show an
isotope is to have the mass
number follow the name of the
element (Carbon-14 or C-14)
Types of Nuclear Radiation
1. Alpha
2.Beta
3. Gamma
Alpha Decay
• Alpha particle—a positively
charged particle made up of
two p+ & two no
• the least penetrating
• can be stopped by a sheet of
paper
Alpha Decay
• An alpha particle looks like a
helium atom (42He)
• mass reduces by 4
• atomic # reduces by 2
• Examples:
238
92 U 
209
84 Po 
Beta Decay
• A beta particle is an eemitted by an unstable
nucleus
• can be stopped by a thin
sheet of metal such as
aluminum
Beta Decay
• A beta particle is written 0-1 e
• mass remains the same & the
atomic # increases by one
• Examples:
214
82 Pb
218
84 Po
Gamma decay
• A gamma ray is a penetrating
ray of energy emitted by an
unstable nucleus
• Gamma rays are energy waves
that travel through space at the
speed of light
Gamma
decay
• atomic # and
mass remain
the same, but
the energy of nucleus decreases
• Gamma rays can be stopped by
several centimeters of lead or by
several meters of concrete
Thanks Cambridge Physics Outlet for amazing graphics!
STAR Questions
• U-238 loses 4 total subatomic particles, 2
being protons.
– What elements are formed?
• Thorium and Helium
– What type of decay has it undergone?
• Alpha decay
• What is the most penetrating decay?
• Gamma rays
Background radiation
• is nuclear radiation that
occurs naturally in the
environment (levels are low
enough to be safe)
– Radioisotopes in the air,
water, rocks, plants, &
animals all contribute
Background Radiation
–Cosmic rays (streams of
charged particles) from outer
space that collide with the
Earth’s atmosphere also
contribute
–When nuclear radiation
exceeds background levels,
cells in your body can mutate
• Devices
used to
detect
radiation
include
Geiger
counters &
film badges
Detecting
Radiation
RATES OF NUCLEAR DECAY
A half-life is the time required for one
half of a sample of radioactive
material to decay
– Unlike chemical reactions, nuclear
decay rates are constant
regardless of temperature,
pressure or surface area
• C-14 has a half life of 5730 years.
– What fraction of a sample will be remaining
after 1 half life?
• After 2 half lives?
• C-14 has a half life of 5730 years.
– If you have a sample of 50 grams. How much of the
sample will be remaining after 1 half life?
• After 2 half lives?
Examples
• Iodine-131 has a half-life of 8.07 days.
What fraction of a sample of iodine-131 is
left unchanged after 16.14 days?
Examples
• The radioactive isotope Ni-63 has a halflife of 100 yrs. How much of a 10g sample
remains after 300 yrs?
Examples
• How long will it take a sample of Po-194 to
decay to 1/8 of its original amount, if Po194 has a half life of 0.7 seconds?
Examples
• A sample of Cl-38 is observed to decay to
25% of its original amount in 74.4 min.
What is the half-life of Cl-38?
RATES OF NUCLEAR DECAY
Transmutation is the
conversion of atoms of one
element to atoms of another
Transuranium elements are
elements with atomic
numbers higher than 92
(Uranium)
A quark is a subatomic particle
theorized to be among the
basic units of matter
FISSION AND FUSION
Fission is the
splitting of an
atomic nucleus
into two smaller
parts
Fusion is a
process in which
the nuclei of two
atoms combine
to form a larger
nucleus
Fission
• Advantages: is the
lack of air
pollution.
• Disadvantages:
include the risk of
exposure &
radioactive waste
Harris plant,
near Raleigh
Lake Harris
Fusion
• release huge
amounts of
energy
• occur in the
sun and stars
(plasma)
Fusion
• We do not use fusion reactions
for energy b/c of the extremely
high temperatures needed to
start the reaction & because
the plasma would need to be
contained.
Star Questions
• The combining of two nuclei
• Fusion
• Alpha particle looks like the atom of which
element?
• Helium
• This type of nuclear radiation is the most
penetrating?
• Gamma
• Boron-10, what is the nuclide look like?
Fission
• A tremendous amount of energy
is produced during a fission
reaction
• A chain
reaction is a
chain of
fission
reactions
triggered by
neutrons
released
during the
fission of a
nucleus
Fission
About 20% of the
electricity in the US
comes from fission
reactions
Not in my backyard…
Temporary Storage
(6 months - 5 years)
Wet Storage
Dry Storage
Then sealed and transported by way of trucks and
trains for more permanent storage. Low-level
wastes will stay above ground until they become
“stable”.
If high-level, the wastes are stored deep underground, where
they wait for hundreds to thousands of years to become “stable”.
RECYCLE
• France and Pakistan reprocessing spent
nuclear fuel
• Call it MOX fuel (Mixed oxide) refers to a
blend of plutonium and natural uranium,
reprocessed uranium, or depleted uranium
– The use of MOX does change the operating
characteristics of a reactor, and the plant
must be designed or adapted slightly to take it
THREE MILE ISLAND
• Three Mile Island power station is near Harrisburg,
Pennsylvania
• In 1979 at Three Mile Island nuclear power plant a
cooling malfunction caused part of the core to
melt in the # 2 reactor. The TMI-2 reactor was
destroyed.
• Some radioactive gas was released a couple of
days after the accident, but not enough to cause
any dose above background levels to local
residents.
• There were no injuries or adverse health effects
from the Three Mile Island accident.
CHERNOBYL
• The Chernobyl accident in 1986 was the result of a
flawed reactor design that was operated with
inadequately trained personnel & without proper regard
for safety.
• The resulting steam explosion & fire released at least
five percent of the radioactive reactor core into the
atmosphere and downwind.
• 28 people died within four months from radiation or
thermal burns, 19 have subsequently died, & there have
been around nine deaths from thyroid cancer apparently
due to the accident: total 56 fatalities as of 2004.
• An authoritative UN report in 2000 concluded that there
is no scientific evidence of any significant radiationrelated health effects to most people exposed. This was
confirmed in a very thorough 2005-06 study.
Fukushima Japan…