What is radioactivity?Spontaneous emission of radiation when
the nucleus of an atom breaks down to form a different element.
Background RadiationThe constant level of radioactivity always
present around usCaused by:
Cosmic rays Naturally occurring uranium Radon in the air Radioactive isotopes in food and environment
What is your radiation exposure?National Average: 500 mremBackground Average: 360 mrem
How do nuclear and chemical reactions differ?
Nuclear reactions involve the nucleus (protons and neutrons)
BUTchemical reactions involve the
transfer and sharing of electrons
Band of Stability
After element 83 (Bismuth)the elements are naturally unstable
and may emit decay particles
The bigger the atom gets and the further from a 1:1 ratio of
protons and neutrons, the less stable the
atom is
What holds the atom together?Electromagnetic Force
Force of repulsion between positive charges of the protons in the nucleus
Strong Force Force present that holds quarks together and
therefore keeps the protons and neutrons tightly packed in the nucleus
When the electromagnetic force wins out, the nuclei break apart!
Review: Types of Decay
Decay Type Symbol Charge Reaction
Particle StrengthCan be
stopped by…
AlphaBeta
Gamma
Nuclear Symbols Review
• The superscript indicates the mass number and the subscript indicates the atomic number.
XAZ
Mass Number Atomic Number
Element Symbol
Steps to writing decay reactions:
1. Write the nuclear symbol for the element that is given.
2. Draw an arrow.3. Identify the type of particle that has decayed
and write it after the arrow.4. Balance the mass number (top) and the
atomic number (bottom). 5. Identify the new element.
Gamma Decay Loss of a gamma particle
Does it effect the outcome of the reaction?
Alpha and gamma decay of:
00γ
239Pu 94
Half-LifeTime required for half a sample to decay
The stability of the isotope is what determines the rate of decay.
Less Stable = Faster Decay
Half-Life After each half-life, half of
the sample decays. Start = 100%
40 blue particles are present 1 half-life = 50%
20 blue remain 2 half-lives = 25%
10 blue remain 3 half-lives = 12.5%
5 blue remain 4 half-lives = 6.25%
2.5 blue remain
Amount never becomes zero!!
Half-Life After 10 half-lives sample considered
nonradioactive because it approaches the level of background radiation.
Because the amount never reaches zero, radioactive waste disposal and storage causes problems. Would you want radioactive waste stored in your community?
How can we get rid of nuclear radioactive waste?
Half Life PracticeExample 1:
The half-life of mercury-195 is 31 hours. If you start with a sample of 5.00 g, how much of it will still be left after 93 hours?
Half Life Practice ContExample 2:
How many half lives have passed if there is only 1.875 g left of a 30 g sample?
If the half life for this sample is 1 hour, how many total hours have gone by?
Where do we use nuclear chemistry?
Sun is powered by nuclear reactionsElectricity from nuclear power plantsMedical:
x-rays, cancer treatment, radioactive tracers Industrial:
Sterilize equipment, sterilize (irradiate) food, x-rays of metal equipment (scan for cracks in airplanes)
Military
Radiation ExposureExposure to radiation can cause cell mutations
and illness.Four factors that affect exposure:
Dose (strength of radiation) Exposure time Area exposed Tissue exposed
FissionOne heavy atom breaks down into two or more
smaller atoms and produces energyThis becomes a chain reaction
(as one atom splits and hits more, and those split and hit more)
Supercritical:creates a great release of energy - atomic bomb
Ping Pong Video
Will a chain reaction always occur?Particles reacting must have critical mass:
The minimum amount of mass needed for the neutron to hit and react with
No critical mass = no reaction
Fission reactions can also be controlled to contain the energy.